Integrated analysis of controls on deformation sequences of the thin-skinned fold-and-thrust belt in the eastern Sichuan Basin, China

<p>Maturity assessment of solid bitumen is significant for the construction of the thermal evolution history of Sinian carbonate reservoirs in the eastern and central Sichuan Basin because of the absence of vitrinite. Occurrence characteristics of solid bitumen in the Sichuan Basin were investigated by petrography observation. Based on Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy analyses of solid bitumen, the thermal maturity of solid bitumen in the Sinian reservoir was evaluated, and the thermal history of the Sinian reservoirs in the eastern and central Sichuan Basin was further reconstructed. The results show that solid bitumen occurred within intercrystalline pores, intercrystalline dissolution pores, karst caves, fractures, and stylolites in the eastern and central Sichuan Basin. The FTIR spectrums of solid bitumen are characterized by depleted aliphatic carbon and C=O group, and enrichment of aromatic carbon. The FTIR spectrums of solid bitumen indicate that the thermal maturity of solid bitumen in the Sichuan Basin exceeds at least 1.3%. The calculated Ro of solid bitumen in the eastern Sichuan Basin ranges from 3.8 to 4.09%, that of solid bitumen in the central Sichuan Basin ranges from 3.51 to 3.77%, and that of bitumen inclusions in the central Sichuan Basin varies from 3.54 to 3.64% inferred from Raman spectroscopy analysis. The thermal evolution history of Sinian reservoirs in the eastern and central Sichuan Basin can be divided into two heating–cooling stages. At the end of the second heating stage, that is, the Late Cretaceous, the Sinian reservoir reached the highest temperature of 250 °C in the eastern Sichuan Basin and 225 °C in the central Sichuan Basin.</p>

Maturity assessment of solid bitumen is significant for the reconstruction of the thermal evolution history and obtaining the key periods of hydrocarbon generation for the Qiongzhusi source rocks in the eastern and central Sichuan Basin because of the absence of vitrinite in the marine mudstones. Based on the Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy analyses of solid bitumen, the thermal maturity of solid bitumen in the Sinian reservoir was evaluated, which was used to calibrate the thermal maturation history modelling results of the Qiongzhusi source rocks. The FTIR spectrums of solid bitumen are characterized by depleted aliphatic carbon and CO group, and enrichment of aromatic carbon, which indicates that the vitrinite reflectance equivalent (VReq) values of solid bitumen in the Sichuan Basin exceed at least 1.3%. The calculated VReq values of solid bitumen inferred by Raman spectroscopy analysis are 3.8%–4.09% and 3.51%–3.77% in the eastern and central Sichuan Basin, respectively. The calculated VReq values of bitumen in fluorite and calcite inclusions of the central Sichuan Basin vary from 3.54% to 3.64%. The thermal evolution history of the Qiongzhusi source rocks can be divided into two heating–cooling stages. At the end of the second heating stage, which is the Late Cretaceous, the Qiongzhusi source rocks reached the highest temperature of 250 and 225°C in the eastern and central Sichuan Basin, respectively. The different burial and thermal history of the Qiongzhusi source rocks controls their key periods of hydrocarbon generation in the eastern and central Sichuan Basin. Two episodes of intense oil generation of the Qiongzhusi source rocks were determined at 440–380 Ma and 290–260 Ma, and one phase of gas generation from oil cracking was from 260 to 85 Ma in the eastern Sichuan Basin. The intense oil generation of the Qiongzhusi source rocks occurred at 240–185 Ma and the oil cracking phase was from 185 to 90 Ma in the central Sichuan Basin.

Abstract: Sichuan Basin is one of the structurally stable and gas‐rich basins, being regarded as one of China's important natural gas industry bases. Puguang and Jiannan gas fields, located in the eastern Sichuan Basin are two large fields with gas derived from Permian and Lower Triassic marine carbonate. The genesis of marine carbonate natural gas was examined using carbon isotope composition and hydrocarbon components of natural gas samples from the eastern and western Sichuan Basin, and compared with that of acidolysis gas derived from marine source rock in the eastern Sichuan Basin. It is concluded that the natural gas in the marine carbonate reservoir originated from pyrolysis of the earlier crude oil and light‐oil, and then mixed with kerogen pyrolysis gas of the Permian and Lower Silurian source rock.

