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Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
Direct Numerical Simulation of Fluid Driven Fracturing Eventswith Application to Carbon Sequestration
Joseph Morris and Scott Johnson
LLNL-PRES-404894
2Lawrence Livermore National Laboratory
Geomechanical response represents a primary source of risk to successful CO2 storage
Low permeability caprockE.g: Shale
Injection of enormous volumes of CO2 will cause• Increased pore pressures• Large scale reservoir
deformation
These mechanisms alter stresses in• Caprocks• Pre-existing fractures and
faults High porosity/permeability reservoirE.g: Saline aquifer
3Lawrence Livermore National Laboratory
Need to establish what CO2 pressures will lead to risk of caprock failure under reservoir conditions
Caprock seal failure mechanisms
Create new open fractures?
PressurizedsupercriticalCO2
Water
Activate existing tight fractures?
Activate existing fault?
Create new open fractures?
PressurizedsupercriticalCO2
Water
Activate existing tight fractures?
Activate existing fault?
We are investigating three sources of risk:• Creation of new fractures• Activation of faults• Activation of fracture networks
4Lawrence Livermore National Laboratory
Livermore Distinct Element Code (LDEC):Key Features and Capabilities
Fully 3-D fully coupled fluid-solid solver
Distinct Element Method (DEM) Module• Rock mass represented by arbitrarily shaped polyhedral blocks
Can accommodate realistic joint-sets• Empirical joint models – slip, hysteresis, dilation• Block representations:
Rigid / Uniform deformation (“Cosserat blocks”) / Finite elements• All block types support:
Dynamic contact detection Dynamic fracture/fragmentation
Smooth Particle Hydrodynamics (SPH) Module• Fully coupled fluid dynamics
Flow network solver• Fully coupled fluid dynamics confined within fractures
Fully parallelized: Demonstrated on up to 8000 CPUs
Will be available under license from LLNL shortly
5Lawrence Livermore National Laboratory
Need to establish what CO2 pressures will lead to risk of caprock failure under reservoir conditions
Caprock seal failure mechanisms
Create new open fractures?
PressurizedsupercriticalCO2
Water
Activate existing tight fractures?
Activate existing fault?
Create new open fractures?
PressurizedsupercriticalCO2
Water
Activate existing tight fractures?
Activate existing fault?
We are investigating three sources of risk:• Creation of new fractures• Activation of faults• Activation of fracture networks
6Lawrence Livermore National Laboratory
Dynamic Fracture:Experiment with a notched plate
It is observed that as loading rate is increased, crack velocity is limited and falls short of the Rayleigh wavespeed
[From Zhou, F., Molinari, J.-F., and T. Shioya, 2005]
7Lawrence Livermore National Laboratory
Dynamic Fracture: Cohesive Elements
Nodes split when specified fracture criteria are met• Tensile• Shear
Introduce cohesive element between new nodes:• Ensures correct energy is
dissipated (proportional to surface created)
• Reduces mesh size dependence
Currently fracture must follow existing element boundaries
8Lawrence Livermore National Laboratory
Dynamic Fracture: LDEC Cohesive Elements
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1.0Experiment LDEC
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(/
c)2
v/vR
Block, Rubin, Morris and Berryman (2008)
9Lawrence Livermore National Laboratory
We have recently added a network flow capability to support simulation of hydraulic fracture
LDEC: Add coupling with matrix
geomechanical response
Triangular finite volumes with element-centered pressure
Fully coupled with solid elements to model hydrofracture
Koudina et. al. (1998): Flow through fractures on an unstructured mesh Lacks coupled geomechanics
Triangular finite volumes with node-centered pressure
10Lawrence Livermore National Laboratory
LDEC Demonstration of hydraulic fracture
Pressurized crack propagates into the rock
Prediction of caprock and reservoir rock integrity Characterization of seismic sources for far-field
detection and interpretation
y: 4 cm
x: 6 cm
z: 6 cm
Initial fracture
11Lawrence Livermore National Laboratory
Need to establish what CO2 pressures will lead to risk of caprock failure under reservoir conditions
Caprock seal failure mechanisms
Create new open fractures?
