Vanishing Interfacial Tension Algorithm for MMP Determination in Unconventional Reservoirs

摘要

Minimum miscibility pressure(MMP)is the minimum pressure at which the interfacial tension between reservoir oil and injected gas phase disappears.In the slim-tube experiment,MMP is the minimum pressure,which achieves maximum oil recovery in a sand-packed tube flow experiment.In Rising Bubble Apparatus(RBA),MMP is the pressure of gas phase disappearance at increasing pressures as a single gas bubble moves through the reservoir oil in a thin glass tube.In the Vanishing Interfacial Tension(VIT)technique,MMP is determined experimentally by measuring the decrease of the gas-oil IFT with increasing pressure,and extrapolating the trend to zero. In this paper,we determine the vanishing interfacial tension trend of equilibrium gas-oil with increasing pressure in subsurface pores,which includes capillary pressure.We extrapolate the decreasing IFT trend to zero IFT,at which the pressure is the MMP.This method resembles the experimental VIT approach for determining MMP,but obviously is faster, more convenient,and broader in scope.The result of our algorithm compares favorably with results from the multiple- mixing-cell algorithm for conventional and unconventional reservoirs.We also calculate the miscibility pressures for Bakken and Niobrara shale reservoirs for hydrocarbon and non-hydrocarbon gas injection.Our result show that the MMP of the reservoir oils occurs at lower MMPs compared to conventional reservoirs if the pore throat radius is less than 10 nm.The gases used in MMP calculation are CO2,N2,CH4,CO,H2S,LPG,and NGL.Miscibility of N2,CH4 and CO is much lower in the same shale environment.