Reservoir Engineering Design of a Tertiary Miscible Gas Drive Pilot Project

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. 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 Information relative to the design and implementation of a tertiary miscible gas drive pilot project, located in West Texas, is presented. This pilot was initiated to test the carbon dioxide multiple contact tertiary miscible displacement technique utilizing acid gas (71% CO2, 29% H2S) as the miscible fluid. Pilot sizing and evaluation approach, operating considerations, and data collection aspects are briefly discussed. The primary scope of this presentation is the use of a streamline numerical miscible displacement program to match the classical secondary waterflood performance of this pilot and to predict and design the tertiary pilot and to predict and design the tertiary miscible gas phase as to slug size, gas water ratio, buffer slug size, and number and size of cycles. Introduction Improved recovery pilots are recognized as a vital step in the development of methods for recovering the vast amounts of oil remaining in reservoirs after secondary recovery. The use of carbon dioxide as a tertiary miscible solvent has the advantage of low fluid costs and therefore warrants particular attention. It has been established that carbon dioxide can provide miscible type displacement under appropriate conditions. While only limited laboratory information is available on the carbon dioxide multiple contact tertiary miscible displacement technique, laboratory tests have demonstrated that this improved recovery method is equally effective under secondary and tertiary modes. However, direct application of laboratory information to actual field endeavors has severe limitations, and only field testing in a total reservoir environment can demonstrate the operability and provide information on practical problems that must be solved before an economical tertiary recovery method is developed for an entire field. Therefore, a site for a pilot test of tertiary oil recovery by carbon dioxide flooding was selected in a carbonate reservoir in West Texas. An available acid gas stream will actually be injected as the miscible fluid. Gas plant residue gas (predominantly methane) plant residue gas (predominantly methane) will be used as the chase fluid.