Practical Aspects of Solids Production in CSG Wells

SPE Brisbane Section
Practical Aspects of Solids Production in CSG Wells
16 May 2012
Brisbane
Khalil Rahman, Ph.D.
Baker Hughes | GMI Geomechanics Services
© 2010 Baker Hughes Incorporated. All Rights Reserved.
SPE Queensland Section – May 2012
Luncheon Talk
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
– Theoretical foundations
– Rock testing issues.
• One case study from literature.
• One case study from GMI.
• Questions/Discussion
4
© 2010 Baker Hughes Incorporated. All Rights Reserved.
USA & Australia Coal Deposit & Production
(SPE 106850)
5
© 2010 Baker Hughes Incorporated. All Rights Reserved.
Small Independent CSG Producers in Qld
RLMS Report,
Nov. 2009
6
© 2010 Baker Hughes Incorporated. All Rights Reserved.
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.
7
© 2010 Baker Hughes Incorporated. All Rights Reserved.
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;
– 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.
8
© 2010 Baker Hughes Incorporated. All Rights Reserved.
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)
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.
9
© 2010 Baker Hughes Incorporated. All Rights Reserved.
Sources & Mechanisms of Solids in CSG Wells
Failure at fracture face
due to injection-induced
stress change
Increased shear failure when
stress differential is higher
natural fractures are inclined
w.r.t. the in situ stresses.
Isotropic pre-stress
10
© 2010 Baker Hughes Incorporated. All Rights Reserved.
Shear pre-stress
Solids/Sand Management Strategy
will well
produce
solids?
geomechanical
model
tolerate
or
control ?
transport /
erosion models.
facilities review
11
© 2010 Baker Hughes Incorporated. All Rights Reserved.
if so, where
from, when,
how much?
• data
• time
• resource
solids prediction
model
options
other than
active
control ?
delay installation,
Select right completion,
choke management
optimum
solids
control
technique
?
selection based on
quality process
and clear criteria
What Influences Solids Production?
Desorption in
CSG reservoir
12
© 2010 Baker Hughes Incorporated. All Rights Reserved.
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
(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.
13
© 2010 Baker Hughes Incorporated. All Rights Reserved.
Numerical Finite Element
Modelling:
• A thorough laboratory rock strength
testing such as multiple triaxial
strength (UCS) and advanced thick
wall cylinder tests (ATWC).
• 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
Pressure and Stress Profile
Bunga
T Tulip
Field Field
Rock Strengths (psi)
Sv
Pp hydrostatic
Shmin
SHmax
Pp BK-1
Pp BK-A1
Pp NBR-1
Pp BT-1
Pp BTA-1
Pp BTA-2
Pp BTA-3
MW BT-1
MW BTA-2
MW NBR-1
MW BK-1
LOT QC'd
LOT/FIT reported PM3
SHmax modeling points
BTA-3 Formation tops
BTA-3 Casings
200
400
600
Sv
SHmax
Shmin
Pp
~19.0 + 0.2 ppg
~17.9 + 0.3 ppg
~17.3 + 0.3 ppg
~8.33 ppg
Shmin < SHmax < Sv
Normal Faulting Stress
Regime
Azimuth of maximum
horizontal stress ~ N 10º N45º (from regional info)
800
1000
1200
1400
0
2000
4000
6000
4265
UCS
TWC
4270
Measured Depth (m)
0
Initial (non-depleted) Stress
and Pressure Model
I-90
sand
@@2020m
Target
sand
2020m TVDSS
TVDSS
(Helix RDS 2006-2007-2008)
4275
4280
4285
4290
1600
4295
1800
2000
100
2200
90
4300
80
1000 2000 3000 4000 5000 6000 7000 8000
Pressure and Stress (psi)
Percentile
Other Inputs:
Well/Perf. trajectory (devi. & Azi.)
Openhole or C&P completion
FBHP for production
70
60
50
40
30
20
UCS-Vernick Model
TWC_Global Model
10
0
0
14
© 2010 Baker Hughes Incorporated. All Rights Reserved.
2000
4000
6000
8000
10000
Log Derived Rock Strength (psi)
12000
8000
10000
Solids Production Evaluation Work Flow
Drilling & Production Data
Core Data
Well Logs
mud weights/ECD, PWD, survey,
drilling history & events, XLOT/XLOT,
RFT/MDT DST, production info
Routine &SCAL
UCS, TWC, PSD, thin section,
SEM, dispersion, chemical
Caliper, Gr, Rhob, Sonic,
Geomechanical Model
stress magnitudes & orientation,
pore pressure & rock strength
image, dipmeter, MWD/ LWD
Geolo. Geophys. & Petrophy.
