ABSTRACT
Antrim Shale multicomponent gas storage mechanisms of adsorption, porosity and solution in bitumen preclude the use of conventional gas-in-place volumetric calculations. Total in-situ gas content has been measured using canister degassing techniques adapted from coalbed methane technologies. Gas measurements ranged from approximately 5 scf/t to 166 scf/t. Gas contents exceed apparent gas-filled porosity by 6 to 8 times where organic content is high. Cross plots of gas content to companion TOC and density measurement resulted in a direct correlation between increasing gas content corresponding to progressive increases in organic matter and an inverse relationship between increasing gas content and decreasing density. The linear function relating density and gas content can be used in conjunction with open-hole log bulk density measurements to calculate gas-in-place.
A side-by-side comparison of gas content measurements from rotary sidewall core and whole core demonstrated that the measurements from both core sampling types are of equal accuracy. From the standpoint of cost, sample homogeniety and sampling selection, rotary sidewall cores are preferred over whole core. The total gas contained in the shale can be completely released as a single measurement by crushing the core upon retrieval. Utilizing the on-site gas content measurements, density/gas content relationship and density log it is possible for the first time to locate and quantify gas bearing Antrim shale intervals from well logs.
