First Miscible Gas Injection EOR Pilot in Kuwait: Integrated Reservoir Modelling Challenges & its Implications for Full Field CO2 EOR Development

Abstract

A hydrocarbon gas injection pilot was successfully conducted in a complex heterogeneous multilayered Oolitic carbonate reservoir in Kuwait. The pilot strived towards de-risking technical and commercial feasibility for field-scale deployment of miscible CO2-WAG EOR development. The pilot consisted of a pre-flush water-injection phase (2016-19) followed by a gas injection phase (2021-22). This paper describes modelling challenges of pre-flush waterflood & miscible HC gas injection phase and its implications for Full-field CO2 development. The injection phases were carried out sequentially in three target layers, injecting a range of pore volumes in each layer and gathering wealth of data including Inter-well tracer data, PLT/ILT, time-lapse saturation logging, coring, PTA and VIT to assess the impact of heterogeneity on the displacement process. Detailed compositional simulation studies were undertaken on sector models of the pilot area created from full-field models, incorporating new data & full-field fluxes. Model calibration was challenging as variable tracer arrival and concentration profiles indicated high heterogeneity. Experimental designs were conducted leading to sector models calibration, by identifying layer-connectivity and baffle introduction. Detailed integrated static and dynamic modeling of the pilot area were conducted using compositional simulation models, incorporating pre-flush water and gas injection data, history-matched to production, injection, GOR, water-cut, pressure, tracer production concentration and arrival time, ILT/PLT and time-lapse saturation logs. This detailed assessment revealed the impact of heterogeneity including horizontal baffles and barriers on the displacement process. The knowledge gained from 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. For the gas injection phase, calibration and improvement in history-match of the hybrid dynamic model was achieved by updating relative permeability end-points and baffles adjustment to match the observed gas tracer results. An integrated analysis of the gathered data, reservoir modeling & Residence Time Distribution analysis of water and gas tracers was conducted, providing an insight on reservoir de-saturation, inflow and sweep for the pre-flush and gas injection phases along with the achieved oil gain, assisting better understanding of the implications for future CO2 Water Alternating Gas (WAG) Enhanced Oil Recovery (EOR) full-field development. Novel integrated workflow consisting of robust surveillance techniques, reservoir modelling workflows along with tracer analysis techniques were used in this complex heterogeneous multi-layered carbonate reservoir study in understanding pore scale and reservoir scale sweep efficiency and its impact on oil recovery. The excellent result from the gas injection performance in pilot and surrounding wells has provided KOC an opportunity in designing a road map for full-field deployment of CO2 WAG in this world class field.