A Computer-Implemented Data Base for Coalbed Methane Resource Characterization and Research

Abstract

Summary The USBM has obtained gas content data on more than 1,500 coal samples from approximately 250 coalbeds in 17 states. A computer implemented coalbed methane data base has been established to respond more efficiently to health, safety, and mine-planning related data requests from the coal industry and to the resource characterization needs of those interested in using coal bed methane. The system also will be used for coalbed methane research, including multivariate statistical analysis of the physical, chemical, and geologic province factors influencing the methane generation and storage capacity of coal, with the ultimate goal of developing an indirect method of estimating the gas content of coalbeds. Introduction The USBM began measuring the gas content of exploration coal cores by the direct method in 1972. Since that time, more than 1,500 coal samples have been tested. As data volume increased and additional analytical procedures were included in the research program, the need for more efficient responses to industry data requests and for in-house data analysis became apparent. For these reasons, a coalbed methane data base has been established and is available for use. Direct Method Gas Content Testing The direct method test procedure was developed by the USBM as an aid in estimating the amount of methane that would be released in underground coal mines. Our initial research results were used to construct a graph (Fig. 1) that related direct method test values to actual measured methane emissions from nearby mines. The correlation was good for large deep mines that had been in operation for several years and that had a sustained coal production of at least several thousand tons per day. The gas content data production of at least several thousand tons per day. The gas content data also can be used in conjunction with basic coal geology mapping to delineate geographic areas of probable high (or low) volumes of in-situ gas. Detailed studies of this type have been documented. This information is useful for both mine planning and resource recovery and utilization applications. A list of estimated in-situ gas volumes for selected coalbed areas is given in Table 1. Test Procedures The direct method test procedure is performed on fresh exploration coal cores collected at the drillsite. After the core's physical characteristics are described, the sample is sealed in a desorption canister. Periodically, the accumulated gas is bled into a water-filled graduated cylinder (Fig. 2) to measure the volume of gas released. The total gas content of a sample is composed of three parts: lost gas-that portion lost before the coal is sealed in the canister (estimated by a portion lost before the coal is sealed in the canister (estimated by a graphical procedure); desorbed gas-that portion liberated from the sample while sealed in the canister (measured directly by the water displacement method); and residual gas-that portion remaining in the coal sample at the end of the desorption period that will not freely desorb (determined by crushing the sample in a sealed ball mill and measuring the released gas by the water displacement method). Database System The software of the database system is a menu-driven program (Fig. 3) which selects data from the main data bank for database processing (reports for requestors) or as a file suitable for statistical analysis. The data base is on our PDP 11/70 TM computer. Database processing is executed with a commercially available storage, sorting, retrieval, and report-writing software package (Datatrieve 11 TM). Information requests are processed with the system, and the data in the desired output format are printed and forwarded to the requestor. Information such as coalbed name, location (state and county), depth of sample, gas content, and coal rank is available from the system. A representative printout is shown in Fig. 4. Data analysis is executed by extracting data from the main data bank and transferring it to an output file (Fig. 3) with a FORTRAN-compatible format. These data can be read as input to statistical analysis programs. The database system is being used in the first attempt to evaluate the influences and interactions of all measured physical, chemical, and geologic province parameters on measured in-situ gas contents. JPT p. 846