observing reservoir dynamics and changing reservoir...
TRANSCRIPT
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Kes Heffer, Reservoir Dynamics Ltd.
Acknowledgements:David Bamford, New Eyes ExplorationStuart Crampin, The Univ of Edinburgh, BGSIan Main, The Univ of EdinburghJohn Greenhough, The Univ of EdinburghSchlumberger Geomechanics CentreBP, Statoil, Nexen
Observing reservoir dynamics and changing reservoir management
New ideas in Improved Recovery and EORFinding Petroleum, 18 April 2012
Finding Petroleum; 18 April 20122
Talk outline1. Stress-aligned microcracks at near-critical
densities from shear-wave splitting2. Flow Directionality & recovery in reservoirs3. Other evidence for near-criticality of stress 4. Interwell correlations in rate fluctuations
– General characteristics– Reservoir physics– Rate diffusivities
5. Results & microseismicity in Valhall6. Aggregated results from 6 North Sea fields
– consistency with 1. and 2.
Approximately chronological
7. Effect on recoveries – field data8. Conclusions
Finding Petroleum; 18 April 20123
Increasing differentialhorizontal
stress
Shmax
Shmin
Anisotropic PoroElastic model (APE)
Shear wave splitting indicates stress-aligned microcrack / fractures near critical density
Stuart Crampin et al.http://www.geos.ed.ac.uk/homes/scrampin/opinion/
S-wave vel. anisotropyCrack densityCrack radius
Most frequent crack densities in all rocks
Long-range
Stress-related
Highly sensitive
Finding Petroleum; 18 April 20124
0102030405060708090
100
0.1 1.0 10.0Mobility ratio
IsotropicFavourableUnfavourable
Areal sweep efficiency, % To breakthough:
Physical model with Kmax/Kmin = 16
IsotropicFavourableUnfavourable
To 90% watercut:
Field Directionality: The Prize – theoryAreal sweep efficiency and anisotropic permeability(classic: Caudle 1959)
Orientation of well pattern relative to permeability axes can change recoveries by 10’s of % points
unfavourable
For a 5 spot pattern of wells:
I
P
P
P
P
favourable
Permeability axes
Finding Petroleum; 18 April 20125
Flood directionalityField data (“unfractured” reservoirs)
Shmax
47 field cases(“unfractured”)
Numerical FEModelling
Shmax
and Stress
Finding Petroleum; 18 April 20126
Flood Directionality & Stress StateField evidence
01020304050
60708090100110
120130140150160170
180190200210220230
240250260270280290300310320330340350
‘Fractured’Reservoirs(33 cases)
010203040
5060708090100110
120130
140150160170180
190200210220230
240250260270280290300310
320330340350
‘Unfractured’Reservoirs(47 cases) Shmax
0102030405060
708090100110
120130140150160170180
190200210220230240250260270280290300310320330340350
AllReservoirs(80 cases)
Finding Petroleum; 18 April 20127
Flow rate fluctuations
Producers
Injectors
Finding Petroleum; 18 April 20128
First principal component of matrix of rate correlations between all wells in field B – independent mode ‘explaining’ largest proportion of fluctuation variance
Interwell correlations between rate fluctuations -general characteristics
Long-range
Fault-related
Stress-related
Injector-Producer pairs only>0.5x106 pairs; 8 field areasbroadband fluctuationshigh frequency fluctuations__ zero correlation
Shmax
Finding Petroleum; 18 April 20129
Reservoir physics
• Communications are not just Darcy fluid flow, but…
• …coupled fluid flow and geomechanics • incorporating pre-existing microcracks,
fractures and/or faults• influenced by modern-day stress state• involving changing permeabilities
• … near a critical point• long-range interactions
Finding Petroleum; 18 April 201210
Extraction of rate diffusivities from time-behaviour of rate correlations
For triangles between wells:
Extract tensors related to diffusive rate behaviour:
Takes some account of spatial relationship of wells & of time-behaviour of correlations.
