Characteristics and controlling factors of dolomite karst reservoirs of the Sinian Dengying Formation, central Sichuan Basin, southwestern China

Zhou, Yong; Yang, Fengli; Ji, Youliang; Zhou, Xiaofeng; Zhang, Chenhe

doi:10.1016/j.precamres.2020.105708

Cited by 48 publications

(56 citation statements)

References 26 publications

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“…The Z 2 dn 4 in the GMA is mainly modified by eogenetic karstification prior to a complete deep burial stage. The Z 2 dn 4 in the GMA had never been uplifted to subaerial conditions to undergo epigenetic karstification following the deep burial stage, and episode Ⅱ of the Tongwan Movement came up immediately followed by a shallow burial stage (Zhou et al, 2020). Large-scale exposure of the Z 2 dn 4 occurred only in the eogenetic stage.…”

Section: Paleogeomorphology and Karstificationmentioning

confidence: 99%

“…The Sinian Z 2 dn of the Gaoshiti-Moxi area in the Central Sichuan Basin has been discovered in recent years to be a giant gas field, which was a major breakthrough (Liu et al, 2015;Luo et al, 2017;Xie et al, 2019;Zhou et al, 2020). The proven total reserves of natural gas were as high as 1 × 10 12 m 3 , and the cumulative gas production had reached 4.19 × 10 10 m 3 by the end of 2018 (Li et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

“…The interface between the Z 2 dn 4 and the overlying Maidiping Formation (Є 1 m) or Qiongzhusi Formation (Є 1 q) is a disconformity. It is widely understood that the disconformity is a consequence of meteoric freshwater leaching and eroding after the regional tectonic uplift of the Tongwan Movement episode II (Luo et al, 2015;Yang et al, 2016;Wei et al, 2016;Zhou et al, 2016;Luo et al, 2017;Hao et al, 2017), though a debate co-exists on which karstification type (eogenetic, hypogenetic, or epigenetic) dominates the formation of numerous karst products in the Z 2 dn 4 (Tang et al, 2013;Luo et al, 2015;Zhou et al, 2016;Jin et al, 2017;Che et al, 2019;Li et al, 2019;Jin et al, 2020;Zhou et al, 2020). Karstification is regarded as the vital diagenetic alteration in the formation of Z 2 dn 4 reservoirs in the Gaoshiti-Moxi area (Luo et al, 2017;Shan et al, 2017;Duan et al, 2019;Zhou et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

“…It is widely understood that the disconformity is a consequence of meteoric freshwater leaching and eroding after the regional tectonic uplift of the Tongwan Movement episode II (Luo et al, 2015;Yang et al, 2016;Wei et al, 2016;Zhou et al, 2016;Luo et al, 2017;Hao et al, 2017), though a debate co-exists on which karstification type (eogenetic, hypogenetic, or epigenetic) dominates the formation of numerous karst products in the Z 2 dn 4 (Tang et al, 2013;Luo et al, 2015;Zhou et al, 2016;Jin et al, 2017;Che et al, 2019;Li et al, 2019;Jin et al, 2020;Zhou et al, 2020). Karstification is regarded as the vital diagenetic alteration in the formation of Z 2 dn 4 reservoirs in the Gaoshiti-Moxi area (Luo et al, 2017;Shan et al, 2017;Duan et al, 2019;Zhou et al, 2020). However, it is difficult to quantitatively and precisely evaluate and predict paleokarst reservoirs via a single approach such as through paleogeomorphological reconstruction, paleokarst development characterization, or some other petrophysical parameters.…”

Section: Introductionmentioning

confidence: 99%

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Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China

Zhou

Wang²,

Yang³

et al. 2022

Front. Earth Sci.

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The evaluation of reservoirs is of great importance in exploration practices, and reservoir distribution is dependent on multiple geological factors. The carbonate platform of the fourth member (Z2dn4) of the Dengying Formation (Z2dn) in the Gaoshiti-Moxi area (GMA) was uplifted above sea level during episode II of the Tongwan movement and underwent prolonged karstification by meteoric freshwater in the terminal Sinian, leading to a strong heterogeneity in reservoirs. Paleogeomorphology reflects hydraulic gradients that can affect the intensities of surface karstification and may be approximated by terrain slope gradients. Karst products (especially solution vugs and caverns) exist prevailingly in the Z2dn4; their development mirrors the extents of internal dissolution. Based on paleogeomorphological reconstruction using the elevation method, the slope angles of single boreholes were calculated through the digital elevation model (DEM). In accordance with single-borewell Fullbore Formation MicroImager (FMI) logging data, four electrofacies (host rock, vug, fracture, and cave) were identified in boreholes possessing FMI data. The identified electrofacies were matched with corresponding conventional logging curves to obtain the training data. A model generalized for other boreholes without FMI data was established with the random forest algorithm and the thicknesses of the four electrofacies in each borehole were determined to characterize the extent of karstification. Slope gradients and electrofacies thicknesses, together with multiple physical parameters of reservoirs in boreholes, were utilized for factor analysis. Four factors were obtained and fused into one comprehensive score based on their ratios of variance proportions. The favorability of reservoirs was described by the comprehensive scores of each borehole. These analyses showed that the most advantageous reservoirs are distributed in the vicinity of the platform margin in the west of the GMA, where they enjoy several benefits. Deposition of porous mound-shoal complexes occurs predominantly in the platform margin where large-scale caves are more developed in the mixing karst zone of seawater and freshwater. Meanwhile, the transmeridional lateral migration of hydrocarbons from the regional hydrocarbon-generating center abutting the west of the GMA contributes to earlier entrapment and accumulation in the mound-shoal complexes in the platform margin.

