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Archie's parameters are substantial to be investigated in the evaluation of water saturation. Many researchers adhered to the opinion that Archie's equation can still be applied to water saturation calculation in shale if the accuracy of relative parameters could be improved. External conditions, such as temperature, confining pressure, water salinity, wettability, and displacement, may influence the determination of Archie's parameters. The aim of the study is to investigate the effect of salinity on Archie's parameters and their correlation with mineral composition and pore structure. The mineral contents and petrophysical properties were firstly acquired through X-ray diffraction (XRD) and basic measurements. Rock-electric experiments under different salinity were conducted on deep shale samples taken from Longmaxi (LMX) Formation in Luzhou (LZ). The results indicate that Archie's parameters of " a ," " b ," " m ," and " n " under actual brine salinity are assigned to 1.47, 1, 1.26, and 1.6, respectively. Our cementation factor is lower than that in other studies including (shaly) sandstones, carbonates, and shales, probably due to the extremely low porosity in study area. Salinity has a positive effect on cementation factor (m) and saturation exponent (n), suggesting the traditional assignment to Archie's parameters is inappropriate. It was concluded that the complicated pore structure and high porosity mainly associated with clay mineral may trigger the increased cementation factor. Further mathematical derivations confirmed that the rock resistivity is inextricable from pore system and establish a physical model. The paper provides a solid evidence base for further understanding and evaluation of water saturation in unconventional shale reservoirs, more significantly, innovatively unveils the research into Archie formula in deep shale reservoirs of southern Sichuan basin. [ABSTRACT FROM AUTHOR]

Many factors need to be considered in the evaluation of tight conglomerate reservoirs, including the microscopic pore-throat structure, pore connectivity, lithology, porosity, permeability, and clay mineral content. The contents and types of clay minerals reflect the mineral evolution process during the deposition of the reservoir and can reflect the reservoir's physical properties to a certain extent. In this study, cores from the Baikouquan Formation in Mahu were used to comprehensively analyze the effects of the clay mineral content on the physical properties of a tight conglomerate reservoir, including field emission scanning electron microscopy (FE-SEM), casting thin section observations, X-ray diffraction (XRD), interface property testing, high-pressure mercury injection, low temperature N2 adsorption, and nuclear magnetic resonance (NMR)-movable fluid saturation testing. The results revealed that differences in different lithologies lead to differences in clay mineral content and pore structure, which in turn lead to differences in porosity and permeability. The interface electrification, adsorption, and specific surface area of the reservoir are positively correlated with the clay mineral content, which is mainly affected by the smectite content. As the clay mineral content increases, the proportion of nanoscale pore throats increases, and the core becomes denser. The saturation of the movable fluid controlled by the >50 nm pore throats in the tight conglomerate ranges from 8.7% to 33.72%, with an average of 20.24%. The clay mineral content, especially the I/S (mixed layer of Illite and montmorillonite) content, is negatively correlated with the movable fluid. In general, the research results clarified the relationship between the lithology and physical properties of clay minerals and the microscopic pore structure of the tight conglomerate reservoirs in the Baikouquan Formation in the Mahu area. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) has emerged as an essential method for appraising gas-shales, quantifying their petrophysical properties, classifying their fluid types, and discerning their productivity. Comprehensive measurement campaigns, as well as reliable thermal-heating experiments, are required to fully understand the NMR mechanism of shale and to further develop future gas-shale exploitation strategies. NMR signatures from individual matrix components, which comprise shale, are investigated to gather data to better estimate its petrophysical parameters. Subsequently, we perform T 1 and T 2 measurements of kerogen, solid bitumen, and clay minerals. Next, we analyze the temperature effect on the NMR signal interpretation of different compositions of gas-shale samples in detail, coupled with the position of clay minerals and solid bitumen from the T 1 -T 2 mapping. A shale plug sample was quantified by the NMR T 1 -T 2 relaxation signals under initial conditions and different temperature conditions of 110 °C, 250 °C, 450 °C, and 650 °C. The fluid volume significantly decreased as the temperature increased. The organic matter maturity changed at 450 °C and 650 °C. According to a thermal-heating experiment with powdered clays, we obtained the hydroxyl group and crystal water signals and determined the critical temperature for different dried types of water in clay mineral. It is reasonable to infer that deconvoluting the entire shale sample into different components can further determine the NMR relaxation mechanisms. The ultimate goal of this project was to develop a holistic methodology to understand the NMR mechanisms of isolated components and to assess the positions of kerogen, solid bitumen, illite, kaolinite, smectite, and chlorite from T 1 -T 2 mapping. This work contributes to the fundamental understanding of shale formations by quantifying the NMR relaxation mechanisms of various constituents in shale and provides implications for shale rock evaluations. • To investigate the T 1 -T 2 correlation spectrum of isolated components of the shale. • Accurately quantifying the relaxation mechanism of the specific constituents in clay mineral. • To complement the position of bitumen and clay mineral in T 1 -T 2 mapping of gas-shale. • To imply temperature affects on the relaxation times on kerogen, bitumen, and clay mineral. [ABSTRACT FROM AUTHOR]