DETERMINING GAS CONTENT FROM MUD GAS LOGS - EXAMPLES FROM NORTHEASTERN BRITISH COLUMBIA

The gas content of shale is a critical input for both the regional exploration of shale gas plays and as an input into economic evaluations. Shale contains hydrocarbons both within pore space and adsorbed onto disseminated organic matter; therefore gas content is a function of depth (pressure), porosity and total organic carbon content. Canister desorption of conventional core, sidewall cores or drill cuttings is the most accurate method to determine gas contents. However, this analysis cannot be performed on existing wells and coring and analysis costs usually restrict the number of analysis performed on new wells thereby reducing the resolution of the data.

Heterogeneities within the shale can create significant variation in gas contents leaving the exploration geologist to exclaim “If only there was a tool that could continuously determine the gas content of my shale, and that it was run on every old well in my exploration area!” However, mud gas detectors are run on most wells in the Western Canadian Basin and are a constant record of the gas liberated during drilling. This data, if calibrated, can be a continuous record of the gas contents of shale units drilled through, thereby giving an initial exploration tool in the hunt and evaluation of potential shale gas horizons.

This talk will demonstrate the authors' attempts to calibrate older gas logs, and compare the results from several potential gas shale units from British Columbia to canister desorption analysis.