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.

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Cellulose-based polymers have been successfully used in many areas of petroleum engineering especially in enhanced oil recovery drilling fluid, fracturing and cementing. This paper presents the application of cellulose-based polymer in oil well cementing. These polymers work as multifunctional additive in cement slurry that reduce the quantity of additives and lessen the operational cost of cementing operation. The viscosity of cellulose polymers such as hydroxyethyl cellulose (HEC), carboxymethylcellulose (CMC) and hydroxypropyl methylcellulose (HPMC) has been determined at various temperatures to evaluate the thermal degradation. Moreover, polymers are incorporated in cement slurry to evaluate the properties and affect in cement slurry at 90 °C. The API properties like rheology, free water separation, fluid loss and compressive strength of slurries with and without polymer have been determined at 90 °C. The experimental results showed that the viscosity of HPMC polymer was enhanced at 90 °C than other cellulose-based polymers. The comparative and experimental analyses showed that the implementation of cellulose-based polymers improves the API properties of cement slurry at 90 °C. The increased viscosity of these polymers showed high rheology that was adjusted by adding dispersant which optimizes the rheology of slurry. Further, improved API properties, i.e., zero free water separation, none sedimentation, less than 50 ml/30 min fluid loss and high compressive strength, were obtained through HEC, CMC and HPMC polymer. It is concluded that cellulose-based polymers are efficient and effective in cement slurry that work as multifunctional additive and improve API properties and cement durability. The cellulose-based polymers work as multifunctional additive that reduces the quantity of other additives in cement slurry and ultimately reduces the operational cost of cementing operation. The comparative analysis of this study opens the window for petroleum industry for proper selection of cellulose-based polymer in designing of cement slurry.

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.