Paleo-pressure evolution and its origin in the Pinghu slope belt of the Xihu Depression, East China Sea Basin

Su, Ao; Chen, Honghan; Lei, Mingzhu; Li, Qian; Wang, Cunwu

doi:10.1016/j.marpetgeo.2019.05.017

Cited by 37 publications

(24 citation statements)

References 35 publications

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“…The paleo-overpressure in the Lower Shihezi Fm. occurred in the Middle Jurassic, whose formation time was consistent with the gas generation, suggesting that the gas generating by III-type kerogen probably played a significant role on the formation of paleo-overpressure [58]. The highest paleo-temperature of the formations in the study area was lower than the oil-cracking start temperature of 160 • C (Figure 10) [59], indicating that the cracking of oil contributes little to the overpressure generation.…”

Section: Origin Of the Abnormal Pressurementioning

confidence: 62%

Reservoir Densification, Pressure Evolution, and Natural Gas Accumulation in the Upper Paleozoic Tight Sandstones in the North Ordos Basin, China

Wang

Shi

et al. 2022

Energies

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The vague understanding of the coupling relationship among natural gas charging, reservoir densification, and pressure evolution restricted the tight gas exploration in the Lower Shihezi Formation of the Hangjinqi area, north Ordos Basin. In this study, the quantitative porosity evolution model, the pressure evolution process, and the natural gas charging history of tight sandstone reservoirs were constructed by integrated investigation of the reservoir property, the thin section, SEM and cathode luminescence observations, the fluid inclusion analysis and the 1D basin modeling. The results show that the compaction and cementation reduced the primary porosity by 21.79% and 12.41%, respectively. The densification of the reservoir occurred at circa 230 Ma, which was before the natural gas charging time from 192 to 132 Ma. The paleo-overpressure within the tight reservoirs occurred since the Middle Jurassic with the pressure coefficients between 1.1 and 1.55. The continuous uplifting since the Late Cretaceous resulted in the under- and normal-pressure of the Lower Shihezi Formation with the pressure coefficients ranging from 0.67 to 1.05. The results indicate that the densification of the reservoirs was conducive to the formation of paleo-pressure produced by gas generating. The gas predominantly migrated vertically, driven by gas expansion force rather than buoyance and displaced the pore water in the reservoirs near source rocks.

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Section: Origin Of the Abnormal Pressurementioning

confidence: 62%

Reservoir Densification, Pressure Evolution, and Natural Gas Accumulation in the Upper Paleozoic Tight Sandstones in the North Ordos Basin, China

Wang

Shi

et al. 2022

Energies

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“…In this paper, the pressure coefficient method was used to depict the magnitude of abnormal pressure. The pressure coefficient is defined as the ratio of the pore-fluid pressure to the hydrostatic pressure at the same depth (Su, Chen, He, Lei, & Liu, 2017;Su, Chen, Ping, Lei, & Wang, 2019).…”

Section: Samples and Methodsmentioning

confidence: 99%

Hydrocarbon gas leakage from high‐pressure system in the Yanan Sag, Qiongdongnan Basin, South China Sea

Chen

Yang

et al. 2021

Geological Journal

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Despite high pressure being ubiquitous in the Yanan Sag of the Qiongdongnan Basin, South China Sea, its potential effect on gas migration-accumulation remains unclear.In this study, a series of geochemical indicators combined with the origin of high pressure were used to elucidate the cause of gas accumulation failure in the overpressured YC19-1 structure. Drill-stem tests, mud weights, and well-loggings reveal two vertical overpressure systems. Pore pressure in the deep Lingshui and Yacheng formations almost reaches a lithostatic magnitude, which was interpreted as a result of gas generation and disequilibrium compaction triggered by the Pliocene-Quaternary rapid subsidence. A thermal anomaly above the high-pressure system was evidenced by high homogenization temperature (Th) of fluid inclusion, abnormally high vitrinite reflectance, and a rapid transformation from kaolinite to illite. The high thermal field likely resulted from a cross-stratal fluid migration from the deep high-pressure system. Both methane-bearing inclusions in sandstones and abnormal Rock-Eval data of mudstones above the high-pressure surface suggest an influx of external hydrocarbons. Based on primary aqueous inclusion Th and salinity, carbon and oxygen isotope compositions, and petrographic observations, widespread silica and carbonate cements near the overpressure surface were interpreted to be derived from extraformational materials carried by deep-seated basinal fluids. Fluid inclusion Th coupled with burial model suggests that the gas leakage took place at circa 1.6 Ma, coinciding well with the stages of both gas generation and overpressure.These observations suggest an upward leakage of gas-bearing fluids induced by pressure release, thus leading to the existence of only non-commercial gas-bearing aquifers in the overpressured YC19-1 structure.

