Abstract

This paper describes research directed at developing a new downhole analysis method to determine critical desorption pressure and gas content in coals and carbonaceous formations. In this report, 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 analysis technique in representative field surveys

WellDog’s technology uses a Raman-spectroscopy-based sensor capable of detecting and quantifying trace amounts of solution gas. The solution gas level in 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 law such as Henry’s Law. Determining the effective partial pressure of methane in a reservoir via a solution gas measurement can provide a convenient and accurate route to determining key reservoir properties like gas content.

Representative field surveys within coal gas development areas show a high degree of variability in gas content not only between coal seams but also geographically for individual coal seams. This high degree of variability underscores the need to collect a large number of gas content values in an area in order to identify attractive development targets when assessing the gas resource.