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Section: Paleogeomorphology and Karstificationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China

Zhou

Wang²,

Yang³

et al. 2022

Front. Earth Sci.

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“…Based on the lithology and algae content, the Z 2 dn Formation can be divided into four members from the bottom to the top, namely the first member of Z 2 dn Formation (Z 2 dn 1 ), the second member of Z 2 dn Formation (Z 2 dn 2 ), the third member of Z 2 dn Formation (Z 2 dn 3 ), and the fourth member of Z 2 dn Formation (Z 2 dn 4 ), respectively. The Z 2 dn 2 and Z 2 dn 4 are mainly composed of microbial dolomite and granular dolomite with a high algae content, while the Z 2 dn 1 consists of poor algal dolomite and the Z 2 dn 3 is dominated by mudstone (Zhou et al, 2020). The Z 2 dn 2 and Z 2 dn 4 dolomites in the Sichuan Basin constitute high‐quality reservoirs in which natural gas and solid bitumen were found (Liu et al, 2010; Liu et al, 2011).…”

Section: Geological Settingmentioning

confidence: 99%

Maturity assessment of solid bitumen in the Sinian carbonate reservoirs of the eastern and central Sichuan Basin, China: Application for hydrocarbon generation modelling

Chen

Guo

et al. 2022

Geological Journal

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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 (VR eq ) values of solid bitumen in the Sichuan Basin exceed at least 1.3%. The calculated VR eq 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 VR eq 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.

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Hydrothermal silicification in Ediacaran Dengying Formation fourth member deep dolomite reservoir, Central Sichuan Basin, China: Implications for reservoir quality

Wang

Jiang

Yang³

et al. 2023

Geological Journal

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The Ediacaran Dengying Formation fourth member in Central Sichuan Basin is the deep dolomite gas reservoir with the largest natural gas reserves in China, providing an excellent example for understanding the effect of hydrothermal silicification on deep dolomite reservoir quality. By integrating petrology, geochemistry and physical property measurement, this study aims to reveal the genesis of different quartz phase and their corresponding diagenetic events, and to discuss the temporal relationship of diagenetic events and their effects on the quality of deep dolomite reservoir in Dengying fourth member. Three phases of quartz cement are identified in Ediacaran Dengying Formation deep dolomite reservoirs of Central Sichuan Basin as follows: (1) first‐stage quartz filled in primary reservoir spaces, (2) second‐stage quartz mainly filled in secondary reservoir spaces, and (3) third‐stage quartz filled in secondary reservoir spaces with Mississippi Valley‐Type minerals. By analysing petrographic and temporal relationships between these fabrics, it is suggested that the first‐stage quartz precipitated during the syndiagenetic stage, the second‐stage quartz precipitated during middle diagenetic stage, and the third‐stage quartz precipitated during middle diagenetic stage as well. Silicification during syndiagenetic stage is characterized by replacement of cryptocrystalline quartz and cementation of first‐stage quartz within matrix dolomite (MD). After syndiagenetic silicification, the mineral composition of the MD changed from magnesium calcium carbonate to silica, and the later constructive diagenetic alterations were almost ineffective. The distribution of syndiagenetic silicification during syndiagenetic stage gradually decreases from the platform‐interior to the platform‐margin. The second‐stage and third‐stage quartz cements, derived from two‐stage hydrothermal silicification in the middle stage, are both destructive for reservoir preservation. This study, combined with coeval vapour–liquid inclusions Th data and thermal‐burial models, constrains the time of the second‐stage quartz to ca. 403–408 Ma, suggesting an hydrothermal silicification related to the Caledonian movement. The time of the third‐stage quartz cement is constrained to ca. 259.4 Ma, associated with Late Permian eruption of Emeishan flood basalts.

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Characteristics and controlling factors of dolomite karst reservoirs of the Sinian Dengying Formation, central Sichuan Basin, southwestern China

Cited by 48 publications

References 26 publications

Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China

Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China

Maturity assessment of solid bitumen in the Sinian carbonate reservoirs of the eastern and central Sichuan Basin, China: Application for hydrocarbon generation modelling

Hydrothermal silicification in Ediacaran Dengying Formation fourth member deep dolomite reservoir, Central Sichuan Basin, China: Implications for reservoir quality

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