An Improved Coal Permeability Model with Variable Cleat Width and Klinkenberg Coefficient

Improved Permeability Model of the Binary Gas Interaction within a Two-Phase Flow and its Application in CO2-Enhanced Coalbed Methane Recovery

“…Recently, a broad variety of works related to the mechanical deformation, sorption/desorption, and transport property of gas on the permeability variation of coal seams were researched. − These permeability models are broadly classified into two types of strain-based models that consider volumetric deformation of the coal and stress-based models that consider geomechanical deformation. , With the advancement of the recognition of physical properties of the reservoir, the conceptual model of naturally fractured reservoirs has been improved from a single-porosity single-permeability model , to a dual-porosity single-permeability (fracture permeability) model, , a dual-porosity dual-permeability model (both matrix and fracture permeability), , and a triple-porosity dual-permeability (both fracture permeability and inorganic permeability) . The factors affecting reservoir permeability also extend from a single mechanic effect , to adsorption-induced strain effects ,,− or even coupled with the effect of slip flow. − Modeling the permeability evolution of coal during CBM recovery or CO 2 -ECBM is an attractive interest area with numerous models being proposed.…”

Role of Pore-Size Distribution in Coals to Govern the Klinkenberg Coefficient and Intrinsic Permeability

“…They showed that the Klinkenberg coefficient increases with pore pressure at constant effective stress for an adsorbing gas. 14,15 Initially, the Klinkenberg coefficient increases with increasing pore pressure at constant confining stress; however, at even higher pore pressures, the Klinkenberg coefficient may continue to rise 14 or decrease. 15 At constant pore pressure, the Klinkenberg coefficient increases slowly with increasing effective stresses, but after a threshold effective stress, the Klinkenberg coefficient increases rapidly for both inert 20 and adsorbing 15 gases.…”

“…χ is determined via experiments with certain assumptions ,,, and also with numerical models. , Characterization of gas permeability evolution as a function of pressure in the laboratory using eq is a common practice . However, experimental or real field gas permeability in tight reservoirs is better estimated if the slippage or slip effect is considered along with the effective stress changes. ,− The slippage effect describes the permeability enhancement associated with gas flow in microporous conduits due to the acceleration of the nonstationary layer of gas molecules in contact with the pore capillary walls (see Figure of Letham and Bustin). The governing equation of slippage effect, applicable for the gas flow in tight capillaries, combines Poiseuille’s and Darcy’s laws and is expressed as where k a and k ∞ denote apparent and Klinkenberg corrected/intrinsic permeabilities, respectively, and b is the Klinkenberg coefficient, also known as the slippage factor or the slip factor.…”

“…The Klinkenberg corrected permeability in tight reservoir rocks have been studied through state-of-the-art novel experiments ,,,− and also by numerical and analytical models. ,− , The studies were mostly focused on the variation of the Klinkenberg coefficient as a function of stress and demonstrate that permeability evaluation of tight reservoirs, such as coal seams at depth, should consider the role of effective stress and the Klinkenberg coefficient. They showed that the Klinkenberg coefficient increases with pore pressure at constant effective stress for an adsorbing gas. , Initially, the Klinkenberg coefficient increases with increasing pore pressure at constant confining stress; however, at even higher pore pressures, the Klinkenberg coefficient may continue to rise or decrease .…”

“…The Klinkenberg corrected permeability in tight reservoir rocks have been studied through state-of-the-art novel experiments ,,,− and also by numerical and analytical models. ,− , The studies were mostly focused on the variation of the Klinkenberg coefficient as a function of stress and demonstrate that permeability evaluation of tight reservoirs, such as coal seams at depth, should consider the role of effective stress and the Klinkenberg coefficient. They showed that the Klinkenberg coefficient increases with pore pressure at constant effective stress for an adsorbing gas. , Initially, the Klinkenberg coefficient increases with increasing pore pressure at constant confining stress; however, at even higher pore pressures, the Klinkenberg coefficient may continue to rise or decrease . At constant pore pressure, the Klinkenberg coefficient increases slowly with increasing effective stresses, but after a threshold effective stress, the Klinkenberg coefficient increases rapidly for both inert and adsorbing gases.…”