Carbon Dioxide Solvent Flooding for Increased Oil Recovery

Abstract

Published in Petroleum Transactions, AIME, Volume 216, 1959, pages 225–231. Abstract Laboratory flooding experiments on linear flow systems indicated that high oil displacement, approaching that obtained from completely miscible solvents, can be attained by injecting a small slug of carbon dioxide into a reservoir and driving it with plain or carbonated water. Data are presented in this paper which show the results of laboratory work designed to evaluate this oil recovery process, particularly at reservoir temperatures above 100F and in the pressure range of 600 to 2,600 psi. Under these conditions CO2 exists as a dense single-phase fluid. It was found that a bank, rich in light hydrocarbons, was formed at the leading edge of the CO2 slug during floods on long cores. Formation of this bank is probably due to a selective extraction by the CO2 and, it is believed, partially accounts for the attractively high oil recoveries. In addition to the efficient displacement of oil from the pores of the rock by this process, the favorable mobility ratio related to a CO2-water flood also contributes to high oil recovery. A further advantage of this process is noted on limestone and dolomite rock, in that the CO2 reacts with the porous medium increasing its permeability. Flooding experiments were conducted on sandstone and vugular dolomite models. The results of this experimental work show the effect on oil recovery of type of porous medium, pore geometry, flooding length, and flooding pressure. The porosity of the cores and models varied from 16 to 25 per cent and their permeabilities ranged from 100 to 200 md. A reconstituted West Texas reservoir oil, a West Texas stock tank oil, an East Texas stock tank oil and Soltrol were used to represent reservoir oils in this study. Oil recoveries ranging from 60 to 80 per cent of the original oil in place in these cores were obtained by CO2-carbonated water floods at pressures between 900 and 1,800 psi, compared with conventional solution gas drive and waterflood recoveries of 30 to 45 per cent on the same cores. Oil recoveries greater than 80 per cent resulted from floods at pressures above about 1,800 psi. These high recoveries were noted from both the sandstone and the irregular porosity carbonate cores.