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Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
B. Hagemann, J. Wegner, L. Ganzer
Milan, 11.10.2012
Excerpt from the Proceedings of the 2012 COMSOL Conference in Milan
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B. Hagemann, J. Wegner, L. Ganzer 2
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
OUTLINE
RE-FRACTURING CONCEPT IN TIGHT GAS RESERVOIRS
IMPLEMENTATION IN COMSOL
NUMERICAL SIMULATION
BASE CASE SIMULATION
IMPACT OF PERMEABILITY
CONCLUSIONS
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B. Hagemann, J. Wegner, L. Ganzer 3
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
RE-FRACTURING CONCEPT IN TIGHT GAS RESERVOIRS
Low matrix permeability in tight gas reservoirs
Hydraulic fracturing required for economic production rates
Production from the well and its initial fracture declines
Re-fracturing required to accelerate recovery
Field cases show different orientation of re-fracture
Connection to a less depleted region in the reservoir
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B. Hagemann, J. Wegner, L. Ganzer 4
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
Concept of stress reversal during pressure depletion
RE-FRACTURING CONCEPT IN TIGHT GAS RESERVOIRS
Stress reversal region
Isotropic point
Initial fracture
Re-fracture
Well Lsr
(Redrawn after Siebrits and Elbel, 1998)
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B. Hagemann, J. Wegner, L. Ganzer 5
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
RE-FRACTURING CONCEPT IN TIGHT GAS RESERVOIRS
Is the re-fracture orientation predictable?
How far does the re-fracture propagate into the perpendicular direction?
What is the best time for re-fracturing?
Which parameters influence the propagation?
Set up of numerical reservoir model in COMSOL Multiphysics
-Coupling of fluid flow and geomechanics -Use of “Poroelasticity” physics interface
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B. Hagemann, J. Wegner, L. Ganzer 6
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
IMPLEMENTATION IN COMSOL – Geometry
Well
Fracture
Reservoir Boundary
12
00
m
1600 m
x
y
200 m
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B. Hagemann, J. Wegner, L. Ganzer 7
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
No flow
Initial pressure = 300 bar
Pressure = 50 bar
No flow
No
flo
w
No
flo
w
σ=38.5MPa
σ=38.5MPa
σ=3
9.5
MPa
σ=3
9.5
MPa
IMPLEMENTATION IN COMSOL – Initial and Boundary Conditions
Fluid flow
Geomechanics
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B. Hagemann, J. Wegner, L. Ganzer 8
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
IMPLEMENTATION IN COMSOL – Parameters
Class Parameter Value Unit Reservoir Rock
Permeability 0.01 mD
Reservoir Rock
Porosity 0.1 -
Reservoir Rock
Young’s Modulus 2.75*105 bar
Reservoir Rock
Poisson’s Ratio 0.25 -
Reservoir Rock
Biot’s Coefficient 0.7 -
Natural Gas Relative Density 0.6 - Natural Gas Temperature 110 °C
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B. Hagemann, J. Wegner, L. Ganzer 9
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
After one year
Elliptical shaped drainage area
Higher pressure gradient in y-direction in the vicinity of the wellbore
After five years
NUMERICAL SIMULATION – Base Case Simulation
Pre
ssu
re, b
ar
Pre
ssure
, bar
x
y
x
y
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B. Hagemann, J. Wegner, L. Ganzer 10
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
Elliptical shaped stress reversal region
Bypassing of stress lines around this region
Initial maximum principal stress direction
Maximum principle stress direction after five years
NUMERICAL SIMULATION – Base Case Simulation
Stress reversal region
x
y
x
y
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B. Hagemann, J. Wegner, L. Ganzer 11
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
Pressure distribution after five years
Maximum principle stress direction after five years
Possible re-fracture propagation after five years
Attaining of less depleted reservoir region with about 200 bar
NUMERICAL SIMULATION – Base Case Simulation
Stress reversal region
Isotropic point Re-fracture
Pre
ssu
re, b
ar
x
y
x
y
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B. Hagemann, J. Wegner, L. Ganzer 12
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
NUMERICAL SIMULATION – Impact of Permeability
Equal maximum dimension for all cases
Higher permeability effects shifting advanced in time
Lower permeability effects shifting delayed in time
0
20
40
60
80
100
0 20 40 60 80 100
Lsr,
m
Time, Years
k = 0.1 mD k = 0.01 mD k = 0.001 mD
Lsr
Stress reversal region
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B. Hagemann, J. Wegner, L. Ganzer 13
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
CONCLUSIONS
COMSOL Multiphysics enables the coupled simulation of fluid flow and geomechanics
Based on simplified model the optimum time for re-fracturing treatment can be predicted
In this model optimum time corresponds to maximum distance to isotropic point as most additional gas is connected to the new fracture
Quantity of permeability changes the time frame of stress reversal region
Impact of anisotropy and heterogeneity has been investigated showing:
-Anisotropic permeability changes maximum dimension and time frame
-Heterogeneous permeability deforms the elliptical shape of the stress reversal region
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B. Hagemann, J. Wegner, L. Ganzer 14
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
Thank you for your attention!
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B. Hagemann, J. Wegner, L. Ganzer 15
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
BACKUP
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B. Hagemann, J. Wegner, L. Ganzer 16
Investigation of Hydraulic Fracture Re-Orientation Effects in Tight Gas Reservoirs
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