Geomechanical Technology for Seal Integrity Analysis: The Three-Step Approach

A clear understanding of the subsurface pore pressure and the presence of geological seals are significant considerations when designing safe wells and optimal production strategies for oil and gas resources. This paper highlights geomechanical techniques and tools which have been developed to assure injection operations for largescale EOR projects in South-East Asia. A key concern is if depletion or injection will lead to reservoir or seal failure by tensile fracturing or shear faulting. If so, will these fractures and faults “grow” upwards and provide a pathway for fluids to escape to the seafloor? First, a 1D-model is made of the total stresses and pore fluid pressures and how these change as a function of depth and depletion/injection. This empirical approach helps to highlight the zones of relatively low minimum effective stress where there is greater risk of rock deformation which will impact operations. Where more detail and refinement is required in terms of the identified risks, we analytically describe the reservoir and overburden deformation with the theory of poro-elasticity, Mohr-Coulomb-type shear faulting, and tensile fracturing. Analytical geomechanics aims at a mechanistic understanding using simplified geology and simplified pore pressure patterns, but with realistic mechanical rock properties. The third step delivers greater detail of the technical complexity using a 3D finite-element simulator. These numerical techniques can simulate the effects of complex structural geology or intra-reservoir compartmentalization, inhomogeneous depletion, and spatial variation in rock mechanical properties. It makes sense to start simple and gradually bring in more complexity whilst adjusting geomechanics support accordingly. We demonstrate the above three-step approach with examples from projects in the South China Sea, offshore Malaysia, which illustrate the multi-disciplinary aspect of geomechanics and its impact on safety, efficiency (costs), and the technical reputation of our company and industry.