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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.

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Stress influence on permeability has been extensively studied by various authors, as the stress can significantly affect reservoir's productivity. This paper displays the features of permeability stress sensitivity in tight gas sandstone in Kirthar fold belt lower Indus Basin, Sindh, Pakistan. The experiments performed under a range of pore pressure and confining stress, and the results were analyzed by integrating with microstructural observations. The results obtained were used, to explore the combined effects of changing pore pressure on slippage and absolute permeability. The results revealed that the stress sensitivity increases as the permeability decreases; this is because of existence of microfractures and the presence of larger pore throat radius. In addition, the effective pore size was calculated from the gas slip parameter, and at low confining stress levels, this value was in the same order of magnitude as the microfracture width. Moreover, the pore size calculated from gas slip parameters was reduced at higher stress levels, which indicated grain boundary fractures closures.