Effect of CO2 content on the natural gas production from tight gas sandstone reservoirs

Abstract

The simulation of the gas flow in tight sandstone reservoir is a very complicated process. Several mechanisms contributed to the natural gas production in tight sandstone reservoirs. One of the main mechanisms is the gas desorption from the rock surface to the pore body. All the existing models did not consider the effect of CO2 content in the natural gas on the gas desorption from the rock surface. Also all the existing models used desorption models from the literature and they neglect the effect of rock type and reservoir conditions on the gas desorption behavior. In this study and for the first time we will investigate the effect of CO2 content (0 to 20 vol%) on the natural gas desorption from the tight sandstone rocks. Accurate desorption isotherm will be developed based on the rock type and gas composition. Adsorption/desorption experiments will be carried out at different pressures and temperatures to develop a robust model for the natural gas desorption from the rock. Also the effect of tight sandstone rock mineralogy was investigated on the adsorption/desorption of the natural gas. Increasing CO2 fraction in the mixture from 0% to 10% CO2 the total gas uptake is increased to approximately 28%, 22% and 33% at 50 C, 100 C and 150 C respectively which reflects the high affinity toward CO2 from the tight sandstone core. The tight sandstone mineralogy also affected the desorption behavior of the natural gas. The presence of water bearing clay minerals such as illite exhibited a vast sensitivity to temperature causing damage to crystal structure and expulsion of bounded water which resulted in huge increase in the adsorption uptake. The results of the experimental studies showed that the CO2 content in the natural gas has a big effect on the desorption of the natural gas from the tight sandstone rocks. The CO2 content also affected the desorption isotherm model for the natural gas. The tight sandstone mineralogy also affected the desorption behavior of the natural gas. The output from this study is a robust model that explain the contribution of the desorption of the natural gas to the total gas production. Also, it will enhance the simulation and flow models that describe the flow of natural gas in porous media in tight sandstone reservoirs.