Finding Petroleum; 18 April 201211
Case studies (6) in North Sea Diffusivity of flow rates: orientational distributions relative tomaximum horizontal stress
Highly anisotropichorizontal stressesStrike-slip/thruststress state
~Isotropic horizontalstressesNormal stress state
Finding Petroleum; 18 April 201212
010
2030
40
50
60
70
80
90
100
110
120
130
140150
160170
180190
200210
220
230
240
250
260
270
280
290
300
310
320330
340350
SHmax
Orientational component of correlation in xx strain
max at 33.2 deg from y
x
zero at 33.5 from x
Heffer & King, 2006
Aggregated orientational frequency distributions of major diffusivity axes - for 6 N Sea fields
Reches & Lockner, 1994
z
x
Healey et al, 2006
t 33 2 d ft 33 2 d f
XX-S TRES S VARIATION AROUND A CRACK (AT LARGE DIS TANCE RELATIVE TO CRACK
LENGTH)
SIN(T)S IN(3T)ZEROX
tens ile
compres s ive
After Pollard
Finding Petroleum; 18 April 201213
Min. path distribution around a well ~ isobars of pressure field. Equivalent to flood progression.
Healey et al, 2006
Flood progress through interacting fracturesin matrix of medium permeability
30o
10o
permeability
Fracture dilation
______
most favoured breakthrough directions for injected fluid in 47 ‘unfractured’ fields worldwide
Finding Petroleum; 18 April 201214
Flowstreams through interacting fracturesin matrix of low permeability
Healey et al, 2006Fracture dilation
30o
Min. path distribution around a well ~ isobars of pressure field. Equivalent to flood progression.
______
most favoured breakthrough directions for injected fluid in 33 ‘fractured’ fields worldwide
0o
permeability
Finding Petroleum; 18 April 201215
Possible mechanism (2): reactivation of polymodal faults (Reches, 1978, 1983; Krantz, 1988, 1989)
PLANE STRAIN 3-D STRAIN
Dihedral angle related to ratio of intermediate and minimum extensional strains – related to local stress tensor
Finding Petroleum; 18 April 201216
Valhall: Microseismic events and interpreted diffusivity axes from rate correlations
Fast shear waves = fracture strikes Teanby et al. (GJI 2004)
Zoback & Zincke (PAGeophys, 2002) Focal mechanism: normal slip
Finding Petroleum; 18 April 201217
The Prize – field data
Water-oilratio
Oil
Shmax Cumulative production per well
Oil production is greatest perpendicular to stress
WOR greatest sub-parallel to stress
|_____|1 MMBO
|_____|WOR 1.0
Increased oil recoveryIncreased oil rateFewer wellsLower watercuts
Finding Petroleum; 18 April 201218
The Prize – theory Lower watercuts
0.0
0.2
0.4
0.6
0.8
1.0
0 20 40 60 80 100
% total area swept
Wat
ercu
t favourableunfavourableisotropic
Save ~$0.6/bbl* of produced water
*SPE 73853 Khatib & Vermeek, 2002e.g. $22million p.a. at 100,000 bwpd
mobility ratio = 1Increased oil recoveryIncreased oil rateFewer wells
Finding Petroleum; 18 April 201219
Rate correlations can identify faults /fracture paths involved in the processes to aid reservoir modelling
North Sea ‘unfractured’ field: 1st principal component from rate correlations superimposed on fault trace map
Input to reservoir model history-matching
Finding Petroleum; 18 April 201220
Time-lapse monitoring:Magnus daily rate data: changes with time in first principal component
/ /////////
Average reservoir pressure
Effective stresses
Strike-slip / thrust
Strike-slip / thrust
normal
Years of development
Stress regime
Finding Petroleum; 18 April 201221
Conclusions• Coupled geomechanics-flow near a critical point is an
integral part of reservoir physics affecting commercially important behaviour; in particular it influences flood directionalities
• Inter-well correlations in rate fluctuations are max. in shearing directions; (micro-) fracture interactions explain this as well as being consistent with flood directionalities. Some shear slip also likely.
• Analysis of inter-well correlations in rate fluctuations offers a low cost means of interpreting specific flowpaths between wells, esp. for input to reservoir model history-matching; also allowing time-lapse.
• Modes of deformation can change during field’s life.• Integration with s-wave data will give most info’.
Finding Petroleum; 18 April 201222
Acknowledgements of grants
NERC CONNECT grant GR3/C0022 with matching funding from BP
COFFERS project, under the Industry Technology Facilitator (sponsors: Amerada Hess, BG Group, BP, Conoco-Phillips, DTI, Kerr-McGee, StatoilHydro, Shell and Total)
RESURGE project, sponsored by theTechnology Strategy Board