7150_p3

Model 7150 Fluid Migration Analyzer (FMA)

Part Number 7150-0089

Revision P.3 – January 2008

S/N _____________

P.O. Box 470710

Tulsa, Oklahoma 74147 Phone: 918-250-7200 FAX: 918-459-0165

Email: [email protected] Website: www.chandlereng.com

Copyright © 2007, by Chandler Engineering Company L.L.C.

All rights reserved. Reproduction or use of contents in any manner is prohibited without express permission from Chandler Engineering Company L.L.C. While every precaution has been taken in the preparation of this manual, the publisher assumes no responsibility for errors or omissions. Neither is any liability assumed for damages resulting from the use of the information contained herein.

TABLE OF CONTENTS T-1

Table of Contents General Information.................................................................P-1

Purpose ..................................................................................................................................P-1 Description ............................................................................................................................P-1 Theory....................................................................................................................................P-1

Cement Slurry Gel Strength Measurements ....................................................................P-1 Fluid Migration Test Design............................................................................................P-2

Features and Benefits ............................................................................................................P-3 Collecting Data during the Test.............................................................................................P-3 Specifications ........................................................................................................................P-3 Safety Requirements..............................................................................................................P-4 Where to Find Help ...............................................................................................................P-4

Section 1 – Installation............................................................. 1-1 Unpacking the Instrument ..................................................................................................... 1-1 Utilities Required................................................................................................................... 1-1 Tools/Equipment Required.................................................................................................... 1-1 Setting up the Instrument....................................................................................................... 1-1 Installing 5270 Data Acquisition System.............................................................................. 1-2

System Requirements....................................................................................................... 1-2 Upgrading from an Earlier Version ................................................................................. 1-3 Before You Install 5270 DACS ....................................................................................... 1-3 Starting the 5270 Installation ........................................................................................... 1-3

To install 5270 ........................................................................................................... 1-4 Configuring the Instrument.............................................................................................. 1-4

To configure the instrument....................................................................................... 1-4 Starting and Stopping a Test ............................................................................................ 1-5 Software Setup and Data Display .................................................................................... 1-6

Section 2 – Operation............................................................... 2-1 Keys to a Successful Test ...................................................................................................... 2-1 Function of Pressure Regulators and Valves......................................................................... 2-2

Regulators ........................................................................................................................ 2-2 Valves .............................................................................................................................. 2-2

Preparation for a Test ............................................................................................................ 2-3 Initial Cell Preparation..................................................................................................... 2-3 Filling Transducer Lines in Preparation for Testing........................................................ 2-4 Cement Slurry Preparation............................................................................................... 2-5 Loading of the Cement Slurry.......................................................................................... 2-6 Filling Water Reservoirs and Lines ................................................................................. 2-6 Test Setup......................................................................................................................... 2-7

Conducting the Test............................................................................................................... 2-7 Part 1: Fluid Loss ............................................................................................................. 2-7 Part 2: Fluid/Gas Migration ............................................................................................. 2-8

Test Duration ......................................................................................................................... 2-9 Shutting Down the Test ......................................................................................................... 2-9

T-2 TABLE OF CONTENTS

Opening the Cell.................................................................................................................... 2-9 Cleaning the Test Cell ......................................................................................................... 2-10

After Every Test............................................................................................................. 2-10 Flushing the Sample and High Pressure Lines. ....................................................... 2-10 Pressure Cylinder ..................................................................................................... 2-10

Section 3 - Maintenance Schedule........................................... 3-1 Calibration Procedures .......................................................................................................... 3-1

Monthly............................................................................................................................ 3-1 Filter........................................................................................................................... 3-1

Six Months ....................................................................................................................... 3-1 Tubing/Fittings........................................................................................................... 3-1

Annually........................................................................................................................... 3-1 Pressure Cylinder ....................................................................................................... 3-1 Temp Controller/Thermocouples............................................................................... 3-1

Section 4 - Troubleshooting Guide .......................................... 4-1 Potential Problems and Solutions.......................................................................................... 4-1

Section 5 – Replacement Parts................................................. 5-1

Section 6 – Drawings and Schematics ..................................... 6-1

Reference Section SPE Paper #55650 SPE Paper #19522 Application Notes

PREFACE P-1

General Information Purpose

The Chandler Engineering Model 7150 Fluid Migration Analyzer (FMA) was developed to provide a bench-top laboratory device to realistically test cement recipes for use in controlling formation flow (gas/brine) invasion after the cement job. The apparatus realistically simulates parameters such as temperature, hydrostatic head, fluid formation pressures, and pressure gradients driving the flow through a cement column.

Description The FMA test cell has the same internal diameter as an API HTHP Fluid Loss cell. A hollow hydraulic piston at the top of the cell is pressurized with water to simulate the effect of the hydrostatic pressure on the cement. Filtrate from the cement slurry can be collected from the bottom of the cell through standard fluid loss 325 mesh screens or other desired mesh size screens. The formation pore pressure and fluid inflow is simulated at the bottom of the cell. Fluid migration through the cement is monitored using pressure transducers and flow meters. All pressures, filtrate volume s, temperatures, and formation fluid inflow rate are automatically measured, computer logged, and displayed on a continuous basis.

Theory The Model 7150 FMA is designed to perform the “Scale-Down Method” testing described by Beirute1 and Cheung (SPE 19522) and provides a great deal of operator flexibility for custom procedures. The scale-down method is intended to study migration through the cement column before the cement sets (short-term migration studies). Cement Slurry Gel Strength Measurements In order to perform the needed calculations for the test, a measure of the gel strength development versus time at realistic down hole conditions should to be made prior to the Scale-Down test. State-of-the-art acoustic technology allows measurement of the gel strength development of cement slurry at down-hole conditions using Chandler Engineering Model 5265 Static Gel Strength Analyzer. Moon and Wang (SPE Paper #55650) describe this methodology. A copy of this paper is located in the Reference section of this manual.

1 Beirute, R.M. and Cheung, P.R.: "A Scale-Down Laboratory Test Procedure for Tailoring to Specific Well Conditions, the Selection of Cement Recipes to Control Formation Fluids Migration After Cementing," SPE 19522, 64th SPE Annual Technical Conference, San Antonio, Texas, October 8-11, 1989.

P-2 PREFACE

Fluid Migration Test Design Table 1, which was calculated using formulas found in Beirute and Cheung (SPE 19522), shows an example of an FMA test designed using the Scale-Down Method. The assumed well conditions are also given in the table. As indicated before, the test schedule calculated using the Scale-Down Method is different for each set of well conditions and for different slurries with different gel strength development characteristics. In order to prepare the table below for a particular set of well conditions, it is critical to understand the path of migration that the invading fluid or gas will take.

Well Conditions Measured Depth, High Pressure Zone, Ft: 14800 Pore Pressure, High Pressure Zone, PSI: 10900 Measured Depth, Thief (Lower Pressure) Zone, Ft: 13000 Pore Pressure, Thief Zone, PSI: 8800 Measured Top of the Cement Column, Ft: 8000 Pipe O.D., In: 7 Hole Diameter, In.: 9 Equivalent Mud Density (From Mud and Spacer Column Lengths), Lb/Gal: 14.8 Cement Density, Lb/Gal: 15.8 Simulated gas zone pressure to be used in the test, PSI: 300 (This is the backpressure bottom during the fluid loss portion of the test. During the fluid/gas migration portion of the test, this is the base inject pressure.) See Table 1 sections A and B below.

Table 1 – Pressure Schedule Fluid/Gas Migration Test Designed Using the Scale-Down Method

A. Fluid Loss Portion of the Test

Time (min)

Slurry Gel Strength (lb/100 ft2)

Cement pore pressure (PSI)

Gas Zone Pressure (back pressure

bottom) 0 1.4 1128 300 6 8.3 1050 300

10 14 985 300 15 21 906 300 20 28 826 300 25 33 770 300 30 42 668 300 35 49 588 300 40 56 509 300 45 63 430 300 50 69 362 300

PREFACE P-3

B. Fluid/Gas Migration Portion of the Test Time (min)



Gas Zone Pressure (Injection Pressure)

Back Pressure Top

55 75 300 300 288 57 98 300 300 286 59 113 300 300 285 60 128 300 300 284 63 166 300 300 281 65 181 300 300 280 68 265 300 300 280

To end of test 394 300 300 280

Features and Benefits • Best features of the industry standard Gas Migration Device developed by Dr. Robert

Beirute. • Accurate temperature control to 400oF (205oC). • Accurate pressure control to 2000 PSI (14 MPa). • Deviated well-bore simulation. • Ability to test with standard fluid loss screens. • Removable top and bottom of the test cell to simplify sample removal and clean up. • Both liquid and gas flow monitored and recorded. • Multi-channel data acquisition by PC for real-time display.

