균열탄산염암의 암체 내 오일유동 증진을 위한 CO2-Foam 주입공법 시뮬레이션 연구

Abstract

Most carbonate reservoirs are heterogeneous in terms of pore distribution and the matrix is extremely low permeable hindering the flow of oil, while highly permeable fractures are the primary flow conduit. The reservoir simulation for the fractured carbonate reservoirs is generally conducted by dual-porosity continuum model, however, it is not practical to describe the direction of each fracture. Moreover, discrete fracture network (DFN) model with multiphase flow, up to now, is also commercially unavailable. Along these lines, this study presents the hybrid DFN approach to represent fracture network, more realistically, which is a continuum approach equipped with local grid refinement (LGR). The LGR is adapted at the cells that fractures are passing through, in order to describe the fracture width less than 0.1 ft. In general, LGR is mostly applied for well block, rather than the fractures. In this approach, control volume of the well lying on the fracture is extremely small and thus the well radius cannot be described by LGR cell. Therefore, in this study, four-leg horizontal well concept substitutes the vertical well with the use of equivalent well radius for overcoming the numerical convergence problem. The hybrid DFN approach was applied for CO2-foam injection in fractured carbonate reservoirs to investigate the effect of conformance control. This foam injecting method yields more imbibition of CO2-foam into low permeable matrix, which contains most of the oil. From the numerical results, it shows that the foam controls CO2 velocity and this increases the contact time between CO2 and the rock matrix. This is because CO2 mobility is controlled by foam, that decreases relative permeability of CO2 and increases its viscosity. Furthermore, the CO2 breakthrough (BT) was occurred at 300 days in the case of only CO2 injection, meanwhile, it was not observed when CO2-foam was applied, indicating that the foam prevents early CO2 BT.