Volume 66

Study on Oil Displacement Characteristics of Impure-COâ‚‚ in Offshore Low-Permeability Reservoirs Based on NMR Yiqi Zhang, Shenglai Yang, Fanlu Wang, Qing Liu

Abstract

The mixed displacement of CO â‚‚ and associated gas (EOR) in oil fields is an important path for the green transformation of the upstream petroleum industry, but the actual characteristics of the coupled flow of impurity CO â‚‚ – crude oil in porous media are still unclear. This article uses online low field nuclear magnetic resonance (LF-NMR) technology to systematically explore the flow characteristics of impurities CO â‚‚ and crude oil in porous media by real-time monitoring of transverse relaxation time (T2) and one-dimensional (1D) signals, and analyze the flow differences of pores with different sizes and positions. The results indicate that impurity gases accelerate gas breakthrough and breakthrough through a dual mechanism of reducing miscibility and enhancing pressure gradient, resulting in a 3-9% decrease in recovery rate; The flow of CO â‚‚ – crude oil has significant stages: in the initial stage, the physical driving force preferentially uses large and medium-sized pores, and impurity gases can enhance this process; The mid-term gas expands the utilization of small pores through diffusion extraction miscibility effects; After breakthrough, the use of small and medium-sized pores is maintained through the mixing extraction oil carrying effect of the surrounding pores, but this effect will be weakened by impurity gases in the middle and later stages. Injecting gas for sweeping presents spatial heterogeneity: the front section has a more balanced sweeping effect due to the resistance effect, and the utilization effect is significantly better than that of the middle and rear sections; Due to finger penetration and gas channeling, a large number of unused medium and large pores remain in the middle and rear parts. This article provides an important reference for a deeper understanding of the flow mechanism of CO â‚‚ flooding with impurities.

Keywords CO2 flooding, Oilfield associated gas reinjection, 1D distribution of oil, Nuclear Magnetic Resonance