scholarly journals Diagenetic Fluid and Its Impact on Sandstone Reservoirs in the Southern Boxing Sag, Dongying Depression, Bohai Bay Basin, China

Geofluids ◽  
2022 ◽  
Vol 2022 ◽  
pp. 1-25
Author(s):  
Zhenhuan Shen ◽  
Zhuang Ruan ◽  
Bingsong Yu ◽  
Shujun Han ◽  
Chenyang Bai ◽  
...  
Keyword(s):  
Clay Minerals ◽  
Late Stage ◽  
Homogenization Temperature ◽  
Mineral Dissolution ◽  
Bohai Bay ◽  
Carbonate Cements ◽  
Dongying Depression ◽  
Carbonate Cementation ◽  
Diagenetic Fluids ◽  
Sandstone Reservoirs

Diagenesis typically exerts a crucial impact on the formation of high-quality sandstone reservoirs in the Eocene Shahejie Formation, Dongying Depression. To better understand the formation process of petrophysical properties, this research conducts petrographic and geochemical analyses to investigate the nature of diagenetic fluids. Petrographic observations suggest that the dominant cements are carbonate, authigenic quartz, and clay minerals, accompanied with the dissolution of feldspar and calcite. The homogenization temperature of aqueous inclusions in quartz overgrowth usually exceeds 90°C corresponding to the maturity of organic matter. Quartz overgrowths contain higher amounts of CaO and Al2O3 than detrital quartz. This indicates that the siliceous fluid mainly originates from the dissolution of feldspar. Moreover, the conversion of clay minerals also provides trace amounts of silica into pore water during the burial process. Carbonate cements consist of early-stage calcite as well as late-stage Fe-calcite and ankerite. Calcite with relatively higher MnO proportions shows yellow luminescence and dissolution signs. Fe-calcite and ankerite cements have a higher homogenization temperature than that of quartz overgrowth and mainly concentrate in FeO and MgO as well as contain a small amount of Na+, K+, and Sr2+. The rare earth element (REE) pattern of bulk mudstone and carbonate cements as well as C–O isotopic evidences indicate that the diagenetic fluids of carbonate cementation are primarily controlled by the adjacent mudstone, whereas mineral dissolution and altered clay minerals in sandstone provide additional cations for the local reprecipitation of late-stage carbonate. Therefore, diagenetic fluids within sandstone reservoirs are typically subject to alkaline–acid–alkaline conditions and are influenced by internal sources in a closed system. Compaction significantly reduces the pore space of sandstone reservoirs in the Boxing Sag. Carbonate cementation further increases the complexity of pore structure and obeys the principle of mass balance.

Carbonate cements in Eocene turbidite sandstones, Dongying depression, Bohai Bay Basin: Origin, distribution, and effect on reservoir properties

AAPG Bulletin ◽  
2022 ◽  
Vol 106 (1) ◽  
pp. 209-240
Author(s):  
Guoqiang Luan ◽  
Karem Azmy ◽  
Chunmei Dong ◽  
Chengyan Lin ◽  
Lihua Ren ◽  
...  
Keyword(s):  
Bohai Bay ◽  
Bohai Bay Basin ◽  
Reservoir Properties ◽  
Carbonate Cements ◽  
Dongying Depression

Origin of multiple-phase carbonate cements in the sandstones of the third member of the Shahejie Formation in the Niuzhuang Sag, Bohai Bay Basin

2020 ◽  
Vol 8 (3) ◽  
pp. SM83-SM101
Author(s):  
Yongwang Zhang ◽  
Feng Li
Keyword(s):  
Early Phase ◽  
Late Phase ◽  
Bohai Bay ◽  
Bohai Bay Basin ◽  
Rock Interaction ◽  
The Third ◽  
Carbonate Cements ◽  
Shahejie Formation ◽  
Sandstone Reservoirs ◽  
Ferroan Dolomite

Authigenic carbonate cement is one of the most abundant diagenetic minerals in sandstone reservoirs. Determining its origin and distribution may provide useful information for understanding the sandstone reservoir quality. In this study, we report results from a suite of analytical techniques to investigate the origin and evolution of carbonate cements in the third member of the Shahejie Formation in the Bohai Bay Basin. Our data indicate that the carbonate cements mainly occur in three phases: the early-phase calcite, late-phase ferroan calcite, and late-phase ferroan dolomite and/or ankerite. The early-phase calcites show depleted δ18O of the early-phase calcite (−11.8% to −7.8%), suggesting an 18O-depleted fluid origin from the mixing between lacustrine and meteoric waters. They were precipitated earlier than the quartz overgrowth at 40°C–63°C based on the oxygen isotope. The late-phase calcites were precipitated at 70°C–115°C, and they originated from water-rock interaction modified pore water at the same time or later than feldspar leaching. They show a lower average δ13C value (1.27%) than the early-phase calcite (1.65%), indicating that the interbedded shales within the sandstones most likely provided the required components for the precipitation of the late-phase calcite. Also, some Fe2+ was released during the organic acid release and then precipitated the late-phase ferroan calcites. The late-phase ferroan dolomite and/or ankerite were precipitated at 90°C–137°C in a deep diagenetic condition. They show depleted δ13C values (mean [Formula: see text]), and the carbons were mainly sourced from the thermal decarboxylation of organic matter and lacustrine carbonate. The early-phase calcite inhibits compaction while filling the pores, and the dissolution of ferroan calcite cements was the main reason for the development of secondary pores in the sandstone reservoirs. The late-phase ankerite reduces the reservoir porosity.

