Performance evaluation of DME-CO₂ huff-n-puff and continuous DME injection in heavy oil reservoirs through numerical simulation

Dimethyl ether (DME) is a gas that is completely soluble in crude oil and slightly soluble in water at standard conditions. Previous studies have emphasized DME injection in light and medium oil reservoirs. However, the application of DME in heavy oil reservoirs has yet to be extensively studied. In this study, a compositional simulator (CMG: GEM) has been used to investigate the continuous injection of DME and DME-CO₂ huff-n-puff in heavy oil (733 mPa·s) reservoirs of X field of Pakistan. In the first phase, different injection fluids, sequences and slug sizes were examined for the best optimum scheme. The findings concluded that the optimal sequence for heavy crude oil is water flooding to 96% water cut + 0.15 PV DME + 0.45 PV polymer + water flooding to 96% water cut. The recovery factor for the best sequence continuous DME flooding is 59.20% in heterogenous reservoirs, more than in homogenous reservoirs. The DME can reduce the viscosity of heavy crude oil up to 10 mPa·s. The DME-CO₂ huff-n-puff simulations showed excellent reducing effects of the heavy crude oil. The optimum injection rates, volumes, and soaking time for DME-CO₂ huff-n-puff are 5375 m³·d⁻¹, 200,000 m³ and 15–30 days, respectively. The cumulative oil production for five (05) cycles of DME-CO₂ reaches 3229.06 m³. The cumulative oil production of DME-CO₂ huff-n-puff (one cycle) in the heterogenous and homogenous reservoirs for 1826 days reaches 2002.75 m³ and 1947.82 m³, respectively. This study concludes that DME injection is an appropriate solvent which significantly enhances heavy oil recovery.