Gas EOR Methodology and Integrated Basin Forecast of Offshore Sarawak Fields, Baram Delta Malaysia

摘要

Gas injection, both Hydrocarbon Water Alternating Gas (HC WAG) and Carbon Dioxide (CO2) WAG, are possible Enhanced Oil Recovery (EOR) technologies to further develop and extend the field life of the Baram Delta Operations (BDO), located offshore Sarawak Malaysia. BDO consists of nine fields with an estimated STOIIP of about 4 BSTB. Over 100 reservoirs are in production within the cluster, with many wells operating as dual completions. The 6 largest fields in BDO have been on production for more than 30 years with an average recovery factor to date around 30%, mainly through natural depletion and aquifer support. Most of the fields contain light, undersaturated oil and after initial screening, gas injection is the most likely technology to extend the life of BDO and boost its recovery. The size, geological complexity of BDO, the number existing and aging offshore platforms and facilities; and then to design and execute a large scale, technically and economically optimal gas injection project, makes producing a fully integrated basin wide forecast challenging. From a reservoir engineering perspective, simulation of miscible and near miscible gas injection requires compositional characterization and fine model gridding, compared with the size of reservoir, to be able to capture the physics (mass transfer, mixture properties and reduce numerical dispersion) to produce reliable results. Moreover, the economical assessment needs to have reliable estimates of incremental recovery, gas breakthrough times, gas utilization and gas recycling. Hence, small scale sector models rather than full field simulations are preferred so more robust results can be generated. The small scale model predictions, essentially building blocks, can then be scaled-up to generate full field forecasts. Likewise, the implementation of a gas injection project requires an appropriate balance between enhancing oil recovery and facility constraints. The size and cost of facilities, the cost of gas supply, and the acceleration in oil production control the economic viability, and a good design comes from a balance between these variables. Consequently, there is the need to create multiple scenarios of how the gas injection will be managed not only for each reservoir and/or each field, but also the integration and timing of injection of neighboring fields. Rapid forecasting of dozens of reservoirs and 6 fields is required to adequately assess optimal staging and economical viability before selecting a final concept. This paper presents the methodology used to build robust full field forecasts capturing key physics for the Baram Delta gas injection study. In addition to the methodology employed, a brief description will be given of the models developed and used as input into the full field forecasts, a brief description of the scale-up tool used, examples of forecasts developed will be shown and a summary of strengths and future enhancements.