Fractured Reservoirs Part 2b
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Transcript of Fractured Reservoirs Part 2b
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Part 2 How to Characterize a Fractured Reservoir?
Hydraulic characterization
How to characterize a fractured reservoir?
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Part 2 How to Characterize a Fractured Reservoir?
Hydraulic characterization
Outcrops
Seismic facies analysis
Wireline Logs
Core data
Image Logs
Mud Losses
Transient well tests
Curvature analysis
Dynamic analysis
Well data Inter-well data
Static analysis
Production data
Drilling reports,
Pressure data,
Tracer tests, etc
Flowmeter
Simulation grid Block
4
Full field simulation
Fracture Up-scaling
Equivalent parameters
(Kfx, Kfy, Kfz, a, b, c, ff)
3
DFN model
(Discrete fracture model)
2
Log-Logplot
Static & dynamic calibration
HOW TO MODEL A
FRACTURED
RESERVOIR ?
1
Locallyconnected fractures
Regionaldiffuse fractures
Locallyconnected fractures
Regionaldiffuse fractur
es
Conceptual model
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Part 2 How to Characterize a Fractured Reservoir?
OBJECTIVES: Estimate the impact of natural fractures on fluid flow Validate the fracture network geometry
Determine the distribution of fracture conductivities
Estimate the fractures aperture
APPROACHES: Conventional dynamic data analysis
Flow simulation of well tests and/or flowmeters in the discrete
fracture network models and comparison/tuning to actual well
test results
History match using a full field model
Hydraulic characterization of fractures
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Part 2 How to Characterize a Fractured Reservoir?
Useful data for hydraulic characterization
Drilling reports: mud losses and rate of penetration
Well testing:
Drawdown, bui ldup: equivalent permeability, dual-medium parameters (l, w) Interference: flow anisotropy
Tracer in ject ion: main flow paths, block size (single well test)
Production logs (flowmeters, TC):
Location of conductive fractures, conductivity
Production history:
Maps of PI and II: correlation with the density of conductive fractures
Pressure maps: idem + communication between panels (sealing faults)
WOC maps (evolution): conductive sub-seismic faults and fracture swarms
Individual wells water-cut/GOR evolution with time
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Part 2 How to Characterize a Fractured Reservoir?
Example 1
Mud losses due to conductive joints
Mud losses at a depth where GR is higher than 70 APIConductive or resistive joints
Mud losses due to resistive joints
Fracture characterization using mud losses
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Part 2 How to Characterize a Fractured Reservoir?
Example 2
Fracture characterization using mud losses
1300 ft (400 m)
100% loss
100% loss
100% loss
3% loss
Highest fracture density
250 m
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Part 2 How to Characterize a Fractured Reservoir?
Fracture characterization using well tests
Transient well test signature
Specific signatures are expected in a fractured reservoir:
- large wellbore storage
- fracture corridor
- hydraulic fracture
- constant pressure boundary
- Dual porosity signature
Transient well test parameters: Equivalent permeability (KH)
Dual-medium parameters (, )
Conductivity of the fracture crossing the well
Distance between the well and the fracture swarm / fracture network / fault
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Part 2 How to Characterize a Fractured Reservoir?
Build-up
- -3 0 .0 1 0 .1 1 1 0 1 0 0 1 0
10 0
1 0 0 0
0 0 0 0
Semi-log plot - Horner plot Log-log plot
Transient well tests analysis
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Part 2 How to Characterize a Fractured Reservoir?
KH_2000
KH_500 (ref )
KH_1000
Log-Log plot
KH_2000
KH_500 (ref)
KH_1000
Semi-Log plot
History plot
Kh = 2000 mD.ft
Kh = 500 mD.ft
Kh = 1000 mD.ft
KH impact on well test plots
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1Part 2 How to Characterize a Fractured Reservoir?
History plot
Log-Log plotSemi-Log plot
C = 0.001 bbl/psi
C = 0.1 bbl/psi
C = 0.01 bbl/psi
Wellbore storage effect
Th L l l t i t t ti
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Part 2 How to Characterize a Fractured Reservoir?
