Integrated Modelling and Forecasting of Gas Injection Pilot in a Heterogeneous Oolitic Carbonate Reservoir, West Kuwait

Abstract

Hydrocarbon gas flooding is one of the most applied miscible EOR processes in the oil industry. The process becomes extremely challenging in heterogeneous carbonate reservoirs. An inverted four-spot hydrocarbon (HC) gas injection pilot has been under execution since 2016 to address these challenges, in a heterogeneous multi-layered Oolitic carbonate reservoir in West Kuwait. The pilot consisted of a pre-flush phase of water injection (2016-19) followed by a gas injection phase (2021-2022). This paper describes modelling and history matching of pre-flush waterflood phase and forecasting ahead of gas injection phase. The pre-flush waterflood was carried out sequentially into four target layers, injecting a range of pore volumes in each layer and gathering wealth of pilot data including Inter-Well Tracer Test (IWTT), PLT/ILT, time-lapse saturation logging, coring, and VIT to assess the impact of heterogeneity on the displacement process. Integrated review of the acquired dataset was conducted leading to better understanding of the reservoir performance. Model calibration was challenging as variable tracer arrival and concentration profiles indicated high heterogeneity. Detailed compositional simulation studies were undertaken on hybrid sector models of the pilot area created from full-field models, incorporating newly drilled well tops, reservoir properties and full-field fluxes. High-level experimental designs were conducted leading to dynamic sector models calibration, by identifying layer connectivity and baffle introduction as the main modelling gaps. The results showed baffles to vertical flow play a key role in reservoir and fluid flow performance. The knowledge gained from the pre-flush pilot data review and modelling were instrumental in forecasting the pilot gas injection performance. Activities undertaken to forecast the gas injection pilot performance include a two-pronged strategy of using calibrated hybrid sector model realizations and simple box models. The box-models captured range of gas injection phase outcomes on a simplified finer resolution of injector-producer models, testing gas injection strategy sensitivities without any dependency on history match quality, while the calibrated hybrid sector models offered pilot gas injection outcomes accounting for pilot area wells interaction and full-field streamline fluxes, testing gas injection programme robustness. The approach tremendously helped with the surveillance programme design of the pilot gas injection phase. Novel integrated modelling workflows, history matching techniques and forecasting approaches were used in this study of a complex heterogeneous multi-layered carbonate reservoir. Results of which assisted KOC to plan and successfully implement the pilot gas injection phase and formulate a robust surveillance programme to capture the effects of gas injection process. Further, it will help in designing a road map for commercial deployment of gas injection on a field scale.