spe brisbane section hughes | gmi geomechanics services spe queensland section –may 2012 luncheon...

SPE Brisbane Section

Practical Aspects of Solids Production in CSG Wells

© 2010 Baker Hughes Incorporated. All Rights Reserved.

16 May 2012

Brisbane

Khalil Rahman, Ph.D.

Baker Hughes | GMI Geomechanics Services

SPE Queensland Section – May 2012

Luncheon Talk

SPEAKER: Dr Khalil Rahman

Topic: Practical Aspects of Solids Production in

CSG Wells

SPEAKER: Dr Khalil Rahman

Technical Geomechanics Advisor, Baker Hughes

16 May 2012

The Queensland Irish Club

171 Elizabeth St, Brisbane

Remembering Dr. Henry Salisch

• Passed away on 3 May 2012, at the age of 87

• A dedicated academic; lectured to the last week of his life

• Longest serving member of the SPE NSW/ACT Section

Committee

• A founding member of the UNSW School of Petroleum

Engineering

Presentation Outline

• Solids production in sandstone versus CSG reservoirs, and in USA

versus Australian CSG reservoirs.

• CSG well completions and solids production mechanisms.

• Solids production assessment methodology:

– Input elements– Input elements

– Theoretical foundations

– Rock testing issues.

• One case study from literature.

• One case study from GMI.

• Questions/Discussion

© 2010 Baker Hughes Incorporated. All Rights Reserved. 4

USA & Australia Coal Deposit & Production

© 2010 Baker Hughes Incorporated. All Rights Reserved. 5 © 2010 Baker Hughes Incorporated. All Rights Reserved. 5

(SPE 106850)

Small Independent CSG Producers in Qld


RLMS Report,

Nov. 2009

How is Solids Production Different in CSG Wells?

• Solids production in sandstone reservoirs is mainly driven by:

– Depletion-induced stress path causing changes mainly in horizontal

stresses;

– Failure of mainly sandstones apart from interbedded non-depleting shales

– Often perforation failure in cased and perforated wells (openhole

completion is very rare)

• Solids production in CSG reservoirs are driven by:

– Depletion plus desorption resulting in higher stress path and hence higher

changes in horizontal stresses

– Interbedded sand failure during the dewatering phase

– Shear failure of naturally fractured coals on the wellbore wall

– Coal and/or sandstone failure mainly in openhole completion.


CSG Solids Production Risks in Australia VS USA

• Historically, solids production in CSG wells has not been a major

issue in the USA.

• Why may it be in Australia?

– Reservoir stress condition is different;

– Australian CSG reservoirs are shallower and hence weaker coals and

interbedded sandstones;interbedded sandstones;

– Stringent environmental restrictions may limit the number of wells that

can be drilled. Therefore, CSG wells in Australia are expected to produce

longer up to its full potential resulting in higher depletion and higher rock

failure risks;

– Even within Australia, filed to field experience may be different.

• The best safeguard is to integrate the solids production risk

assessment in the field development planning study, which has been

almost a routine practice in sandstone reservoir development.


CSG Well Completion Techniques

• Four major completion techniques for CSG

wells:

– Topset under-ream (openhole)

– Openhole cavity

– Cased hole with hydraulic fracture

– Horizontal well (mainly openhole)– Horizontal well (mainly openhole)


Two good readings:

Ramaswamy, S., Ayers, W.B. & Holditch, S. A.: Best drilling, completion and stimulation

techniques for CBM reservoirs. World Oil (online), Vol.229, No.10, 2008.

Palmer, I.: Coalbed Methane Wells are Cheap, but. The Driller’s Club, March 22, 2008.

Sources & Mechanisms of Solids in CSG Wells

Failure at fracture face

due to injection-induced

stress change


Shear pre-stressIsotropic pre-stress

Increased shear failure when

stress differential is higher

natural fractures are inclined

w.r.t. the in situ stresses.

Solids/Sand Management Strategy

• data

• time

• resource

geomechanical

modelsolids prediction

model

will well

produce

solids?

if so, where

from, when,

how much?


selection based on

quality process

and clear criteria

delay installation,

Select right completion,

choke management

transport /

erosion models.

facilities review

tolerate or

control ?

options other than active

control ?

optimum solids control

technique?

What Influences Solids Production?

Desorption in


Desorption in

CSG reservoir

Solids Production Prediction Approaches

Analytical method

(SPE116633):

• Based on elastic properties and

requires standard Thick Wall

Cylinder (TWC) test data.

• Uses an Effective Strength Factor

Numerical Finite Element

Modelling:

• A thorough laboratory rock strength

testing such as multiple triaxial

strength (UCS) and advanced thick

wall cylinder tests (ATWC).

‐‐‐‐

• Uses an Effective Strength Factor

(ESF) to consider the effective TWC

strength at the reservoir scale and

the post-elastic residual strength.

• Rock failure is predicted if maximum

effective stress > effective TWC.

