De-Risking the Steam Injection Project with Comprehensive Geomechanical & Geochemical Assessment, Sultanate of Oman

Abstract The subject field has a cretaceous clastic sandstone reservoir which has been producing heavy oil (16-17° API). The reservoir is overlain by thick shale cap rock with an unconformity. The study area is bounded by two faults on the eastern and western sides of the field. Enhanced oil recovery methods are deployed to improve the productivity, including cyclic steam stimulation (CSS). A steam flood pilot was performed on a few wells with the aim to implement the full-field steam injection in the near future. As part of this full-field deployment, comprehensive Geomechanical & Geochemical risk assessment was carried out with multi-disciplinary reservoir data integration. This paper discusses the relevant workflow for risk assessment in detail. Understanding and evaluating the state of in-situ stress is essential before and during steam injection operations. This requires building calibrated Geomechanical models for key wells based on the best available data. A normal stress setting prevails in the reservoir at initial pressure and temperature conditions. In order to simulate the complex geological structure of the reservoir, 3D finite element (FE) modeling is deployed with the aim to compute stress and strain changes in the reservoir and cap rock due to changes in reservoir pressure and temperature. A watertight structural framework for the 3D Geomechanical model is built covering overburden, reservoir and underburden formations along with faults capturing the complexity. The full field 3D Geomechanical model is populated with rock mechanical properties with guidance from a static geological model. Then, the 3D Geomechanical model is coupled with a reservoir dynamic model that has forecasted pressure and temperature at different time intervals as per the planned steam injection. This model computes the stress/strain changes in and around the reservoir with forecasted changes of pressure and temperature with time. Furthermore, geochemical assessment was conducted considering the reservoir mineralogy and estimated the fines production risk as well as the risk to the integrity of the formations as a result of the introduction of steam into the formations. Results of the finite-element modeling are evaluated to quantify the geomechanical-related risks, which includes compaction/heave in the reservoir, cap rock integrity, and fault reactivation. Additionally, an estimated safe operating envelope for injection was defined to avoid risking reservoir integrity. A customized multi-technology monitoring strategy is developed for further field development planning. This integrated study has systematically de-risked the development plan with safe operating envelopes and further recommendations to develop the reservoir.