Field Test of Reverse-Combustion Oil Recovery From A Utah Tar Sand

Abstract

Abstract A field experiment to recover oil from tar sand by reverse combustion was conducted at Northwest Asphalt Ridge, near Vernal, Utah. This test was in a 10-foot interval of the Rim Rock sandstone member of the Mesa Verde Formation at a depth of approximately 300 feet. Ignition was accomplished on November 25, 1975, and the reverse combustion front was propagated successfully through the formation. Results of the field experiment differed significantly from the -results of laboratory tests that were used in the design of the field test. This difference is attributed primarily to the extreme heterogeneity of the tar sand formation. Observed temperatures in the burned area were lower than expected, but a large portion of the tar sand within the pattern boundaries was heated to the extent that the bitumen became mobile enough to be produced. After 31/2 weeks of operation, the project was terminated because of the inability of the surface production equipment to accommodate the heavy hydrocarbons being produced. Although the formation of the cracked products of reverse combustion was less than expected, this recovery process may be used successfully to heat the tar sand reservoir to a temperahl.re high enough that the bitumen become mobile enough to be produced. Introduction THE RECOVERY of oil from tar sands in the United States has received only limited interest in the past. Recently, oil price increases and the decline of domestic oil reserves have made this source of energy more attractive. Deposits of tar sand are widely distributed throughout the U.S., but the most significant tar sand deposits are in the state of Utah. An efficient means of recovering oil from tar sands could increase the hydrocarbon reserves of this country by billions of barrels. One area of research within the Laramie Energy Research Center of ERDA is devoted to development of methods for recovering oil from tar sands. 1nsitu methods are of primary consideration, because only a small portion of the tar sand resource is thought to be mineable, and because of environmental concern. After a laboratory study using Utah tar sands(1), the reverse-combustion oil recovery processwas selected for further investigation in a field test. The reverse-combustion process was designed to recover oil from formations containing very viscousor semi-solid hydrocarbons(2). This method differs from forward combustion in that the combustion front travels in the direction opposite to the direction of air flow. An advantage of the reverse-combustion method is that the hydrocarbons flow with the combustion gasses through the hot region of the reservoir. In forward combustion, hot mobile oil can flow into the cooler region ahead of the front where it can congeal, plugging the formation to further flow. Another attractive feature of reverse combustion is that the original bitumen is cracked into a lighter oil as the combustion front passes through the formation. This oil remains in the vapour state while passing through the hot, previously burned zone.