Reservoir Simulation of Gas Injection Processes

Abstract In reservoirs with favorable rock and fluid properties, application of gas injection processes can enhance the recovery efficiency and value of a field development. ExxonMobil employs a systematic approach to evaluating and selecting recovery processes during the full life-cycle of each reservoir. Once a gas injection project has been implemented, ongoing surveillance programs and optimization studies are performed to ensure that maximum value is obtained from the resource. One important aspect of managing these resources has been the use of reservoir flow modeling to understand performance expectations and to develop reservoir management strategies to optimize recovery. Because ExxonMobil's experience with reservoir simulation of gas injection processes has covered many types of injection processes over many years, a full suite of simulation approaches has been used for reservoir flow modeling. The gas injection processes studied and implemented have included miscible floods, immiscible floods, Water-Alternating-Gas (WAG) floods, as well as gas disposal. A full range of injection gases such as CO2, H2S, N2 and hydrocarbon injectants has been used. The fit-for-purpose simulation approach is chosen based on specific needs and objectives for each reservoir. The approaches have ranged from coarsely-gridded black oil simulation to finely-gridded compositional simulation depending upon the specific requirements for a given field. In recent years, the emphasis has been on state-of-the-art compositional simulation. ExxonMobil has applied compositional simulation to design and manage more than 25 gas injection projects covering the full range of injectants and lithologies. Because each gas injection project is unique, the evaluation of benefits must be comprehensive and adaptable. Case studies are presented illustrating a range of gas injection processes and reservoir types. The case studies highlight important aspects of data collection, issue identification, simulation technique evaluation, process evaluation, and long-term project stewardship.