Collecting Data during the Test All the pressures, temperatures, linear displacement transducer position, and filtrate volumes are recorded and displayed using the computer that comes with the instrument. The provided software continuously displays the data and is very flexible, allowing the display of all desired information at any time during the test.

Specifications Operating Conditions: 75°F - 400°F (24°C - 204°C) Maximum Temperature: 400°F (204°C) Maximum Pressure: 2000 PSI (14 MPa) Input Voltage: 200-240 VAC; 50/60 Hz Power: 1000 Watts Dimensions: 45” (114cm) high x 63” (160cm) wide x 24” (61cm) deep Shipping Dimensions: 47” (119cm) high x 57” (145cm) wide x 48” (122cm) deep Net Weight: 205 lbs (93 kg) Shipping Weight: 455 lbs (206 kg)

P-4 PREFACE

Safety Requirements Note: Before attempting to operate the instrument, the operator should read and

understand this manual. The Chandler Engineering Model 7150 Fluid Migration Analyzer is designed for operator safety. Any instrument that is capable of high temperatures and pressures should always be operated with CAUTION!! To ensure safety: • Locate the instrument in a low traffic area. • Post signs where the instrument is being operated to warn non-operating personnel. • Read and understand instructions before attempting instrument operation. • Observe caution notes. • Observe and follow the warning labels on the instrument. • Never exceed the instrument’s maximum temperature and pressure ratings. • Always disconnect main power to the instrument before attempting any repair. • Turn off the heater at completion of each test. • Locate an appropriately rated fire extinguisher within close proximity. After conducting a test, there is a strong possibility of trapping pressure inside the cement matrix in the cell. In some cases, it will take time for the gas to permeate through the cement in order for this pressure to be released. To make sure that the pressure in the cell is fully bled off prior to opening the cell, read Opening the Cell in Section 2 - Operation of this manual, and carefully follow the instructions. Note: All Chandler Engineering equipment is calibrated and tested prior to shipment.

Where to Find Help In the event of problems, the local sales representative will provide assistance, or contact the personnel at Chandler Engineering using the following:

• Telephone: 918-250-7200 • FAX: 918-459-0165 • E-mail: [email protected] • Website: www.chandlereng.com

Contact Chandler Engineering with all other inquiries, orders for spare parts, and technical support.

SECTION 1 - INSTALLATION 1-1

Section 1 – Installation Unpacking the Instrument

Carefully remove the instrument from the packing crate. The unit comes fully equipped with all of the necessary components and ordered spare parts. Make sure that no parts are lost when discarding the packing materials. Place the instrument on a firm table, close to the water source and required electrical outlets. Make sure that the location permits easy access to the nitrogen bottles required to conduct the tests. After the instrument is removed from the shipping crate, the equipment and spare parts should be checked against the packing list to ensure that all parts have been received and none are damaged. Note: File an insurance claim with your freight carrier if damage has occurred

during shipping. Verify all parts shown on the enclosed packing list have been received. If items are missing, please notify Chandler Engineering immediately.

Utilities Required • Filtered tap water source – filtered to 7 micron • Chilled water/coolant source • Nitrogen bottle • 220V outlet • Drain

Tools/Equipment Required Standard hand tools including wrenches

Setting up the Instrument Refer to Figure 1 below for illustration of the installation. 1. Attach water out bulkhead to a drain source. 2. Attach water in from a filtered tap water source to the water in bulkhead. 3. Attach coolant in from a tap water source (does not need to be filtered), or chiller if

desired. 4. Attach coolant out from bulkhead to drain, if using tap water, or back to chiller if desired. 5. Plumb nitrogen from the source to the nitrogen bulkhead. 6. Place balance A and balance B underneath the instrument and plug them into the

corresponding connections at the rear of the instrument. 7. Attach the data cable from the computer to the rear of the instrument. 8. Plug the power cord into the rear of the instrument and then into a proper electrical outlet

source.

1-2 SECTION 1 - INSTALLATION

Figure 1: Depiction of Rear of Fluid Migration Analyzer with Bulkhead Connections

Installing 5270 Data Acquisition System If a computer was purchased from Chandler Engineering with the FMA, the computer software needed to conduct the tests comes already loaded. The computer is ready to be used during the tests. Refer to Model 5270 - Data Acquisition and Control Software (5270 DACS) manual for details. This section describes the 5270 DACS installation process. Before installing 5270 DACS on the computer, read the system requirements section below to familiarize yourself with the hardware and software requirements. System Requirements The following table (Table 2) outlines the recommended system requirements for installing and running 5270 DACS under Windows 95, Windows 98, or Windows NT4.0.

Table 2: Recommended System Requirements Equipment Recommended Operating System Windows 95/98/2000/XP

Windows NT 4.0 Computer • Pentium processor computer, mouse, CD-ROM drive,

SVGA graphics display (1024 x 768), and a LAN connection

• The computer must be dedicated to the 5270 DACS system to avoid possible interference from other software

• Internet Explorer 5.0 or greater (5270 uses advanced graphics support in IE5.0.)

Computer Memory Minimum 128 MB Hard disk space - Typical Installation (approximate)

Minimum 2MB for 5270 files Minimum 1 MB additional free space for data files Additional space for temporary installation files


Equipment Recommended Email Microsoft Outlook 97, 98, 2000, XP or other MAPI

compliant email software Internet access

Serial ports One or more unused serial communication ports Parallel port One unused parallel communication port to be used with

the software security key and printer Printer Windows-compatible printer that supports graphic output

- HP Color Inkjet or LaserJet products (network printer or printer on parallel port)

Power An Uninterruptible Power Supply (UPS) is recommended Upgrading from an Earlier Version If you are upgrading from an earlier version of 5270 DACS, you do not have to uninstall your previous version since the setup program automatically detects and upgrades the previous version. In addition, when you upgrade by installing over a previous version, 5270 DACS retains your data and customizations. If you want to install 5270 DACS without your prior customizations, uninstall the older version of 5270 DACS before upgrading. In either case, the 5270 installation software will not normally delete the data files. Before You Install 5270 DACS To ensure a smooth installation, we recommend you follow the procedure below before installing 5270: 1. Exit all programs. 2. Check for sufficient disk space. See Reviewing System Requirements. 3. If you are upgrading from a previous version of 5270, see Upgrading from an Earlier

Version. 4. Verify that an unused serial port and parallel port are available. Locate them at the back

of the computer. 5. If using LAN resources, verify that the computer is logged into the network. Starting the 5270 Installation The setup program guides you through the installation process by prompting you for information and automatically determining your system configuration and available disk space. Note to Windows NT users: If you are installing 5270 under Windows NT, you must have administrative privileges.


To install 5270 1. Start Windows. 2. Insert the 5270 DACS installation CD into the CD-ROM drive. 3. If the installation does not start automatically, you can start the installation manually.

Click the Windows Start button and click Run. The Run dialog appears. In the Open field, type D:\SETUP.EXE, where “D” is the letter of your CD-ROM drive.

4. Follow the instructions on the screen. Click Next to proceed. Unless absolutely necessary, choose the default options and file locations for the program.

5. Attach the software security key to the LPT1 parallel port on the computer. Note that the key may be placed inline to the cable to the printer.

Configuring the Instrument Once the program is installed, it is necessary to connect the serial port(s) to the instrument and configure the instrument(s). To configure the instrument 1. Locate the serial port to be used to communicate with the instrument (COM1, COM2,

and COM3). 2. Connect the serial cable to the COM port at the back of the computer and the RS232C

port on the first instrument. 3. Turn on the instrument. 4. Verify that the communication hardware addresses of the Analog Devices modules are

configured properly. Each signal must have a unique hardware address. Note: The addresses are normally pre-configured by Chandler before the instrument

is shipped. 5. Start the 5270 DACS program. 6. Select the Tools – I/O Connection option (see Figure 2 below). Select New as specified

in the documentation for the particular instrument. Configure a New I/O Connection using the Analog Devices protocol.

Figure 2: Configuring I/O Connections


7. Select the “AD6B” protocol name. 8. Select Tools – Configure. Select New. Choose the Instrument Type Cement Fluid Gas

Migration Analyzer (Figure 3).

Figure 3: Selecting Instrument Type

9. Assign a name for the instrument to be displayed on the main screen. 10. Assign the serial number of the instrument. 11. Select the signals that will be used with the instrument. Uncheck any signals that are not

used. For Example: For the Model 7150 FMA, 11 signals are used to indicate temperatures, pressures, flow rates, and fluid volumes. Digital outputs are not used. 12. One at a time, double-click each signal and assign the I/O connection that was previously

created in Step 6, and the hardware I/O address. 13. To verify that the serial communication is functional, select the calibration button for

each signal and confirm that live data is displayed. If not, check the serial communication cable and the I/O address configurations of the devices (controllers, etc.).

