5.1 Canister desorption is a widely used technique to measure the gas content of coal. The gas content data when normalized to volume/weight and multiplied by coal mass is used to estimate the gas in place in an area around the cored well.
1.1 This practice describes methods for the direct determination of the gas content of coal by desorption using samples obtained by drill coring methods from the surface. It sets out guidelines for the equipment construction, sample preparation and testing procedure, and method of calculation.
1.2 Indirect methods for the determination of the gas content of coal (not covered in this practice) are based on either the gas absorption characteristics of coal under a given pressure and temperature condition or other empirical data that relate the gas content of coal to such other parameters as coal rank, depth of cover, or gas emission rate.
1.3 This practice covers the following two direct methods, which vary only in the time allowed for the gas to desorb from the core, or sidewall core, before final crushing:
1.3.1 The slow desorption method in which volumetric readings of gas content are taken frequently (for example, every 10 to 15 min) during the first few hours, followed by hourly measurements for several hours, and then measurements on 24-h intervals until no or very little gas is being desorbed for an extended period of time.
1.3.2 The fast desorption method in which after initial desorbed gas measurements to obtain data for lost gas calculations are taken, the canister is opened and the sample is transferred to the coal crusher. The remaining gas volume is measured on a crushed sample.
1.4 This practice is confined to the direct method using core, or sidewall core obtained from drilling. The practice can be applied to drill cuttings samples; however, the use of cuttings is not recommended because the results may be misleading and are difficult to compare to the results obtained from core desorption. The interpretation of the results does not fall within the scope of the practice.
1.5 Units—The values stated in either SI units or inch-pound units are to be regarded separately as the standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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