The Mancos shale core sample investigated in the present research has been extracted from the late Cretaceous (upper cretaceous) geologic formation of USA. Shale gas is usually obtained by horizontal drilling which induces fractures to increase the flow ability of hydrocarbons. Therefore, it is important to understand the mechanical properties, heterogeneity, and their complexities associated with elastic properties of shale. An experimental study was conducted to examine the morphological characteristics of the Mancos shale core sample both pre- and post-treatment with cryogenic liquid nitrogen (LN2) for various immersion times, namely, 30, 60, and 90 min. The atomic force microscopy technique is used to understand the surface roughness, irregularities in core samples, and for more accuracy. Scanning electron microscopy (SEM) results were employed to visualize the formation of cracks caused by cryogenic liquid nitrogen. Results from SEM showed an increase in the fracture size from 2 to 25 μm with an increase in the aging time up to 90 min under the atmosphere of cryogenic LN2. Nano-indentation measurements revealed that the nano-indentation moduli of the Mancos samples subjected to applied forces of 50 and 200 mN underwent a decrease from 24.6 to 16.8 and 15.6 GPa, respectively, with an increase in cryogenic liquid nitrogen treatment time to 90 min. The permeability of the shale samples after LN2 treatment showed a significant increase, whereas increasing net confining stress from 1000 to 7000 psi for all untreated and treated rock samples exhibited a decrease in permeability, which is attributed to increased compaction between the pore spaces. Moreover, the porosity of the Mancos shale increased from 3.78 to 6.92% for pretreated and treated rock samples.

Tight gas sandstone production faces enormous challenges from marginal matrix porosity and permeability in rock formations. In this regard, the liquid nitrogen (LN 2 ) treatment remedy has been suggested as an appropriate stimulation approach to resolve this issue. An experimental study was carried out to investigate the cryogenic liquid nitrogen fracturing of tight rock sandstone to enhance gas recovery from such reservoirs. Three core samples from the Kirthar fold belt were subjected to LN 2 treatment for 30, 60, and 90 min. Petrophysical characterization was performed through scanning electron microscopy, atomic force microscopy, nanoindentation measurements, and quantitative X-ray diffraction technique. The results reveal wide conductive fractures with an optimum size of 30 μm in the 90 minutes treatment case. Moreover, petrophysical measurements show that porosity increases from 8 to 19% at an optimal liquid nitrogen (LN 2 ) treatment duration (90 minutes). Furthermore, the permeability of the samples increased from 31 to 53 md after treatment with liquid nitrogen. Results from nanoindentation studies after LN 2 treatment revealed a significant decrease in nanoindentation moduli because of the increase in cracked rock compressibility.

The production of gas from conventional reserves has shown steep decline, whereas the demand of hydrocarbons as energy source is rising. Hence, the resulting deficit of energy can be met by developing the unconventional energy resources. Among all unconventional energy resources, shale gas is relatively the potential source of energy to be developed in a sustainable way. However, the degree of uncertainty is large for sustainable development of shale gas reservoirs. The shale gas found is held in extremely low-permeability formations having poor porosity; the free gas and the adsorbed gas are also found together. Therefore, the production mechanisms of shale gas reservoirs are quiet complex than the conventional gas reservoirs. Hence, the shale gas resources sustainable development remain ambiguous. In order to find sustainable way of exploitation of shale gas resources, this manuscript reviews in detail, the shale gas potential in Pakistan and the world in terms of its distribution, production mechanism, policy implications and development trends.