logging cased hole

Cased Hole Logging

• Surveillance and by-passed pay

Cased Hole – Fluid Composition

Capacitance, Fluid Di-elect. Fluid type - hydrocarbon vs. water.

Fluid Resistivity Fluid type - hydrocarbon vs. salt water.

Pulsed Neutron Capture 3-phase ID in well, req. homogeneous formation

Gradiomanometers Fluid type - oil and water, looses resolution in high deviation,

limited in high rate and high oil cut.

Fluid Density Fluid type- oil vs. water, better in high GLR.

Temperature Fluid entry (zones/leaks) rate/temp limits.

Noise Leak/zone entry. Channel flow behind pipe, depending on

rate.

Fluid Level Survey Fluid level only, confused by foams, froths and emulsions.

Spinners Total flow rates and entry/exit points. Deviated wells are a

challenge.

Radioactive Tracer Tool Total flow rates and entry/exit points. Not useful in deviated

wells.

Oxygen Activation Velocity of water phase. Holdup and leak detection.

Cased Hole – Casing/Cement Inspection

Caliper Log Accuracy depends on number of

fingers, speed, tool type. Casing Inspection

Eddy Current Inner wall investigation. Shows some

smaller flaws, measures ID Casing Inspection

Flux Leakage Casing body inspection. Id of inner /

outer wall, and body casing

problems, not in OBM

Casing Inspection

Ultrasonic Casing body inspection. Affected by

fluids, used in thicker wall pipe

(>0.2”)

Casing Inspection

Electromagnetic Phase Shift Casing body inspection. ID and wall

thickness, averaging tool may

miss small defects

Casing Inspection

Conventional Acoustic Cement presence. Averaged data, not

really useful for most problem

identification

Cement Evaluation

Segmented Acoustic Channels, Bond. 360o, channels and

voids, bond under right

conditions.

Cement Evaluation

Ultrasonic Casing and Cement bond. 360o,

channels, voids, bond, pipe

conditions w/ right application.

Cement Evaluation

Cased Hole – Correlation/Evaluation

Gamma Ray Lithology and correlation

Inexpensive. No porosity.

Correlation

Neutron log – single detector Lithology and correlation

Inexpensive. No porosity.

Correlation

Neutron log – dual detector Porosity. RA source needed,

accuracy less than OH log.

Formation

Evaluation

Acoustic Porosity. Limited in cased wells,

requires good bonds for accuracy

Formation

Evaluation

Pulsed Neutron Capture

PNC

Water saturation. Does not work in

low or changing salinity, or low

porosity

Formation

Evaluation

Pulsed Neutron

Spectrometry PNS C/O

Water saturation. Does not work

well in low porosity

Formation

Evaluation

Cased Hole Resistivity Water Saturation. Salinity

dependent, stationary reading,

relative deep reading

Formation

Evaluation

Problem or

Information Needed

Rec. Logging Tools

Procedure/Level of Detail

Detection of

Crossflow or

Underground

Blow out

Temperature

Survey

Difference in slope of temperature gradient – will

detect flow rates down to 25 BPD if liquid and

temperatures of fluids are different. Figures on

temperature vs. flow distance help estimate water

flow in the annulus.

Noise Log

Best performance of noise logs is with gas flow.

Gas flow to about 10 actual ft3/D (Note – not

standard ft3/day). At very low gas flow rates

(q<400 actual ft3/D), gas flow can be estimated

from millivolts of noise between the 200-Hz and

600-Hz frequencies:

q = 0.35 (N200 – N600). Where q is the actual gas

flow in ft3 and N = noise log cut at that frequency.

Oxygen

Activation Survey

Open hole or channels behind single string.

Accuracy is sharply reduced for investigating

channels behind two strings (use temp or noise

tools).

Detection of Crossflow

Problem or

Information Needed

Rec. Logging

Tools

Procedure / Level of Detail

Location of Cement

Top

Temperature

Survey

OK if run within 12 to 24 hrs of cement job.

Little temperature variation with the formation

may make cement top difficult to see.

CBL (cement

bond log)

Best results after 3 days or when cement has

developed 70%+ of the compressive strength.

These tools may be too large for slim hole wells.

Gravel-pack

logging (GR)

Tool response depends on density difference

between cement and annular fluid.

Location of Cement Top

Problem or

Information Needed

Rec. Logging

Tools


Evaluation of Cement

Placement

Open hole

caliper

Accuracy depends on caliper and hole roughness

and washouts. Caliper tools with more than 4

arms are needed for hole volume measurement

accuracy.

Sweeps with

markers after

running casing

Sweeps give decent estimates of hole volume, but

sweeps may not reach all of the annular space in

uncentralized cased holes. Useful for swept hole

% analysis.

Temperature

Survey

OK if run within 12 to 24 hrs of cement job.

Little temperature variation with the formation

may make cement top difficult to see.

Gravel Pack Log

Good if fluid density difference greater than 0.3

gm/cc (0.13 lb/bbl). Could run before and after

cement for background data.

