scholarly journals Origin of Bedding-Parallel Calcite Veins from Lacustrine Shale in the Eocene Dongying Depression, Bohai Bay Basin, China

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-23
Author(s):  
Zhenhuan Shen ◽  
Bingsong Yu ◽  
Chenyang Bai ◽  
Shujun Han ◽  
Huimin Liu
Keyword(s):  
Host Rock ◽  
Thermal Evolution ◽  
Source Rocks ◽  
Bohai Bay ◽  
Shale Oil ◽  
Dongying Depression ◽  
Calcite Veins ◽  
Swelling Clay Minerals ◽  
Intercrystalline Pores ◽  
Host Rocks

Calcite veins, which developed parallel to the bedding, are widespread in laminated source rocks in the Eocene Dongying Depression. However, there is a lack of systematic description and classification of the veins. This study presents a systematic characterization of the calcite veins, host rocks, and micritic carbonate laminae by applying petrographic and geochemical methods to understand vein-forming mechanisms. Antitaxial and syntaxial veins are examined. Antitaxial veins contain typical fibrous crystals with the most intense fluorescence, and the median zone of these veins is often the micritic carbonate. Calcite crystals in syntaxial veins develop a blocky morphology of various sizes, indicating obvious growth competition. Data of rare earth elements and trace elements obtained from the micritic laminae, host rocks, and calcite veins are very similar. This indicates that the vein-forming nutrients originated from the carbonate in the host rocks and micritic laminae. The minor difference in C and Sr isotopes between calcite veins and micritic carbonate within the host rock and the negative shift in O isotopes in the veins are caused by ion exchange and dehydration of swelling clay minerals in the burial environment. This further proves that the calcite veins are formed in a closed system. Geochemical analysis suggests that the rocks are in the oil window and have good hydrocarbon potential. Thermal evolution of the acidic fluids generated from organic matter (OM) resulted in the dissolution of carbonate and formed fluid overpressure in the rocks. Fluid overpressure induced the formation of fractures in the interlayer and expanded the veins with the force of crystallization due to fibrous calcite growth. Blocky crystals grow in the fractures from the margins toward the center. Hydrocarbon expulsed via OM maturation in the host rock fills the intercrystalline pores. Moreover, shale with bedding-parallel calcite has the characteristics of high-quality shale oil reservoirs. These characteristics will probably provide guidance for shale oil exploration.

scholarly journals Thermal Maturation Regime Revisited in the Dongying Depression, Bohai Bay Basin, East China

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Haiping Huang ◽  
Hong Zhang ◽  
Zheng Li ◽  
Mei Liu
Keyword(s):  
Organic Geochemistry ◽  
Vitrinite Reflectance ◽  
Source Rocks ◽  
East China ◽  
Burial Depth ◽  
Bohai Bay ◽  
Hydrocarbon Generation ◽  
Bohai Bay Basin ◽  
Dongying Depression ◽  
Hydrocarbon Maturation

To the accurate reconstruction of the hydrocarbon generation history in the Dongying Depression, Bohai Bay Basin, East China, core samples of the Eocene Shahejie Formation from 3 shale oil boreholes were analyzed using organic petrology and organic geochemistry methods. The shales are enriched in organic matter with good to excellent hydrocarbon generation potential. The maturity indicated by measured vitrinite reflectance (%Ro) falls in the range of 0.5–0.9% and increases with burial depth in each well. Changes in biomarker and aromatic hydrocarbon isomer distributions and biomarker concentrations are also unequivocally correlated with the thermal maturity of the source rocks. Maturity/depth relationships for hopanes, steranes, and aromatic hydrocarbons, constructed from core data indicate different well locations, have different thermal regimes. A systematic variability of maturity with geographical position along the depression has been illustrated, which is a dependence on the distance to the Tanlu Fault. Higher thermal gradient at the southern side of the Dongying Depression results in the same maturity level at shallower depth compared to the northern side. The significant regional thermal regime change from south to north in the Dongying Depression may exert an important impact on the timing of hydrocarbon maturation and expulsion at different locations. Different exploration strategies should be employed accordingly.