Starting and Stopping a Test Once the system is configured, selecting File – New, Ctrl-N, or clicking on the instrument graphical icon will start a test. Verify that all signals are active as evidenced by a green light to the left of each active signal. Select the test profile for the Cement Fluid Migration Analyzer. The user will be prompted to choose a file name and to enter pertinent data for the test. The test information may be updated after the test is started by selecting the Test Properties button on the menu bar. Once the test is started, three graphs are used to display different groupings of the data values. Each graph is accessible by selecting the correct tab at the bottom of the graphical display (see Figure 4 on the following page).

Cement Fluid Gas Migration Analyzer


Figure 4: Graphical Display

To change the graph formatting during a test, right-click within the graphical area and select from the options that appear. Permanent changes to the test profile are made using the Tools – Configure – Test Profiles features (see Figures 5 and 6).

To stop a test, click on the Stop Test button on the menu bar, or close the window. In either case, the user will be prompted to save the data file.

Figure 5: Configure Test Profile Figure 6: Editing Test Profile Configuration

Software Setup and Data Display Please see installation and setup information in the accompanying 5270 DACS manual.

Graph Tabs

Test Start, Stop, Pause Buttons

Test Properties Button

SECTION 2 – OPERATION 2-1

Section 2 – Operation Keys to a Successful Test

The industry consensus indicates the following cement properties are necessary for fluid/gas migration control cement: non-settling, low fluid loss, and short transition time. Before running a fluid migration test, other standard cement tests should be run to verify that the slurry formulation is acceptable. These other tests may include fluid loss, static gel strength, and thickening time. If the results of any of the preliminary tests are unsatisfactory, the cement should be re-formulated before proceeding to the Fluid Migration Test. The Fluid Migration Test should be the final double-check that a cement formulation is performing as desired. The most crucial step in performing a good fluid migration test is the selection of the cement slurry to be tested. This instrument was designed to test true gas migration control cement slurries with the characteristics listed above. Testing of standard cement slurries, which are not designed to control migration, will typically provide unsatisfactory test results. It is critical that a static gel strength test is run on the cement prior to the fluid migration test. The results of the static gel strength test are used to calculate the pressure differentials on the scale-down method presented in the theory section of this manual. If the slurry being tested exhibits poor fluid loss control, it will be impossible to maintain the cement pore pressure schedule indicated in Table 1. The cement pore pressure will drop rapidly as the slurry loses fluid. If this occurs, the migration portion of the test can be started when the cement pore pressure reaches the formation pore pressure. The bulkhead fitting on the side of the cylinder is used to measure the pore pressure and must be completely filled with grease in order to prevent cement from plugging the line and causing pore pressure readings to be inaccurate. We have suggested using glass wool in addition to the grease to aid in preventing cement intrusion into the lines. However, some cement formulas may tend to form a pressure blocking structure very rapidly with the glass wool in place. If this happens, the pore pressure will drop off prematurely. In these instances, remove the glass wool and use grease only. If the slurry being tested begins to settle, this may be indicated by several different test results. First, the cement pore pressure may decline as a filter cake is formed near the measurement port. Second, when the migration stage is started, excessive fluid leak-off may be seen from the top of the cylinder. This can be an indication of free water at the top of the column due to settling. If pre-heating of the test cylinder is desired, the pre-heat temperature should be the same temperature that the slurry is conditioned at. For best results, the slurry should be the same temperature as the cylinder when it is introduced to the cylinder. If the cylinder has been pre-heated to a temperature higher than the cement, the heat may “shock” the cement causing it to set prematurely.

2-2 SECTION 2 – OPERATION

Function of Pressure Regulators and Valves

Figure 7: Front of Model 7150 FMA with Valve/Regulator Layout

Refer to Figure 7 for the following descriptions:

Regulators Cell base inject pressure regulator Used to adjust the nitrogen or water injection pressure during the Fluid/Gas Migration portion of the test. Back pressure nitrogen regulator Used to control the two back pressure regulators. Confining pressure regulator Used for applying pressure to the top of the piston and holding it against the cement slurry. (Also called the hydrostatic pressure.) The confining pressure applied to the sample is displayed on the Eurotherm pressure controller readout on the front panel of the Model 7150. Valves Cell discharge valve (Base) Used to apply or remove backpressure from the bottom of the cell.

OFF


Cell discharge valve (Top) Used to apply or remove backpressure from the top of the cell. Cell supply water valve Used to fill and drain water lines.

Cell base effluent valve Allows fluid loss from the cement slurry to be collected. Cell base inject valve Used with the cell base inject pressure regulator to select either nitrogen or water injection during the fluid/gas migration portion of the test. Cooling water valve Used for cooling the cell after a test, or when attached to a chiller to simulate deep water or artic conditions (located on the left side of the instrument). Cylinder Injection Valve Used for injecting gas or liquid through the cement column (unlabelled, located at the bottom of the cylinder). Back pressure valves Used with the back pressure nitrogen regulator (located at the bottom of the front panel of the instrument). Water reservoir vent valves Used for filling the two water reservoirs and for maintaining confining pressure (located on the right side of the instrument).

Preparation for a Test Initial Cell Preparation The cell and all of its parts, including the piston, bottom and top lids, screens, etc., must be clean and dry prior to each test. 1. Grease the thermocouples before they are inserted into the cell at the beginning of each

test. Remove the Cylinder Side Top Line from the cylinder shown in Figure 8. Remove the bulkhead fitting and pack the fitting completely with grease (supplied) in order to prevent cement intrusion into the pressure line. This fitting also needs a small ball of glass wool (supplied) to prevent cement migration.

2. Assemble the bottom of the cell with the bottom screen as indicated. Refer to drawing 7150-0007 Fluid Migration Cell Assembly located in Section 6 - Drawings and Schematics section of this manual for a schematic of the cell assembly.

3. Lightly grease the O-Rings and threads as needed.


4. Assemble the piston with the top screens, as indicated on the drawing (7150-0007), and lightly grease the O-Rings and threads as needed.

IMPORTANT NOTE: Successful operation of the FMA has a great deal to do with

proper initial setup of the system as well as correct maintenance and preparations made between tests. A very important item to remember is that all transducer lines should be fluid-filled before starting a test. Do not grease the inside of the cylinder

Filling Transducer Lines in Preparation for Testing

Figure 8: Depiction of Lines on the Cell

CYLINDER T/C

SLURRY T/C


Figure 9: Rear of Instrument

5. Unscrew the cap from the top of the Oil Fill Tee shown in Figure 9. 6. Using a syringe, inject oil into the line until it fills the line up to the Oil Fill Tee. Replace

the cap on the tee and re-connect the line to the cylinder. 7. Follow the same procedure for the water lines shown in Figure 8. (The unlabelled Cell

Base Valve should be closed for this procedure) Warning: Before placing cement in the cell, be sure that there is NO OIL on the

inside of the cell. If necessary, place some solvent on a paper towel and clean the inside of the cell.

Cement Slurry Preparation 1. Prepare the cement slurry according to API RP 10B. 2. Condition the slurry in an atmospheric or pressurized consistometer at the desired BHCT

or 190˚F, whichever is lower. 3. The length and schedule for the conditioning period should simulate as closely as

possible the expected cement job conditions. 4. The test cell requires approximately 550mls of cement per test. 5. Turn the main power switch ON. 6. Connect the thermocouples to the cell. The cement slurry thermocouple is the top

thermocouple while the cylinder thermocouple is the bottom thermocouple on the cell body.

7. Set up the temperature controller for the desired temperature profile. 8. Start the heater and pre-heat the cylinder to the desired temperature. The cylinder should

be pre-heated to a temperature equivalent to the conditioning temperature for best results. If a higher temperature test is desired, pre-heat the cylinder to the conditioning temperature and then heat to the desired test temperature AFTER the cement is introduced into the cylinder.


Loading of the Cement Slurry 1. Check to ensure that the unmarked valve at the bottom of the cell is closed before pouring

the cement slurry in. 2. After conditioning the slurry, pour it into the cell and fill to about 2.0" or 5 cm below the

inner shoulder. Be careful not to get any cement on the threads or sealing surfaces. Use the funnel in order to avoid contaminating the threads with cement.

3. Clean the threads and sealing surfaces as needed if they are contaminated with cement. 4. Slightly tap the sides of the test cell to help remove any air trapped in the cement slurry. 5. Add more slurry as needed. 6. Using a syringe, gently place about 10 ml of water on top of the cement slurry. This

volume of water will be used later in the assembly of the piston to fill the piston shaft to keep the top screen (on the piston) submerged in water, and to prevent plugging of the screen during the early stages of the test.

