Simulation of triggering and geodeformation processes induced by fluid injection into the geomedium

Аннотация

A module for simulation of seismic and geodeformation processes when fluid is injected into and extracted from the geomedium is developed. Calculation of the stress–strain state of the geomedium involves a modified Biot model that takes the rate of bulk strain in the Darcy equation into account. For software implementation of the module simulating the processes during fluid motion in terms of the Biot model, we applied the OpenFOAM 2.4.0 free package of C++ libraries. This package is a set of compiled modules and their source codes; the latter encapsulate all of the most commonly used objects and operations from computational continuum mechanics in accordance with the principles of object-oriented programming. Development of the stress calculation module is based on the standard solver for elastic deformation of an isotropic body from the OpenFOAM package. Its code was supplemented with the procedure of discretization and solution of the Darcy equation for pore pressure. Geodeformation effects are estimated by direct calculation of free surface displacements near the sources of fluid injection and extraction; these displacements can lead, in particular, to dangerous subsidence and induced seismicity. Triggering seismic effects are estimated by calculation of the accumulation rate for excessive tangential stresses in a fault zone at the depth of the seismogenic layer (5–15 km), with the ratios linking the historical seismicity and the tectonic stress accumulation rate in terms of the modified Dietrich’s model being taken into account. Seismological validation of the possible maximum magnitudes of technogenic earthquakes and their recurrence periods in the NE Sakhalin region of intensive oil and gas development is performed. The models of seismic process activation during technogenic impacts on the geomedium are specified.