lesson 15 special considerations.ppt

8/12/2019 Lesson 15 Special Considerations.ppt

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Harold Vance Department of Petroleum Engineering

PETE 689 - UBD

Lesson 15

Special Considerations

Read: UDM - Chapter 6


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Special Considerations

Safety in UBD

Regulatory Requirements

Environmental Issues

Directional Drilling


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Safety in UBD

Since significantly greater volumes ofoil and gas are produced in

underbalanced drilling (compared tooverbalanced drilling), and becausethese products are highly combustible,considerable attention must be paid to

safety procedures. Produced fluids must be handled safely.


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Hydrogen Sulfide

Provide necessary notice of theproposed operations and hazards.

Provide adequate training.

Special Safety equipment, such assensors, warning alarms, wind socks,concentration measuring devices,

portable and fixed air breathingrespirators.


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An H2S emergency contingency plan withthe site specific information and detailedprocedures.

Hydrogen sulfide resistant materials andtraining.

Pressure surface separation vessels andauxiliary vacuum degassing equipment to

isolate all personnel from possibleexposure to this poisonous gas.

Hydrogen Sulfide


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Flaring Gas

Adequate sized flare lines, leading toproperly positioned flare stacks,equipped with automatic flame igniters,

are essential. Take wind direction into consideration.

Height may need adjustment.

Flare lines must be properly anchored.


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Separation and Storage

Liquid hydrocarbon separation and

storage facilities must be: positioned remotely

provide adequate storage volume

proper manifolding for transfer to sales.


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Training

Personnel training must be provided.

Written procedures must be provided.

Redundancy in critical man powermust be provided.

Redundancy in choke manifold.

Emergency ingress and egress must beprovided.


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Downhole Fires

Air drilling can lead to downhole firesand corrosion.


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Drilling with Natural Gas

Surface fires can be a problem.

Prepare for proper handling of

hydrocarbon gasses at the surface.Guidelines can be found in:

API RP 500B

National Fire Protection Association(NFPA) 70

NFPAA 496


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Backflow

Drillstrings need floats to prevent flow

back up the drillstring.Placement of drillstring floats is

important for operational and safetyreasons.


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Well Control

No standards for testing of RH andRBOP has been developed.


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Equipment

Operational and equipment testingprocedures must be established.

Operations should not continue if

pressures exceed the maximumlimits established.

In flowdrilling, emphasis is placed

on monitoring pressure whiledrilling, tripping, and stripping, inaddition to early kick detection.


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To develop testing procedures,prepare a detailed BOP andmanifolding flow diagrams that show

step-by-step testing for system parts.

Test BOPs when installed, each timethey are reinstalled, once each week,

and following repairs.

Equipment


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Regulatory Requirements

In planning an UB well, always

check with local, state, or federalagency governing the wellslocationfor the latest regulations.


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Canada

Interim Directive ID 94-3, from theEnergy Resources ConservationBoard provides the most detailed

regulations in North America.Mandates strict enforcement of:

BOP system configuration.

Tripping procedures. Well control certification of key

personnel.


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United Kingdom

The Department of Trade and Industrysets specific requirements andregulations pertinent to the drilling

and completion of underbalancedwells.

Authority has be delegated to theHealth and Safety Executive to review

operators plans, and to grant or denypermits for proposed work.


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United States

In the United States, a survey of theprimary oil and gas producing statesindicated that there were no special

regulations written specifically forUBD. In most cases, the existingregulations could be broadly

interpreted to cover UBD.


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Issues to Consider

Be certain that the BOP stack, with adiverter System:

permits drilling to proceed while controlling annular pressure. allows connections to be made either with the well flowing or shut-in.

allows tripping of the drillstring under pressure to change bits or bottomholeassemblies.


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Issues to Consider

provides for backup annular control incase of failure of the diverter.

provides for a choke manifoldarrangement which allows annular

pressure to be varied so that it will notexceed related working pressure of theequipment.

Provides a mean to bleed-off pressure

or to kill the well, independent of thediverter system.

Provides a means to quickly and safelyshut-in the well.


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Issues to Consider

Use string float(s) and fire float(s), if airis used.

If sour gas is present, drillpipeprotection and blind shear rams are

needed.Kill fluid is needed.Casing integrity needs to be guaranteed

and full length cementing should beimplemented as regulated.

Surface equipment spacing needs toadhere to appropriate regulations.


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Issues to Consider

Flaring must follow appropriateregulations.

Appropriate separator equipment should

be used, as required.Provide adequate provision for storage

of produced fluids.Crews need to be appropriately certified

and trained.Monitoring and alarms are essential for

H2S environments.Adhere to all safety regulations.


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Environmental Issues

Regulations vary significantly from state-

to-state, and country-to-country.

