Cryogenic Liquid Nitrogen Fracking Effects on Petro-Physical and Morphological Characteristics of the Sembar Shale Gas Formation in the Lower Indus Basin, Pakistan

Abstract

Shale gas resources have emerged as critical resources in global energy. Pakistan has a substantial unconventional shale gas potential. However, shale gas in Pakistan, like in the United States and China, is still poorly developed compared to other unconventional resources. Shale reservoirs exhibit extremely poor permeability for production by conventional means. Numerous approaches have been applied to extract unconventional shale gas energy resources, including acid treatment and hydraulic fracturing. However, due to copious concerns, many countries have banned such practices. Hence, waterless fracturing techniques have the potential to alleviate such issues. In such situations, cryogenic fracturing by liquid nitrogen (LN2) is an imperative stimulation option for tight formations. Hence, we obtained samples from the Sembar shale formation of the lower Indus basin in Pakistan and experimentally investigated the effects of pre- and post-treatment using LN2 under various time cycles (30, 60, and 90 min). The study provides information about mineralogical, microstructural, and petro-physical properties. Sembar shale samples were exposed to LN2 for aging at various time cycles to generate fractures. The cryogenic LN2 pre- and post-treatment effects were quantitatively characterized using atomic force microscopy (for topography), scanning electron microscopy (for microstructural properties), energy dispersive spectroscopy (for elemental composition), petro-physical quantification (for porosity and permeability), and nanoindentation (for rock-mechanical properties). The results reveal that, before LN2 treatment, Sembar exhibited nominal pore-throat sizes. However, the post-treatments of cryogenic LN2 were very effective in creating microcracks of up to 17 μm. Similarly, the petro-physical properties exhibited a significant increase after LN2 treatment. The mean indentation moduli decreased from 24.34 to 12.25 GPa for 50 mN force and 20.15 to 10.42 GPa for 200 mN force. The topographic study found increased surface roughness from 356 to 778 nm due to the LN2 treatment of 90 min. Cryogenic LN2 treatment can improve the pore connectivity of shale samples and significantly enhance the flowing capacity, which may greatly increase the productivity of unconventional shale gas reservoirs.

Mechanisms of Hydraulic Fracture Propagation and Multi-well Effect during Multiple Vertical Well Fracturing in Layered Reservoirs with Low Permeability

“…Low-permeability unconventional oil and gas resources have gradually become important guarantors of energy security as a result of their wide distribution and large reserves. − The stress environment and geologic conditions of unconventional reservoirs with low permeability are complicated and difficult to develop. Currently, hydrofracturing is an important development technology for unconventional reservoirs with low permeability .…”

Wettability Alteration of Limestone Carbonate Cores Using Methylene Blue and Alumina-Based Nanofluid: Implications for EOR

“…Fossil fuels are a significant contributor to the world energy demand [1][2][3][4][5]. It is reported that carbonate reservoir rock formations exhibit a high volume of about 60% of all the global reserves.…”

Shale Wettability Characteristics via Air/Brines and Air/Oil Contact Angles and Influence of Controlling Factors: A Case Study of Lower Indus Basin, Pakistan

“…Thus, it is important to assess the characteristics of shale wettability for unconventional energy resources for successful exploitation and development. , Thus, assessing the wettability characteristics is important as it mainly affects the rock and fracturing fluids, which are treatment fluids following unconventional fracturing operations for reservoir development . Essentially, the shale formation is composed of a combination of various mineral constituents (e.g., clay, quartz, calcite, feldspars, and iron oxides) and organic compounds which are found in varying quantities within heterogeneous shale rocks. − However, the wettability of the shale formation is very complex to understand, which in turn displays the different wetting tendencies from hydrophobic to hydrophilic and to mixed wettability. − In the literature, some published studies reported that the shales possess a hydrophilic behavior; − on the contrary, other studies have claimed that they are hydrophobic, ,, and some of them provided that they exhibit mixed wettability. , The reason for such differences in the wettability of shale rocks is the discrepancies in mineralogical composition and textural parameters, complex pore distributions, ,, and the presence of organic matter in varying quantities. ,, Usually, the wettability of conventional reservoirs is obtained by any of the methods mentioned, such as (i) the contact angle (CA) method, (ii) the drainage and imbibition method, (iii) atomic force microscopy (AFM), and (iv) nuclear magnetic resonance and zeta potential. ,− However, the shale formation is extremely tight, exhibiting magnitude of orders lower permeability than the conventional reservoirs; thus, most of the pores are of micro- to nanometer sizes. Hence, in these ultra-low-permeability formations, most of the above-mentioned methods of wettability quantification are inconvenient except the CA method, which is more suitable.…”

“… 15 Essentially, the shale formation is composed of a combination of various mineral constituents (e.g., clay, quartz, calcite, feldspars, and iron oxides) and organic compounds which are found in varying quantities within heterogeneous shale rocks. 16 − 18 However, the wettability of the shale formation is very complex to understand, which in turn displays the different wetting tendencies from hydrophobic to hydrophilic and to mixed wettability. 19 − 21 In the literature, some published studies reported that the shales possess a hydrophilic behavior; 22 − 24 on the contrary, other studies have claimed that they are hydrophobic, 21 , 25 , 26 and some of them provided that they exhibit mixed wettability.…”