Effects of Kinetic Desorption on Transient Pressure Behavior during Well Testing in Coalbed Methane Reservoirs

  • Zhongliang Su, Yuewu Liu, Shiying Shi
Keywords: Coalbed methane, Desorption kinetics,Dualporosity reservoir,Unsteadystate diffusion, Well test analysis.

Abstract

As a unique phenomenon, gas desorption in coalbed methane (CBM) reservoirs is presumably asort of kinetic process. However, people usually would use the equilibrium model of infinite desorption rate in the CBM exploitation analysis. Since the equilibrium model is found not always adequateinthe initial stage of desorption, the objective of this study,therefore, is to examine the influence of desorption kinetics on transient pressure response of CBM wells. Based on the Langmuir’stheory, a kinetic desorption model with finite mass exchange rate between adsorbed phase and free gas to describe the transient processin CBM production is firstly addressed. The present kinetics model is then verified by comparison with gas release experiment in the lab. While the model is incorporated into well test analysis to clarifythe link between kinetic desorption, unsteady diffusion and seepage flow in CBM reservoirs, thesensitivity of reservoir pressureto kinetic desorption parameters is analyzed. Withenhanced matrix gas compressibility and modified matrix storativity in the equilibrium model, the CBM reservoirbehaveslikea conventional dual-porosity reservoir. In contrast, characteristic of finite desorption rate in the kinetics model,the CBM reservoir exhibits triple-porosity reservoir behavior with retarded boundary response. We finally conclude that the equilibrium model with infinite desorption rateisonly adequate for the description of late-stagedesorption behavior, whereas the kinetic model suitable for the whole desorption process is preferable in the well test analysis of CBM reservoirs.

Published
2020-09-29
How to Cite
Zhongliang Su, Yuewu Liu, Shiying Shi. (2020). Effects of Kinetic Desorption on Transient Pressure Behavior during Well Testing in Coalbed Methane Reservoirs. Design Engineering, 62 - 83. https://doi.org/10.17762/de.vi.595
Section
Articles