Effects of CO2 and CH4 Addition to Steam on Recovery of West Kozluca Heavy Oil

Abstract

Abstract The physical models, cylindrical tube (1-D) and rectangular box (3-D), were used to examine the effects of simultaneous injection of CO2 and CH4 together with steam on the recovery of 12.4 °API gravity heavy oil mixed with unconsolidated limestone. The results of 18 experiments showed that gas-steam injection was a promising technique. Gas/steam ratio was found to be a significant factor among the studied variables in heavy oil recovery. The optimum gas/steam ratio that maximized the recovery was about 9.4 cc/cc for both steam-CO2 and steam-CH4 processes in one-dimensional model. It was 8.7 cc/cc for steam-CO2 process in 3-D model. At 1.5 pore volumes of steam injected; the oil recoveries were 66.5 % of OOIP for steam-CO2, 60.4 % of OOIP for steam-CH4 and 50.9 % of OOIP for steam alone tests in 1-D model and they were 49.9 % of OOIP for steam-CH4, 36.2 % of OOIP for steam-CO2 and 21.7 % of OOIP for steam alone tests in 3-D model. The lower residual oil saturations were obtained in gas-steam injection tests, compared to the values obtained with steam alone. The injected non-condensable gas created a permanent gas phase across the top of the model therefore heat arrived to the producing well earlier than steam alone test. The depression of steam temperature was also observed due to the presence of non-condensable gas. Introduction The application of steam injection in different form of processes is widely used thermal recovery method for recovering heavy oil. Pursley (1975)1 conducted one-dimensional physical model experiments to determine the effects of injecting air, methane and CO2 in steam stimulation process. The results showed a dramatic improvement in the oil/steam ratio for air or methane injection and the addition of CO2 was somewhat less effective. Redford and McKay (1980)2 presented results of physical model experiments. A range of hydrocarbons-methane, ethane, propane, butane, pentane, natural gasoline, naptha, and syncrude were coinjected with steam in displacement and drawdown modes. It was demonstrated that for a given set of conditions of pressure and temperature, and the proper choice of solvent, the use of hydrocarbon additives with steam can markedly increase recovery. The use of higher molecular weight hydrocarbon blends led to improved recovery, provided that enough light ends were present to provide drive energy. This higher recovery, however, was offset by increased losses of hydrocarbon additives to the formation. Redford (1982)3 investigated the effects of adding CO2 or ethane to steam in a 3-D physical model. The improved recovery of Athabasca tar was obtained. This was attributed to a solution gas-drive mechanism. Harding (1983)4 studied the addition of nitrogen and carbon dioxide in a steamflooding process through one dimensional laboratory model. The significant improvement in the ultimate recovery of crude oil was obtained. Leung (1983)5 conducted a computer simulation study to evaluate the effect of simultaneous injection of steam and CO2 on the recovery of heavy oil and tar from Athabasca type deposits. A large volume of the incremental oil is caused by the CO2 viscosity reduction effect increasing the mobility of the oil. Hong and Ault (1984)6 simulated the use of CO2 along with steam in the recovery of 13 °API gravity heavy oil. CO2 injection with steam accelerated oil production from typical heavy oil reservoirs. The accelerated production resulted from the additional gas drive. The cumulative recovery was more closely related to the amount of heat injected. After breakthrough of the CO2 and/or steam through a layer or channel, the gas becomes ineffective in aiding the oil production. Stone and Malcom (1985)7 conducted steam-CO2 experiments in 1-D model for recovering Athabasca tar. The simulation study was also done for comparison. The coinjection of CO2 and steam increased the oil recovery. Stone and Nasr (1985)8 conducted experiments to investigate the use of steam-CO2 and steam-N2 processess in a test bed employed a high-permeability communication path between the injection and production wells. The addidition of CO2 to steam resulted in improved utilization of injected energy and improved the oil recovery.