Seismic, Tectonic history,
sediment., analogs, etc.
Update the model
with new data
Solids Free
Operating Envelope
15
© 2010 Baker Hughes Incorporated. All Rights Reserved.
Solids Production
Prediction
Solids Evaluation log
Hole Trajectory & Perforation
Orientation Optimization
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
16
© 2010 Baker Hughes Incorporated. All Rights Reserved.
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:
– 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).
17
© 2010 Baker Hughes Incorporated. All Rights Reserved.
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;
– 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).
18
© 2010 Baker Hughes Incorporated. All Rights Reserved.
Solids Production Assessment: Example Outputs
Solid Prod. Evaluation Log
Solids Free Operating Envelope
Reservoir Pressure (psi)
19
© 2010 Baker Hughes Incorporated. All Rights Reserved.
Pp depleted
Planned Drawdown
Planned FBHP
Final Pp
BHFP (psi)
Χ Cased hole, top perfs- P10 TWC
Pp initial
MD (ft)
Open hole- P90 TWC
Initial Pp
Open hole- P50 TWC
Solids Free Drawdown for P50 TWC
rock strength @ Pp = 2500 psi,
Open hole- P10 TWC
Critical Drawdown (psi)
Solids Production Assessment: Example Outputs
Optimum Open Hole Trajectory
Polar Plot showing Critical Bottom Hole Flowing Pressure versus well trajectory
3730 psi
3850 psi
CBHFP
~1735 psi
960 psi
1050 psi
vertical and deviated wells in NW-SW directions are
most sand prone
SHmax > Sv
Sv = 0.90 psi/ft
SHmax = 1.05 psi/ft
20
© 2010 Baker Hughes Incorporated. All Rights Reserved.
SHmax azimuth = 70ºN
Shmin = 0.75 psi/ft
Pp = 0.45psi/ft
TWC = 3000 psi
CBHFP
~3700 psi
vertical and low angle wells are
least sand prone
SHmax < Sv
Sv = 1.00 psi/ft
SHmax = 0.83 psi/ft
Field Case 1: Drawdown & Abandonment Planning
by Solids Production Assessment (SPE 96872)
• San Juan Basin
Pp ~ 1260 psi
DD ~ 600 psi
Pp~900 psi
Pp ~ 460 psi
• 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
Solids production assessment:
21
© 2010 Baker Hughes Incorporated. All Rights Reserved.
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
22
© 2010 Baker Hughes Incorporated. All Rights Reserved.
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
SHmax- below 2000 ft, SFIB modeling.
UCS –
Coals: ~2876 psi
Sands: McNally
Shales: BP’s “Worldwide Shale” equation
23
© 2010 Baker Hughes Incorporated. All Rights Reserved.
Shmin<Sv<SHmax
Modeled depths
Coal strength tests
Intact properties
So~710
Mu_i~0.66
->UCS~2648
Properties of cleats
So~30
Mu_i~0.58
From:
GRI Report
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.
24
© 2010 Baker Hughes Incorporated. All Rights Reserved.
Strengths of Different Lithologies in Reservoir
100%
• Coal is the weakest lithology,
P10 UCS ~ 2000 psi
90%
• Sands are the strongest
lithology, P10 UCS > 3500 psi
80%
70%
• Shales have intermediate
strengths
(UCS ~3000-7000 psi), P10
UCS ~ 2100 psi
Cum. %
60%
50%
40%
30%
• Shales are differentiated from
sands based on a GR cutoff,
after filtering out coals
20%
Coal - from 2100m to 2310m
10%
Shale - from 2100m to 2310m
Sand - from 2100m to 2310m
0%
0
5000
10000
UCS (MPa)
25
© 2010 Baker Hughes Incorporated. All Rights Reserved.
15000
20000
Coal Failure Assessment for an Assumed Stress Path
• dSH/dP=1
Limiting BHFP (dSH/dP=1; dSv/dP=0; azi=aziSHmax)
• dSv/dP=0
-1200
Horizontal well along ~ 185o azimuth
SHmax Azi. ~ 145o
1000
-1300
-1400
BHFP, psi
800
-1500
-1600
600
-1700
-1800
400
-1900
• GMI’s current work flow
establishes an
approximate stress path:
– Drilling experience data
– Approximate function of
Poisson’s ratio and Biot’s
constant.
26
© 2010 Baker Hughes Incorporated. All Rights Reserved.
-2000
200
-2100
0
0
200
400
600
800
Reservoir pressure, psi
1000
This operating envelop shows mainly
coal failure below 2000 psi UCS (p10);
so the solids production risk is low.
-2200
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.
27
© 2010 Baker Hughes Incorporated. All Rights Reserved.
You can email your questions:
[email protected]
28