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Shale gas is predominantly stored within the micro- and nano-scale porous matrix of shale formations, existing primarily in adsorbed and free states. In contrast to conventional hydrocarbon reservoirs, shale reservoirs exhibit unique characteristics in their pore and fracture systems. The primary reservoir space resides at the nano-scale, with significantly lower development of natural micro-fractures and fracture networks under in-situ conditions. Consequently, reservoir enhancement through artificial fracturing is essential for effective shale gas production. The porosity and permeability of shale reservoirs are substantially influenced by the nano-scale pore system, which governs the enrichment, accumulation patterns, migration, and production mechanisms of shale gas. Therefore, accurately characterizing the nano-scale pore system of shale reservoirs and identifying factors that contribute to high-quality pore development are crucial for optimizing efficient and economically viable shale gas exploitation and resource evaluation.
The Lower Carboniferous Luzhai Formation in the Guizhong Depression is predominantly characterized by deep-water shelf deposits, with widespread distribution of organic-rich shales. The sedimentary thickness typically ranges from 50 to 300 meters, and the burial depth is moderate. Shale samples exhibit an organic carbon content exceeding 1.5%, with organic matter reaching high to over-maturity stages. The reservoir contains a significant proportion of brittle minerals, resulting in well-developed pore spaces and favorable gas adsorption properties, which provide advantageous geological conditions for shale gas accumulation. Data from the parameter well Guirongye 1 indicate that the sweet spot section of the first member of the Carboniferous Luzhai Formation in the Liucheng slope zone of the Guizhong Depression features substantial continuous thickness, high organic matter abundance, moderate thermal evolution, excellent gas measurement, and high gas content. These characteristics suggest favorable conditions for shale gas accumulation and enrichment. While preliminary studies have been conducted on the pore structure of the shale reservoir using CO2 and N2 isothermal adsorption and scanning electron microscopy (SEM), a comprehensive methodological framework for detailed characterization of the pore system has yet to be fully established. Key parameters such as pore type and distribution, pore connectivity, and the relationship between pores and seepage networks require systematic investigation. Further integration of qualitative observations and quantitative testing is necessary to enhance the precision and quantitative level of pore research. Additionally, the mechanisms governing the formation and development of high-quality shale reservoirs warrant further exploration.
Given that the characterization of shale pore space necessitates an integration of qualitative and quantitative approaches, this study employs a combination of scanning electron microscopy, CT scanning, mercury injection capillary pressure, low-temperature nitrogen adsorption, carbon dioxide adsorption, isothermal methane adsorption, and nuclear magnetic resonance to conduct a comprehensive evaluation of the pore system in shale reservoirs. Samples are obtained from cores within the Liucheng North Block well area. This research systematically examines and describes the pore characteristics of the Lower Carboniferous Luzhai Formation's first member in central Guangxi, including pore types, pore size distribution, specific surface area, pore connectivity, and micro-fracture development. The findings provide valuable guidance for subsequent key tasks such as high-quality reservoir calibration, well location deployment, and reservoir reconstruction in study area.
| Country | China |
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