Quad-porosity shale systems – a review

Abstract

Purpose This paper aims to review the quad-porosity shale system from a production standpoint. Understanding the complex but coupled flow mechanisms in such reservoirs is essential to design appropriate completions and further, optimally produce them. Dual-porosity and dual permeability models are most commonly used to describe a typical shale gas reservoir. Design/methodology/approach Characterization of such reservoirs with extremely low permeability does not aptly capture the physics and complexities of gas storage and flow through their existing nanopores. This paper reviews the methods and experimental studies used to describe the flow mechanisms of gas through such systems, and critically recommends the direction in which this work could be extended. A quad-porosity shale system is defined not just as porosity in the matrix and fracture, but as a combination of multiple porosity values. Findings It has been observed from studies conducted that shale gas production modeled with conventional simulator/model is seen to be much lower than actually observed in field data. This paper reviews the various flow mechanisms in shale nanopores by capturing the physics behind the actual process. The contribution of Knudson diffusion and gas slippage, gas desorption and gas diffusion from Kerogen to total production is studied in detail. Originality/value The results observed from experimental studies and simulation runs indicate that the above effects should be considered while modeling and making production forecast for such reservoirs.

Supercritical Methane Adsorption on Shale over Wide Pressure and Temperature Ranges: Implications for Gas-in-Place Estimation

“…According to petrophysical test results, the shale physical model can be simplified into two parts: mineralogical components and pore space (Figure b). Mineralogical components include brittle minerals (quartz, feldspar, carbonate minerals, and pyrite), clay minerals, and dispersed organic matter, ,, in which organic matter and clay minerals are regarded as the main carriers for shale gas adsorption. ,,, Pore space covers the pores and fractures developed within and between various minerals. ,,, Some pores are isolated, which the fluids (formation water, liquid hydrocarbon, and gas) cannot access. , In the accessible pore space, with the subtraction of the fraction occupied by formation water and oil, the remaining is the available space for shale gas storage in the form of adsorbed gas and free gas.…”

Supercritical Methane Adsorption on Overmature Shale: Effect of Pore Structure and Fractal Characteristics

“…The pore structure in shale is complex and heterogeneous − and plays an important role in shale gas adsorption. ,− , To better understand and characterize the pore structure of shale, it is essential to combine multiple analytical methods. − With the assistance of argon ion polishing during sample pretreatment, clear visual images of pore morphology can be captured and analyzed qualitatively by means of field emission scanning electron microscopy (FE-SEM). − Following the classification suggested by the International Union of Pure and Applied Chemistry (IUPAC), pores are divided into micropores (<2 nm), mesopores (2–50 nm), and macropores (>50 nm) based on pore size. Low-pressure N 2 adsorption (LP-N 2 -GA) analysis is commonly used to characterize the pore structure in shales. ,,, However, it is difficult to accurately characterize very narrow micropores because of kinetic restrictions at cryogenic temperature (77 K) .…”

An Overview on Extension and Limitations of Macroscopic Darcy’s Law for a Single and Multi-Phase Fluid Flow through a Porous Medium

“…, geothermal reservoirs (Suresh Kumar and Ghassemi, 2005; Suresh Kumar and Ghassemi, 2006;Ghassemi and Suresh Kumar, 2007;Rakesh and Suresh Kumar, 2016;Bagalkot et al, 2018), shale gas reservoirs (Patwardhan et al, 2014;Samarth et al, 2015;Samarth et al, 2016), coal bed methane reservoirs and deep saline aquifers (Vivek and Suresh Kumar, 2016;Vivek et al, 2017). Since, flow through a classical homogeneous porous medium in itself has huge complexities, there are still a number of unresolved fundamental queries.…”