Direct evidence for fluid overpressure during hydrocarbon generation and expulsion from organic-rich shales

Geology ◽  
2020 ◽  
Vol 48 (4) ◽  
pp. 374-378
Author(s):  
Miao Wang ◽  
Yong Chen ◽  
Wyatt M. Bain ◽  
Guoqi Song ◽  
Keyu Liu ◽  
...  
Keyword(s):  
Direct Evidence ◽  
Wall Rock ◽  
Source Rocks ◽  
Bohai Bay ◽  
Hydrocarbon Generation ◽  
Calcite Veins ◽  
History Of ◽  
Fluid Overpressures ◽  
Adjacent Wall ◽  
Record Variable

Abstract Fluid overpressures are widely expected during hydrocarbon generation and expulsion from source rocks, yet direct evidence for this phenomenon is lacking in the case of organic-rich shales. Here we show that formation of bed-parallel fibrous calcite veins in mature laminated organic-rich shales in the Eocene Dongying depression, Bohai Bay Basin, east China, occurred in direct response to fluid overpressure due to hydrocarbon generation. The evidence for overpressure is recorded by coexisting primary aqueous and petroleum inclusions in the calcite fibers. Our results show that all analyzed fluid-inclusion assemblages record variable degrees of overpressure during vein dilation, ranging from only modestly in excess of hydrostatic, to approaching and perhaps exceeding lithostatic. Thus, our results indicate that fluid pressures during dilation of horizontal veins are not necessarily equal to the opposing force of overburden throughout the history of opening. This suggests that at least some of the vein dilation is accommodated by concomitant narrowing of the adjacent wall-rock laminae, likely by scavenging (dissolution and reprecipitation) of CaCO3 from the adjacent wall rock.

scholarly journals Distribution and controls of petroliferous plays in subtle traps within a Paleogene lacustrine sequence stratigraphic framework, Dongying Depression, Bohai Bay Basin, Eastern China

2019 ◽  
Vol 17 (1) ◽  
pp. 1-22 ◽  
Author(s):  
Ji-Chang Zhu ◽  
Cai-Neng Zou ◽  
You-Liang Feng ◽  
Shu Jiang ◽  
Wei-An Wu ◽  
...  
Keyword(s):  
Eastern China ◽  
Source Rocks ◽  
Normal Faults ◽  
Dynamic Factor ◽  
Bohai Bay ◽  
Sequence Stratigraphic ◽  
Dongying Depression ◽  
Stratigraphic Framework ◽  
Incised Channel ◽  
Sand Bodies

AbstractThe characteristics of petroliferous plays in subtle traps within a sequence stratigraphic framework in the Dongying Depression are investigated in this study. Sand bodies within lowstand systems tracts (LSTs) of sequences, comprising incised-channel fills, sublacustrine fans, deltas in LSTs, controlled by syndepositional normal faults, and sand bodies within transgressive systems tracts (TSTs) to early highstand systems tracts (HSTs), consisting of beach bars, and turbidites, controlled by the prodelta slope, paleorelief, and syndepositional normal faults, are good subtle reservoirs. Mudstones and shale of deep lake subfacies in TSTs to early HSTs of sequences are source and cap rocks. Abnormal overpressure is the dominant dynamic factor for hydrocarbon migration from source rock to the subtle traps. Normal faults, sand bodies, and unconformities function as conduit systems. Sand bodies distributed in the abnormal overpressure source rocks within LSTs to early HSTs are petroliferous plays in lithologic traps. The petroliferous plays in stratigraphic traps are controlled by unconformities at margins of the Depression.

