Influence of diagenetic features on petrophysical properties of fine-grained rocks of Oligocene strata in the Lower Indus Basin, Pakistan

Nari Formation is considered as one of the most important oil and gas exploration targets. These fine-grained tight sandstone reservoirs face enormous challenges due to their extremely low matrix porosity and permeability. Hence, in this regard, the study was carried out to collect the high-quality data on petrophysical properties along with mineralogy and microstructural characteristics and diagenesis. The experiments performed includes the petrographic study and scanning electron microscopy, and X-ray diffraction analyses. Besides, the measurement of petrophysical properties was carried out to assess the likely influence of the reservoir quality. The petrographic analysis shows predominantly fine- to medium-grained grey samples along with calcite, clay, lithic fragments and iron oxides. Further, the thin-section observations revealed that the quartz is a principal mineral component in all the analysed samples ranging from 52.2 to 92.9%. The bulk volume of clay minerals that range from 5.3 to 16.1% of. The porosity and permeability measured range from 5.08 to 18.56% (average 7.22%) and from 0.0152 to 377 mD (average 0.25 mD), respectively. The main diagenetic processes that affected the sandstones of Nari Formation are mechanical compaction, grain deformation, cementation and quartz dissolution and have played a significant role in influencing the quality of the reservoir rock. Overall, it appears that the primary petrophysical properties (porosity and permeability) were decreased due to the mechanical compaction, lithification, cementation, and framework grain dissolution. Based on the integrated mineralogical, microstructural analysis, and the laboratory-based petrophysical properties, the samples exhibited poor porosity, permeability, and moderate clay content, which indicate that the Nari Formation is a poor quality reservoir

Experimental evaluation of liquid nitrogen fracturing on the development of tight gas carbonate rocks in the Lower Indus Basin, Pakistan

Tight gas carbonate formations have enormous potential to meet the supply and demand of the ever-growing population. However, it is impossible to produce from these formations due to the reduced permeability and lower marginal porosity. Several methods have been used to extract unconventional tight gas from these reservoirs, including hydraulic fracturing and acidizing. However, field studies have demonstrated that these methods have environmental flaws and technical problems. Liquid nitrogen (LN2) fracturing is an effective stimulation technique that provides sudden thermal stress in the rock matrix, creating vivid fractures and improving the petro-physical potential. In this study, we acquired tight gas carbonate samples and thin sections of rock from the Laki limestone formation in the Lower Indus Basin, Pakistan, to experimentally quantify the effects of LN2 fracturing. Initially, these samples were characterized based on mineralogical (X-ray diffraction), petrography, and petro-physical (permeability and porosity) properties. Additionally, LK-18-06 Laki limestone rock samples were exposed to LN2 for different time intervals (30, 60, and 90 mins), and various techniques were applied to comprehend the effects of the LN2 before and after treatment, such as atomic force microscopy, scanning electron microscopy, energy-dispersive spectroscopy, nano-indentation, and petro-physical characterization. Our results reveal that the LN2 treatment was very effective and induced vivid fractures of up to 38 µm. The surface roughness increased from 275 to 946 nm, and indentation moduli significantly decreased due to the decreased compressibility of the rock matrix. Petro-physical measurements revealed that the porosity increased by 47% and that the permeability increased by 67% at an optimum LN2 treatment interval of 90 mins. This data can aid in an accurate assessment of LN2 fracturing for the better development of unconventional tight gas reservoirs

Could shale gas meet energy deficit: its current status and future prospects

Abstract 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

Effect of storage at elevated temperature on the quality and stability of different almond oils: a comprehensive study