7. Put a thin film of grease on the piston O-Rings. 8. Insert piston in the cell until you feel a slight resistance when it reaches the surface of the

cement slurry. 9. Lightly grease the threads and O-Ring before assembling the top cap and retaining nut.

Tighten using the spanner wrench (supplied). The caps need only be tightened adequately enough to bottom out. Over-tightening will not aid in sealing. (See Piston Assembly drawing 7150-0007).

10. Keep your thumb over the top of the piston while screwing on the cap in order to keep the cement from exiting the cell and filling the top piston.

11. Mount the position transducer assembly on the top of the piston shaft. The transducer shaft should be fully extended and will not contact the cylinder plug until confining pressure is applied and sample is being collected.

Filling Water Reservoirs and Lines This procedure will also purge air from the backpressure regulators and lines to the cell. Refer to drawing 7150-0057 for the following steps. 1. Apply 100 PSI backpressure by setting both of the backpressure regulators to 100 PSI

and opening both backpressure valves (Base and Top). These valves are located on the front of the instrument below the front panel.

2. Close the backpressure valves. 3. Set the confining pressure regulator to 100 PSI. 4. Turn the water switch ON. 5. There are two Water Reservoir Vent valves on the right side of the machine. Turn the

valve closest to the front of the instrument to the VENT position. Wait until there is only water flowing through the sight tube then close the valve.

6. Turn the second Water Reservoir valve to the VENT position. Wait until there is only water flowing through the sight tube then close the valve.

7. Turn the cell supply water valve to the Fill/Vent position. 8. Turn the cell base effluent valve to the Fill/Flush position. 9. Turn the cell discharge valve to the Base position. 10. Wait about 2 minutes. Water should be seen flowing through the sight tube on the right

side of the FMA. 11. Turn all valves OFF and then turn the water switch OFF.


Test Setup Note: Test conditions used in these directions are from the test example given in the

theory section of the manual. Your actual test schedule must be designed to simulate the cement job at your particular site.

1. Open the Base Backpressure valve and set the backpressure regulator at the pressure used

to simulate the gas zone pressure (300 PSI in the example of Table 1). 2. Apply the initial simulated confining pressure (1128psi in our example) using the

confining pressure regulator. This pressure will appear on the digital pressure display on the front panel.

3. Turn the front water reservoir valve on the right side of the instrument to the Confining Pressure position. The piston shaft will move down and the position sensor shaft will contact the cell.

4. For deviated well-bore simulations, the cell may be rotated at this point.

Conducting the Test Part 1: Fluid Loss 1. Place effluent flasks “1” and “3” on the balances. Fill effluent flask “2” with water and

place in the middle, not on a balance. The line going into flask “2” should be below the level of the water. Be sure that all the flasks are tightly capped.

IMPORTANT NOTE: Flask “1” located on top of scale “A” collects the filtrate

from the bottom and top of the test cell. Flask “2” located in between the scales allows water displacement into flask “3” located on top of scale “B”. The tube going from flask “2” to flask “3” must be located below the water level. If gas is produced through the cement specimen, the gas displaces water from flask “2”, and the weight of the displaced water is recorded via scale “B.” The gas flow meter and scale “B” are calibrated to show gas flow in ml at atmospheric conditions.

2. Tare the balances. 3. Turn on the computer control software and start the test. 4. Observe the cement pore pressure displayed on the computer. Adjust the confining

pressure as needed in order to achieve the required 1128 psi cement pore pressure. 5. Open the cell discharge (base) valve. 6. Turn the cell base effluent valve to sample. Open this valve slowly.

Note: Fluid should now be entering the flask that is on the right side scale. The rate

of fluid collection will depend on the fluid loss characteristics of the cement. As fluid is collected and the cement begins to develop gel strength, the cement pore pressure will naturally begin to decrease. In order to follow your test schedule, you must continually adjust the confining pressure in order to maintain the required cement pore pressure at each specific time interval. The confining pressure will be approximately 10% less than the pressure applied to the top of the piston. This is due to the force balance across the floating


piston and the fact that part of the piston on the topside is not exposed to the applied pressure (due to the rod that exits the top of the cell). Decrease the confining pressure until you have reached your predetermined gas zone pressure. In this case, the confining pressure should not be reduced below 300 psi. Even though the piston pressure is easily calculable, the actual observed pressure through the piston will always be somewhat lower, due to the fact that this pressure is measured through a filter cake formation on the piston screen.

When the fluid loss portion of the test is complete, perform the following steps: 1. Close the cell discharge (base) valve. 2. Close the backpressure (base) valve. 3. Turn the cell base effluent valve to OFF.

Part 2: Fluid/Gas Migration 1. Open the backpressure (top) valve. 2. Set the backpressure regulator as required (initially 288 psi as in Table 1 example). Set

the base inject pressure regulator as required (300 psi as in Table 1 example). 3. Turn the cell base inject valve to the N2 or water position. 4. Open the cell discharge (top). 5. Open the cell base valve (unlabeled, see figure 8). 6. Slowly turn the cell effluent valve to the sample position. 7. In order to follow the requirements on the test schedule, you must continually adjust the

backpressure (cell discharge pressure) at the required time intervals (following the example of Table 1).

Note: During a test, care must be taken to make sure that the pressure inside the

cell is never higher than the pressure on top of the piston. Also monitor the pressures and the position of the piston by watching the graph of the piston location versus time, particularly around the time of the start of the application of pressure differential across the cement specimen. It is critical to maintain the downward force on the floating piston such that the pressure of the fluid (nitrogen or water) injected at the base of the cell does not cause the floating piston to move upward. The piston must never move in the upward position. If this happens, the cement will be artificially allowed to move. If for any reason during a test (generally due to operator error) the piston moves up, formation fluid or gas can artificially enter the cell. If the cement moves artificially, the test should be immediately terminated.

Caution: There is a drain tube from the hydrostatic regulator to the tray containing

the fluids to be pumped. If the pressure is released too quickly, water will be forced from the regulator into the pan holding the fluids to be pumped. Some air and water spattering may be heard.


Test Duration Carry through with the test for as long as it takes to make sure that flow migration through the cement is taking place, flow from the simulated formation is fully detected and stabilized. FMA tests may take several hours past the time the pressure differential across the cell (using the Scale-Down Method) is brought to a constant level. High temperature tests may require approximately 4 to 6 hours to reach a slurry temperature of 400°F, depending on the starting temperature of the cement. Since flow through the cement will most likely occur during the cement gelation stage, the very minimum duration of the test needs to be the time needed for the cement slurry to develop at least 1000 lb/100ft2 of gel strength. However, often the test needs to be conducted for longer periods if the test is indicating that migration is beginning to take place or if the influx of formation fluid is not stabilized (often influx starts and increases with time until it becomes stabilized).

Shutting Down the Test 1. Close the 5270 test and turn off the heater. 2. Set the temperature controller to “0.” 3. Close all three regulators and turn all the valves off. 4. Wait until the temperature is 190°F or 87°C. 5. Turn ON the cooling water. 6. Turn the cell supply water valve to the fill/vent position. 7. Turn the cell base effluent valve to the fill/flush position. 8. Turn the two reservoir vent valves on the right hand side to the vent position. 9. Run water through the cooling coil to allow the cell to cool down. 10. Cycle the cell water supply, cell base effluent, and water reservoir vent valves repeatedly

from vent to off position. Repeatedly cycle the unlabelled valve at the cylinder base open and closed. This procedure gives the best assurance that any residual pressure in the cylinder and lines has been relieved.

Warning: The cell supply water valve should never be turned to drain/vent base

position if there is confining pressure on the cell.

Opening the Cell 1. After the cell has cooled, unplug the top plug piston pressure line and remove the linear

displacement transducer from the top of the cell. 2. Back out both thermocouples from the cell and remove the two-side mount and bottom

plug pressure lines. Note: There are residual pressure pockets in the cell that cannot be relieved,

especially, the side thermocouple and side pressure ports. If the knurled threaded rings are tight and the plug tends to follow the ring as they are loosened, there must still be some pressure trapped in the cell pushing the plug. In that case, you must wait until this pressure is dissipated before attempting to


open the cell. Check each of the ports on the cell for plugging. If necessary, clear the opening with a small tool.

3. Rotate the cell assembly 90 degrees and remove the cell assembly. 4. Loosen the large knurled threaded rings at each end. 5. Provided no pressure has been detected, open the cell and remove the piston. Remove

the bottom plug of the test cell. 6. Press the cement sample from the cell and record the force required. This value can be

used for comparing relative shear bonds between samples. 7. Inspect the sample for evidence of channels, etc., that would contribute to fluid

migration.

