Impact of total organic carbon and specific surface area on the adsorption capacity in Horn River shale

Abstract

Among unconventional gas reservoirs, shale gas has become an increasingly important source of natural gas supply in North America and around the world. Horizontal drilling and multi-stage hydraulic fracturing are the two key technologies for the economic development of shale gas reservoirs. Generally, natural gas in shale reservoirs is stored as free gas state in both larger mineral pores and natural fractures, as well as adsorbed gas state within organic matter and clay minerals. Since a considerable fraction of the gas in place (GIP) is in the adsorbed state, investigation of gas adsorption can provide critical insights into the evaluation of resources volume in shale. In this study, several experiments are carried out on fourteen shale core samples obtained in a vertical well drilled in Horn River Basin, Canada. The total organic carbon (TOC) content, specific surface area (SSA), and CH4 adsorption isotherm are measured for the samples. In order to measure the volume of adsorbed gas at reservoir pressure, the high pressure Belsorp-HP equipment applying volumetric method is used. As results, it is observed that adsorption capacity is a function of not only the TOC but also the SSA. When the samples have similar TOC, adsorption capacity becomes higher as SSA increases and Langmuir volume increases too. We also consider the relationship between SSA and adsorption capacity for each kerogen quality that it shows a linear trend. Also, we attempt to find a correlation of TOC and SSA to the adsorption capacity by categorizing experimental results. Finally, gas in place calculation is carried out for the free gas and adsorbed gas in Horn River shale, respectively.