Influence of cryogenic liquid nitrogen cooling and thermal shocks on petro-physical and morphological characteristics of Eagle Ford shale

Abstract

Eagle Ford shale formations have great hydrocarbon potential to minimise the supply and demand problems of the overgrowing population. Whereas, due to reduced permeability and marginal porosity, it is very difficult to produce from these formations. Previously, hydraulic fracturing and acidizing techniques are used to produce the hydrocarbons from tight gas shale formations; however, due to technical difficulties and environmental problems have led to a ban on these techniques in many countries. Therefore, it is suggested to use water-less fracturing methods to avoid these problems. Recently, liquid nitrogen (LN2) cooling have shown a great potential to mitigate technical and environmental flaws, which works on the principle of providing sudden thermal shocks in the pore matrix, thus inducing micro-cracks and enhancing the petro-physical potential.In this study, we have collected tight gas shale samples from the Eagle Ford shale's Upper Late Cretaceous geologic formation in the United States. Initially, these samples were exposed to LN2 for various time intervals of 30, 60, and 90 min and were characterised based on their petro-physical, morphology, topography, and rock mechanical properties before and after LN2 exposure. To accomplish that, various techniques were used such as core flooding, porosity determination, microstructural characterisation via field emission scanning electron spectroscopy (FESEM) and energy dispersive spectroscopy (EDS), topographic characterisation via atomic force microscopy (AFM), and rock mechanical characterisation via nano-indentation technique.It is evident from our results that LN2 cooling has a substantive effect on petro-physical properties by increasing permeability from 12 nano-Darcy (nD) to 2.6 milli-Darcy (mD) and porosity from 2.32% to 4.46%. Similarly, topographic properties have shown an increase in surface roughness from 177 nm to 692 nm, and hardness (indentation moduli, GPa) was substantially reduced due to optimum exposure of LN2 at 90 min. Further, thermal shocks of LN2 cooling have induced vivid micro-cracks in the pore matrix up to 7 μm. In a nutshell, it is vital to augment the effects of LN2 cooling on microstructural, petro-physical, topography, and rock mechanical properties for better understanding in the development of hydrocarbon potential in Eagle Ford shale formations.