PressurizedsupercriticalCO2
Water
Activate existing tight fractures?
Activate existing fault?
Create new open fractures?
PressurizedsupercriticalCO2
Water
Activate existing tight fractures?
Activate existing fault?
We are investigating three sources of risk:• Creation of new fractures• Activation of faults• Activation of fracture networks
12Lawrence Livermore National Laboratory
Simulation of fault activation due to fluid injection:Application to Teapot Dome
0.E+00
1.E+05
2.E+05
3.E+05
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1.E+06
0 10 20 30 40 50 60 70
Peak change in Pp on fault (MPa)
Fau
lt A
rea
Act
ivat
ed (
sq.
m)
Change in pore pressure that will result in activation of given location on S1 fault (similar to Chiaramonte et al, 2007). Plot of fault area activated as a
function of increase in pore pressure on fault surface
Facets of fault considered in isolationFull geomechanics with LDEC
13Lawrence Livermore National Laboratory
Need to establish what CO2 pressures will lead to risk of caprock failure under reservoir conditions
Caprock seal failure mechanisms
Create new open fractures?
PressurizedsupercriticalCO2
Water
Activate existing tight fractures?
Activate existing fault?
Create new open fractures?
PressurizedsupercriticalCO2
Water
Activate existing tight fractures?
Activate existing fault?
We are investigating three sources of risk:• Creation of new fractures• Activation of faults• Activation of fracture networks Caprock/reservoir
14Lawrence Livermore National Laboratory
Simulation of injection into a heavily fractured reservoir
Fracture network Delta-Pore pressure field
Small test problem:• 13 thousand, variably oriented fractures
Anisotropic stress field: east = overburden, north = 0.6 overburden
Distinct element model with explicit fracture elements modeled between arbitrary polyhedral blocks
15Lawrence Livermore National Laboratory
Simulation of injection into a heavily fractured reservoir
The proportion of joints of each orientation relative to North that have failed during fluid injection
Joints of all orientations fail due to redistribution of stress• Predominantly those initially experiencing shear stress
Provide predictions of permeability change Predict energy release from fractures during injection
Joint orientations activated during injection
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Joint normal orientation from North
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po
rtio
n o
f jo
ints
th
at s
lipp
ped
16Lawrence Livermore National Laboratory
Conclusions
Caprock integrity represents a significant potential source of risk to successful geologic storage of CO2
LDEC has demonstrated capabilities for predicting:• Fluid driven fracturing events• Activation of existing faults• Activation of existing networks of fractures
Moving forward:
• Parameter studies to evaluate risk to CO2 containment
• Funded to participate in large scale field projects
Other applications:• Unconventional gas/oil recovery
17Lawrence Livermore National Laboratory
Extras…
Extras…
18Lawrence Livermore National Laboratory
We are developing interfaces between LDEC and FRAC-HMC to span the scales of interest
O(1 km)
O(1
m)
O(1
0 m
)Local fracture network scale:Simulation of consequent fracture network permeability and local stress change FRAC-HMC/LDEC
Individual Fracture scale:Simulation of activation and creation of caprock fractures
LDEC
Reservoir Scale:Simulation/Measurement of insitu conditions during operation NUFT, partners in industry
19Lawrence Livermore National Laboratory
Simulation of fault activation due to fluid injection
5 km2 km
reservoirFault plane
5 km
well
Finite element model with fault modeled by material with shear strength dictated by prescribed coefficient of friction
20Lawrence Livermore National Laboratory
Simulation of fault activation due to fluid injection
Mounding due to injection
Slip on fault results in discontinuity in surface expression
Slip on fault results inreduced displacement on other side of fault Injection source at
1500m depth