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Direct Numerical Simulation of Fluid Driven Fracturing Events with Application to Carbon Sequestration Joseph Morris and Scott Johnson. Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551. LLNL-PRES-404894 .

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Direct Numerical Simulation of Fluid Driven Fracturing Events

with Application to Carbon Sequestration

Joseph Morris and Scott Johnson

Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551

LLNL-PRES-404894

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

geomechanical response represents a primary source of risk to successful co 2 storage
Geomechanical response represents a primary source of risk to successful CO2 storage
  • 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 reservoir

E.g: Saline aquifer

Low permeability caprock

E.g: Shale

caprock seal failure mechanisms
Caprock seal failure mechanisms
  • Need to establish what CO2 pressures will lead to risk of caprock failure under reservoir conditions
  • We are investigating three sources of risk:
    • Creation of new fractures
    • Activation of faults
    • Activation of fracture networks
livermore distinct element code ldec key features and capabilities
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
caprock seal failure mechanisms1
Caprock seal failure mechanisms
  • Need to establish what CO2 pressures will lead to risk of caprock failure under reservoir conditions
  • We are investigating three sources of risk:
    • Creation of new fractures
    • Activation of faults
    • Activation of fracture networks
dynamic fracture experiment with a notched plate
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]

dynamic fracture cohesive elements
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
we have recently added a network flow capability to support simulation of hydraulic fracture
We have recently added a network flow capability to support simulation of hydraulic fracture

LDEC:

  • Add coupling with matrix geomechanical response

Koudina et. al. (1998):

  • Flow through fractures on an unstructured mesh
  • Lacks coupled geomechanics
  • Triangular finite volumes with element-centered pressure
  • Fully coupled with solid elements to model hydrofracture
  • Triangular finite volumes with node-centered pressure
ldec demonstration of hydraulic fracture

y: 4 cm

x: 6 cm

Initial fracture

z: 6 cm

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
caprock seal failure mechanisms2
Caprock seal failure mechanisms
  • Need to establish what CO2 pressures will lead to risk of caprock failure under reservoir conditions
  • We are investigating three sources of risk:
    • Creation of new fractures
    • Activation of faults
    • Activation of fracture networks
simulation of fault activation due to fluid injection application to teapot dome
Simulation of fault activation due to fluid injection:Application to Teapot Dome

Full geomechanics with LDEC

Facets of fault considered in isolation

  • 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
caprock seal failure mechanisms3
Caprock seal failure mechanisms
  • Need to establish what CO2 pressures will lead to risk of caprock failure under reservoir conditions
  • We are investigating three sources of risk:
    • Creation of new fractures
    • Activation of faults
    • Activation of fracture networks  Caprock/reservoir
simulation of injection into a heavily fractured reservoir
Simulation of injection into a heavily fractured reservoir
  • Distinct element model with explicit fracture elements modeled between arbitrary polyhedral blocks

Fracture network Delta-Pore pressure field

  • Small test problem:
    • 13 thousand, variably oriented fractures
  • Anisotropic stress field: east = overburden,north = 0.6 overburden
simulation of injection into a heavily fractured reservoir1
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
conclusions
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
extras
Extras…
  • Extras…
we are developing interfaces between ldec and frac hmc to span the scales of interest

O(1 km)

O(1 m)

O(10 m)

We are developing interfaces between LDEC and FRAC-HMC to span the scales of interest

Reservoir Scale:

Simulation/Measurement of insitu conditions during operation

NUFT, partners in industry

Individual Fracture scale:

Simulation of activation and creation of caprock fractures

LDEC

Local fracture network scale:

Simulation of consequent fracture network permeability and local stress change

FRAC-HMC/LDEC

simulation of fault activation due to fluid injection
Simulation of fault activation due to fluid injection
  • Finite element model with fault modeled by material with shear strength dictated by prescribed coefficient of friction

5 km

well

2 km

5 km

reservoir

Fault plane

simulation of fault activation due to fluid injection1
Simulation of fault activation due to fluid injection
  • Slip on fault results in discontinuity in surface expression

Mounding due to injection

Slip on fault results inreduced displacement on other side of fault

Injection source at 1500m depth