Some Advances in Near Wellbore Geomechanics

McLennan, J.D. and Abou-Sayed, A.S.
Presented at: SPE/ISRM Rock Mechanics Conference, Irving, Texas, October 2002.


There has been substantial recent progress in coupling geomechanical effects to reservoir response, thus dramatically improving representation of the consequences of rock response to pressure changes. New reserves have been identified from compaction. Injection geomechanics has gained an increase in interest due to its impact on the reservoir, faults and well hardware. Changes in transmissibility are now seriously implemented in reservoir engineering tools with more attention directed at the presence of compaction and dilatant bands around producers or injectors. Efforts are progressing to ensure adequate coupling between the local effects of the rock deformation near the wellbore, as well as along faults or bedding planes, and the evolving stresses and deformation in the reservoir. This paper attempts to discuss current gaps in understanding the intricacies and details of coupling farfield deformation to well completion. Examples are shown where reservoir compaction or dilatancy is explicitly coupled to near-wellbore behavior, with specific application for assessing well performance and survivability. The analyses can use Reservoir Optimizations coupled with analytical predictions of stresses and deformations in individual simulator blocks. The predicted stresses and deformations form the boundary conditions for finite element modeling that can focus in on the details around the completion itself. This is in contrast to the current approaches that use explicit coupling of pressure and deformation in complete massive finite element representations, with refined gridding around the completion. The intimate details of coupling reservoir deformation to the completion require more intensive consideration. For example, “How can the cement sheath be represented?” or “What are some of the constitutive considerations in the near-wellbore region that impact integrity?” and “How is varying transmissibility related to well integrity?” These issues are considered. There are three goals: 1) Start to recognize completion and production management practices that will improve completion longevity and optimize well productivity. 2) Identify reasonable methodologies for representing the coupling between the completion and the reservoir, including yielded zones (dilatant and/or compactant), compaction bands with varying transmissibility, the cement sheath with or without a microannulus and the mud cake. 3) Delineate approximate methods that will adequately forecast completion distress and permeability impairment without the necessity of expensive and time-consuming detailed finite element simulations.