Check applicable regulations carefully.


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Land and Water Pollution

UBD provides some environmentalbenefits (closed loop systems, lessdrilling mud, etc), but produces moreformation fluids than conventional.

Oil coated cuttings must be disposed of

properly.


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Air Pollution Considerations

Burning hydrocarbons during drilling

can become an environmental concern.Know regulations on air pollution.

Dust during air drilling can be a

problem.


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Produced Water Disposal

Produced water must be disposed of.

Disposal operations can include:

Disposal into surface water drainagesystems.

Reinjection.

Approved land disposal

Overboard offshore disposal

Reserve pits


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Directional DrillingThere is no reason why directional

wells cannot be undertaken withUBD.

However, compressible fluids cancomplicate directional drilling.


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Directional Drilling(Complications)

Conventional downhole motor life is

shorter, and conventional motors arenot as efficient.

Conventional MWD systems do notwork with compressible fluids.

Hole cleaning can be a problem withangles >50 deg


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The horizontal section length is

reduced due to increased drag.Not all formations and lithologies are

suitable for drilling with dry gas,

moist or foam.

Directional Drilling(Complications)


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Bottomhole Assemblies

Main issues for directional drillingunderbalanced are similar to those

for conventional directional drilling: Directional control.

Surveying.

Hole cleaning.

Drillstring friction.


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BHA is designed to control direction andangle.

The deviation tendency is a function ofthe stiffness of the assembly.

Bottomhole Assemblies


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Three Types of BHAs

Building assembliesDropping assemblies

Holding assemblies


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Building Assemblies


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Dropping Assemblies


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Holding Assemblies


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Downhole Motors

Conventional mud motors can berun with compressible fluids, butthere are disadvantages.


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Conventional Mud Motors

DisadvantagesDesigned to run with low volumetric

flow rates and high pressure drops.

Leads to high inlet pressures and lowefficiency with compressible fluids.

Compressible fluids can lead to motorstall.

High inlet pressure results in highenergy stored in the drillstring abovethe motor.


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Volume to clean the hole with airdrilling is three times greater than the

recommended flow rate for theconventional mud motor.

Mud motors are hydrostatic, they can

use only the displacement work, andnot the expansion work of thecompressed air.

Conventional Mud Motors

Disadvantages


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Mud Motors

Mud motors have been developedfor use with compressible fluids.

Advantages:

Boosters are not needed. Efficiency is improved.

Motors do not stall as easily.

Overspeed is less likely. Can be used with compressible and

slightly compressible fluids.


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Surveying

Conventional MWD signals cannot be

sent up compressible fluids.Electromagnetic MWD (EMWD) tools

are being developed.

Steering tools are still available.


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Hole Cleaning

Hole cleaning is more difficult in highlydeviated wells.

A rule-of-thumb is that for adequatehole cleaning in horizontal wells, avolumetric rate of 2.5 times greaterthan a vertical well is necessary.


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Torque and Drag

Friction coefficient in an air-drilledhole can be three to four timesthan expected in mud-filled hole.


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Horizontal Section Length

Additional torque and drag can

lessen the achievable horizontaldisplacement of high angle andhorizontal wells.


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Lithology and Target

Constraints

Lithologies that can be drilled with

air are limited. Younger lessconsolidated rocks are usually notgood candidates for air.

Directional wells sometimes must bedrilled overbalanced to preventwellbore collapse.


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Percussion Drilling

In percussion drilling, rock is brokenby causing the bit to repeatedlystrike the workfront, withoutimparting any significant shearingcomponent to its action.

A hammer tool is used in the BHA.

Normally only used with dry gas,mist, and foam drilling.


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Background

ROP for three different percussion tools with 8 to 8-inch solid-head bits in Sierra WhiteGranite,For a WOB of 5,000 lbf. The flow rate was between 600 and 1,100 scfm for each hammer(after

Finger, 1984 26)


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Approximation of ROP

Assume that the MSE = CoDetermine the hammer manufacturers

power output value. The penetrationrate is related to the rocks unconfinedcompressive strength, the hammer

power output and the hole area by:


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Approximation of ROP

ROP = 2.52*10 6 * [ / (CoD

h

2)]

ROP rate of penetration (ft/hr) hammer power output (hp)

Co unconfined compressive strength, (psi)Dh hole diameter (inches)


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Flat-bottom bits, used in conjunction with an air percussionhammer (anon)

Equipment


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Equipment

Internally ported hammer and a flat-bottom bit (anon)

E i t


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Equipment

Components of an externally ported hammer (anon)


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FPB/HT (flat-bottomed percussion bit/hammer tool) tandemrecommended WOB

Versus hole size (after Whiteley and England, 1986 30)

Bit Diameter (inches)

Reco

mmendedWeig

htonBit(lbf)


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Hole Cleaning

Pratt modified Angels minimumvelocity by:

Using a revised air prediction module inside

the drillstring where the friction factor wascalibrated from actual measurements.

