To Depict Oil Extraction Efficiency from Gas Invaded Zone: Simulation Study

Abstract

Future exploitation scheme of an oil reservoir in each cycle within its production life depends on the profitability of the current extraction scenario compared with predicted recoveries that acquire with applying other available methods. In fractured reservoirs appropriate time to pass from the gas injection process into chemical enhanced oil recovery (EOR) firmly depends on the oil extraction efficiency within the gas invaded zone. Several variables including fluid characteristic, fracture network and matrix units properties, etc., impact gas-oil gravity drainage (GOGD) performance within the gas invaded zone. In this work, CMG GEM and ECLIPSE 300 were used to simulate GOGD mechanism in several 2D cross-sectional models to investigate effects of the matrix height, matrix rock type, fracture network transmissibility, and miscibility conditions on the oil extraction rate, change of average pressure and producing gas-oil ratio (GOR). Results showed that in small heights of the matrix units especially at compacted rock types, GOGD was weak that caused a rapid decrease in oil production rates and early increase in producing GOR. Results also showed that wherever the matrix porosity and permeability values were high, recovery was accelerated and GOR remained constant for longer exploitation times. Furthermore, using high-pressure lean gas injection for miscible GOGD gives higher extraction efficiencies rather than applying rich or enriched gas.