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Schematic map of the Emeishan large igneous province (ELIP) and its thermal effect (Jiang, 2017, modified from Sun et al., 2010). The dashed lines show the boundaries of the inner, intermediate, and outer zones of the ELIP, as defined by He et al. (2003). For the interpretation of the references for color in this figure legend, the reader is referred to the web version of this article. The red column represents the Permian heat flow and the green column represents the present heat flow.
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The Weiyuan (WY) and Changning (CN) fields are the largest shale gas fields in the Sichuan Basin. Though the shale gases in both fields are sourced from the Longmaxi Formation, this study found notable differences between them in molecular composition, carbon isotopic composition, and noble gas abundance and isotopic composition. CO 2 (av. 0.52%) a...
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Context 1
... CN has an overall area of nearly 4000 km 2 (Figure 1). The CN area is closer to the core zone of Emei Large Igneous Province (LIP) than the WY area ( Figure 3). In this area, the Longmaxi shale mainly belongs to type I-II1 organic matter, with a thermal maturity Ro of 2.8% to 3.3% [40,41]. ...
Context 2
... appearance of pyrobitumen in the Sinian-Cambrian reservoirs is clear evidence of an abrupt hydrothermal fluid event, which might correspond to the Emei mantle plume in the late Permian era [60,61]. WY and CN are in the Emeishan large igneous province region (Figure 3). The thermal evolution of source rocks in the WY and CN areas was strongly affected by the ELIP [62][63][64]. ...
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To clarify the implication of alkane carbon and hydrogen isotopes for the genesis and accumulation of over-mature shale gas, we carried out a comparative study on Longmaxi shale gases from eight blocks in the Upper Yangtze area. The results show that the δ¹³CCH4, δ¹³CC2H6, and δ¹³CC3H8 of Longmaxi shale gas are all positively correlated with Ro. Ac...
Citations
... Stratigraphy of southeastern Sichuan Basin showing the potential hydrocarbon regions (modified from(Cao et al., 2020)). ...
Pore pressure prediction is significant in the petroleum industry because, compared to direct measurement, it is cost-effective and it generates an extensive range of data. Mathematical correlations fail to predict pore pressure due to their failure to include lateral transfer in the reservoir, high temperature and mixed lithology and other mechanisms like aqua-thermal expansion, dehydration of clay and mineral alterations. Also, several machine learning techniques provide unsatisfactory results when predicting pore pressures due to poor selection of input data, over-fitting, slow convergence of results, and manual adjustment of model parameters like hidden layers and weights. To counteract these challenges, we employed, for the first time, group method of data handling (GMDH) technique to predict formation pore pressures from well logs data in the Nanye 1 well, southeast of the Sichuan Basin. Then, the performance of the GMDH technique was compared to other machine learning techniques, including polynomial classifier (POL) and artificial neural networks (ANNs). The GMDH technique provided results with the highest accuracy compared with the other two techniques, giving the lowest root-mean-square error (RMSE) of 0.0308 MPa. In addition, the GMDH technique provided a high coefficient of determination of 0.998. The ANN and POL gave RMSEs 0.0322 and 0.5873 MPa, respectively. Apart from the good results, the GMDH technique was able to identify data structure, direct approximate the results, automatically select the model running parameters and select the relevant input data for predicting the pore pressure, which were the challenges for other techniques. Therefore, the GMDH can be applied to predict pore pressure from the well logs data.
... Since the discovery of the first giant gas field in Puguang, Sichuan Basin, large shale gas fields have been successively explored in the Changning, Weiyuan, and Fuling shale gas fields. The Changning, Weiyuan, and Fuling shale gas blocks are located in the southern, southwestern, and near the eastern boundary of the basin, respectively (Figure 3) [56]. The shale blocks have equivalent vitrinite reflectance (EqVRo, %) values ranging from 2.4% to 3.8%, indicating that they are largely thermally over-mature and in a dry gas generation stage [57][58][59]. ...
The geological storage of CO2 is a critical technique for reducing emissions, which significantly contributes to the mitigation of the greenhouse effect. Currently, CO2 is often geologically stored in coal seams, hydrocarbon reservoirs, and saline aquifers in order to store CO2 and improve the oil and gas recovery simultaneously. Shale formations, as candidates for CO2 storage, are drawing more attention because of their rich volumes. CO2 storage through shale formations in the Sichuan Basin, China, has tremendous potential because of the readily available CO2 injection equipment, such as abandoned shale gas wells. Therefore, we review the potential of using these wells to store CO2 in this paper. Firstly, we review the status of the geological storage of CO2 and discuss the features and filed applications for the most studied storage techniques. Secondly, we investigate the formation properties, shale gas field development process, and characteristics of the abandoned wells in the Sichuan Basin. Additionally, after carefully studying the mechanism and theoretical storage capacity, we evaluate the potential of using these abandoned wells to store CO2. Lastly, recommendations are proposed based on the current technologies and government policies. We hope this paper may provide some insights into the development of geological CO2 storage using unconventional reservoirs.
The Sichuan Basin contains many overpressured formations with pore pressure coefficients as high as 2.3. However, in a Nanye 1 well found in the Southeastern (SE) Sichuan Basin, low-pore pressure coefficients as low as 0.9 have been recorded at a depth between 1544.3 and 1903.6 m, indicating the presence of underpressured formations. But the knowledge of normal and underpressured formations is not well studied in the SE Sichuan Basin. In this work, the normal to underpressured formations in the SE Sichuan Basin are identified, and their origins are discussed.
We integrated the pore pressure measurement and estimation, pore pressure coefficient and pore pressure depth plot to identify the normal to underpressured formations. We also integrated basin modelling along with the faults system to determine the origins of underpressured formations. As a result, the Upper Permian Longtan and Middle Permian Maokou Formations (1906.5–2782.9 m depth) in the Nanchuan area, were identified as normal-to-underpressured gas deposits. Also, the study identified the Lower Silurian Longmaxi and Upper Ordovician Wufeng Formations (2072–2160 m depth) in the Pengshui area, SE of the Chongqing region as normal pressured gas formations. The study discovered a decrease in temperature, rock porosity rebound and gas migration out of the formations through faults as the reasons for underpressured formations in this area. The tectonic uplift and erosion resulted in a decrease in temperature and rebound of the rock porosity, which contributed to total pore pressure drop up to 46.62 MPa. The tight overlying seal rocks and underlying rocks helped to sustain the low pore pressures in these formations.
The energy transition to renewable energy is inevitable since fossil fuels are a finite source [...]
