A Field Test of Underground Combustion of Coal

Abstract

A field test of forward combustion in a coal seam is described. The coal was retorted using techniques similar to those developed for conventional oil reservoirs. Relatively high heat-content coal oil and gas were produced. The burned seam was later exposed by strip mining, enabling produced. The burned seam was later exposed by strip mining, enabling visual observation and sampling of the affected coal. Introduction The objective of gasification of coal in place is the recovery of energy and chemicals without mining. The idea is more than 100 years old. Experiments began in Russia around 1931 and by the late 1940's field tests were started in several other countries. In the late 1950's only Russia remained active in this field and it began operation of large-scale plants. One of these plants produced 10 MMcf/D and plants. One of these plants produced 10 MMcf/D and another produced 45 MMcf/D of gas with heat content of about 85 Btu/cu ft. A third plant produced 10 MMcf/D with a heating value of about 120 Btu/cu ft. The gas was used to generate electricity. The cost of the produced gas, in terms of heat content, was about twice that of mined coal in the same region. Improved plants that would have produced gas at a lower cost per Btu than mined coal were designed to be put into operation in the 1960's. However, implementation of these may have been dropped because of the discovery of huge gas reservoirs in Russia. Experimentation on underground combustion of coal was resumed in 1972 by the USBM near Hanna, Wyo., where combustion is being carried out in a 30-ft thick seam. A complete history and useful lists of publications can be found in Ref. 1, and in a more publications can be found in Ref. 1, and in a more recent review of underground gasification of coal. At Gulf Research and Development Co., the study of processing coal in place began with an experimental laboratory program conducted in the early 1960's, and in 1968-69 a test of underground combustion of coal was carried out in a coal seam that was undergoing strip mining. Description and Results of the Tests What follows is a brief description of each phase of the test. A comparison of results of tests done by others is also presented. Location of the Test Site and Wells The project was carried out in No. 14 coal, a typical bituminous coal in Western Kentucky, at a depth of 107 ft. In this area coal seam was about 9-ft thick. See Table 1 for coal analysis. The project consisted of two test patterns that were drilled 100 ft apart. Each pattern contained an injection well, a temperature observation well, and a sampling well in a row perpendicular to the strip mining wall (see Fig. 1). Temperature observation wells were 10 ft and sampling wells were 30 ft from the injectors. The injectors were furthest away from the strip mining wall, approximately 500 ft. They were designated Wells I-1, T-1, and S-1 for the injection, temperature observation, and sampling wells, respectively, for the first pattern, and Wells I-2, T-2, and S-2 for the corresponding wells in the second pattern. pattern. JPT P. 35