Combining 121 new fission track and (U‐Th)/He ages with published thermochronologic data, we investigate the Late Cretaceous‐Cenozoic exhumation/cooling history of the eastern Tibetan Plateau, Qinling, Daba Shan, and Sichuan Basin of east central China. The Qinling orogen shows terminal southwestward foreland growth in the northern Daba Shan thrust belt at 100–90 Ma and in the southern Daba Shan fold belt at 85–70 Ma. The eastern margin of Tibetan Plateau experienced major exhumation phases at 70–40 Ma (exhumation rate 0.05–0.08 mm/yr), 25–15 Ma (≤1 mm/yr in the Pengguan Massif; ~0.2 mm/yr in the imbricated western Sichuan Basin), and since ~11–10 Ma along the Longmen Shan (~0.80 mm/yr) and the interior of the eastern Tibetan Plateau (Dadu River gorge, Min Shan; ~0.50 mm/yr). The Sichuan Basin records two basin‐wide denudation phases, likely a result of the reorganization of the upper Yangtze River drainage system. The first phase commenced at ~45 Ma and probably ended before the Miocene; >1 km of rocks were eroded from the central and eastern Sichuan Basin. The second phase commenced at ~12 Ma and denudated the central Sichuan Basin, Longmen Shan, and southern Daba Shan; more than 2 km of rocks were eroded after the lower Yangtze River had cut through the Three Gorges and captured the Sichuan Basin drainage. In contrast to the East Qinling, which was weakly effected by late Cenozoic exhumation, the West Qinling and Daba Shan have experienced rapid exhumation/cooling since ~15–13 Ma, a result of growth of the Tibetan Plateau beyond the Sichuan Basin.

Paleo-uplift forced regional sedimentary evolution: A case study of the Late Triassic in the southeastern Sichuan Basin, South China

Petrological and geochemical characteristics of the Ordovician–Silurian black shale in eastern Sichuan and western Hubei, South China: Differential sedimentary responses to tectonism and glaciation

Modulations of synoptic and climatic changes on ozone pollution and its health risks in mountain-basin areas

Influence of multiple detachments on structural vergence and evolution of the thin-skinned fold-and-thrust belt in the eastern Sichuan Basin: Insights from numerical modeling

Trillions of cubic meters of gas reserve have been found in the Sinian Dengying carbonate reservoirs with normal pressure in the central Sichuan Basin, while no industrial gas reservoir have been detected in the Sinian Dengying reservoir with normal pressure in the eastern Sichuan Basin. The pore fluid pressure of gas reservoir is usually closely related to total gas content. To investigate the pore fluid pressure evolution and its implication for gas reserve preservation in the Sinian Dengying reservoir of the central and eastern Sichuan Basin, we conducted a comprehensive analysis including fluid inclusion petrography, microthermometry and Raman spectroscopy. The timings of gas inclusions captured in the central and eastern Sichuan Basin occurred from 175 to 92 Ma and 191 to 183 Ma, respectively. The presence of two‐phase vapour‐solid bitumen inclusions with similar phase proportions in a single fluid inclusion assemblage of fluorite provides direct evidence of in situ oil cracking to gas. The widespread solid bitumen from the Sinian Dengying reservoir in the central Sichuan Basin indicates the existence of massive oil cracking, which results in the formation of overpressure in the reservoir. Pore fluid pressure evolution of the Sinian Dengying reservoir of the central Sichuan Basin experiences normal pressure stage (200–155 Ma), overpressure development stage (155–90 Ma) and overpressure release stage (90–0 Ma). The maximum pore fluid pressure and its corresponding pressure coefficient of the Sinian Dengying reservoir of the central Sichuan Basin are approximately 141.4 MPa and 1.95, respectively. The overpressure development stage reflects the processes of oil cracking and gas accumulation, and the overpressure release stage reflects the dissipation of some natural gas in the Sinian Dengying reservoir of the central Sichuan Basin. The pore fluid pressure of the Sinian Dengying reservoir in the eastern Sichuan Basin has maintained at normal pressure since 200 Ma, indicating that the gas reservoir was small during the oil cracking stage and natural gas completely leaked due to tectonic uplift.