CBL – both

regular and

segmented

Semi-quantitative contact measurement of

pipe/cement and cement/formation. Affected by

casing pressure and tool calibration.

Evaluation of Cement Placement and Bond

Problem or

Information

Needed

Rec. Logging

Tools


Detection of

casing wear

from drilling

E-line calipers

Multi-arm calipers generally good, but slick line

calipers may rotate and “over-report” the bad

spots.

EM – eddy

current tool that

measures wall

thickness

Highly accurate if the hole is filled with a non

conductive fluid.

Acoustic wall

thickness tool

Qualitative indicators of wear (thickness

numbers are not very accurate)

Casing Inspection

Problem or

Information

Needed

Rec. Logging

Tools

Level of Detail

Detect casing

collapse

EM – eddy

current wall

thickness survey

Investigation is to 8 to 10” radius. Investigation

ability falls off after the first string encountered.

Qualitative investigation. Splits are more

difficult to see.

Gravel-pack (GR

– density)

Depth of investigation depends on source

strength – may range from 4” to 16”. Splits are

more difficult to see.

Determination of External Casing Corrosion

Problem or

Information

Needed

Rec. Logging

Tools


Annular Flow

Temperature

Survey

Useful where the well has active annular flow.

Can spot flows on the order of 1 bpd (after 24

hrs) if temperature of formation at

measurement and source of water is sufficiently

different. Two surveys, 12 hrs apart is usually

adequate to spot presence of a channel.

OA - oxygen

activation

Accurate, but don’t swap out muds. Migration

of fluids in pipe may be seen as “channel”.

Noise logging

Accuracy depends on channel variations to

accelerate flow and change sound.

Flow Behind Pipe

Problem or

Information

Needed

Rec. Logging Tools


Determine

annular flow

in injector

RA Tracer Survey

- inject slug of I-

131 in brine.

Track from surface to annulus until slug is

completely pumped away. Track any flow that

goes behind pipe and moves up.

OA- oxygen

activation survey

Not as reliable as the chemical tracer, due to

fluctuations in the injection rate.

Temperature

survey

Three temperature surveys are needed: one before

annular injection (base line), one during and one 4 to 6

hours after injection (decay).

Borax Log

Pumping borax/water solution down tbg into the liner,

allowing mix to invade perfs & any channels in

casing/formation annuli. Initial pass, before borate

injection, is w/ Pulsed Neutron log (no Borax),

followed by passes at 20bbls, 40bbls, and 60bbls as

borax mix pumped. Borax affects neutron capture,

leaving a characteristic signature. Overlays of the

Sigma/CNL counts reveal the zones of borax

penetration, and identifies channels taking fluid.

Determination of Flow Behind Pipe for Injector

Problem or

Information Needed

Rec. Logging Tools


Certification

for annular

disposal

Radioactive Tracer

Survey with RA

isotope in brine,

pumped into annulus

while logging with a

GR tool in tubing.

Can distinguish entry points and limited detail

on up or down movement of the inject slug.

Oxygen activation

survey

Not as accurate as RA logging. Fluctuations in

rate create problems.

Temperature

survey

Can determine channels and entry points.

Needs 3 runs – before, during and after.

Borax Log




injection, is w/ Pulsed Neutron log (no Borax), followed by

passes at 20bbls, 40bbls, and 60bbls as borax mix pumped.

Borax affects neutron capture, leaving a characteristic

signature. Overlays of the Sigma/CNL counts reveal the

zones of borax penetration, and identifies channels taking

fluid.

Location of Annular Leak

Problem or

Information

Needed

Rec. Logging

Tools


Location of leak

to annulus or

crossflow behind

pipe

Temperature

survey

Relatively accurate at rates of at 1 bpd or more. Need

minimum of 2 runs, before and during injection. A

third run may help define a qualitative level of leak

rate. Run at 1oF/in sensitivity. Will not see small gas

leak rates through liquid.

Noise log

Best for gas leak detection. Run static log and then

again during flow or negative test. Upward gas

movement (percolation) at actual 10 ft3/D or more

should be detectable.

Oxygen

activation log

Can detect flows of 20 to 40 bpd in the annulus of a

single string well if the leak is directly opposite the

tool. Resolution drops to >200 bpd when two strings

are present

Borax Log




injection, is w/ Pulsed Neutron log (no Borax),

followed by passes at 20bbls, 40bbls, and 60bbls as

borax mix pumped. Borax affects neutron capture,

leaving a characteristic signature. Overlays of the

Sigma/CNL counts reveal the zones of borax

penetration, and identifies channels taking fluid.

Location of Source of Annular Leak

Gamma Ray Tool (Basically a

Geiger Counter) • Uses a scintillation crystal and a photomultiplier tube to

measure naturally occurring and artificially induced gamma-ray radiation.

• The gamma-ray radiation is a signature of the formations in a well – very useful in depth control. Used in open hole or pipe

• Also used to spot changes in radiation (NORM scale) and radioactive tracers.

