Crisman Annual Report 2009 - Harold Vance Department of ...

Modeling and Analysis of Reservoir Response to Stimulation by Water Injection
Objectives
The distributions of pore pressure and stresses
around a fracture are of interest in conventional
hydraulic fracturing operations, fracturing during
water-flooding of petroleum reservoirs, shale gas,
and injection/extraction operations in a geothermal
reservoir. During the operations, the pore pressure
will increase with fluid injection into the fracture
and leak off to surround the formation. The pore
pressure increase will induce the stress variations
around the fracture surface. This can cause the
slip of weakness planes in the formation and cause
the variation of the permeability in the reservoir.
Therefore, the investigation on the pore pressure
and stress variations around a hydraulic fracture in
petroleum and geothermal reservoirs has practical
applications. With the pore pressure distribution,
the failed reservoir volume can be estimated by
considering the failure of rock mass.
Y, ft
3000
2400
1800
1200
(psi)
6558.00
600
6148.33
5738.67
0
5329.00
4919.33
-600
4509.67
4100.00
-1200
-1800
-2400
-3000 -2400 -1800 -1200 -600 0 600 1200 1800 2400
X, ft
Fig. 1. Pore Pressure Distribution around a Hydraulic Fracture.
Approach
In our study, we built up a model (FracJStim model)
to calculate the pore pressure distribution around a
fracture of a given length under the action of applied
internal pressure and in-situ stresses as well as their
variation due to cooling and pore pressure changes
(Fig. 1). In the FracJStim model, the Structural
Permeability Diagram (Fig. 2) is used to estimate
the required additional pore pressure to reactivate
the joints in the rock formations of the reservoir. By
estimating the failed reservoir volume and comparing
it with the actual stimulated reservoir volume, the
enhanced reservoir permeability in the stimulated
zone can be approximated.
0
270 90
180
Fig. 2. Structural Permeability Diagram for Barnett Shale.
P
(psi/ft)
0.50
0.06
Significance
This work is of interest in interpretation of microseismicity
in hydraulic fracturing and in assessing
permeability variation around a stimulation zone.
The work can also be used to assess the accuracy of
more complex numerical models.
Future Work
We will continue developing the model to three
Dimensions, including the stresses variations and
heterogeneous conditions. We will also improve
the application of this work by simulating multiple
fractures.
CRISMAN INSTITUTE
Project Information
2.5.10 Pore Pressure and Stress Distributions around an
Injection-Induced Fracture
Contacts
Ahmad Ghassemi
979.845.2206
ahmad.ghassemi@pe.tamu.edu
Jun Ge
Crisman Annual Report 2009
61