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“…The most recent drilling results conducted in Xihu Sag indicate that coal, carbonaceous mudstone and mudstone in Pinghu Formation are essential source rocks [33,34], and the sand-body of the Pinghu Formation is theoretically rich in coalbed methane and shale gas. The current investigation mostly focuses on hydrocarbon generation [35,36], paleo-pressure evolution [37], geochemical characteristics and the sedimentary control of coal-bearing source rocks from the Pinghu Formation [38].…”

Section: Introductionmentioning

confidence: 99%

Microscopic Characteristics and Formation Mechanism of Effective Reservoirs in the Xihu Depression, China: The Important Role of the Poikilotopic Calcite Cements in Tide-Dominated Delta Systems

Zhang

Wu²,

Liu

et al. 2022

Minerals

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The Xihu depression is an offshore sag located on the East China Sea Shelf Basin, which is currently one of the major oil and gas basins along the coast of China. In this study, an integrated approach using thin sections, scanning electron microscopy (SEM), X-ray diffraction (XRD), cathodoluminescence (CL), high-resolution 3D CT core scanning and stable isotope analysis was applied to examine the diagenetic evolution and investigate the microscopic characteristics and formation mechanisms associated with effective reservoirs. Four types were distinguished: upper conventional reservoirs (UC reservoirs), lower conventional reservoirs (LC reservoirs), “bottom calcium” low-permeability reservoirs (“bottom calcium” reservoirs) and “MI clay” low-permeability reservoirs (“MI clay” reservoirs). Poikilotopic calcite cements play an important role in the diagenetic alterations and reservoir quality evolution, precipitating during early eogenesis, provided a framework that retards the adverse impacts of UC reservoirs by compaction. Conversely, in LC reservoirs, with limited poikilotopic calcite, secondary porosity is mostly due to the dissolution of feldspar or unstable rock fragments. UC reservoirs normally develop in the middle of tidal channels and in subaqueous distributary channels, with the base of the sand-body being extensively cemented by carbonate cements, such as late calcite, Fe-calcite and dolomite, which formed the “bottom calcium” reservoir. Combined evidence from petrographic and geochemical analyses suggests that calcite precipitates from diagenetic fluids of mixed marine and meteoric waters, with additional external sources from calcareous siltstones and bioclasts. The carbon sources of calcite mostly originate from the dissolution of carbonates clacts or bioclasts within sandstone beds or adjacent silty mudstones, while dolomite cements have an isotopic composition that is more comparable to the generation of biogenic methane. This study demonstrates how poikilotopic calcite, developed in tide-dominated delta systems, affects the vertical heterogeneity. The results can be used to improve the reservoir evolution model of tide-dominated delta systems and provide a basic understanding for researchers conducting reservoir studies of similar sedimentary systems. Our results can act as a geological basis for further oil and gas exploration.

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Paleo-pressure evolution and its origin in the Pinghu slope belt of the Xihu Depression, East China Sea Basin

Cited by 37 publications

References 35 publications

Reservoir Densification, Pressure Evolution, and Natural Gas Accumulation in the Upper Paleozoic Tight Sandstones in the North Ordos Basin, China

Reservoir Densification, Pressure Evolution, and Natural Gas Accumulation in the Upper Paleozoic Tight Sandstones in the North Ordos Basin, China

Hydrocarbon gas leakage from high‐pressure system in the Yanan Sag, Qiongdongnan Basin, South China Sea

Microscopic Characteristics and Formation Mechanism of Effective Reservoirs in the Xihu Depression, China: The Important Role of the Poikilotopic Calcite Cements in Tide-Dominated Delta Systems

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