Abstract
Shale rock consists of a complex matrix structure due to presence of nano-scale pores. Owing to such complexity determination and/or prediction of the mineralogical, mechanical, and petrophysical properties (e.g., permeability, porosity, pore size distribution, etc.) of shale is a challenging task. A preliminary estimation of these properties is essential before shale gas exploration. In this study, experimental and numerical analyses are conducted to estimate the permeability, porosity, and pore size distribution of a typical shale sample. Gas adsorption experiments were conducted to characterize the pore spaces of the shale via analysing the isotherms. Using conventional theories, such as BET and BJH methods, surface area, pore volume, and pore size distributions were estimated. On the other hand, gross porosity of the shale samples was measured by conducting gas pycnometry experiment. Finally based on the obtained results an equivalent pore network model is constructed which accounts for the pore size distributions and low pore connectivity in the shale matrix. We have simulated gas flow through the network to estimate permeability of the shale. This model considers Knudsen diffusion and the effects of gas slippage on permeability. Further parametric study shows that the apparent permeability primarily depends on the reservoir pressure, pore coordination number and porosity.
Highlights
Due to the increasing energy demand and uprising oil and gas prices in the world, the traditional exploration of the conventional resources has shifted towards unconventional sources
Coal Bed Methane (CBM), Coad Mine Methane (CMM), Shale Gas, and Tight Gas are considered as typical alternative unconventional sources [1]
The main objective of this study is to develop a three-dimensional nano-scale pore network model (PNM) to simulate the gas flow through shale while considering the micro-scale mechanisms like Knudsen diffusion, slip flow, and transition flow
Summary
Due to the increasing energy demand and uprising oil and gas prices in the world, the traditional exploration of the conventional resources has shifted towards unconventional sources. Prior to gas exploration it is essential to estimate the total gas-in-place within the shale It is a challenging task since, shale is an ultra-thick sedimentary rock having nanoscale pores and a very low permeability in the order of 10−25 to 10−15 m2. Imaging techniques (e.g., SEM, TEM, X-ray micro-CT scan, and FIB) for analysing the pore structure and network extraction algorithms are the most common approaches [5,6]. Other experimental techniques like gas adsorption and mercury intrusion porosimetry have been adopted for pore size distribution by many researchers [8]. These two techniques (imaging and gas adsorption) are the most conventional techniques used in pore network modelling for getting pore size distribution. A detailed microstructural analysis of the shale is carried out via gas adsorption technique
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