The Log-log plot interpretation
t (log scale)
Pressure(logsca
le)
Skin
K.H
C (= fluid in well compressibility . wellbore volume)
Well Bore Storage
Radial Flow
K.H
Large StorageSmall Storage
Large Skin
Small Skin
Horizontal Slope
Pressure curve
Derivative curve
Homogeneous reservoir, WBS + Skin
T i t ll t t l i
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1Part 2 How to Characterize a Fractured Reservoir?
Transient well tests analysis
Log-Log plot Log-Log plot
Homogeneous reservoir Fractured reservoir
2
w
f
m
tmmtff
tff
rk
k
CC
C
l
ff
fw
Omega: storativity ratio the fraction of the pore volume occupied by the fissures to the total
interconnected pore volume.
Lambda: interporosity flow parameter the ability of the matrix to flow into the fissure network.
T i t ll t t i F t d i
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1Part 2 How to Characterize a Fractured Reservoir?
Transient well tests in Fractured reservoir
First radial flowFractures only
K.H fracture
Matrix starts flowing
=> Pressure support
=> Derivative curve decreases
Second Radial Flow
Final Steady state Flow in Matrix & Fractures
K.H (Matrix + Fracture) ~ K.H fracture
T2(Begining 2
nd
R.F.)
T1(End 1
st
R.F.)
TAft(End WBS)
decreases
(block size increases &/or km decreases &/or kf increases)
decreases
(m&/o
rCtmincreases)
Dual porosity signature
Transient well tests in Fractured reservoir
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1Part 2 How to Characterize a Fractured Reservoir?
Transient well tests in Fractured reservoir
2
w
f
m
tmmtff
tff
r
k
k
CC
C
l
ff
fw
Log-Log plot
w=0.1
l=10-6 l=10-7 l=10-8
Kfrac.h
w=0.1
Dual porosity signature
Transient well tests in Fractured reservoir
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1Part 2 How to Characterize a Fractured Reservoir?
Transient well tests in Fractured reservoir
Dual porosity signature
2
w
f
m
tmmtff
tff
rk
k
CC
C
l
ff
fw
History plot
Log-Log plot
l=10-7
w=0.1
w=0.5
w=0.01
Semi-Log plot
w=0.1w=0.5
w=0.01
Transient well tests in Fractured reservoir
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Transient well tests in Fractured reservoir
Dual porosity signature
tmmtff
tff
CC
C
ff
fw
Omega: if Ctf= Ctm, then Omega gives an estimation of the percentage of pore volume present
in the fracture network.
Lambda:
is the Warren & Root shape factor (also called sigma)
Between 10-3 and 10-10. If Lambda is higher, the level of heterogeneity is usually too
small for the dual porosity effects to be of importance.
Example:
rw=8.5/2=0.354 feet
Km=10mD
Kf=1.0 D
= 32/L2 = 0.889 (1 fracture every 6 feet)
Lambda = 1.1 10-3
2
w
f
m
rk
kl
One well test several matched model
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1Part 2 How to Characterize a Fractured Reservoir?
Log-Log plot
Log-Log plot
Model :Well : Storage + skin
Reservoir : Homogeneous
Boundary : One sealing fault at
800 ft
Kh = 563 mD.ft Skin = 0
Model :Well : Storage + skin
Reservoir : Two porosity - sphere
Boundary : Infinite
Kh = 292 mD.ft Skin = -3.7
Radial flow periodRadial flow period
One well test, several matched model
Transient well tests in Fractured reservoir
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1Part 2 How to Characterize a Fractured Reservoir?
Match obtained withl=10-7 &w=0.01
Log-Log plot
Match obtained withl=8.10-8 &w=0.117
Wellbore storage can make the finding of the dual-porosity parameters a very difficult task!
Transient well tests in Fractured reservoir
Influence of wellbore storage
Log-Log plot
Well tests in Fractured reservoir
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1Part 2 How to Characterize a Fractured Reservoir?
Well tests in Fractured reservoir
Influence of Wellbore storage Phase redistribution effect
Changing wellbore storage
Log-Log plot
Dual mediaOmega 0.0275
Lambda 0.0693
Log-Log plot
Increasing wellbore storageCi/Cf = 0.39
Well tests in Fractured reservoir
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2Part 2 How to Characterize a Fractured Reservoir?
