Prediction of Diagenetic Facies using Well Logs: Evidences from Upper Triassic Yanchang Formation Chang 8 Sandstones in Jiyuan Region, Ordos Basin, China

Lai, Jin; Wang, Guiwen; Chai, Yee Ho; Ye, Ran

doi:10.2516/ogst/2014060

Cited by 28 publications

(27 citation statements)

References 46 publications

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“…The siltstones with parallel bedding are mainly deposited in the distal bar microfacies. In contrast, the horizontal bedding can be observed in the dark mudstones, representing a low water energy environment [6].…”

Section: Geologic Settingmentioning

confidence: 95%

“…Sections from Chang 10 to Chang 8 represent a transgression sequence deposited at shallow water level, whereas those from Chang 6 to Chang 2 are regression sequences deposited at lake fading stage [5], and Chang 1 oil layer was deposited during the peneplain period [17]. The lithology of Chang 8 sandstones is mainly composed of grey fine to medium-grained sandstones and siltstones interbedded with dark mudstones [6]. Parallel bedding and wedge-shaped cross bedding can be observed in the fineto medium-grained sandstones, and these clean sandstones are formed in a relatively high water energy environment, for example, the underwater distributary channel and mouth bar of a delta front [27,28,38].…”

Section: Geologic Settingmentioning

confidence: 99%

“…The Chang 8 sandstones are classified as lithic arkose, feldspathic litharenites, and litharenites according to Folk (1980) [6]. Detrital mineralogy is dominated by quartz (mostly monocrystalline), and the dominant feldspars are Ca-feldspars and Na-feldspars.…”

Section: Reservoir Characteristicsmentioning

confidence: 99%

“…The Chang 8 (eighth member of Yanchang Formation) sandstones, which consist of braided-delta subaqueous distributary channels, are important reservoir units [4]. However, the Chang 8 sandstones, which had experienced various types and degrees of diagenesis such as compaction and cementation by carbonates and clays, are typical tight reservoirs with low porosity, low permeability, and strong microscopic heterogeneity (Zeng and Li 2009; [4,6,7]). …”

Section: Introductionmentioning

confidence: 99%

“…Carbonate cement is the predominant diagenetic minerals in Chang 8 sandstones [6]. Mineralogical, petrographic, and geochemical analyses combined with ECS log data were used to describe the petrography and geochemistry of the carbonate cement and associated features in Chang 8 sandstones, with the special aim to unravel the origins, paragenesis, and distribution patterns of carbonate cement.…”

Section: Introductionmentioning

confidence: 99%

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Origin and Distribution of Carbonate Cement in Tight Sandstones: The Upper Triassic Yanchang Formation Chang 8 Oil Layer in West Ordos Basin, China

et al. 2017

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Two generations of carbonate cement as Type I (microcrystalline calcite and dolomite) and Type II (mainly Fe-calcite and Fedolomite) are recognized in Chang 8 sandstones, Ordos basin. Carbonate cement in Chang 8 sandstones is closely related to the dissolved carbon from thermal maturation of organic matters. Carbonate cement in the loosely packed framework grains precipitated shortly after deposition, and late-stage ferroan calcite and ferroan dolomite formed with progressive burial. The early diagenetic carbonate cement is partially to completely replaced by late-stage ferroan calcite and ferroan dolomite. Carbonate cement is much more commonly observed in sand bodies adjacent to Chang 7 source rocks. With increasing distance from the Chang 7 oil layers, the carbonate cement content gradually decreases. However, some tight carbonate cemented zones also occur at the sandstone-mudstone interfaces. Dissolution of Ca-feldspars by organic acids-rich fluids, together with clay mineral transformations such as illitization of smectite, would provide Ca 2+ and Mg 2+ ions for carbonate cementation. Organic acids and CO 2 rich fluids would charge into the reservoirs with the hydrocarbons, and when the CO 2 and acids were buffered by the framework grain dissolution, carbonate cement would precipitate with a decrease in CO 2 concentration.

