Effect of Organic Matter and Thermal Maturity on Methane Adsorption Capacity on Shales from the Middle Magdalena Valley Basin in Colombia

High-pressure methane adsorption isotherms were measured on five shale core samples obtained during exploratory drilling from three boreholes located in the Colombian Middle Magdalena Valley Basin. The experiments were carried out at 50 and 75 degrees C and for pressures ranging up to 3.5 MPa under dry conditions through the use of a homemade manometric setup. The effect of the total organic carbon (TOC) content, thermal maturity, clay content, and specific surface area (SSA) on methane adsorption capacity has been discussed. The excess adsorption data were fitted to a three-parameter (n(L), p(L) and rho(ads)) Langmuir model with the value of the adsorbed phase density, rho(ads) maintained fixed at 421 kg/m(3), which corresponds to liquid-phase density of methane at a normal boiling point. An excellent fit to the experimental data was achieved. The results show that the temperature has a negative effect on the adsorption capacity, while TOC has a positive effect, even if no linear regression was found between TOC and methane adsorption capacity. No correlation was observed between the clay content and the TOC-normalized adsorption capacity to methane, which indicates that clay minerals do not significantly contribute to methane adsorption in the case of our samples. In addition, there is not a general trend between TOC normalized and thermal maturity. Among the factors investigated in the present study, TOC has the major contribution to the adsorption uptake. A similar contribution is found for the SSA, which is consistent, considering the positive correlation between TOC and SSA. This set of data represents meaningful information for indirect estimations of the gas in place during the future recovery strategies. This study furthers the ongoing projects on the understanding of the adsorption effect on shale gas production and assessment.