Paper presented at ATW on Coalbed Methane, Durango, Colorado, 27–29 March 2007. Unsolicited. This paper has been included in the SPE eLibrarywith the permission and transfer of copyright from the author.
This paper describes research directed at developing a new downhole analysismethod to determine critical desorption pressure and gas content in coals and carbonaceous formations. In this paper, we describe the reservoir physics that make the method possible, share laboratory results that illustrate and confirm the underlying physics, and demonstrate the application of the analysistechnique in representative field surveys.
This new technology uses a Raman-spectroscopy-based sensor capable of detecting and quantifying trace amounts of solution gas. The solution gas levelin a coal seam (i.e. the amount of methane dissolved in the coal seam water) is related to the partial pressure of methane via a solubility relationship such as Henry's Law. Determining the effective partial pressure of methane ina reservoir via a solution gas measurement can provide a convenient and accurate route to determining key reservoir properties such as gas content.
Representative field surveys within coalbed methane development areas show ahigh degree of variability in gas content not only between coal seams but alsoaerially for individual coal seams. This high degree of variabilityunderscores the need to collect a large number of gas content values in order to identify attractive development targets when assessing the gas resource.