• Default values of ESF for standard

TWC samples – can be calibrated

with production data.

• A finite element analysis calibrating

the elasto‐‐‐‐plastic style of failure

seen in the laboratory

measurements with available

production test or actual production

data.


Engineering Data Required for Solids Production

Assessment

Initial (non-depleted) Stress

and Pressure Model

I-90 sand @ 2020m TVDSS

(Helix RDS 2006-2007-2008)

Sv ~19.0 + 0.2 ppg

SHmax ~17.9 + 0.3 ppg

Shmin ~17.3 + 0.3 ppg

Pp ~8.33 ppg

S < S < S

0

200

400

600

800

1000

1200

1400

SvPp hydrostaticShminSHmaxPp BK-1Pp BK-A1Pp NBR-1Pp BT-1Pp BTA-1Pp BTA-2Pp BTA-3MW BT-1MW BTA-2MW NBR-1MW BK-1LOT QC'dLOT/FIT reported PM3SHmax modeling points BTA-3 Formation topsBTA-3 Casings

Pressure and Stress Profile Bunga Tulip Field

Target sand @ 2020m TVDSS

T Field

4265

4270

4275

4280

4285

0 2000 4000 6000 8000 10000

Rock Strengths (psi)

Measured Depth (m)

UCS

TWC


Shmin < SHmax < Sv

Normal Faulting Stress

Regime

Azimuth of maximum

horizontal stress ~ N 10º -

N45º (from regional info) 1000 2000 3000 4000 5000 6000 7000 8000

1400

1600

1800

2000

2200

BTA-3 Casings

Pressure and Stress (psi)

4290

4295

4300

Measured Depth (m)

0

10

20

30

40

50

60

70

80

90

100

0 2000 4000 6000 8000 10000 12000

Log Derived Rock Strength (psi)

Percentile

UCS-Vernick Model

TWC_Global Model

Other Inputs:

Well/Perf. trajectory (devi. & Azi.)

Openhole or C&P completion

FBHP for production

Solids Production Evaluation Work Flow

Drilling & Production Datamud weights/ECD, PWD, survey,

drilling history & events, XLOT/XLOT,

RFT/MDT DST, production info

Geomechanical Modelstress magnitudes & orientation,

pore pressure & rock strength

Core DataRoutine &SCAL

UCS, TWC, PSD, thin section,

SEM, dispersion, chemical

Geolo. Geophys. & Petrophy.

Seismic, Tectonic history,

sediment., analogs, etc.

Well LogsCaliper, Gr, Rhob, Sonic,

image, dipmeter, MWD/ LWD


Update the model

with new data

pore pressure & rock strength

Solids Free

Operating Envelope

Solids Evaluation log Hole Trajectory & Perforation

Orientation Optimization

Solids Production

Prediction

Rock Mechanical Test Data of Coals - UCS

• Literature shows that standard triaxial tests of coal samples have been

carried out extensively in the mining industry and some in the petroleum

industry:

– UCS and angle of internal friction (φ) – usually required for wellbore stability analysis


Source: SPE 96872

Rock Mechanical Test Data of Coals - TWC

• Non-existent so far in the literature

• Proper sampling and testing are warranted

• There exists a correlation between TWC & UCS

– Field specific

• Widely-used correlations for sandstone:• Widely-used correlations for sandstone:

– TWC = 80.8765 x UCS0.58; for moderate to very strong sandstones

– TWC = 37.5 x UCS0.6346 ; for very unconsolidated sandstones

• The second correlation was used for solids production prediction in

US CSG well with openhole completion (presented latter).


Rock Mechanical Test Design for CSG Reservoirs

• Hard to get undamaged cores – best practice coring and core

handling are essential

• Plugging test samples to represent reservoir:

– Interbedded sandstone/shale should be sampled;

– Intact coal matrix can be fairly strong and is usually not average

representation of the reservoir;representation of the reservoir;

– Multiply fractured samples may be better representation of reservoir rock

– Bedding planes in interbedded sediments are often weak and should be

included in samples.

• Quality control and interpreting test data may be challenging:

– Do not always expect the nice shear failure planes;

– Poisson’s ratio alone is not the full elastic stress path;

– Remember to derive the correct strengths for the actual wellbore size in

the reservoir scale from the sample strengths (ESF).


