Abstract
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 275to 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.
Highlights
The oil and gas industry and the industrial sector is focusing on new ways for energy production [1], and have been primarily dependent on the energy supply of hydrocarbon resources for many decades [2,3]
We examined the efficiency of LN2 frac turing by determining the topography, morphology, petro-physical, and mechanical properties of rock on Laki limestone core plugs and thin sections of rock from the 18-LK-06 site based on their suitability for these experiments
The results demonstrate that the hardness of the LK-18-06 Laki limestone thin section was 52.63 GPa under 50 mN of applied indentation force
Summary
The oil and gas industry and the industrial sector is focusing on new ways for energy production [1], and have been primarily dependent on the energy supply of hydrocarbon resources for many decades [2,3]. Tight gas formations are typically nonporous or impermeable reservoirs and can exist in both carbonate or sandstone formations with less than 10% pore matrix and 0.1 millidarcy (mD) of permeability [26]. Low permeable carbonate formations contain a substantial amount of gas (60% of the world’s total remaining hydrocarbons exist within carbonate reservoir rocks) [29,30,31], which can be helpful to meet the supply and demand [25]. A precise reservoir quality assessment and extraction tech nique is essential for successfully developing and exploiting tight gas hydrocarbon resources. Several parameters, including permeability, porosity, rock fabric, geological framework, and pore-size distribution, have been investigated for the successful exploitation and development of hydro carbon reservoirs [38,41]
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