Developmental characteristics and geological significance of the bentonite in the Upper Ordovician Wufeng – Lower Silurian Longmaxi Formation in eastern Sichuan Basin, SW China

The influence mechanism of large‐scale topography surrounding the Sichuan Basin (SCB) on its precipitation under two dominant weather patterns that typically trigger the regional hourly extreme precipitation events (RHEPEs) in summer remains unclear. Based on multi‐case simulations, this study revealed how the Tibetan Plateau (TP) and Yunnan–Guizhou Plateau (YGP) affect the precipitation over SCB under different dominant weather patterns of RHEPEs in summer through sensitivity experiments. Results show that under the weather pattern featured by a low‐level vortex (LLV) over western SCB with water vapor transport by southerly winds, the YGP and TP can increase the precipitation in western SCB by 86% and 46%, respectively. The large‐scale terrains of TP and YGP tend to enhance the thermal gradient between the plateau and basin and shape the windward slope over western SCB, accounting for increased precipitation there. Under the weather pattern featured by a LLV over central and eastern SCB with southwesterly winds, the TP can only increase the precipitation in the eastern SCB by 20% due to its limited effects on the atmospheric circulations along the windward slope there, however, the YGP can decrease the precipitation in eastern SCB by 26%, which is attributed to the anomalous northeasterly winds weakening the water vapor transport from the Bay of Bengal, leading to the strengthened stability of stratification and weakened dynamic uplifting along the windward slope in eastern SCB. Finding of this study provides a new perspective on the mechanisms of large‐scale terrain influencing the RHEPEs over SCB.

The Upper Permian Longtan Formation is the main source rock of the Lower Triassic Jialingjiang Formation in the Eastern Sichuan Basin, Southwest China. However, studies of its maturity evolution and oil generation and expulsion histories are lacking, which are not conducive to the accumulation dynamics of the Jialingjiang Formation in the Eastern Sichuan Basin. Based on the study of tectono-thermal history and geochemical parameter data of the source rock, this paper uses basin modeling technology to simulate the maturity evolution and hydrocarbon generation and expulsion histories of the Upper Permian Longtan Formation in the Eastern Sichuan Basin. The results show that the Longtan Formation source rock in the Eastern Sichuan Basin entered the oil generation threshold at the middle stage of the Early Jurassic and reached the high-maturity stage in the north and central regions at the late stage of the Early Jurassic, and the maturity did not increase after the late stage of the Middle Jurassic. The source rock had the characteristic of "one-stage oil generation and one-stage oil expulsion"; the corresponding period of high oil expulsion was 182-174 Ma (the late stage of the Early Jurassic), which was later than the formation time of the trap of the Jialingjiang Formation, possibly providing oil sources for the paleo-oil reservoirs of the Jialingjiang Formation. The results are of great significance to the gas accumulation process and exploration decision-making in the Eastern Sichuan Basin.

There is great controversy regarding the origin and source of natural gas in the Lower Triassic Feixianguan Formation in the Eastern Sichuan Basin. This seriously restricts the study of natural gas dynamics in the Feixianguan Formation and thus hampers natural gas exploration in the region, so further study is urgently required. Using experimental tests of natural gas composition, stable isotopes, and noble gas isotopes with gas chromatography (GC) and mass spectrometry (MS) studies of source rock and reservoir asphalt saturated hydrocarbons, the natural gas geochemical characteristics, the genetic identification and a gas-source comparison of the Feixianguan Formation were studied. Then, constrained by the thermal history, the histories of gas generation and expulsion were restored by basin simulation technology. Finally, a gas accumulation model was established for the Feixianguan Formation. The results showed that (1) the H2S-rich and H2S-poor gas reservoirs of the Feixianguan Formation are distributed on the east and west sides of the Kaijiang-Liangping trough in the Eastern Sichuan Basin, respectively. The carbon and hydrogen isotope compositions of the natural gas in the gas reservoirs are generally heavy and have typical characteristics of high-maturity dry gas reservoirs. (2) The natural gas of the Feixianguan Formation is organic thermogenic gas, which is mainly oil-type gas generated by the secondary cracking of crude oil. The gas-generating parent material is mainly type II kerogen. (3) The natural gas of the Feixianguan Formation in the Eastern Sichuan Basin was mainly generated by argillaceous source rocks of the Upper Permian Longtan Formation. (4) Natural gas accumulation occurred as follows: the paleo-structure heights were filled with crude oil in the Early Jurassic, and paleo-oil reservoirs were formed in the Feixianguan Formation; during the Middle-Late Jurassic, the paleo-oil reservoirs were cracked when the reservoir temperatures rose above 160 °C, and paleo-gas reservoirs were formed. Since the end of the Late Jurassic, the paleo-gas reservoirs have been adjusted and reformed to form the present-day natural gas reservoirs. These results provide a basis for studying natural gas accumulation dynamics of the Feixianguan Formation in the Eastern Sichuan Basin.

Accumulation conditions and exploration directions of natural gas in deep subsalt Sinian-Cambrian System in the eastern Sichuan Basin, SW China

Main factors for large accumulations of natural gas in the marine carbonate strata of the Eastern Sichuan Basin, China