Exit boundary conditions were modified asan input parameter and exit chip velocitywas fixed at zero.

The influence of the BHA and changing holesize were incorporated.

Chip size change was built into the model.


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Gauge Wear

Diamond-Enhanced Insert (after Reinsvold, et al., 1988 31)


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Smooth Hole?

Spiral hole drilled with an industrial hammer and a flat-bottomedbit (after Pratt, 1989 29)


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Smooth Hole?

Ledges drilled with an industrial hammer and a flat-bottomed bit(after Pratt, 1989 29)


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Summary

Maintain proper WOB.

Rotate as slowly.

Provide an air bypass.Deep the threads clean and use

recommended lubricants.

Dope the pins only.Never run on junk.


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When changing out bits, make

sure that the new bit is no morethan 0.25 in larger than the old.

Stabilize as required.

Monitor compressors.Blow the hole clean.

Summary


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High Pressure DrillingSpecial attention should be given

to high surface pressures becauseof the additional force required totrip pipe.

Stringent safety considerations arerequired.


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Flowdrilling in High

Pressured Formations

The use of CT drilling is increasing

with high pressure flowdrilling.Surface well control equipment must

be rated based on maximum

anticipated conditions.RBOPs should replace rotating heads.


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Coiled Tubing Drilling

Design Criteria1. Select the CT size, hole size, drilling

fluid, and BHA.

2. Calculate the reel weight and size.

3. Calculate the tubing forces andstresses. Do not let them exceed

80% of the yield strength, and theminimum WOB can be provided atTD.

C il d T bi D illi


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Coiled Tubing DrillingDesign Criteria

4. In vertical wells.Dmax= (y) / ( 4.245 - 0.06493Wdf)

Dmax

maximum depth (feet)Wdf drilling fluid weight (ppg)y yield stress (psi)

5.In Deviated wells. Ensure that the injector can supply the

necessary push/pull.

il d bi illi


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5.In Deviated wells. Ensure that the injector can supply the

necessary push/pull.

Calculate the drilling fluid pressure dropin the CT, BHA and annulus at 100 %motor flow capacity and determine theabsolute pressure in the CT duringdrilling.

Asses torsional limitations. Thedownhole motor-stall torque should notbe longer than the maximum workingtorque for the CT.


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5.In Deviated wells. Calculate the fatigue life of the pipe.

Asses any hydraulic limits . Considerhole cleaning in vertical, inclined , and

horizontal wellbores. Be sure that directional control is

possible.


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CementingExtremely light cement can be used to:

Provide primary cementing informations with low fracture pressures.

Cure lost circulation in cavernous vugs.

Squeeze depleted zones.

Zonal isolation. Heat Insulation.


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Properties of Foamed Cement

Will the strength be adequate and willthe sheath be destroyed by perforating?

Compressive strength of foamed cementis generally higher than a comparablenon-foamed cement of the same density.

Will there be gas migration through the

cement itself?

Will the bond be different than forconventional cements?


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Systems with Low DensityParticulate Matter

Cement companies have additive in whichthe HSP of the cement can be reduced.

Example is hollow glass micro spheres.


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Design Considerations

Foam quality.

PVT behavior.

Cement system. Free water.

Backpressure.

Permeability.Compressive strength.

Fluid Loss.


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Formation Evaluation


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Evaluation with Logging Tools

Gamma Ray. For formation or bed definition(e.g. distinguishing sands from shales).

Spectra Gamma ray. Quantitative definitionof the gamma ray spectrum; to define claycontent, clay and mineral type, and to aid infracture detection.

Epithermal Neutron. To identify porosity of

liquid-filled zones. Induction Resistivity. To help distinguish

hydrocarbons from saline formation waterand to help quantify the water saturation.


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Evaluation with Logging Tools

High Resolution Density. To quantifyporosity.

Temperature. To indicate liquid level in the

borehole and to delineate zones where fluidsare actually being produced.

Production. Production logs, such asborehole spinners, cam help to quantify the

relative amount of production from eachinterval.

Nuclear Magnetic Resonance. To helpquantify the permeability of formations.


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MWD

If a compressible fluid is used,conventional mud pulse telemetrytools cannot be used.

Electromagnetic devices can.


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Coring Underbalanced

Reducing coring fluid invasionallows for careful determinations offormation properties wherewettability alteration has been

minimized.


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Permeability andDeliverability Assessments

Effective monitoring of productionrates permits real-time decisionsregarding changes in drilling depth,

wellbore orientation, and overallsection length.


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lesson 15 special considerations.ppt

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