Analysis of the effect of experimental adsorption uncertainty on CH4 production and CO2 sequestration in Dadas shale gas reservoir by numerical simulations

The importance of unconventional gas reservoirs such as shale gas reservoirs has increased with the decline of conventional gas reservoirs and advancement in horizontal drilling and hydraulic fracturing in the world. Recently, there have been many exploration activities in Dadas shales, Turkey. Previously, the adsorption capacifies of CH4 and CO2 on Dadas shale samples were measured by using volumetric adsorption experimental set-up. Although adsorption uncertainties of these experiments were calculated, their effects on CH4 production or CO2 sequestration in Dadas shales were not evaluated in field scale. In this study, the numerical simulations for CH4 gas production via 500 m long horizontal well from Dadas shale gas reservoir with different adsorption cases due to experimental adsorption uncertainties were conducted by using TOUGH + RealGasBrine. It was observed that initial CH4 adsorption capacity of Dadas shales varies from 2.1% to 20.9% because of experimental adsorption uncertainty and absorbed gas volume corrections. Numerical simulations showed initial adsorbed gas % and final adsorbed gas % vary significantly. Similarly, the injection of CO2 into the depleted Dadas shale gas reservoir was analyzed by numerical simulations at different adsorption cases due to experimental adsorption uncertainty and adsorbed gas volume correction. Final adsorbed CO2% varies from 18.1% to 27.5%. Furthermore, there are important differences in the amount of CO2 injected, final adsorbed CH4 % and final adsorbed CO2% during CO2 injection simulations. The main reasons of these differences are experimental adsorption uncertainty and adsorbed gas volume correction. This study showed that the volumetric adsorption experimental method is not reliable in low adsorption values as in Dadas shales. It only gives adsorption ranges. The implication of this study is that the effect of experimental adsorption uncertainty obtained with the volumetric adsorption method on CH4 production or CO2 sequestration in Dadas shale gas reservoir is significant in field scale.