Combustion Front Propagation Through Fractured Oil Shale

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract The recovery of oil from oil shale by in-situ combustion requires fracturing oil shale underground to establish permeability and passing air through the fractured shale to passing air through the fractured shale to support a combustion front. The heated products from the flame front contact the untreated shale where kerogen is decomposed and gas and liquid products are swept to a production well. products are swept to a production well. A major difficulty in this technique is characterization and control of the combustion front. An experimental study of flame front propagation through crushed oil shale in a laboratory reactor is presented. The oil shale is ignited at the top of a vertical 2-in.-ID insulated stainless-steel tube and the reaction maintained by air injection above the ignition plane. The structure of the reaction front and flame front propagation rates are studied as a function of propagation rates are studied as a function of oil-shale particle size and air delivery rates. Temperature profiles throughout the reaction front were measured continuously by coated thermocouple probes and oil yield determined for each run. Combustion front advance was found to reach steady state very rapidly and a linear relationship was found between steady flame front propagation rate and air flux and between particle size and flame propagation rate. The particle size and flame propagation rate. The reaction temperature is about 2100 deg. F and is slightly dependent on particle size and air flux. In contrast to sand-pack studies, the flame front was quite narrow without substantial preheating of downstream shale. preheating of downstream shale Introduction The recovery of oil from shale can be accomplished by surface retorting or in-situ combustion. Surface retorting consists of mining the oil shale, crushing, grading, and retorting aboveground. In continuous surface retorting processes such as the Bureau of Mines process, the crushed shale is placed in a retort process, the crushed shale is placed in a retort and falls successively through preheating, retorting, combustion, and cooling zones. Air is introduced above the cooling zone, burning the residual carbon off the shale, producing temperatures of 1600 to 1800 deg. F. This supplies heat for the recycling gases, which decompose the kerogen (800 to 900 deg.). Surface retorting efficiencies are 90 to 100 percent and the process has been demonstrated at a rate of 1,000 process has been demonstrated at a rate of 1,000 tons shale per day. The primary disadvantages of surface retorting are process-water pollution, spent-shale disposal, runoff-water pollution, and mining costs.