Multi-Scale Porosity and Pore Structure Assessment of Shale

A study of shale gas is conducted to investigate the influencing factors of the fundamental pore structure interpretations in shale gas reservoirs. The results reveal discrepancies between multi-scale techniques that are influenced by clay mineral content and organic matter. In this study, novel methods and calculation models are introduced for quantitative determination of nanopore structure parameters in shales. This study provides implications for shale formation evaluation in downhole practice

Investigation on the adsorption kinetics and diffusion of methane in shale samples

© 2018 Elsevier B.V. Shale gas is becoming increasingly important to mitigate the energy crisis of the world. Understanding the mechanisms of gas transport in shale matrix is crucial for development strategies. In this study, methane adsorption kinetics in shale samples were measured under different pressures and temperatures. The results of methane adsorption rate were fitted by the bidisperse diffusion model. Pore structure of the shale samples were characterized by low-pressure N2 and CO2 adsorption. The results showed that pressure has a negative effect on methane adsorption rate and diffusion, while the effect of temperature is positive. Combining the total organic carbon (TOC) and pore structure, methane adsorption rate and effective diffusivity were compared between all the shale samples. The methane adsorption rate under high pressure (50bar) is positively related to the TOC content. The micropore volume showed a moderate positive relation with the methane adsorption rate at 30bar. A weak positive relation exists between the TOC and effective diffusivity at low pressure and the effective diffusivity at low pressure shows an increasing trend with micropore(<2 nm) volume. A hypothetic pore model is proposed: micropore in shales controls gas diffusion as pore throat which connects pores

Connecting packing efficiency of binary hard sphere systems to their intermediate range structure

Using computed x-ray tomography we determine the three dimensional (3d) structure of binary hard sphere mixtures as a function of composition and size ratio of the particles, q. Using a recently introduced four-point correlation function we reveal that this 3d structure has on intermediate and large length scales a surprisingly regular order, the symmetry of which depends on q. The related structural correlation length has a minimum at the composition at which the packing fraction is highest. At this composition also the number of different local particle arrangements has a maximum, indicating that efficient packing of particles is associated with a structure that is locally maximally disordered

A comprehensive review on shale studies with emphasis on nuclear magnetic resonance (NMR) technique

Multi-scale shale studies put a significant emphasis on high-resolution investigations from nanometer to decametre scales. Despite that multiple advanced techniques have been used in shale studies, they are mostly limited to the detection scopes and have restricted capacity for high-resolution characterization of shale nanopores with substantial heterogeneity. Therefore, it remains a challenge for accurate resource estimation in unconventional shales. The nuclear magnetic resonance (NMR) is an advanced technique enabling non-destructive and fast measurements, and has the advantage of high-resolution evaluation of shale formations and nanopore structure. Petrophysical studies using NMR have made breakthroughs in shale studies. However, multi-scale shale investigations with emphasis on NMR technique have not been fully reviewed. This paper thus provides an overview of the capabilities of NMR in multidisciplinary shale studies to largely improve accuracy in unconventional resource estimations. We proposed a multi-scale and quantitative NMR detection method for accurate characterization of the nanopore structure and fast relaxation fluids. The laboratory NMR core analysis and NMR well logging can be applied for the detection from nanometer to decametre scales, respectively, and precisely measure shale reservoir properties, including total/effective porosities, clay-bound water (CBW) contents, pore size distribution, surface relaxivity, absolute permeability, wettability, and fluid types. Importantly, with NMR application, new research areas such as the integrated supercritical CO2 enhanced shale gas recovery (scCO2-ESGR) and carbon geo-sequestration, and the advanced underground hydrogen storage (UHS) in shales can be developed to achieve the target of long-term energy supply and net-zero carbon emission. New techniques such as in-situ kerogen pyrolysis are also improved by using NMR dynamic monitoring