Dataset Information

Pore types, genesis, and evolution model of lacustrine oil-prone shale: a case study of the Cretaceous Qingshankou Formation, Songliao Basin, NE China.

ABSTRACT: A comprehensive characterisation of the pore structure in shale oil reservoirs is essential for forecasting oil production and exploration risks. This study forecasted these risks in the oil-rich Songliao Basin using combination of high-resolution field emission scanning electron microscopy and quantitative X-ray diffraction to analyze the pore genesis and evolution mode within the first member of the Cretaceous Qingshankou Formation (K₂qn₁). The results showed the dominance of inorganic pores over organic pores, wherein diagenetic processes, such as compaction, pressure solution, and cementation, were responsible for the destruction of pore structure in the formation. Notably, the pores formed by dissolution and shrinkage cracks resulting from clay mineral transformation improved the oil storage space. Furthermore, according to the geochemical data and clay composition, the K₂qn₁ shale is in the middle diagenetic stage A, which can be further subdivided into A1 and A2 stages from top to bottom. The porosity slowly decreased in both sub-stages A1 and A2, wherein the decrease was stable in the latter. The diagenetic observations in this study are significant for the exploration of unconventional shale oil in petroliferous basins worldwide.

SUBMITTER: He W

PROVIDER: S-EPMC9568562 | biostudies-literature | 2022 Oct

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Pore types, genesis, and evolution model of lacustrine oil-prone shale: a case study of the Cretaceous Qingshankou Formation, Songliao Basin, NE China.

He Wenyuan W Liu Bo B Sun Mengdi M Wang Liu L Zhang Jinyou J Yasin Qamar Q Tian Shansi S Gao Shuo S Ukaomah Chima Finnian CF

Scientific reports 20221014 1

A comprehensive characterisation of the pore structure in shale oil reservoirs is essential for forecasting oil production and exploration risks. This study forecasted these risks in the oil-rich Songliao Basin using combination of high-resolution field emission scanning electron microscopy and quantitative X-ray diffraction to analyze the pore genesis and evolution mode within the first member of the Cretaceous Qingshankou Formation (K<sub>2</sub>qn<sub>1</sub>). The results showed the dominanc ...[more]

PMID: 36241891

Similar Datasets

Project description:The first member of the Upper Cretaceous Qingshankou Formation (K2 qn 1) stands as the most significant source rock layer in the Songliao Basin, concurrently serving as the principal target for shale oil exploration. Polycyclic aromatic hydrocarbons (PAHs), as one of the main components of soluble organic matter in mudstone and shale, are of significant importance for revealing the hydrocarbon generation mechanisms in source rocks and the formation conditions of shale oil. However, systematic research on PAHs in the K2 qn 1 layer of the Songliao Basin has not yet been conducted. Our study concentrated on a comprehensive set of 34 rock core samples, covering the entire K2 qn 1 layer, retrieved from the SYY3 well in the Sanzhao Sag of the northern Songliao Basin. The geochemical characteristics of a diverse range of PAHs were meticulously assessed through gas chromatography-mass spectrometry (GC-MS). Meanwhile, this study preliminarily discussed possible influential factors on the formation of alkylated PAHs (a-PAHs) and the isomerization of parent PAHs (p-PAHs) in our samples. The results revealed that PAHs predominantly consist of the phenanthrene, naphthalene, and chrysene series, trailed by the pyrene, fluorene, dibenzothiophene, and benzopyrene series. In contrast to the lower unit (>2015.00 m) of the K2 qn 1 layer, the upper unit (<2015.00 m) exhibits generally lower PAH concentrations and reduced levels of dibenzothiophene series, implying lower biological productivity and more oxidized sedimentary waters. The upper unit exhibits a higher content of 1,2,5-trimethylnaphthalene, 1,2,5,6-tetramethylnaphthalene, retene, pyrenes, fluoranthene, benzopyrenes, and benzofluoranthene, suggesting elevated levels of contributions from terrestrial higher plants. Maturity parameters of alkyl naphthalene and methylphenanthrene, along with vitrinite reflectance (R o), indicate a close maturity in both units. Most of the a-PAHs/p-PAH ratios are higher in the lower unit than in the upper unit, indicating more pronounced alkylation. The ratios of p-PAH isomers, including benzo[b]fluorene/benzo[a]fluorene, benzo[a]pyrene/benzo[e]pyrene, and benzo[a]anthracene/chrysene, exhibit a vertical distribution pattern similar to the a-PAHs/p-PAH ratios, indicating that less stable p-PAH isomers are more prevalent in the lower unit. By comparing the a-PAHs/p-PAH ratios and the ratios of p-PAH isomers with conventional geochemical parameters of saturated hydrocarbons, it was preliminarily revealed that the catalytic effects of clay minerals, along with fluctuating biological inputs, can substantially affect PAH alkylation and p-PAH isomerization. Sediment reductivity slightly enhances PAH alkylation without obviously impacting p-PAH isomerization, and salinity shows no significant effect on these processes. The above insights offer molecular geochemical evidence of PAHs, which aids in understanding the heterogeneity of the K2 qn 1 source rock, facilitates oil source correlation, and optimizes the selection of sweet spots within shale oil formations.