Cleaning the Test Cell After Every Test Flushing the Sample and High Pressure Lines See drawing 7150-0057 sheets 6 and 7. This drawing schematic shows a suggested method for circulating water through the sample lines and back pressure regulators which will pressure flush out any residual “gray” water from the system. The cylinder does not need to be in place to flush out these lines. Tube fittings are provided in the accessory kit. As an alternative, flush out each water fill line via a syringe inserted into the tee on the back of the unit. The braided stainless steel high pressure lines should be removed and cleared of cement by inserting a 1/8” tube through the braided line repeatedly until the cement particles are cleared. The braided tubes are lined with Teflon to facilitate cement removal.

Pressure Cylinder 1. Refer to the cell assembly drawing 7150-0007 for the following cleaning and

maintenance procedures. Thoroughly and completely clean all cement residue from the test cell, end plugs, screens, etc. Be very careful not to scratch the bore of the cell or any sealing surfaces on the bottom and top portions of the test cell. Clean the screens thoroughly using a fine brush and/or muriatic acid. Inspect them for any damage. The screens must be in perfect condition to prevent cement particles from fouling the tubing connections to the cell. If a screen is damaged in any way, replace it before the next test. Inspect and replace the O-Rings on the cylinder plug and piston if cuts, damage, or imbedded particles are present. If none of these conditions are noted, wipe the O-Rings and the plug grooves free of cement particles or other foreign matter and lubricate the O-Rings with a light film of grease. Chandler Engineering recommends that you change the seals after each test, which has met or exceeded 250 degrees, or after every third test.

2. Clean out the pressure ports and thermocouple ports on the side of the cell and replace the

glass wool and repack the side pressure port fitting with grease. Clean and check the condition of the bulkhead fitting O-Rings (See Figure 8).


3. Unscrew the cell base manifold assembly from the bottom of the cylinder and clean any residual cement from the fittings. Disassemble the filter and dip the element in muriatic acid or another cleaner to remove residual cement.

SECTION 3 – MAINTENANCE SCHEDULE 3-1

Section 3 - Maintenance Schedule Calibration Procedures

Periodically calibrate components as recommended by the manufacturers instructions included with the instrument. Monthly Filter Replace the filter on the cell base injection line.

Six Months Tubing/Fittings 1. Replace the plastic high-pressure lines. 2. Replace the bulkhead fittings on the cylinder.

Annually Pressure Cylinder Have the test cell factory pressure tested and certified for pressure integrity.

Temp Controller/Thermocouples Calibrate by a qualified factory service technician.

Note: If you must replace a thermocouple due to damage or failure, note the position

of the ferrule on the original thermocouple. The slurry thermocouple ferrule is positioned to allow the probe to extend into the cylinder approximately ½”. The cylinder thermocouple ferrule is positioned to allow the probe to flush with the cylinder wall. Position the ferrule on the replacement thermocouple accordingly.

3-2 SECTION 3 – MAINTENANCE AND SCHEMATICS

Maintenance Schedule

COMPONENT EACH TEST MONTHLY 6 MONTHS ANNUALLY Cell Assembly and all Internal Components

Disassemble, Clean, Inspect

Pressure Test and Certify by Factory for Pressure Integrity

Screens Clean, Inspect

Replace Screens

Cell Base Inject Filter Replace Filter Pressure Lines Clean, Flush,

Inspect Replace

Plastic Lines Replace Pressure Lines

Temperature Controller Thermocouples

Calibrate by Qualified Factory Service Technician

Cylinder Side Ports Glass Wool

Replace Wool

Cylinder Side Port Bulkhead Fittings

Clean, Inspect

Replace O-Rings

Replace Fittings

Back Pressure Regulators

Disassemble, Clean, Inspect diaphragm

SECTION 4 – TROUBLESHOOTING GUIDE 4-1

Section 4 - Troubleshooting Guide Potential Problems and Solutions

Problem Cause Solution

Pressure transducers not accurately recording pressure in the cell

Transducer lines may be cemented up. Transducer lines may not be properly filled with oil or water – voids may exist in the lines. Flow lines may not be full of water.

Clean out lines completely Re-fill with oil following the procedure outlined in Flushing the High Pressure Lines in Section 3 – Maintenance. Re-fill with oil following the procedure outlined in Filling the Transducer Lines in Section 2 - Operation Follow the detailed instructions included under Filling Water Reservoirs found in Section 2 – Operation of this manual.

Weight from the balances is not reading correctly

Balance may not have been zeroed before the test was started. Specific gravity of the effluent is not entered into the software correctly. Flask 2 is not full of water or the line is above the surface of the water.

Check to see that the balance was zeroed at the beginning of the test. Adjust the specific gravity of the effluent in the software if necessary. Check to see that Flask “2” is full of water and the line entering the flask is below the surface of the water.

Piston moves up during the test

Confining pressure is less than the injection pressure.

Test must be immediately terminated. Check to see that the hydrostatic (confining pressure) is greater than the fluid injection pressure. It should be the calculated level plus an additional 10%.

Thermocouple is not reading Thermocouple(s) are not properly attached.

Check to see that both thermocouples are plugged into the cell.

4-2 SECTION 4 – TROUBLESHOOTING GUIDE

Problem Cause Solution Heater is not heating Thermal overload is tripped The thermal overload trips when the

thermocouples are unplugged (as when the cell is disassembled). Perform the following steps to clear the overload:

1. Plug in the thermocouples. 2. Push the red reset button on

the side of the instrument. 3. Power down the instrument

using the main power switch. 4. Power the instrument back

up. The overload should now be cleared and the heaters should function properly.

SECTION 5 – REPLACEMENT PARTS 5-1

Section 5 – Replacement Parts PART NUMBER DESCRIPTION

70308-53 Nut and Ferrule 7150-0041 Heater 7150-0042 Drilled Bulkhead Fitting 7150-0056 Piston Screen 7150-0065 Back-up Screen 7150-0073 Coil Top, Cylinder Side 7150-0074 Coil Bottom, Cylinder Side 7150-0094 Diaphragm C00596 O-Ring (Bulkhead fitting) C03318 Check Valve C08033 Anti-seize Compound C08984 Peek Tubing C09421 O-Ring C09427 Regulator C09467 O-Ring C09473 2-Way Valve C09699 Retaining Ring C09726 O-Ring C09731 Seal, Poly-pack C09750 Potentiometer, Linear C09751 Plunger, Spring C09777 Filter Housing C09778 Pressure Differential Transducer C09779 Pressure Transducer C09784 Gauge C09787 Flask C09793 Mass Flow Meter C09794 Balance C09834 O-Ring C09862 Glass Wool C09872 Filter C09873 Flexible Metal Hose C09990 Funnel C10395 Rubber Stopper P-0308 Needle Valve P-1663 O-Ring P-2137 Spanner Wrench P-2298 3-Way Valve P-2747 Thermocouple Assembly P-2839 Fluid P-3107 Solenoid Valve P-3156 Screen Assembly P-3217 Lithium Grease P-3554 Tygon Tubing

SECTION 6 – DRAWINGS AND SCHEMATICS 6-1

Section 6 – Drawings and Schematics

Drawing Number Description 7150-0001 Assembly, Fluid Migration Analyzer 7150-0007 Fluid Migration Cell Assembly 7150-0017 Plumbing Diagram 7150-0030 Wiring Diagram 7150-0057 Flow Schematic 7150-0060 Assy, Back Pressure Regulator

SPE 55650

Acoustic Method for Determining the Static Gel Strength of Slurries Jeff Moon, P.E., Steven Wang, Chandler Engineering

Copyright 1999, Society of Petroleum Engineers Inc. This paper was prepared for presentation at the 1999 SPE Rocky Mountain Regional Meeting held in Gillette, Wyoming, 15–18 May 1999. This paper was selected for presentation by an SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Papers presented at SPE meetings are subject to publication review by Editorial Committees of the Society of Petroleum Engineers. Electronic reproduction, distribu-tion, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.

Introduction Abstract

Well cement slurries are complex substances that must be tested and characterized prior to use in a well cementing op-eration. The reasons are numerous and often determine the success or failure of the cement job. Test methods and in-struments have been developed over the last 50 years to meas-ure cementing characteristics such as thickening time, com-pressive strength, fluid loss, settling, rheology and many oth-ers. Almost all of these methods involve mechanical meas-urements under HP/HT conditions to simulate well conditions.

Complex chemical reactions are occurring within a cement matrix as it becomes a solid. During the initial phase of the cement hydration, the cement exhibits polymer characteristics that exhibit a shear yield point that has been described as “static gel strength” (SGS). Due to this behavior, the cement slurry develops SGS after it has been pumped downhole. The start of gel strength development signals the point at which the cement slurry begins to change from a true hydraulic fluid that transmits full hydrostatic pressure to a solid material that has measurable compressive strength. The cement gel strength is important for two reasons:

More recently, non-destructive test (NDT) methods have

been developed for use in measuring the compressive strength (Ref. 8) and static gel strength of well cement. These instru-ments provide nearly continuous measurements as the proper-ties and testing conditions change.