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Section: Geologic Settingmentioning

confidence: 95%

Section: Geologic Settingmentioning

confidence: 99%

Section: Reservoir Characteristicsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Origin and Distribution of Carbonate Cement in Tight Sandstones: The Upper Triassic Yanchang Formation Chang 8 Oil Layer in West Ordos Basin, China

et al. 2017

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Diagenesis and reservoir quality in tight gas sandstones: The fourth member of the Upper Triassic Xujiahe Formation, Central Sichuan Basin, Southwest China

Lai

Wang

Cai³

et al. 2017

Geological Journal

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Mineralogical, petrographic, and geochemical analyses were performed to investigate the sandstone composition and texture, pore system, and diagenetic minerals of Upper Triassic sandstones in the Central Sichuan Basin, Southwest China. The results show that authigenic quartz, clay minerals, and carbonates are the main pore‐filling constituents. The pore systems consist of intergranular porosity, secondary porosity, microporosity, and microfractures. Loss of depositional porosity is greater due to compaction than to cementation. Eodiagenesis includes mechanical compaction, precipitation of early calcite cements, kaolinite, and smectite, and leaching of feldspars by meteoric water. Mesodiagenesis consists of compaction, framework grain dissolution, and subsequent precipitation of illite, quartz, and late carbonate cements. Six lithofacies were identified on the basis of petrographic analyses, namely, (a) argillaceous sandstones; (b) poorly sorted sandstones; (c) quartz‐cemented sandstones; (d) carbonate‐cemented sandstones; (e) clay‐mineral‐cemented sandstones, and (f) clean sandstones with abundant secondary porosity. The best reservoir‐quality rocks have high percentages of detrital quartz but low percentages of matrix, quartz, and carbonate cement. Differences in textural and compositional attributes of various lithofacies significantly affect porosity‐depth trends. The diagenetic evolution pathways and reservoir‐quality prediction models of various lithofacies are reconstructed by integrated petrographic data. This work provides insights into describing the different lithofacies by petrographic analysis and helps to investigate how detrital composition and texture influence the diagenesis and reservoir quality evolution in tight gas sandstones.

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Prediction of lithology in lacustrine carbonates using well logs: The Cretaceous Barra Velha Formation in Santos Basin, offshore Brazil

Wang¹,

Zhang

Fan³

et al. 2023

Geological Journal

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Abundant hydrocarbons have been produced from the pre‐salt lacustrine carbonates of the Cretaceous Barra Velha Formation in the Santos Basin of offshore Brazil. The highly heterogeneous lithology and pore systems make it difficult to predict the reservoir quality via petrophysical well logs. Core description, computed tomography (CT) scanning, thin sections and wireline well logs are utilized to characterize the lithology, pore spaces are reservoir quality of the Cretaceous Barra Velha Formation pre‐salt lacustrine carbonates in the Santos Basin. The results show that the lithology mainly includes shrubstone, grainstone, laminated micrite and massive micrite. The pore systems are dominated by secondary pores, such as intergranular pores, dissolution pores and intercrystalline pores as well as modified primary pores. Geological well logs (conventional well logs, electrical and sonic image logs and nuclear magnetic resonance [NMR] logs) are integrated to build the predictable models of the carbonate reservoirs. The shrubstone, which is dominated by intergranular pores, has the highest reservoir quality, which can be derived from NMR logs. Grainstone contains both primary intergranular pores and abundant secondary dissolution pores. The laminated and massive micrite contain only micropores and therefore have the lowest reservoir quality. Lastly, conventional well logs integrated with electrical and sonic image logs are utilized to predict the distribution of lithology and reservoir quality in single wells, and the results are testified by the NMR log data. The shrubstone and grainstone are future exploration targets of the Cretaceous Barra Velha Formation in the Santos Basin. The results are hoped to give insights into the petrophysical behaviours of various lithologies, and provide theoretical and technical guidance for reservoir evaluation and prediction.

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Prediction of Diagenetic Facies using Well Logs: Evidences from Upper Triassic Yanchang Formation Chang 8 Sandstones in Jiyuan Region, Ordos Basin, China

Cited by 28 publications

References 46 publications

Origin and Distribution of Carbonate Cement in Tight Sandstones: The Upper Triassic Yanchang Formation Chang 8 Oil Layer in West Ordos Basin, China

Origin and Distribution of Carbonate Cement in Tight Sandstones: The Upper Triassic Yanchang Formation Chang 8 Oil Layer in West Ordos Basin, China

Diagenesis and reservoir quality in tight gas sandstones: The fourth member of the Upper Triassic Xujiahe Formation, Central Sichuan Basin, Southwest China

Prediction of lithology in lacustrine carbonates using well logs: The Cretaceous Barra Velha Formation in Santos Basin, offshore Brazil

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