Model Optimisation of Waterflood and Low Salinity Brine Injection to Enhance Gas Condensate Recovery – A Case Study of A Rich Gas Condensate Sandstone Reservoir in The Offshore Tano Basin of Ghana

Abstract

To enhance production of entrapped condensate in gas-condensate reservoirs without delay in produced gas sales, this study looked at the impact of waterflood and low saline brine injection on an offshore gascondensate reservoir in the Tano Basin, Ghana, West-Africa. The injector well placements, rate, and pressure were optimised using three optimisers (Differential Evolution, Particle Swarm Optimisation, Design Exploration and Controlled Evolution). Condensate and gas recovery increased by 30.3% (from 19.1% to 24.9%) and 11.7% (from 65.4% to 73.1%) respectively after waterflooding. Waterflood Optimisation saw an 89.5% increment in condensate production (from 19.1% to 36.2%). While low saline brine injection improved condensate recovery by 130.8% (from 19.1% to 44.1%). After a hundred and fifty optimisation scenarios were investigated, an optimum Ca2+ concentration of 4.8880 mol/L, Mg2+ and Na+ concentration of 0.0005 mol/L and 0.6398 mol/L respectively was obtained for the optimum gascondensate production. Increasing the low saline brine concentration beyond the optimum concentration for Ca2+ led to a reduction in gas-condensate production, while Na+ increment had the opposite effect. Mg2+ however, had negligible impact on the gas-condensate recovery. This study therefore shows that, recovery of gas-condensate can be enhanced without delay in gas sales through low saline brine injection. This would ensure the availability of the much needed produced gas while enhancing the valuable condensate production.