• The static gel strength development determines the

shut down safety factor on the job. If the cement slurry is stopped prior to placement, then the static gel strength allows the calculation of the pressure required to restart circulation.

The Ultrasonic Cement Analyzer (UCA) was developed

for measurement of the compressive strength of a slurry using acoustic velocity measurement and, through the use of pro-prietary algorithms, the velocity is related to compressive strength. (Ref. 2)

• The static gel strength affects the hydrostatic pressure

distribution and the flow of gas or water into the ce-ment filled annulus, known as fluid or gas migration.

Recently, the Static Gel Strength Analyzer (SGSA) was

developed for the measurement of the static yield point, also known as the "static gel strength” of a slurry. Similar in na-ture to the UCA in some respects, acoustics, digital signal analysis and proprietary algorithms are used to perform the measurements.

This paper describes the discovery that as some slurries de-velop static gel strength, the attenuation of a high frequency acoustic signal transmitted through the slurry decreases. This change in amplitude correlates with the actual static gel strength of the slurry.

An acoustic method and system for determining the static gel strength of a cement slurry sample has been developed that provides nearly continuous, accurate, non-mechanical meas-urements of the static gel strength of cement slurry samples. The measurements are made at wellbore temperatures and pressures up to 400°F, 20000 psig.

Static Gel Strength

As cement changes from a slurry to a solid, the matrix de-velops a structure that behaves neither as a liquid or a solid. This process occurs before any measurable compressive strength has developed. This gelation characteristic must be

2 JEFF MOON, P.E., STEVEN WANG SPE 55650

Understanding gas or fluid migration in a cement slurry

can be accomplished either though the use of large physical models (ref. 1, 3, 8), or through the measurement of one of the fundamental controlling properties, Static Gel Strength. The first approach requires large-scale models as described by Jamth in Ref. 8. The second approach involves laboratory scale instruments that are used to quantify the parameters gov-erning the gas/liquid migration behavior into the annulus. In the first case, large-scale models provide a means for simulat-ing gas/liquid flow behavior but are constrained by the large sample volumes and have temperature and pressure limitations due to the size of the apparatus. In the second case, laboratory instruments are used to quantify the significant parameters, such as SGS. Although designed to be specific to the parame-ter being measured, the laboratory instruments allow the use of a manageable sample and can provide extreme HP/HT test-ing conditions. There is a need for each type of instrument, but for day-to-day slurry testing and practical reasons, the laboratory approach must take precedence.

understood and measured since it determines the gas or liquid in-flow potential and it may cause lower formations to be sub-jected to high pressures if the job is halted and restarted.

As a cement slurry develops static gel strength, it may be-

come self supporting in the annulus. In some respects, during the gel phase, cement may be considered as a material with similarities to a polymer. This is true since the cement matrix exhibits non-newtonian rheological behavior and exhibits a yield point, also known as static gel strength (SGS). Com-monly expressed in units of shear stress (lbf/100ft2), the term may be considered as the shear stress that exists at the wall boundaries at the onset of movement of a column of cement in an annulus due to the presence of a head pressure.

Previous investigators (Ref. 1,3,4) studied static gel

strength and developed laboratory models and methods for measurement of SGS. The following equation may be used to predict the pressure required to overcome the effects of SGS in a column of cement:

Clearly, there was a need for a laboratory instrument that is

capable of making measurements of the cement static gel strength prior to the development of compressive strength.

DLSP gs

300= Equation 1 Instrument Development

where, The acoustic characteristics of cement that relate to com-pressive strength were determined as a part of the develop-ment of the Ultrasonic Cement Analyzer (UCA). Using this instrument, the acoustic velocity through the sample indicates the compressive strength of the sample using correlations de-scribed by Rao et al over 15 years ago (Ref. 2, 6).

P = differential pressure to overcome SGS, psig Sgs = static gel strength, lbf/100ft2 L = length of column, ft D = diameter, inches (hole diameter – pipe diameter) One model for use in studying SGS involved measuring

the differential pressure across a cement column as the cement is moved at an infinitesimal rate within a known internal di-ameter and length tube (Ref. 1). A constant pressure is ap-plied at the head of the column and a motorized screw pump is used to withdraw volume from the bottom of the column at a rate ranging from 0.020 – 5.0 ml/min. The column is main-tained at a known temperature using a constant temperature bath. The differential pressure is measured and used to calcu-late the development of SGS.

A development project was undertaken with an independ-

ent consulting firm to develop an instrument capable of meas-uring the SGS of a cement slurry under HP/HT conditions using ultrasonics. During the proof of concept phases, initial experiments indicated that the attenuation of a signal that is transmitted through the slurry changes in a predictable manner prior to the onset of compressive strength. Further experi-ments were conducted to find the optimum acoustic frequency at which to make these measurements. Another approach involves API slurry cup geometry used

in adapted HP/HT cement consistometers to measure the static gel strength of the slurry (Ref. 7). The paddle is rotated at a rate of 0.5 - 2.0 degrees/minute using a stepper motor drive and the torque on the paddle due to the gel structure is meas-ured. The assumption that the rotating paddle induces plug flow of the slurry within the cup justified a calculation of the SGS using the swept area and length of the paddle. The rota-tional rate of the paddle is adjusted to be slightly less than the rate of development of the SGS. However, this approach to measuring SGS lacks sensitivity and resolution due to friction in the magnetic drive system and the continuous shearing of the sample may bias the measurement of SGS.

Early in the project, most of the effort was directed to-wards developing mathematical relationships between the sig-nal attenuation and the SGS of the sample. To determine these equations, the slurries listed in Table 1 were tested using the apparatus in Figure 1. Simultaneously, each sample was placed in a modified acoustic vessel and the signal attenuation characteristics were measured as a function of time. A variety of slurry designs were chosen to represent the spectrum of designs that are in common use, as shown in Table 1.

The tube apparatus shown in Figure 1 was not used for

every comparison. A shearometer, consisting of a known di-

SPE 16550 ACOUSTIC METHOD FOR DETERMINING THE STATIC GEL STRENGTH OF SLURRIES 3

ameter tube upon which a varying mass is placed to induce motion in the sample, was used for some of the data values.

Additionally, the effects of temperature (T) and pressure

(P) on the new method were studied. The objective was to establish that the methods used to measure the cement charac-teristics were independent from the effects of T & P. As a result of the studies, as summarized in Figure 4, the effects of temperature on the cement measurements were judged to be negligible. Additional studies indicated that the effect of pres-sure on the measurement was greatly reduced when the sample was pressurized to a minimum pressure of 500 psig to elimi-nate the effects of entrained air.

An acoustic pressure vessel similar to that used in the

UCA was chosen for use in the new instrument (Ref. 6). Changes were made to the end plugs in the vessel to improve the acoustic coupling between the piezo transducers and the sample.

Although the vessel is similar in design to that used in the

UCA, the captured signal analysis is much more complex. The UCA design measures the acoustic velocity, whereas, the SGSA measures the signal content. Consequently, the SGSA incorporates an embedded system that performs digital proc-essing of the signal to determine the signal attenuation. This process involves high speed sampling of the signal, FFT analysis, and calculation of intermediate signal attenuation values. Once this process is complete, each attenuation value is transmitted to the host computer. When the data set is com-plete, post-analysis of the data calculates the SGS values as a function of time. Refer to the system block diagram and sam-ple report in Figures 5 and 8.

Due to the nature and content of the stored data, the acous-

tic velocity (transit time) is also determined. Using the pro-prietary UCA algorithms developed by Rao et al (Ref. 2), the compressive strength of the sample is calculated after the SGS development is complete. Consequently, the new instrument provides SGS data and compressive strength as a function of time (Figure 8).

Basis for the Measurement

Intuitively, one could suggest that the Static Gel Strength

Analyzer (SGSA) is a viscometer that uses acoustic signal analysis as a basis for the SGS measurement. This is not the case. A viscometer measures the shear stress corresponding to a known fluid shear rate. From this data, the viscosity of the sample is determined. One of the advantages of an acoustic measurement is that the sample is not sheared, thereby provid-ing a fluid property measurement at zero shear rate. Research of existing literature discovered comparable techniques for fluid property measurement used in the polymer industry. There are precedents where acoustic signal analysis provides measurements of the gelation characteristics of epoxy samples and curing agents. Interestingly, based on the data presented

in Ref. 5, the signal waveforms are similar to those found with a cement slurry analysis.

Additional study of the process suggests that the change in

the transmitted signal energy occurs due to the chemical reac-tions in the slurry. For example, as the amount of the unre-acted water decreases during hydration, the transmitted signal energy increases. From this observation, it is expected that a continuous measurement of the unreacted water within a slurry will be achieved.

