Dynamic 4D coal permeability-the benefits of a constant volume reservoir
Much research and many field trials have shown that the permeability of coal seams varies inversely with the effective stress acting on coal. It was theorized by Gray (1992) that desorption-induced matrix shrinkage may counter-act the effect of external stresses, allowing permeability to increase, depending on the relative strength of the two phenomena. This paper explores the geomechanical theory of reservoir stiffness and the arch-bridging effect, and uses geotechnical engineering principles and operating coal mine evidence to support the development of the important principle of a constant volume (CV) boundary condition applying to most deep CBM reservoirs, as opposed to the traditional assumption of a constant external stress condition, whether horizontal or vertical. This CV principle allows for an initial external stress state to exist in a coal seam and allows the acting stress state to be dynamic, generally trending lower with matrix shrinkage, thus allowing permeability to increase as depletion of the CBM reservoir proceeds. Laboratory data on measured permeability under both constant external stress conditions and constant volume conditions shows the importance of this principle)permeability increases of between 100% and 1 200% can be experienced, depending on the stage of depletion and thus desorption. Field performance from producing CBM reservoirs will be referenced to confirm the reality and significance of permeability enhancement due to matrix shrinkage in the context of constant volume behaving deep CBM reservoirs.
P. Massarotto D. G. Suzanne V. Rudolph
The University of Queensland, St. Lucia, Qld 4122, Australia
国际会议
徐州
英文
271-286
2009-09-24（万方平台首次上网日期，不代表论文的发表时间）