Well tests in Fractured reservoir
Conductive fracture at well
Log-Log plot: dp and dp' [psi] vs dt [hr]
Slope between 0.5 (CDf= 0) and 1
The productivity of fractured wells is so high that wellbore storage isnt seen in
most cases.!
Well tests in Fractured reservoir
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2Part 2 How to Characterize a Fractured Reservoir?
Log-Log plot
Selected ModelModel Option Standard Model
Well Uniform Flux
Reservoir Two Porosity PSS
Boundary Intersecting Faults
ResultsC 0.0612 m3/bar
Skin 0 --
Xf 12.8 mk.h 8.13 md.m
Omega 0.146 --
Lambda 0.00656 --
L1 - Constant P. 18 m
L2 - Constant P. 30.9 m
N 2 --
Log-Log plot
Selected ModelModel Option Standard Model
Well Storage + Skin
WBS Type Changing
Reservoir Homogeneous
Boundary Circle
ResultsC 0.555 m3/bar
Ci/Cf 0.189 --Alpha 214 --
Skin -1.65 --
k.h 20 md.m
Re - No Flow 130 m
Hydraulically fractured well (gas field)
Well tests in Fractured reservoir
Well tests in Fractured reservoir
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2Part 2 How to Characterize a Fractured Reservoir?
Log-Log plot
Gas field - Europe
Selected ModelModel Option Standard Model
Well Storage + Skin
WBS Type Changing
Reservoir Two Porosity PSS
Boundary Circle
Results
C 2.28E-7 m3/Pa
Ci/Cf 2.25 --
Alpha 8830 --
Skin 2.33 --Delta P Skin 30.4574 bar
Pi 387.101 barak.h 6.26 md.m
k 1.25 md
Omega 0.0201 --
Lambda 1.16E-5 --
Re - Constant P. 52.4 m
Constant pressure
boundary at 50 m
Well tests in Fractured reservoir
Transient well tests in fractured reservoirs
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2Part 2 How to Characterize a Fractured Reservoir?
Comparison KHtest Vs KHmatrix
KHmatrix estimated from core or from synthetic permeability log
The principal difficulty is to estimate H
1
10
100
1000
10000
100000
1 10 100 1000 10000 100000
KHmatrix (mD.m) from synthetic permeability log
KHtest(mD.m
)fr
om
transientwelltestsinterpertation
Transient well tests in fractured reservoirs
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Change of KHtest with stimulation
Can indicate the presence of nearby heterogeneities
0
500
1000
1500
2000
2500
0 500 1000 1500 2000 2500
KH test before hydraulic fracture (mD.m)
KHtestafterhydraulicfracture(mD.m
KHtestafterhydraulic
stimulation(mD.m
)
0
500
1000
1500
2000
2500
0 500 1000 1500 2000 2500
KH test before hydraulic fracture (mD.m)
KHtestafterhydraulicfracture(mD.m
KHtestafterhydraulic
stimulation(mD.m
)
Transient well tests in fractured reservoirs
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Comparision between KHtest and distance to nearby faults
Can indicate the presence of fracture corridors
Vertical wells drilled in the area covered by the 3D seismic
0.1
1
10
100
0 200 400 600 800 1000 1200
Distance between wells and the closest fault / lineament (m)
KHtest/KHmatrix(mD.m
)
Hydraulic characterization of fractures
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What can be expected from well test analysis in a fractured
reservoir ?
