An Investigation of Oil Recovery by Injecting CO2 and LPG Mixtures
Authors: Kumar Naresh , Von Gonten W.D. 
Published: December 2007

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
The efficiency of LPG to miscibly displace oil from porous media is very well documented in literature, but the cost of LPG prohibits its widespread use in spite of its good displacement efficiency. CO2, on the other hand, is relatively cheap depending upon the availability, but it is miscible with most crude oils only at high pressures and low temperatures. CO2 requires still higher pressure to be miscible with heavy crude oils.
The purpose of this investigation was to find out whether or not the miscibility of CO2 and, thus, the recovery can be improved by adding a small percentage of LPG to CO2.
In this study, Woodruff reservoir oil of 8.9-cp viscosity and 36.5 degrees API gravity was used to saturate Berea sandstone cores 4 ft 6 in. long with a 2-in. square cross-section. The cores were first waterflooded down to residual oil saturation of approximately 45 percent of the initial oil in place. Displacement tests were conducted at a pressure of 2,000 psig and at a temperature of 100 degrees F, at which conditions CO2 was found to be immiscible with this crude oil.
A minimum CO2 slug of 30 percent of the pore volume, followed by water, gave a recovery pore volume, followed by water, gave a recovery of 75 percent of the initial oil in place.
A miscible flood using 30 percent PV slug of LPG, which was found to be the minimum slug size to displace this crude oil under the above conditions of temperature and pressure, gave a recovery of the order of 95 percent of the initial oil in place.
In the third stage, mixtures of CO2 and LPG in 85:15, 75:25, 50:50 and 25:75 proportions were used. A 30 percent PV slug of these mixtures was followed by water in all the above displacement tests. It was observed that the CO2 and LPG mixture of 75:25 proportion was the optimum mixture. A recovery of 84.75 percent of the initial oil in place was achieved by this mixture, which is about 11 percent more than that achieved by CO2 flood alone.

Introduction
Improving recovery from known deposits is a problem common to every extractive operation problem common to every extractive operation involving minerals, and oil is no exception. Due to the recent imbalance between supply and demand and difficulty and expense in finding new reserves, it has become very important for the oil industry to improve recovery from the already proved fields. With the present-day recovery proved fields. With the present-day recovery techniques, an enormous amount of oil will be left underground unrecovered.