Approaches to geomechanical modeling in reservoir engineering

Historically, much of reservoir simulation has accounted for rock mechanics only by simple use of a constant compressibility. In reality, in many reservoirs fluid flow is intimately coupled with rock mechanics. Therefore, rigorous reservoir simulation should include simultaneous solution of multiphase flow and stresses, and account for the appropriate dependencies between these two processes. The technical literature shows several theoretic approaches to model reservoir behaviour considering different degrees of coupling between rock deformation and fluid flow: from partially coupled to fully coupled methods. Even if these couplings physically exist to some extent in all reservoirs, the need for using more complex, fully coupled geomechanical modeling is generally acknowledged limited to the cases of compacting reservoirs or high-pressure injection operations. The rock stress-strain conditions must be assessed when conceiving gas storage in aquifers or in other potential new unconventional sites due both to their technical characteristics and to the increasing environmental and public acceptance constraints. Additionally, in the case of underground gas storage the system integrity includes the absence of leakage through the cap rocks over the entire life of the storage and under the alternate injection and withdrawal cycles and, therefore, often requires geomechanical studies.