Solids Production Assessment: Example Outputs

Solids Free Operating Envelope

BHFP (psi)

Open hole- P10 TWC

Open hole- P50 TWC

Open hole- P90 TWC

Χ Cased hole, top perfs- P10 TWC

Initial Pp

Solids Free Drawdown for P50 TWC

rock strength @

Pp = 2500 psi,

Solid Prod. Evaluation Log

Pp initial

Pp depleted


Reservoir Pressure (psi)

BHFP (psi)

Final Pp

Planned FBHP

Solids Free Drawdown for P50 TWC

rock strength @

Pp = 2500 psi,

Critical Drawdown (psi)MD (ft)

Planned Drawdown

Solids Production Assessment: Example Outputs

Polar Plot showing Critical Bottom Hole Flowing Pressure versus well trajectory

1050 psi

3850 psi

CBHFP

~3700 psi960 psi

3730 psi

CBHFP

~1735 psi

Optimum Open Hole Trajectory


SHmax < Sv

Sv = 1.00 psi/ft

SHmax = 0.83 psi/ft

vertical and low angle wells are

least sand pronevertical and deviated wells in NW-SW directions are

most sand prone

SHmax > Sv

Sv = 0.90 psi/ft

SHmax = 1.05 psi/ft

SHmax azimuth = 70ºN

Shmin = 0.75 psi/ft

Pp = 0.45psi/ft

TWC = 3000 psi

Field Case 1: Drawdown & Abandonment Planning

by Solids Production Assessment (SPE 96872)• San Juan Basin

• Openhole horizontal well

• Depth ~ 2800 ft

• Sv ~ 1 psi/ft

• SHmax = Shmin ~ 0.64 psi/ft

• Pp = 0.45 psi/ft

• Young’s modulus ~ 300,000 psi

• Poisson’s ratio ~ 0.35 psi

Pp

~ 1

26

0 p

si

DD

~ 6

00 p

si

Pp

~9

00

psi


• Poisson’s ratio ~ 0.35 psi

Pp

~ 4

60

psi

DD

~ 6

00 p

si

Pp

~9

00

psi

� Solids production assessment:

� Solids-free drawdown at initial Pp ~

1050 psi

� Can be produced solids-free with a

constant drawdown of 600 psi until

the reservoir depletes to 900 psi

� For Pp < 900 psi, sloids-free

production with adjusted

drawdown.

� No solids-free production for Pp <

460 psi; abandonment.

GMI SOLIDS PRODUCTION ASSESSMENT IN

CSG WELL IN SAN JUAN FIELD IN 2007


Developed Geomechanical Model for the Field

Pp- constrained using mud weights and

pressure buildup results.

Shmin ~ 0.83 psi/ft (below 2000 ft) based on

a compilation of LOT and minifrac data

and wellbore failure experience.

Sv- pseudo-density from sonic log


Shmin<Sv<SHmax

Modeled depths

SHmax- below 2000 ft, SFIB modeling.

UCS –

Coals: ~2876 psi

Sands: McNally

Shales: BP’s “Worldwide Shale” equation

Coal strength tests

Intact properties Properties of cleats

So~30

Mu_i~0.58

So~710

Mu_i~0.66

->UCS~2648


Traditional triaxial tests can over estimate the strength of coals if highly fractured.

However, coals tested above did not appear to be highly fractured. Tests run on

cores from this well are expected to be a good measure of the strength.

From:

GRI Report

Strengths of Different Lithologies in Reservoir

60%

70%

80%

90%

100%

Cum

. %

• Coal is the weakest lithology,

P10 UCS ~ 2000 psi

• Sands are the strongest

lithology, P10 UCS > 3500 psi

• Shales have intermediate

strengths


0%

10%

20%

30%

40%

50%

0 5000 10000 15000 20000

UCS (MPa)

Cum

. %

Coal - from 2100m to 2310m

Shale - from 2100m to 2310m

Sand - from 2100m to 2310m

strengths

(UCS ~3000-7000 psi), P10

UCS ~ 2100 psi

• Shales are differentiated from

sands based on a GR cutoff,

after filtering out coals

Coal Failure Assessment for an Assumed Stress Path

• dSH/dP=1

• dSv/dP=0

600

800

1000

BH

FP

, psi

Limiting BHFP (dSH/dP=1; dSv/dP=0; azi=aziSHmax)

-1600

-1500

-1400

-1300

-1200

Horizontal well along ~ 185o azimuth

SHmax Azi. ~ 145o


0 200 400 600 800 10000

200

400

600

Reservoir pressure, psi

BH

FP

, psi

-2200

-2100

-2000

-1900

-1800

-1700

This operating envelop shows mainly

coal failure below 2000 psi UCS (p10);

so the solids production risk is low.

• GMI’s current work flow

establishes an

approximate stress path:

– Drilling experience data

– Approximate function of

Poisson’s ratio and Biot’s

constant.

Summary

• CSG reservoir development in Australia is following the US track,

though later and slower.

• Solids production and its management in Australian CSG development

should get more attention than USA.

• Solids production prediction methodology is a mature technology

requiring geomecahnics modeling, rock testing and production planning.

• Rock testing data and techniques, particularly TWC testing for coal

samples are not as rich as for sandstones, and hence require:

– Careful sampling,

– New learning of testing procedures and interpretations.

• Every field, every well and every production plan is different and should

be assessed case by case basis.

• Integrating solids production assessment in the workflow of field

development planning study is a rational safeguard against potential

undesirable production interruption in the CSG industry. © 2010 Baker Hughes Incorporated. All Rights Reserved. 27

You can email your questions:

[email protected]@bakerhughes.com

28

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