Once the gelation phase of the cement is complete and pre-

sumably, most of the water has been absorbed by the reaction, the signal attenuation characteristics are no longer of interest with respect to SGS measurements. In fact, the acoustic ve-locity begins to change rapidly as the sample develops com-pressive strength. Intuitively, one would expect this to be true since a substance that exhibits compressive strength is no longer a gel. Note from Figures 8 and 9 that the initial devel-opment of compressive strength coincides with the peak value of the SGS.

As evidenced by each UCA test, there are changes to the

acoustic velocity, or transit time, during the initial phases of the cement reaction prior to the onset of compressive strength. Based on additional observation of the data, one finds that monitoring the signal attenuation provides a much higher reso-lution measurement of the gelation characteristics. Refer to Figure 3 as well as Figures 9 as examples of this observation. Analytical Results

Once the technique of correlating signal attenuation to static gel strength was established, many cement samples (Ta-ble 1) were evaluated to test and optimize the correlation(s). A typical example of these numerous data sets is provided in Figure 9. In all cases, the results were compared with data obtained from the tube rheometer apparatus and shearometer with good results.

An example of the fit between measured SGS and the cor-

related result is found in Figure 6. The comparison results for most slurries were similar and allows one correlation to be used for most slurry compositions. Ongoing efforts to en-hance and extend the applicable range of the correlation are underway.

The data presented in Figure 10 represents part of the de-

sign verification testing of the completed instrument. Five slurries where chosen for testing in the production model of the instrument and for comparison with earlier results.

Additional data is presented in Figure 11 that indicates the

effect of worn mixer blades on the development of static gel strength. Although not the subject of this paper, this data il-lustrates the type of information that may be obtained using the SGSA instrument.


Results that illustrate differences in Class H API cement

from different manufacturers is shown in Figure 12. For this study, the same slurry design and temperature and pressure schedules were used. The API Class H cement used as sam-ples was obtained from separate manufacturers.

The data shown in Figure 13 indicate the excellent SGS measurement repeatability that is possible using the SGSA instrument when identically prepared slurries are tested under the same conditions. Conclusions

1. The characteristic of a cement slurry to develop a gel structure as a function of time prior to setting has been studied and modeled extensively. The term static gel strength (SGS) is used to quantify this characteristic behavior.

2. SGS is one of several variables that are being evalu-ated in attempts to model gas or liquid migration after well cementing operations.

3. Existing methods to measure SGS as a function of time involve large-scale laboratory models or the use of rotating paddle type instruments.

4. Ultrasonic measurements may be used to measure SGS using correlations that relate signal attenuation to SGS.

5. A new laboratory instrument has been developed that provides SGS measurement as a function of time un-der HP/HT conditions (Figures 7, 8).

Nomenclature

P Pressure, psig Sgs Static gel strength, lbf/100ft2 L Length of column, ft

D Diameter, inches (hole diameter – pipe di-ameter)

NDT Non-Destructive Testing SGS Static Gel Strength HP/HT High pressure, high temperature UCA Ultrasonic Cement Analyzer

Acknowledgements

The authors wish to thank the management of Chandler Engineering for permission to publish this paper. Addition-ally, the cooperation with Fred Sabins and Voldi Maki with Westport Technology Center International during the devel-opment of this instrument is acknowledged and appreciated. References 1. Sabins, F.L., Sutton, D.L., “The Relationship of Thickening

Time, Gel Strength, and Compressive Strength of Oilwell Ce-ments”, SPE Paper 11205, 1986

2. Rao, P.R., Sutton, D.L., Childs, J.D., Cunningham, W.C., “An Automatic Device of Nondestructive Testing of Oilwell Ce-ments at Elevated Temperatures and Pressures”, SPE Paper 9283, 1982

3. Bannister, C.E., Shuster, G.E., Wooldridge, L.A., Jones, M.J., Birch, A.G., “Critical Design Parameters To Prevent Gas Inva-sion During Cementing”, SPE Paper 11982

4. Bannister, C.E., “Rheological Evaluation of Cement Slurries: Methods and Models, SPE Paper 9284

5. Matsukawa, M., Nagai, I., “Ultrasonic Characterization of a Polymerizing Epoxy Resin with Imbalanced Stoichiometry”, Journal Acoustical Society of America, April 1996

6. Rao, P., Moon, J.J., “High Pressure-High Temperature Auto-clave System for Testing Fluid Samples Ultrasonically”, U.S. Patent #4,567,765, 1986

7. Moon, J.J., Surjaatmadja, J.B., Ehlert, M.C., “Consistency and Static Gel Strength Measuring Device and Method”, U.S. Patent #4,622,846, 1986

8. Jamth, J., Justnes, H., Nodland, N.E., Skalle, P., Sveen, J., “Testing System to Evaluate the Resistance of Cement Slurries to Gas Migration During Hydration”, CADE/CAODC Spring Drilling Conference, 1995

Metric Conversion Factors Inch3 x 1.648706 E01 = cm3 Feet x 3.048 E-01 = meter (°F –32)/1.8 x 1.0 E00 = °C inches x 2.54 E00 = cm lbf/ft2 x 4.788026 E00 = kPa psi x 6.894757 E00 = kPa


Table 1 Cement Compositions

Slurry Number

Slurry Composition Density, lbm/gal

Temperature, °F

1 H, neat 16.5 85 2 H, 1% CaCl 16.5 85 3 H, 8% Bentonite, 2% CaCl 12.5 85 4 H, 8% Bentonite, 2% CaCl 13.5 85 5 H, 6% Bentonite, 2% CaCl 14.5 85 6

Figure 9 H, 35% sand, 0.5% Halad-344 17.0 120

7 H, 15% NaCl 16.4 120 8 H, 35% Sand, 18% Hematite, 0.5% Halad 344,

0.5% HR-12 18.5 230

9 H, 0.1% HR-5 16.5 120 10 H, 35% Sand, 0.5% CFR-3, 1% Halad 22A 17.0 120 11 H, 2gps Latex, 0.2gps S-434B, 0.1% CFR-3 16.5 150 12 H, 35% Sand, 0.5% CFR-3 17.0 120

Comparison Study

Varies, See notes on plot Varies Varies

ForceTransducer

SteppingSteppingMotorMotorTorque

TimeTime

PULLEY ROTATES PADDLE

SAMPLESHEARING

0.50 - 2 DEGREES/MINROTATIONAL SPEED

SCREW PUMP

CONSTANTPRESSURE

SOURCE

HEATING/COOLING BATH

dPTRANSDUCER TEST COLUMN

dP = SGS/300 x L/D

Figure 2 – Rotating Paddle SGS Measuring Device Figure 1 – dP Static Gel Strength Measurement Apparatus


Signal Amplitude

Time, minutes

Figure 4 – Temperature Effect Study using Water Figure 3 – Acoustic Velocity versus Signal

Amplitude Study

Acoustic Velocity

Signal Amplitude

CementSlurry

TransducerPulsing

Electronics

AcousticWaveformCapture

Measurement ofSignal

Amplitude

DigitalSignal

Processing

Calculationof SGSValue

Figure 5 – SGSA Block Diagram Figure 6 – Verification of the Accuracy of the SGS Correlation


Figure 7 – Static Gel Strength Analyzer

Figure 8 – Static Gel Strength Analyzer Report


H, 35% sand, 0.5% Halad-344

Calculated Static Gel Strength

Signal Amplitude

Acoustic Velocity

Figure 9 – Typical Data Sets of Signal Amplitude, Transit Time, and Calculated SGS

0

200

400

600

800

1000

1200

1400

0 30 60 90 120 150 180 210 240 270 300Time(minutes)

Sample 1 : Class H, Neat, BHT 85FSample 2 : Class H, 0.1% Retarder, BHT 120FSample 3 : Class H, 2% CaCl2, 8% Gel, BHT85FSample 4 : Class H, 35% Sand, 39% Hematite,0.5% Fluid Loss, BHT 120FSample 5 : Class H, 0.1% Retarder, 18.44%Latex, BHT 150F

Sample 1

Sample 5

Sample 4

Sample 2

Sample 3

Figure 10 – Comparison of Results from Various Slurries


0

200

400

600

800

1000

1200

1400

0 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240

Time(minutes)

SGS(

#/10

0ft^

2)

Class H, 2% CaCl2, 8% Gel, BHT 85F

New Mixer Blade

Worn Mixer Blade

0

200

400

600

800

1000

1200

1400

1 31 61 91 121 151 181 211 241 271 301 331 361 391 421

Time(minutes)

Stat

ic G

el S

tren

gth(

lb/1

00ft2

)

0

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Class H, Neat, 85F, 3000 psig

Figure 11 – Comparison of Results using New versus Worn Mixer Blades

Figure 12 – Comparison of Results using Cement from Different Manufacturers


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Figure 13 – Repeatability Study using Identical Slurries

Application Note

Model 7150 FMA Application Sheet

BACKGROUND ON FLUID MIGRATION IN CEMENTING A cementing job is typically performed with a pressure differential going into the formation in order to maintain control of the well. The diagram below depicts a typical cement job in which migration would be a concern.

