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Shale gas mainly exists in organic-rich shale in the form of free gas and adsorbed gas. Shale gas content has a direct impact on the productivity and life of the gas well, and is also an important indicator for areal selection and reservoir evaluation. Through the study of gas content experiments of shale gas, we can better guide the exploration and development of shale gas. According to the isothermal adsorption and desorption experiments of Wufeng-Longmaxi Formations in Jiaoshiba block of the Fuling shale gas field in Sichuan basin, China, 7 core samples from isothermal adsorption experiment and 30 core samples from desorption experiment were analyzed. The experimental results show that the isothermal adsorption experiment is an effective way to obtain Langmuir Volume (V L) and Langmuir Pressure (P L). The total gas content obtained from shale desorption experiment in the drilling site is mainly adsorption gas content, and the free gas content is relatively small. The desorption rate is different in different desorption stages, and the samples with higher total organic carbon (TOC) content have faster desorption rate and higher total desorption gas content. The carbon isotope value of methane gradually increases with the increase of desorption time. The results of methane isotope analysis in the desorption experiment are compared with the results of carbon isotope monitoring in the producing process. The findings reveal that after years of development in Jiaoshiba block of the Fuling shale gas field, the methane isotope in gas wells has basically remained unchanged, and the current gas production should be dominated by free gas. • Compare the analysis results of isothermal adsorption and desorption experiment. • The change law of carbon isotope with time in desorption process is studied. • The producing status is determined for the first time by using this law. [ABSTRACT FROM AUTHOR]

The article presents a study on the implication of shale gas accumulation and the sedimentary facies in the Lower Silurian Longmaxi Formation at Eastern Sichuan region in China. The lithofacies identified in the study include dark grey lamellar silty mudstone, dark grey massive silty mudstone, and fossil-bearing mudstone. It concludes the formation of the deposit in a deep-water and low-energy reducing environment and the development of a large number of zooplankton and phytoplankton.

A large volume of water is required in shale gas development, especially for large-scale hydraulic fracturing in horizontal wells. This study focuses on 334 shale gas wells in the largest production field Fuling in China. Models are formulated to estimate the water use at each stage of the development process, including pre-drilling preparation, drilling and cementing, fracturing, gas testing, production testing. Domestic water used by employee community of shale gas companies are also fully considered. The results show that the average fracturing water use per well was 34,756.0 m3 in Fuling, which accounted for 98% of the total water use. By the end of 2017, the total fracturing water used in Fuling was 1.09 × 107 m3, and a total of 2.28 × 106 m3 of flowback fluid was achieved with 2.16 × 106 m3 of water reused. In addtion, the domestic water used by the employee community was found to be 2.19 × 106 m3, which was equivalent to the water saved from the flowback fluid. China's special "development campaign" mode for shale gas extraction is the reason. The results improve the understanding of water use in China's shale gas development and also provide important implications for water management. Image 1 • The water use at each stage is analyzed. • Domestic water used by the employee community is fully considered. • Fracking water accounted for 98% of the total water consumption. • The reuse rate of fracking water increased to 67.26% in 2017. [ABSTRACT FROM AUTHOR]

The Wufeng-Longmaxi Formations are the focus of shale gas exploration in China. Their sedimentation is affected by global and regional geological events, and the resulting heterogeneity hinders the expansion of exploration results. This study combines logging, mineralogy, and geochemistry to reconstruct the sedimentary mechanisms of shale in the southern Sichuan Basin and discusses its implications for exploration. The shale can be divided into third-order sequences, in which the Wufeng Formation and lower Long-1 Member are transgressive systems tracts (TST1 and TST2), and the Guanyinqiao Member and the middle-upper Long-1 Member are highstand systems tracts (HST1 and HST2). Volcanic eruption and glaciation evolution are the driving factors of the sedimentary environment during the TST. The area is in a cold-warm climate, characterized by anoxic conditions, slow sedimentation, booming productivity, and low terrigenous influx, thereby depositing four types of siliceous shale. The siliceous shale is rich in biogenic microcrystalline quartz and high TOC, which are the keys to becoming the "sweet spot" of shale gas. Microcrystalline quartz fills the intergranular pores to support the entire pore network framework. The organic matter undergoes thermal evolution to produce abundant organic matter pores, which constitute the main place for adsorbed gas and free gas. For the highstand systems tract, HST1 is the product of the peak of glaciation, mainly composed of calcareous shale and carbonate rocks. The sedimentation of HST2 is affected by turbidity currents and violent orogeny. The area is in a warm climate, characterized by high terrigenous influx, dysoxic-oxic conditions, medium productivity and rapid sedimentation rates. The lithofacies gradually changed from siliceous shale to mixed shale and argillaceous shale. Excessive clay minerals and low TOC make it difficult for HST2 to realize the commercial development of shale gas. • The Wufeng Formation-Long 1 Member was divided into two 3rd sequences, and four geological events were identified. • Volcanism and postglaciation created conditions for the enrichment of organic matter and microcrystalline quartz. • Kwangsian Orogeny and turbidity currents led to the formation of organic-poor shale. [ABSTRACT FROM AUTHOR]