Using eCalc™ for Designing a Low Emission Reservoir Drainage Strategy for Oseberg C

Oseberg is a large offshore field in North Sea with 4 main installations and several subsea developments. Production started in 1988. The field is covering the BRENT group. The study focuses on the Oseberg C platform which produces from the northern area of the Oseberg Main field. The Oseberg C involves a low-pressure production project executed in the fall of 2022. The timing of when to eventually reduce the topside separation pressure even more, and/or stop or reduce stop gas injection and instead export the produced gas via an existing multiphase pipeline to the Field center will be investigated in this study. The main objective is to illustrate a workflow that allows revising the drainage strategy while simultaneously reducing scope 1 CO2 emissions to attain a low emissions reservoir management strategy along with minimizing the losses in reserves. Mitigating reserves losses will be studied through different sensitivities. Several factors must be considered when studying modifications in the drainage strategy. Well delivery potential, gas export pressure to the Field center and the gas capacity at Field center are all important boundary conditions. A reservoir simulation model is used to study the reservoir impact of lowered OSC inlet pressure and effect of stopping the gas injection at different dates. A set of scenarios capturing consistently reservoir simulation and topside models are designed to assess the optimal timing of when to stop gas injection on Oseberg C. The optimal timing is evaluated by considering reservoir recovery and CO2 emissions. Reserves evaluation is performed using a reservoir simulation model (ECLIPSE), and emission forecasts are performed using eCalc™ (Skjerve et al., 2022). eCalc™ is the name of a software tool for high-quality emission forecasting. eCalc™ allows the integration of subsurface and operational knowledge and calculates emission forecasts directly relating drainage strategy to operational strategies and process equipment. The emission sources change significantly with the drainage strategy assumptions leaving correlation models less suited. eCalc™ is using mechanistic models of the topside processes and therefore can predict the effects of large changes in the drainage strategy and topside process.