New Seismic Base Reservoir Characterization (SBRC) Geomechanical Model Based on Mogi Empirical Rock Failure Relationship

摘要

The objective of this paper is to develop a seismic based reservoir characterization (SBRC) geomechanical model using a non-linear relationship between the maximum and minimum principal stress and taking into account the intermediate principal stress. The proposed geomechanical model is constructed based on Mogi's (1967) empirical rock failure relationship. This allows introducing for the first time in the SBRC the intermediate principal stress. In order to do it, in-situ stress variations as a function of depth are used to match failure stresses for five groups of rock failure experiments that have different values of least principal stress. Next the relationship is integrated with the diffusivity equation for estimating large-scale permeability. German Continental Deep Drilling Project (KTB) data are used to test the validity of the new SBRC model. Two 'hydraulic fracturing' depths (9100 and 6360m) in the KTB site are used to demonstrate the methodology. Minimum permeabilities are calculated with the new SBRC to be 2.9 X 10~(-20） m~2 at 6360 m and 3.1 X 10~(-20) m~2 at 9100 m. Maximum permeabilities are 2.3X10~16 m2 at 6360 m and 2.9 X 10~(-16) m2 at 9100m. Thus the maximum permeability is approximately 4 orders of magnitude larger compared with the minimum permeability (1 m~2 = 1.013E15 md). Novelties of the approach can be summarized as follows: (1) the use of Mogi's (1969) empirical rock failure relationship for integrating intermediate principal stress into the SBRC geomechanical model (this cannot be done when using for example the Mohr-Coulomb rock failure criterion), (2) using a nonlinear relationship between the maximum and minimum principal stress and (3) calculating large-scale permeability.