Low Pressure Zone (Thief)

Casing Cement

Impermeable Barrier Between Zones (typically shale)

High Pressure Zone (Source)

In the diagram above, the cement must control flow (migration) from the high pressure zone to the low pressure zone before it sets. When the cement is initially placed in the well, the cement pore pressure will be greater than the formation pressure by design. However, as the cement develops gel strength and simultaneously leaks-off into the formation, the cement pore pressure decreases. When the cement pore pressure reaches the formation pressure, then migration can occur. A general guide is that if the cement has greater than 500 lb/100ft2 of gel strength when the cement pore pressure reaches the formation pressure, than migration will not occur. However, if the gel strength is not yet that high, then migration may occur. The plot below shows the cement pore pressure decline with time for a theoretical job. The critical time shown below is the time when migration can begin if it is not properly controlled by the cement.

P.O. Box 470710, Tulsa, Oklahoma 74147-0710 U.S.A. Telephone: 918-250-7200, FAX: 918-459-0165, Email: [email protected]

Application Note


Illustration of Critical Time

Time (min)

Pres

sure

Formation PressureCement Pore Pressure

Tc (Critical Time)

METHOD DESCRIPTION

The Model 7150 FMA is designed to perform the “Scale-Down Method” testing described by Beirute and Cheung (SPE 19522) and provides a great deal of operator flexibility for custom procedures.1 The scale-down method is intended to study migration through the cement column before the cement sets (short-term migration studies). The scale-down method is a standard test method developed in an attempt to closely simulate real well conditions in the laboratory. Previous gas migration testing methods have been unable to realistically simulate hydrostatic head, gas formation pressure, and pressure gradients driving the gas through the cement column. Some test methods have used a constant hydrostatic pressure during testing that is not a realistic representation of what happens in the well. Finally, other methods have not allowed leak-off of the cement to occur. The scale-down method is tailored to each individual well and more closely represents actual well conditions than previous test methods. In order to properly test a cement slurry with this instrument, it is essential to know the well conditions for which the slurry is being designed, particularly the path of expected migration. The well conditions are used to design the test schedule for a fluid migration test. The method also requires that the exact cement slurry proposed for the job be tested in the test device.

The scale-down method is a worst-case scenario for testing. It assumes that the invading gas has enough permeability, thickness and volume to fully invade and pressure-charge the cement column. The pressure decline that is used for the testing, represented in the figure

Application Note above, is the MAXIMUM pressure decline that the cement could experience in the well. In reality, the pressure decline in the well may be less. In the laboratory procedure, the gel strength development of the slurry is used to estimate the maximum potential pressure decline in the cement column. The maximum possible hydrostatic pressure decline with time due to gel strength development is normally calculated using the following equation:

∆P = (GS/300) x (L/D)

Where:

GS = Gel strength of the given proposed cement slurry vs. time in lb/100 ft2

∆P = Pressure head decline in PSI

L = Length of the cement column in feet

D = Mean diameter of annulus (Hole-Casing) in inches.

300 = Conversion factor

The calculated pressure decline schedule is then used to allow dehydration from the cement into the simulated gas formation and to predict when a pressure differential needs to be applied across the slurry to potentially drive gas through the sample. The magnitude of the pressure differential placed across the cement specimen is calculated using Darcy's Law, assuming that equal "bulk permeabilities" exist in the well and in the test cell. The gas influx into the cement is measured. At the end of the test, it is possible to tell if the proposed slurry formulation will control the gas migration problem in the given well across the zone of interest.

FLUID MIGRATION TEST DESIGN Table 1 shows an example of an FMA test designed using the Scale-Down Method. The assumed well conditions are also given in the table. As indicated before, the test schedule calculated using the Scale-Down Method is different for each set of well conditions and for different slurries with different gel strength development characteristics. In order to prepare the table below for a particular set of well conditions, it is necessary to predict the path of migration that the invading fluid or gas will take. In addition, the GS development vs. time of the proposed cement slurry needs to have been measured at downhole conditions, prior to making the calculations. The following sequence of calculations must be made. Complete definitions for these equations are explained in SPE 19522, included in the owner’s manual.

• Confining pressure (mud weight) on the cement column. • Initial confining pressure (mud & cement). • Cement pore pressure drop (due to gel strength development). • Confining pressure and resulting cement pore pressure at a given time and zone. • Pressure differential into a cemented zone at a given time. • Discharge pressure (pressure differential across the cell) and injection pressure.


Application Note

Well Conditions Measured Depth, High Pressure Zone, Ft: 14800 Pore Pressure, High Pressure Zone, PSI: 10900 Measured Depth, Thief (Lower Pressure) Zone, Ft: 13000 Pore Pressure, Thief Zone, PSI: 8800 Measured Top Of The Cement Column, Ft: 8000 Pipe O.D., In: 7 Equivalent Mud Density (From Mud and Spacer Column Lengths), Lb/Gal: 14.8 Cement Density, Lb/Gal: 15.8

Simulated gas zone pressure to be used in the test, PSI: 300 (This is the backpressure bottom during the fluid loss portion of the test. During the fluid/gas migration portion of the test, this is the base inject pressure.) See Table 1 sections A and B below.

Table 1 – Pressure Schedule Fluid/Gas Migration Test Designed Using the Scale-Down Method

A. Fluid Loss Portion of the Test

Time (min)



Gas Zone Pressure (back

pressure bottom) 0 1.4 1128 300 6 8.3 1050 300 10 14 985 300 15 21 906 300 20 28 826 300 25 33 770 300 30 42 668 300 35 49 588 300 40 56 509 300 45 63 430 300 50 69 362 300

B. Fluid/Gas Migration Portion of the Test Time (min)



Gas Zone Pressure (Injection Pressure)

Back Pressure Top

55 75 300 300 288 57 98 300 300 286 59 113 300 300 285 60 128 300 300 284 63 166 300 300 281 65 181 300 300 280 68 265 300 300 280

To end of test

394 300 300 280


Application Note Test Description The FMA is designed to be the last step in a series of tests to verify that a particular cement formulation will perform as desired in a particular well. A static gel strength test must be run on the cement before the migration test is run. The static gel strength development is used to calculate the pressure decline schedule for the migration test. The industry consensus indicates the following cement properties are necessary for a fluid/gas migration control cement: non-settling, low fluid loss, and short transition time. Before running a fluid migration test, other standard cement tests should be run to verify that the slurry formulation is acceptable. These other tests may include fluid loss, static gel strength, and thickening time. If the results of any of the preliminary tests are unsatisfactory, the cement should be re-formulated before proceeding to the Fluid Migration Test. The Fluid Migration Test should be the final double-check that a cement formulation is performing as desired. The FMA is designed to test cements that are formulated specifically for migration control. Cements with high fluid loss and settling problems will not perform well with the FMA. The choice of cement formulation is one of the most critical steps in performing a successful test with the FMA. If the slurry being tested exhibits poor fluid loss control, it will be impossible to maintain the cement pore pressure schedule indicated in Table 1. The cement pore pressure will drop rapidly as the slurry loses fluid. If this occurs, the migration portion of the test can be started when the cement pore pressure reaches the formation pore pressure.

If the slurry being tested begins to settle when the migration stage is started, excessive fluid leak-off may be seen from the top of the cylinder. This may be an indication of free water at the top of the column due to settling.

The pre-heat temperature of the cylinder should be the same temperature at which the slurry is conditioned. For best results, the slurry should be the same temperature as the cylinder when it is introduced to the cylinder. If the cylinder has been pre-heated to a temperature higher than the cement, the heat may “shock” the cement causing it to set prematurely. The instrument uses a 550 ml sample of cement to perform the test. The sample is heated to the bottom-hole temperature of the well and a confining pressure is placed on the column that is equivalent to the hydrostatic head on the cement column in the well being simulated. Leak-off from the cement is collected and recorded until the cement pore pressure reaches the formation pressure. As the cement pore pressure reaches the formation gas pressure, invasion of a gas or fluid from the formation can occur. After the leak-off portion of the test


Application Note


has concluded, a gas or fluid is injected into the cement column with a pre-calculated pressure differential and the flow rate through the column is measured. At the conclusion of the test, the cement is cooled and removed. The cement sample may then be visually inspected and/or cored for further analysis.

7150_p3

Documents

chandler engineering

table of contents t

system requirements

data acquisition system

fluid migration analyzer

fluid migration test

safety requirements

express permission