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Modelling and simulation of gas adsorption in shale gas reservoirs

Student thesis: Doctoral Thesis

Gas adsorption accounts for a large portion of total gas in place in most shale gas reservoirs. However, the mechanism of contribution of gas adsorption to total gas recovery from shale gas reservoirs is hardly understood. Gas adsorption can be expressed both as a function of pressure and temperature. In most studies of gas adsorption, it is only expressed at a single temperature by using Langmuir isotherm. Very often, erroneous calculations are obtained for gas in place and prediction of production performance since the isotherm used might not represent the true reservoir temperature. Very few adsorption models have addressed gas adsorption as a function of both pressure and temperature with majority of the models currently used in reservoir simulation and gas in place calculation ignoring the dependence of gas adsorption on temperature. Therefore, the use of temperature-dependent models for shale gas adsorption is crucial not only because it accounts for the effect of temperature in gas adsorption/desorption but also for conducting numerical reservoir simulation where the need for thermal stimulation could be explored as an enhanced recovery mechanism in shale gas reservoirs.

On the other hand, in material balance calculations for unconventional reservoirs such as coal bed methane and shale gas, temperature-dependent gas adsorption models can be incorporated in analytical methodologies to predict useful information such as gas in place calculations and future production performance analysis once data is obtained for adsorption capacities at several temperatures. This would ensure accurate representation of gas adsorption throughout the reservoir and better predictions of gas in place, pressure and future production performance.

This thesis presents new methodology for incorporating temperature-dependent gas adsorption models into material balance calculations for unconventional gas reservoirs and also explores the use of microwave heating as a thermal stimulation strategy for enhancing gas recovery in shale gas reservoirs. A dual porosity –dual permeability model is developed for the system of shale gas with the account of both viscous and Knudsen diffusion in the matrix. This is coupled with the microwave heating by solving Maxwell’s equation for the electric field using a finite difference time domain methodology. Furthermore, a coupled v electromagnetic –thermal model is developed to investigate the production of gas from shale gas reservoir using microwave heating as a novel enhanced gas recovery technique. Simulation results indicate higher production of gas when microwave heating is used through the elevation of formation temperature around the waveguide prompting desorption of gas into the well compared with when no thermal stimulation is used. The findings from this work can provide a better insight into modelling gas adsorption in shale formations and open avenues for obtaining higher ultimate estimated recoveries from these unconventional reservoirs through the use of microwave heating.
Original languageEnglish
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Award dateMar 2019

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