Measurements of gas permeability and diffusivity of tight reservoir rocks: different approaches and their applications

Abstract

Permeability and diffusivity are critical parameters of tight reservoir rocks that determine their viability for commercial development. Current methods for measuring permeability and ⁄ or diffusivity may lead to erroneous results when applied to very tight rocks including gas shales, coal, and tight gas sands, as well as rocks considered as seals for nuclear waste repositories and strata for geological sequestration of CO 2 . The use of He as routinely applied to measure porosity, permeability, and diffusivity may result in non-systematic errors because of the molecular sieving effect of the fine pore structure to larger molecules such as reservoir gases. Utilizing gases with larger adsorption potentials than He, such as N 2 , and including all reservoir gases to measure porosity or permeability of rocks with high surface area is a viable alternative, but requires correcting for adsorption in the analyses. This study expands several approaches to measure permeability and diffusivity with considerations for gas adsorption, which has not been explicitly considered in previous studies. We present new models that explicitly correct for adsorption during pulse-decay measurements of core under reservoir conditions, as well as on crushed samples used to approximate permeability or diffusivity. We also present a method to determine permeability or diffusivity from on-site drill-core desorption test data as carried out to determine gas in place in coals or gas shales. Our new approach utilizes late-time data from experimental pressure-decay tests, which we show to be more reliable and theoretically (and practically) accurate than the early-time approach commonly used to estimate gastransport properties.

High-pressure adsorption of methane on montmorillonite, kaolinite and illite

“…Abundant studies have focused on CH 4 adsorption in organic matters of shale, and the results have revealed a positive correlation between the organic content and the CH 4 adsorption capacity in raw shale samples (Cui et al, 2009;Lu et al, 1995). The mechanism of CH 4 adsorption in organic matters has been well documented, illustrating that the surface functional groups and micropores provided the adsorption sites for CH 4 (Loucks et al, 2009;Ross and Bustin, 2007Zhang et al, 2012).…”

“…Pressures and temperatures were proposed to be the main factors that influence CH 4 adsorption and CH 4 reservoir (Cheng and Huang, 2004;Cui et al, 2009;Lu et al, 1995;Ross and Bustin, 2009). The experimental evaluation showed that the CH 4 adsorption capacity of shale increases with the increment of pressure (Cheng and Huang, 2004;Loucks et al, 2009;Lu et al, 1995;Bustin, 2007, 2008), implying that the high pressures in the actual shale gas reservoir might result in a large CH 4 adsorption amount.…”

Laboratory Investigation to Assess the Impact of Pore Pressure Decline and Confining Stress on Shale Gas Reservoirs

“…This was done primarily to avoid the potentially significant effects of adsorption and/or associated swelling that might impact permeability [17][18][19]. Sample preparation included cutting, grinding, drying, and prestressing.…”

Information support for processes of quality functionals measurement in the CAD of casting of steel castings in sand molds

“…Here, first of all, modern infrared methods of measuring temperature [5][6][7], hydraulic ones -gas perme ability [8], capacitive -densities [9], eddy current -sand burning [10]. Structural [11] and intellectual [12] identi fiers and much more are used for obtaining information about the casting process.…”