Skin: fracture connectivity, damage of mud losses
Dual porosity signature: w, l Direct measurement of fracture conductivity
Reservoir KH
Constant pressure boundary: presence of conductive fault/swarm,
distance to this fault/swarm
No flow boundary: width of fractured zone, presence of a sealing fault,
distance to this fault
y
Fracture characterization using flowmeters
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Correlation between fracture density and flowmeter data
Determination of conductivity using flowmeter data
Hydraulic characterization use of flowmeter data
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Well fracture log
Depth 5
Depth 4
Depth 3
Depth 1
Depth 2
N60
N150
N100
N100
Well production log
Dynamic fracture characterisation Qualitative estimation from PLT
Fault conductivity from flowmeter
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Presence of
a fracture
swarm
Fault conductivity from flowmeter
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Facies (KM)
Fracture density log
Flowmeter
0
100
M
M
FF K
QQLc
sub-seismic fault (SSF)
QF QM + QF
cF: fault conductivity
L: length of measurement (homogeneous facies)
KM: matrix permeability
QM: matrix rate
QF: fault rate
Fault conductivity from flowmeter
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CF ~ 70 Darcy.m
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Fracture characterization using history data
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Validation of a fracture network using:
well productivity data
water/gas production
breakthrough times
signature of water/gas production
Validation of fractures against dynamic data
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highly fractured
PI = 33
poorly fractured
Water at the last
500ft
moderatly fractured
PI = 22
High water cut
highly fractured
Up. Res PI = 78
Bot. ResPI = 79
non fractured
PI = 7
Seismic
facies
Influence of faults on well productivity
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Determination of the lineament influence zone in the WEST part of ZONE 1
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
18.00
0 200 400 600 800 1000 1200
Distance from the we ll to the lineament (m)
PI/LengthinAsmari(stb/d/psi/m)
N130
EW
3247200 3247200
3247800 3247800
3248400 3248400
3249000 3249000
3249600 3249600
511500
511500
512000
512000
512500
512500
513000
513000
513500
513500
514000
514000B61
B84
Validation of fractures: use of history data
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18
19
91
92
103
105
106
118
13942
304
318
319
320
316
132
Wet
Dry
Injectors
Fracture swarm and water breakthrough
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t
wcut
t
wcut
Well Well
Fracture swarmIncreasing Rate
Fracture swarm and water breakthrough
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Well near a fracture swarmWell far from a fracture swarm Well on a fracture swarm
Hydraulic characterization of fractures
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Simulation approach:
Simulate transient or steady-state well tests on the detailedgeological model incorporating fracture and sedimentological data
Tune fracture flow properties (conductivities) to match the
measured pressures (distribution of rates) conductive sets
If major discrepancies remain: re-analyse/change the geological
model (fracture attributes in relation with facies properties, faults, ...)
with the help of other information (production history, ...)
Advantages:a flow simulation model better constrained by the geology:
- higher reliability,- possibility of evolution
Well test simulation on a DFN
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Ref.:"Hydraulic Characterization of Fractured Reservoirs: Simulation on Discrete Fracture Models," S. Sarda,L. Jeannin, R. Basquet and B. Bourbiaux, SPE 66398, Res. Sim. Symp. 2001 (to be published in SPEFE)
Single-phase compressible flow of oil to well-bore :
from the matrix to the nearest fracture
through the fracture network to the well
The simulation model:
Explicit discretization of the fracture network (nodes and cells)
Aspecific matrix block assigned to each fracture cell
Pseudo steady-state M-F exchanges
Fracture cell definition
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Computation nodes
(intersections)
Fracture cell
Fracture cell limits placed at: - fracture extremities- mid points between two intersections
Matrix block determination
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XY
Matrix block
Fracture nodes
Fracture cell
Matrix-fracture flow transfers
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Pseudo-steady-state approach: flux is proportional to
pressure drop
M-F transmissivity Tmf:
no time dependence
dependence on the matrix block geometry
Assumption: the local matrix pressure varies linearly with
the distance to the nearest fracture.
)mfmf PTF
Well test in a dense fracture network
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400 m
Build-up test simulation
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Simulated pressure maps
T1
T1 (fracture-dominated)
T2
T2 (end of transition)
T3
T3 (pseudo-steady-state)
log(Dt)
dP/dt
P
Well test simulation in a 3D network
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WELL
Complex 3D fracture
network
Exact location of
well-fracture
intersections
Pseudo steady-state
matrix-fractureexchanges
Visualisation of rates
in fractures:
Increasing
rate
Hydraulic characterization - well test simulation
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Fracture sets conductivity determination through well test matching
well
Log-Log plot
History plot
Variable adjusted :
Conductivity Fracture length
of each fracture set
Complex well test match
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Log-Log plot
Constant pressure
boundary
(KH)2
(KH)1
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