The Modeling and Simulation of Tight Gas Reservoirs Incorporating Desorption Phenomena

Abstract

Tight gas reservoirs are categorized as unconventional gas reservoirs. One of the main characteristics of a tight gas reservoir is the adsorption of gas on the rock surface due to high specific surface area. Desorption is the process of adsorbing gas by the reservoir rock on its surface that is dependent on factors, such as reservoir pressure, reservoir rock type, and temperature. Therefore, analysis of production data using conventional methods is expected to be problematic. In this study, there was an endeavor to model and simulate the desorption phenomena in tight formations to investigate its effect on different properties and to study related reservoirs. The purpose of this work is to model the single-phase radial gas flow in tight gas reservoirs including equilibrium desorption phenomena on the rock surface and Darcy flow in a reservoir. Considering a control volume, the gas desorption rate as a function of time and space is incorporated into the radial continuity equation as a source term. Using a Langmuir-type sorption isotherm, the gas desorption rate is determined at any radius of the reservoir. The resulting governing equation is solved numerically using a finite difference approach. The simulator is used to model a tight reservoir to identify how important parameters affect the performance of a tight gas reservoir. The results suggest that the development of tight gas reservoirs with significant gas desorption can lead to higher production rates and improve the productivity of the gas reservoir. The model developed here can be used as an engineering tool for evaluating the role of adsorbed gases in improving the productivity and extending the life of tight gas reservoirs.

Keywords:

• desorption phenomenon
• gas-rock interaction
• numerical simulation
• reservoir modeling
• tight gas reservoir