scholarly journals Chemical compaction of deep buried mudstone and its influence on pressure prediction

2020 ◽  
Vol 600 (1) ◽  
pp. 012012
Author(s):  
Li Chao ◽  
Luo Xiaorong ◽  
Zhang Likuan ◽  
Lei Yuhong ◽  
Chen Ming ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Clay Minerals ◽  
Eastern China ◽  
Bohai Bay ◽  
Dongying Depression ◽  
Pore Pressure Prediction ◽  
Shahejie Formation ◽  
Vertical Effective Stress ◽  
The Impact ◽  
Transformation Of Clay Minerals

Abstract The chemical compaction of mudstones which is dominated by the transformation of clay minerals leads to significant changes in the mineral composition and microstructure of mudstone during process of deep burial. In particular, the transformation of smectite to illite in mudstones results in noticeable impact on the pore pressure formation and the overpressure logging responses. At present, the study about the pressurization mechanism of chemical compaction and the impact on overpressure logging responses is really weak, which made it hard to pore pressure identification and pressure prediction for deep buried formations. Taking the Paleogene Shahejie Formation in the Dongying depression of the Bohai Bay Basin in eastern China as typical case, this paper analyses the characteristics of clay mineral transformation of the Shahejie Formation in the Dongying depression, the logging responses of overpressures, and the influence of chemical compaction on the prediction of pore pressure. The results showed that the chemical compaction of mudstones changes the relationship between the petrophysical properties of mudstone and vertical effective stress and the logging responses of overpressure. The typical characteristic of chemical compaction manifested as density increase continuous with the depth. The normal compaction trends of the different compaction stages are the basis for overpressure mechanisms identification and pore pressure prediction. The depth of the rapid transformation of clay minerals has a good consistency with the top of overpressure zone (2000–2800 m) in Dongying depression, which indicates that the overpressure and its logging responses may be related to the chemical compaction of mudstones. The measured pressure in intervals deeper than 3000 m is closer to the predicted pressure based on the normal compaction trend of chemical compaction.

scholarly journals Origin of carbonate cements in deep sandstone reservoirs and its significance for hydrocarbon indication: A case of Shahejie Formation in Dongying Sag

2021 ◽  
Vol 13 (1) ◽  
pp. 1375-1394
Author(s):  
Tianjiao Zhang ◽  
Yuelin Feng ◽  
Xinmin Ge ◽  
Wei Meng ◽  
Hongwei Han ◽  
...  
Keyword(s):  
Late Stage ◽  
Early Stage ◽  
Middle Stage ◽  
Dongying Sag ◽  
Carbonate Cements ◽  
Material Sources ◽  
Lacustrine Carbonate ◽  
Sandstone Reservoirs ◽  
Late Diagenesis ◽  
Guantao Formation

Abstract Carbonate cements are primary cement types formed in deep sandstone reservoirs of Dongying Sag. We have proposed three stages of carbonate cements with different origin and material sources: carbonate cements in early stage are rim-shaped high-Mg calcite, which is the product of quasi-contemporaneous period; and calcite filled with primary pores without obvious compaction and diagenetic transformation is mudstone compaction during the drainage process. Carbonate cements in middle stage are calcite and dolomite filled with feldspar secondary dissolved pores. The rich Ca2+, Mg2+, and CO 3 2 − {\text{CO}}_{3}^{2-} in overpressure fluid enter the reservoir and mix with Ca2+ in the original formation water. Carbonate cements in late stage are ferrocalcite and ankerite that filled the dissolution pores of early- and middle-stage carbonate cements. They were products of CO 3 2 − {\text{CO}}_{3}^{2-} formed by organic acid splitting decomposition in late diagenesis and CO 3 2 − {\text{CO}}_{3}^{2-} formed by dissolution of carbonate cements in early and middle stages, combined with Mg2+, Ca2+, Fe2+ plasma in pore fluid. Dissolution–reprecipitation of the lacustrine carbonate rocks is responsible for obvious positive drift in the δ 13CPDB‰ values of carbonate cements. Carbonate cements in middle stage and late stage, respectively, represent the early hydrocarbon charging of Dongying Formation and the end of Guantao Formation to the present.

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