• GR is sensitive to logging speed and factors/statistics that govern radioactive decay.

• Used as one measurement of shaliness, correlation tool for stacked beds and in shales, seal/barrier location, id of organic rich zones, gross and net reservoir thicknesses.

Multi-sensor caliper (cased hole)

• Multi-arm feeler – gauges the shape and

smoothness of the casing id.

– Corrosion and pit detection

– Pipe collapse and deformation

– Pipe wear

Production Logging (PLT)

• Spinner or radioactive tracer ejector that is

useful for identifying and quantifying fluid

entry and exit points in the well.

• Challenged by deviated wells if the tool is

not in the predominant flow stream.

PLT in Gas Lift Wells

• Very common to run PLTs in gas lift wells – w/ precautions.

• W/ fullbore spinners, choke the well back and reduce or shut-in the lift gas to reduce the chance of getting the tool stuck. Make sure the well is stable before logging.

• Run in at 50 to 75 ft/min. A pressure / density log may show some gas lift problems that a flowing gradient survey will not.

• There is very little chance of getting the PLT stuck in a GLM if a series of gauging runs is made immediately prior to the log (insures full ID).

• The fullbore centralizer collapses to the tubing ID and the tool is run with the spinner centralized so the point / bull-nose on the tool does not contact the walls of the tubing. There is a possibility of the centralizer holding up in the mandrel, but picking up and running a little faster should take care of this.

• Adhere to the service companies recommendation on minimum tool clearance.

Sources: Duane Toth and Franklin Bohla

PLT Sticking Hazard

• Greatest risk of tool hang-up is in the tubing tail (TT).

• Also watch the reservoir (may not be able to run a full ID drift gauge) for scale build up. Running a slim hole GR prior to the spinner to look for potential barium scale deposits is a good idea. Other scales and non-NORM BaSO4 scale may require a tool-sized drift.

• Lost Tool Experiences (from Duane Toth): – Lost one in Alaska where we didn't shut-in the well before going from the 7"

production casing into 2-7/8" tubing. The tool was off center, hung-up on the TT, and the wire came loose. We were able to fish this tool.

– The other was in Algeria where we lost the tool across the reservoir section. Believed to be result of excessive barium scale deposition, but fill may have also been a problem. This tool string was never recovered, and since it had the GHOST tool, it was an expensive mistake.

Source – Duane Toth

Cement Bond Tool

• Transmitter-receiver tool measures the

signal received back from a segment. Helps

assess cement presence and bond to the

formation and the pipe.

Temperature Tool

• A recording of the wellbore temperature.

– Identify fluid entry or exit

– Gas channeling

– Tubular leaks

– Hydraulic frac height

– Cement top

– Fluid levels

– Differential temperature curve

Down Hole Static Temperature Varies with

Depth - Effect of the Geothermal Gradient

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

50 100 150 200 250 300

Temperature, F

De

pth

, ft

"cellar effect - temperature normally cools from surface

temperature to about 100 ft below surface, then temperature

begins to increase with increasing depth. Watch for

anomolies.

This response is about 2.1oF per 100

ft

Temperature log – Saaman Well –

Trinidad. Leak at packer using

annular injection after base line at

same rate.

Gradiomanometer

• Measures the differential pressure of a 24”

column of fluid – calculates the fluid

density.

– Determine gas or liquid entry points

– Identify static fluid interfaces

– Determine exact depth of fluid density change

– Assist production logs

Flow meter

• Measures fluids moving past the tool.

Moving fluids turn the spinner

– To determine fluid entry or exit points

– Evaluate perforations

– Evaluate cross-flow occurrence

– Helps evaluate completion design

Tension Measurement Device

• A component of the tool string that records the

tension during logging in various parts of the

wellbore. Helps spot increased drag and break

free points (tool jumps) that may signal poor

logging tool records.

• Used for quality control on logs, as an indicator of

depleted zones (fluid loss sticking), dog-legs,

location of sticking (above or below tool when

compared with a surface record).

Logging Behind Casing

• Key Elements:

– Understand the condition of the casing

– Understand the connection of casing to the

formation – cement bond.

– Inclination, diameter, geometry

Information Sought Logging Tools Used

Casing Condition USIT, Multi-arm Calipers, Sonic Calipers, Downhole TV

Cement Condition Cement Bond Logs (sonic)

Saturation Resistivity Tools (CH), C/O Logs, Reservior Saturation Tools, DSS

Lithology Gamma Ray, Density, Neutron, Sonic

Porosity Resistivity Tools (CH), Porosity (CH), CNL, Dipole Shear Sonic

Formation Strength Dipole Shear Sonic,

Oil Resistivity, Casing Wall Coring Tools,

Gas Neutron and Sonic Tools

By-passed Pay Resistivity, O/C Logs,

Pressure Casing Wall Coring Tools

Partial List of Information Sought and

Cased Hole Logging Tools

logging cased hole

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