The genesis and evolution of carbonate minerals in shale oil formations from Dongying depression, Bohai Bay Basin, China

2018 ◽  
Vol 189 ◽  
pp. 8-26 ◽  
Author(s):  
Chenyang Bai ◽  
Bingsong Yu ◽  
Huimin Liu ◽  
Zhonghuai Xie ◽  
Shujun Han ◽  
...  
Keyword(s):  
Bohai Bay ◽  
Shale Oil ◽  
Bohai Bay Basin ◽  
Carbonate Minerals ◽  
Dongying Depression

Origin of bedding-parallel fibrous calcite veins in lacustrine black shale: A case study from Dongying Depression, Bohai Bay Basin

2019 ◽  
Vol 102 ◽  
pp. 873-885 ◽  
Author(s):  
Guoqiang Luan ◽  
Chunmei Dong ◽  
Karem Azmy ◽  
Chengyan Lin ◽  
Cunfei Ma ◽  
...  
Keyword(s):  
Black Shale ◽  
Bohai Bay ◽  
Bohai Bay Basin ◽  
Dongying Depression ◽  
Calcite Veins

Evaluating shale oil in the Dongying Depression, Bohai Bay Basin, China, using the oversaturation zone method

2018 ◽  
Vol 161 ◽  
pp. 291-301 ◽  
Author(s):  
Yan-Rong Zou ◽  
Jia-Nan Sun ◽  
Zheng Li ◽  
Xingyou Xu ◽  
Maowen Li ◽  
...  
Keyword(s):  
Bohai Bay ◽  
Shale Oil ◽  
Bohai Bay Basin ◽  
Zone Method ◽  
Dongying Depression

scholarly journals Lamination Texture and Its Effects on Reservoir and Geochemical Properties of the Palaeogene Kongdian Formation in the Cangdong Sag, Bohai Bay Basin, China

Minerals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1360
Author(s):  
Mengying Li ◽  
Songtao Wu ◽  
Suyun Hu ◽  
Rukai Zhu ◽  
Siwei Meng ◽  
...  
Keyword(s):  
Vertical Distribution ◽  
Thin Section ◽  
Organic Geochemistry ◽  
Source Rocks ◽  
Diffraction Field ◽  
Bohai Bay ◽  
Geochemical Properties ◽  
Vertical Distributions ◽  
Single Well ◽  
Intercrystalline Pores

The characteristics of laminae are critical to lacustrine shale strata. They are the keys to the quality of source rocks and reservoirs, as well as engineering operations in shale plays. This study uses organic geochemistry, thin section identification, X-ray diffraction, field emission scanning electron microscopy, and other analytical methods, to reveal the detailed lamination texture and vertical distribution of laminae in the second Member of the Kongdian Formation in Cangdong Sag. The principal results are as follows: (1) A classification of laminae is proposed to characterize reservoir and geochemical properties. The five types of laminae are as follows: feldspar-quartz laminae (FQL), clay laminae (CLL), carbonate laminae (CAL), organic matter laminae (OML), and bioclastic laminae (BCL). There are also four significant lamina combinations (with the increasing TOC values): FQL-CLL combination, FQL-CLL-BCL combination, FQL-CLL-OML combination, and FQL-CAL-CLL-OML combination; (2) differences between laminae occur because of the variability in pore types and structures. There appears to be a greater abundance of intercrystalline pores of clay minerals in the FQL, CAL, BCL, and OML, and well-developed organic pores in the CAL and CLL, and the counterparts of intragranular pores of bioclastic material in the BCL. This detailed characterization provides the following comparative quantification of the thin section porosity of laminae in the second Member of the Kongdian Formation can be differentiated: CAL > FQL > OML > BCL > CLL; (3) differentiation between vertical distributions of laminae is carried out in a single well. The FQL and CLL are widely distributed in all the samples, while the BCL is concentrated in the upper part of the second Member of the Kongdian Formation, and CAL is concentrated in the lower part. This detailed classification method, using geochemical analysis and vertical distribution descriptions, offers a detailed understanding of lamination texture and its effects on reservoir and geochemical properties, which will provide a scientific guidance and technical support to better estimate reservoir quality and to identify new sweet spots in the second Member of the Kongdian Formation in the Cangdong Sag.

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