Stress dependence of fracturing-stimulated permeability inferred from microseismic signatures. (Invited)
Abstract
For developments of hydrocarbon or geothermal reservoirs knowledge of the hydraulic transport is of importance. A substantial contribution in understanding of the permeability evolution as an anisotropic function of stress can be obtained from the evolution of stimulation-induced seismicity in space and time. We focus on analyzing spatio-temporal characteristics of seismicity recorded during different hydraulic fracturing treatments in tight hydrocarbon reservoirs. Pore pressure diffusion based on a power-law pressure dependence of permeability frequently explains well corresponding spatio-temporal features of induced seismicity. We show that in hydraulically anisotropic shale a model of the factorized anisotropic pressure-dependent permeability is in agreement with the microseismic data. Hydraulic stimulation of rocks is accompanied by microseismic activity not only during but also after termination of the fluid injection. The evolution of the growing from the injection borehole seismic quiescence zone (which is enveloped by the so-called back-front of the induced seismicity) yields additional information on the permeability dependence on stress. We observe that under some conditions a power-law pressure dependence of the stimulated permeability can well explain this evolution. However, frequently an exponential pressure dependence of the permeability seems to be more adequate. To explain these different observations we compare the behavior of permeability and elastic properties of rocks as functions of the tectonic stress and pore pressure. We propose that different parts of the pore and fracture space differently contribute to a control of these two types of physical properties of rocks. The stress dependence of elastic moduli of drained rocks is mainly controlled by deformations of the compliant part of the pore (including fractures) space. This leads to saturating exponential functions expressing load dependencies of seismic velocities and of related seismic parameters. It seems that in some rocks permeability is controlled by the stiff part of the pore space. This leads to a power-law pressure dependence of the permeability. Sometimes permeability can be controlled by compliant pores (e.g., cracks or grain contact vicinities ). Then exponential type of permeability as function of pressure can be observed. We propose a permeability model taking these two parts of the porosity into account.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMNS23C1590S
- Keywords:
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- 1859 HYDROLOGY Rocks: physical properties;
- 4440 NONLINEAR GEOPHYSICS Fractals and multifractals;
- 4445 NONLINEAR GEOPHYSICS Nonlinear differential equations;
- 7230 SEISMOLOGY Seismicity and tectonics