Comparative Analysis of Limited and Fully Compositional Simulation of a Niger Delta Gas-Condensate Reservoir

Abstract

Numerical simulators estimate the recovery volumes and the volume of fluids in-place in the reservoir as a function of time and space by solving complex partial differential fluid flow equations. For gas condensate reservoirs, fully compositional modelling is preferred because, in addition to determining fluid saturations, it tracks the compositional changes for each hydrocarbon component. Nonetheless, the complex data requirements, computing memory, costs, and the time required to undertake a fully compositional simulation can be significant. Limited compositional simulation extends the application of conventional black oil models to composition-dependent systems by utilizing modified phase behaviour to determine phase pressures and fluid saturation. This research work evaluates the performance of a gas condensate reservoir using both fully and limited compositional simulators to investigate the pressure depletion, gas injection, water injection, simultaneous water and gas injection (SWAG), and water-alternating-gas (WAG) injection scenarios. The limited compositional case incorporates a four-component miscible flood model and Todd Longstaff mixing parameter to simulate the recovery schemes. Fluid composition was obtained from a reservoir fluid in the Niger Delta for analysis and tuned to match experimental data using the Peng Robinson EOS, to describe fluid behaviour and generate PVT properties. Comparative studies are conducted for the cumulative condensate and gas production, field water cut, reservoir pressure decline, injectivity, and ultimate recovery of the reservoir for the limited and fully compositional models, respectively. Results indicate that the limited and fully compositional models give comparable values of the initial fluid-in-place volumes. The fully compositional model always predicts a higher condensate recovery than the limited compositional model for all the recovery schemes. SWAG injection scheme provides the maximum pressure maintenance and recovery of condensate. However, gas injection minimizes water production. The limited compositional simulator can be used as a screening tool and for the rapid evaluation of reservoir performance at the early stages of condensate reservoir development when data is scarce.