This study aimed to investigate the chemical changes and oxidative stability of almond oil varieties (Australian, American, and Iranian) during storage at 60 °C for 21 d. The physicochemical properties of oil were analyzed at various time intervals to determine its stability. The peroxide value, free fatty acid, p-anisidine, TOTOX, fatty acid composition, and effect on functional groups were evaluated to assess the quality of the almond oil during storage. The results showed a significant increase in PV and FFA, p-AV, totox of the almond oil during storage, indicating that oxidative degradation had occurred. During the oxidation process, some changes were observed in the following spectral regions: 3,700–3,150, 3,010–2,999, 1,800–1,600, and 1,200–900 cm−1. Whereas, the fatty acid composition of the almond oil remained relatively stable during storage, except for a small variation in oleic acid. Comparatively, American and Iranian almond oils showed better stability than the Australian almond variety. The findings of this study provide important insights into the oxidative stability of different almond varieties during storage and can aid in the development of strategies to prevent or mitigate oxidation in almond oil. The findings of this study could have significant implications for the food, cosmetics, and pharmaceutical industry, particularly in the formulation and production of products that use almond oil as an ingredient

Comparison of Klinkenberg-Corrected Gas and Liquid Permeability in Kirthar Fold Belt Tight Gas Sands

A detailed laboratory study was carried out to investigate the controls and differences between Klinkenbergcorrected gas and liquid permeability. For this reason outcrop core samples were collected from Kirthar fold belt of lower Indus basin, the plugs were horizontally taken, in cylindrical shape having dimension of 3.5-5.32 cm length and with maximum of 3.2 cm diameter. The sample porosity measurements were performed using calculations from grain volume and bulk volume method. For the purpose of comparison, slippage free gas permeability tests using nitrogen gas was measured and liquid permeability of samples was measured using brine (NaCl) of different compositions. The data obtained showed that liquid permeability was lower by an order of magnitude than the permeability of samples measured with gas. However, the gas permeability corrected for Klinkenberg effects showed difference of half an order of magnitude when compared with liquid permeability. Hence the differences in liquid permeability and gas permeability could be described by other mechanism of particles mobilization and dissolution and pore blocking phenomena. Moreover, the obtained data of gas and liquid permeability was then used to develop permeability estimation correlations. The results suggests that there is scatter in the measured values and predicted values of gas and liquid permeability data, which means that such correlations should not be used where accurate liquid permeability values of tight sandstones are needed. Permeability predicted using the existing correlations developed based on gas permeability data lead to an overestimation of permeability also the flow rates might be over predicted within such low permeability reservoirs

Synthesis of biodiesel via pre-blending of feedstocks: an optimization by the polynomial curve fitting method

Use of abundant indigenous energy crops for biofuel production contributes to enhance the economy and reduce the dependence on fossil fuels. This article aims to shed light on two energy crops available in Pakistan; castor (Ricinus communis L.) and cottonseed (Gossypium hirsutum L.). Although castor has excellent oil content (54%), its high viscosity is not acceptable. Therefore, pre-blending with cottonseed oil was proposed. Physical and chemical properties of crude oils, pure biodiesels and binary blends besides fatty acid composition and degree of unsaturation were analyzed. Biodiesels were checked for quality parameters within limits of American Society for Testing Materials (ASTM) and European Standards. Improvement in kinematic viscosity and density of castor biodiesel were noticed following this concept. Moreover, the developed empirical formula indicated that an optimized blending ratio of 93.86% cottonseed oil and 6.14% castor oil accomplished biodiesel yield of 91.12%, kinematic viscosity of 6 mm(2)/s and cetane number of 48.79, respectively, which all satisfy ASTM D6751. This technique also indicated that pre-blending can raise the ester content of castor biodiesel. In conclusion, it is recommended to adopt the concept of pre-blending to improve the quality of biodiesel and thus the engine and emission performance in compression ignition engines

Synthesis of Biodiesel via Pre-blending of feedstocks: An Optimization through Polynomial Curve Fitting Method

