Coupled Reservoir Simulation and Finite-Element Modeling of Shear Failure Potential on Reservoir Boundary Faults in the Lower Tertiary (Paleogene) Plays in the Gulf of Mexico

Brown, Jeremy A.¹; Zoback, Mark; Hornby, Brian; and Stauber, Doug
¹[email protected]

The ultra-deepwater lower Tertiary plays of the Gulf of Mexico, also known as the Paleogene, are HPHT reservoirs that will require cutting-edge technology to be successfully produced. In this study we report a coupled reservoir-geomechanical simulation analysis used to model potential stress changes due to reservoir depletion and potential shear failure on pre-existing faults.

A geomechanical model has been developed that constrains the overburden stress, the minimum horizontal stress, rock properties from available lab tests on core, and pore pressure. Constraining the maximum horizontal stress is difficult based on available data. Given that the reservoir is severely overpressured in a normal faulting environment, several realizations were generated where the maximum horizontal stress lies between the minimum horizontal stress and overburden stress. The orientations of the horizontal stresses have been estimated from the orientation of active faults in the area.

Two idealized Paleogene structural models were built with the primary reservoir sands lying beneath large salt bodies. A reservoir grid was created and populated with known reservoir properties. Realistic primary recovery fluid-flow reservoir simulations were performed in a commercial reservoir simulator with the resulting fluid pressure changes over the life of the reservoir being transferred to the finite-element geomechanical simulator (ABAQUS) to update porosity, permeability, and deformational changes in the reservoir. Based on earlier work, we seek to confirm that, given substantial depletion, fault re-activation is likely to occur for a given stress path. Depending on the amount of depletion and the magnitude of the maximum horizontal stress, shear failure is possible on the bounding faults that compartmentalize the Paleogene reservoir. These results have implications on well placement and pressure management of the field.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013