Experimental Study of Extent and Rate of Gravity Drainage of Oil From Matrix into Fractures in Presence of Miscible and Immiscible CO2

摘要

Gravity drainage is the dominant production mechanism in fractured reservoirs,where injection of hydrocarbon gases is believed to improve oil recovery.This paper presents the results of an experimental study of the effect of injecting CO2 into fractured media and its influence on the performance of gravity drainage and ultimate oil production.Both miscible (i.e.high pressure) and immiscible (i.e.low pressure) schemes for CO2 are investigated in this study.The results obtained from these experiments are used to compare the effect of miscible versus immiscible gases,i.e.CO2,on gravity drainage.For these experiments a special stain steel holder was designed allowing an open space around a core of 30 cm long and 5 cm in diameter,simulating a matrix with surrounding fractures.Carbon dioxide and normal decane were used as solvent and oil,respectively.While all experiments were conducted at constant temperature of 35 deg C,six series of experiments were carried out at 250,500,750,1000,1250,and 1500 psi.A high pressure calibrated glass-gauge was connected to the bottom of the fractured media model allowing the produced oil be collected and measured continuously under the pressure and temperature conditions of the experiments.Analyzing the results show that injecting CO2 at higher pressures improves the recovery factor of gravity drainage mechanism in fractured media,significantly.