Page 363 - Numerical Analysis and Modelling in Geomechanics

344 RESERVOIR COMPACTION, SUBSIDENCE AND WELL DAMAGE

Table 11.1 Material parameters required for a coupled geomechanical surface

its hardening behavior. These tests are often difficult to perform, especially for
very soft, highly compactive sands. Moreover, once the general shear failure
parameters, d and β, and compactive yield data, and , have been generated from
tests, the constitutive model parameters, such as R and α must be determined by
fitting data. For very unconsolidated sands with high porosity, such as are found
in the Gulf of Mexico off the southern coast of the United States, Cernocky et al. 85
have developed a procedure for using uniaxial strain, compaction tests (referred
to by civil and geotechnical engineers as oedometer tests) to develop the
constitutive parameters for the Drucker-Prager/Cap model in the ABAQUS
program. The uniaxial strain tests are used in lieu of the hydrostatic
compression test, since such tests are generally easier to perform.

Coupling between pore pressure and rock deformation
It is clear from Biot’s linear elastic constitutive theory that deformation of a fluid
filled rock depends on both the pore pressure in the rock and the total stress on
the rock. That is, the deformation depends on a coupling between stress and pore
pressure. Given a volume of fluid-filled rock and subjecting it to an increase in
confining compressive stress, the pore pressure will increase if the pore fluid is