Abstract
The lower Silurian Longmaxi Formation hosts a highly productive shale gas play in the Zhaotong region of southern China. According to core observation, X-ray diffraction analyses, and scanning electron microscopy (SEM) observations, the shale comprises primarily quartz, carbonate minerals, and clay minerals, with minor amounts of plagioclase, K-feldspar, and pyrite. The clay mineral content ranges from 15.0% to 46.1%, with an average of 29.3% in the Zhaotong region. Organic geochemical analyses show that the Longmaxi Formation has good potential for shale gas resources by calculating total organic carbon, vitrinite reflectance, and gas content. Scanning electron microscope images demonstrate that reservoir pore types in the Longmaxi shale include organic pores, interparticle pores, intercrystalline pores, intraparticle pores, and fractures. Reservoir distribution is controlled by lithofacies, mineral composition, and geochemical factors. In addition, we investigated the relationships between reservoir parameters and production from 15 individual wells in the Zhaotong region by correlation coefficients. As a result, the brittleness index, total organic carbon (TOC), porosity, and gas content were used to define high-quality reservoirs in the Longmaxi shale. Based on these criteria, we mapped the thickness and distribution of high-quality reservoirs in the Longmaxi Formation and selected highlighted several key sites for future exploration and development.
Highlights
Shale gas is one of the main forms of unconventional natural gas
Gas content (m3/t) reservoir parameters and gas production, we found that the brittleness index, total organic carbon (TOC), porosity, and gas content have the strongest influence on gas production, with correlation coefficients > 0:35, while Ro, pore pressure gradient, argillaceous content, siliceous content, and calcium content have little effect on gas production, with correlation coefficients < 0:35
Reservoir characteristics of the lower Silurian Longmaxi shale were analyzed in the Zhaotong region, southern China
Summary
Shale gas is one of the main forms of unconventional natural gas. It occurs within certain organic-rich shale and is generally present in an adsorbed or free state [1,2,3,4]. China has great potential for additional shale gas exploration, and the production of shale gas in the country is forecast to reach 800 – 1000 × 108 m3 by 2030 [9]. Despite their production potential, shale gas reservoirs are often highly heterogeneous [10, 11] and have poor petrophysical properties [12,13,14]. Successful shale gas development is dependent on the discovery of high-quality reservoirs [18]
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