Elastic Dislocation Modelling and Coulomb Stress Change Investigations

Abstract

Elastic Dislocation modelling based on angular dislocation theory is able to predict displacement fields and the distribution of strain in a poroelastic medium for any slip introduced on a discrete fault. Assuming linear elasticity, the magnitude and distribution of fault-induced stresses can then be calculated and following on from this, the Coulomb stress changes in the surrounding rock can be determined from shear and normal stresses acting upon fractures. In addition, a key application of Coulomb stress change is the ability to determine optimal fracture orientations. Outputs from elastic dislocation and Coulomb stress change modelling have numerous applications for hydrocarbon exploration and production, but a key driver for this new development is the ability to model lateral variation of mechanical properties, such as elastic moduli, strength, and friction. Lateral variations in mechanical properties have not been considered in any of the currently available software packages. For the first time, users have the ability to laterally vary mechanical properties, such as Poisson's ratio, Young's modulus and friction, allowing natural lithological variations to influence the calculation of various stress attributes. We will present details on how Elastic Dislocation Modelling and Coulomb stress change calculations have been implemented in Midland Valley's Move” software. The new module, called Fault Response Modelling, has been specifically designed to offer this higher degree of freedom. Additionally, the user can use two different friction models in the calculation: (1) an apparent frictional model, and (2) a pore pressure responsive model. The application and potential limitations of these two friction models to geological problems relevant to hydrocarbon exploration and production will be discussed using a combination of illustrative examples and case studies. Significantly, the calculations for optimally oriented fracture planes are based on a general tensor description, which allows users to consider any slip direction and an opening or closing component. Various other stress attributes, including slip tendency, fracture stability and retention capacity can then be calculated for these fractures to assess which fractures are likely to fail in the stress field and potentially act as fluid pathways.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015