A pulse-decay method for low permeability analyses of granular rock media

Abstract

Abstract. Nano-darcy level permeability measurements of porous media, such as nano-porous mudrocks, are only practically feasible with gas invasion methods into granular-sized samples with short diffusion lengths and thereby reduced experimental duration; however, these methods lack rigorous solutions and standardized experimental procedures. For the first time, we resolve this by providing an integrated technique (termed as gas permeability technique) with coupled theoretical development, experimental procedures, and data interpretation workflow. Three exact mathematical solutions for transient and slightly compressible spherical flow, along with their asymptotic solutions, are developed for early- and late-time responses. Critically, one late-time solution is for an ultra-small gas-invadable volume, important for a wide range of practical usages. Developed as applicable to different sample characteristics (permeability, porosity, and mass) in relation to the storage capacity of experimental systems, these three solutions are evaluated from essential considerations of error difference between exact and approximate solutions, optimal experimental conditions, and experimental demonstration of mudstone and molecular-sieve samples. Moreover, a practical workflow of solution selection and data reduction to determine permeability is presented by considering samples with different permeability and porosity under various granular sizes. Overall, this work establishes a rigorous, theory-based, rapid, and versatile gas permeability measurement technique for tight media at sub-nano darcy levels.

Small angle neutron scattering studies of shale oil occurrence status at nanopores

“…Shale, recognized as a typically polydisperse porous medium, garners a substantial attention owing to its complex geometric characteristics and vast utilities in geological systems such as being unconventional hydrocarbon reservoirs (Nelson, 2009;Ross and Bustin, 2009;Clarkson et al, 2012). The topics of ultra-low matrix permeability (Zhang et al, 2023), wide pore size distribution (PSD) (Sakurovs et al, 2012;Kuila and Prasad, 2013;Xu, 2020), complex oil occurrence status (Xu et al, 2022), and µm-scale mixed wettability (Hu et al, 2015) have emerged as crucial foci for an efficient development of shale oil, thereby receiving considerable studies. However, despite recent advancements (Wang et al, 2016;Hu et al, 2021;Li and Cai, 2023a), achieving direct nm-scale insights of oil occurrence status still remains challenging, resulting in a gap of a comprehensive understanding of shale oil mobility within pore spaces and subsequent production in wellbores (He et al, 2015;Saif et al, 2016).…”