Critical Evaluation of Chemical Additives in Reducing the Minimum Miscibility Pressure for Gas Injection Process

Abstract

Abstract It is highly desirable to achieve minimum miscibility pressure (MMP) between injection gas and reservoir crude oil phase under the reservoir pressure in the gas injection (Huff-n-Puff) process, despite the obvious challenges, in order to gain more productive sweep efficiency and hence higher oil recovery yield. Here, we report on the evaluation of the performance of five discrete chemical additives in lowering the MMP of a hydrocarbon gas mixture with a representative crude oil through utilization of a microfluidic MMP measurement device. In the current study, a microfluidic platform was developed to accurately measure the MMP of a hydrocarbon gas and crude oil system in the presence and absence of chemical additives at 77°F and 150 °F, respectively. The gas stream consists of 70 mol% methane and 30 mol% propane, representing a typical hydrocarbon gas used for gas injection operations. A group of selected chemical additives were individually premixed with the oil phase at 1 wt% loading prior to the microfluidic testing to quantify the reduction in the MMP. The highly sensitive fluorescent microscopy was also employed to provide real-time insight into the porescale of the oil displacement during the gas injection process. The MMP of the gas and oil system was measured to be 3060 Psia at 77 °F. All the chemical additives demonstrated an effective reduction in the MMP within in a range of 9–21% with one of the additives outperformed the best, lowering the MMP to 2410 Psia. The direct fluorescent optical access into the microfluidic porous structure, however, showed considerable deposition occurred during injection for some of these chemical additives, a potential concern for formation damage. The top two chemical additives were then tested at 150 °F and compared with the gas–oil MMP with no chemical additive (3785 Psia at 150 °F). The selected two chemical additives lowered the MMP to 3425 Psia (10% reduction) and 3495 Psia (8% reduction) with no depositions observed in the porous media. The use of selected chemical additives to lower the MMP can make a significant contribution to the gas injection EOR processes in depleted reservoirs that can in turn potentially improve the performance of the reservoir-scale productions. This work reveals critical insight in chemical additive selection, plus dosages, for effective MMP reduction. Although the extent of MMP reduction was decreased at higher temperature, 10% reduction is nevertheless remarkable, given its low dosage, and can be improved further by adjusting the chemical loadings for high pressure operations. The microfluidic MMP testing platform is advantageous over the conventional slim tube method in significantly shortened turnaround time and minimized fluid consumption.