Use of abundant indigenous energy crops for biofuel production contributes to enhance the economy and reduce the dependence on fossil fuels. This article aims to shed light on two energy crops available in Pakistan; castor (Ricinus communis L.) and cottonseed (Gossypium hirsutum L.). Although castor has excellent oil content (54%), its high viscosity is not acceptable. Therefore, preblending with cottonseed oil was proposed. Physical and chemical properties of crude oils, pure biodiesels and binary blends besides fatty acid composition and degree of unsaturation were analyzed. Biodiesels were checked for quality parameters within limits of American Society for Testing Materials (ASTM) and European Standards. Improvement in kinematic viscosity and density of castor biodiesel were noticed following this concept. Moreover, the developed empirical formula indicated that an optimized blending ratio of 93.86% cottonseed oil and 6.14% castor oil accomplished biodiesel yield of 91.12%, kinematic viscosity of 6mm2/s and cetane number of 48.79, respectively, which all satisfy ASTM D6751. This technique also indicated that pre-blending can raise the ester content of castor biodiesel. In conclusion, it is recommended to adopt the concept of pre-blending to improve the quality of biodiesel and thus the engine and emission performance in compression ignition engines</p

Laboratory Investigation to Assess the Impact of Pore Pressure Decline and Confining Stress on Shale Gas Reservoirs

Four core samples of outcrop type shale from Mancos, Marcellus, Eagle Ford, and Barnett shale formations were studied to evaluate the productivity performance and reservoir connectivity at elevated temperature and pressure. These laboratory experiments were conducted using hydrostatic permeability system with helium as test gas primarily to avoid potential significant effects of adsorption and/or associated swelling that might affect permeability. It was found that the permeability reduction was observed due to increasing confining stress and permeability improvement was observed related to Knudsen flow and molecular slippage related to Klinkenberg effect. Through the effective permeability of rock is improved at lower pore pressures, as 1000 psi. The effective stress with relatively high flow path was identified, as 100-200 nm, in Eagle Ford core sample. However other three samples showed low marginal flow paths in low connectivity

Effect of Temperature and Alkali Solution to Activate Diethyl Carbonate for Improving Rheological Properties of Modified Hydroxyethyl Methyl Cellulose

The applications of cellulose ethers in the petroleum industry represent various limitations in maintaining their rheological properties with an increase in both concentration and temperature. This paper proposed a new method to improve the rheological properties of hydroxyethyl methyl cellulose (HEMC) by incorporating diethyl carbonate (DEC) as a transesterification agent and alkali base solutions. Fourier transform infrared (FTIR) analysis confirmed the grafting of both composites onto the HEMC surface. The addition of sodium hydroxide (NaOH) improved the stability of the polymeric solution as observed from ζ-potential measurement. Shear viscosity and frequency sweep experiments were conducted at concentrations of 0.25–1 wt % at ambient and elevated temperatures ranging from 80–110 °C using a rheometer. In the results, the increase in viscosity at specific times and temperatures indicated the activation of DEC through the saponification reactions with alkali solutions. All polymeric solutions exhibited shear-thinning behavior and were fitted well by the Cross model. NaOH-based modified solution exhibited low shear viscosity compared to the DEC-HEMC solution at ambient temperature. However, at 110 °C, its viscosity exceeded that of the DEC-HEMC solution due to the activation of DEC. In frequency sweep analysis, the loss modulus (G″) was greater than the storage modulus (G′) at lower frequencies and vice versa at higher frequencies. This signifies the viscoelastic behavior of modified solutions at 0.50 wt % and higher concentrations. The flow point (G′ = G″) shifted to a low frequency, indicating the increasing dominance of elastic behavior with the rising temperature. At 110 °C, the NaOH-based modified solution exhibited both viscous and elastic behavior, confirming the solution’s thermal stability and flowability. In conclusion, modified HEMC solution was found to be effective in controlling viscosity under ambient conditions, enhancing solubility, and improving thermal stability. This modified composite could play a significant role in optimizing viscoelastic properties and fluid performance under challenging wellbore conditions