Project description:Pyrite is a common mineral in sedimentary rocks and is widely distributed in a variety of different morphologies and sizes. Pyrite is also widely distributed in the Es3x shale of the Eocene Shahejie Formation in the Zhanhua Sag, Bohai Bay Basin. A combination of geochemical and petrographic studies has been applied to address the formation and distribution of pyrite in the Es3x shale. The methods include thin section analysis to identify the representative samples of the shale-containing pyrite, total organic carbon (TOC) content analysis, X-ray fluorescence, X-ray diffraction, electron probe micro-analysis, and field emission scanning electron microscopy (FE-SEM) coupled with the energy dispersive spectrometer, to observe the characteristics, morphology, and distribution of pyrite in the lacustrine shale. The content of pyrite in the Es3x shale ranges from 1.4 to 11.2% with an average content of 3.42%. The average contents of TOC and total organic sulfur (TS) are 3.48 and 2.53 wt %, respectively. Various types of pyrites are observed during the detailed FE-SEM investigations including pyrite framboids, euhedral pyrite, welded pyrite, pyrite microcrystals, and framework pyrite. Pyrite framboids are densely packed sphere-shaped masses of submicron-scale pyrite crystals with subordinate large-sized euhedral crystals of pyrite. Welded pyrite forms due to the overgrowth and alteration of pyrite crystals within the larger pyrite framboids. Pyrite microcrystals are the euhedral-shaped microcrystals of pyrite. The framework pyrite is also observed and is formed due to the pyritization of plant/algal tissues. Based on the growth mechanism, the pyrites can be divided into syngenetic pyrites, early diagenetic pyrites, and late diagenetic pyrites. The presence of pyrite, especially the abundance of pyrite framboids, suggests that the environment during the Es3x shale deposition in the lacustrine basin was anoxic. Their dominant smaller size suggests the presence of an euxinic water column, which is consistent with the lack of in-place biota and high TOC contents. This research work not only helps to understand the pyrite mineralization, role of organic matter, and reactive iron in pyrite formation in the shale but also helps to interpret the paleoredox conditions during the deposition of shale. This research work can also be helpful to other researchers who can apply these methods and conclusions to studying shale in other similar basins worldwide.

Project description:Pore types and pore structure parameters are the important factors affecting the storage capacity of a shale oil reservoir. Pore morphology and mineralogical composition of shales have diverse effects on the upgrading of various phases of shale oil. To interpret the formation and distribution of different pore types and their structure parameters in the lacustrine calcareous shale, a combination of polarizing microscopy, X-ray diffraction, total organic carbon (TOC), field-emission scanning electron microscopy, and low-pressure nitrogen adsorption experiments were conducted on the Es3x shale of the Eocene Shahejie Formation in the Zhanhua Depression. The interpretations regarding pore types, pore structure parameters, and pore size distribution indicate that the pore morphology and pore size distribution in the lacustrine shale are very complicated and demonstrate strong heterogenic behavior. Inorganic pores (interparticle pores, intraparticle pores, intercrystalline pores, dissolution pores, and microfractures) are the most commonly distributed pore types in the studied shale. However, organic matter pores are poorly developed due to the lower thermal maturity of the Es3x shale. The Brunauer-Emmett-Teller specific surface and pore volume range from 0.026 to 1.282 m2/g (average 0.697 m2/g) and 0.003 to 0.008 cm3/g (average 0.005 cm3/g), respectively. The shape of the pores varies from slit-like to narrow slit. Different minerals develop different types of pores with various sizes extending from micropores (<2 nm), mesopores (2-50 nm), to macropores (>50 nm). The relationship between mineral components and pore parameters indicates that the carbonate minerals act as the main contributors to the formation and distribution of different pore types in the studied shale. Pore volume and the pore specific surface area did not show a good relationship with mineral composition and TOC due to disordered pores, but pore size shows a good relationship with mineral composition and TOC of the Es3x shale. The whole pore system description showed that the mesopores and macropores are abundantly distributed and are the main contributors to the pore system in the Es3x shale. A comprehensive understanding of the formation mechanism and structural features of various sized pores in a variety of different minerals can provide a good tool for the exploration and development of shale oil reservoirs.

Project description:Lower Cretaceous lacustrine source rocks in the Erlian Basin are highly heterogeneous. It is important to assess and explain these heterogeneities for the reconstruction of paleoenvironments and the prediction of high-quality source rock distributions. In this study, well-logging, organic, and elemental geochemical data were comprehensively analyzed for the source rocks of Member 4 of the Aershan Formation (Fm) and Member 1 of the Tengger Fm in the southern Bayindulan (BNAN), southern Wulanhua (WLHs), Anan, Aer, and southern Wuliyasitai sags of the Erlian Basin. The variability in sedimentary environments, sources of organic matter of the source rocks in different sags, and the influence of hydrothermal and volcanic activity on the source rock quality in the Erlian Basin were assessed. The results reveal that the source rocks can be divided into four types of organic facies (A, B, BC, and C). Organic facies A-B present hydrogen indices (HIs) higher than 400 mg/g and are mainly composed of mudstone and thick (average thickness >50 m) dolomitic mudstone, with biomarkers characterized by a Pr/Ph ratio lower than 1.0, a gammacerane/C30 hopane (Gam/C30H) ratio higher than 0.2, and a C19 tricyclic terpane/C23 tricyclic terpane (C19/C23TT) ratio lower than 0.6. Organic facies BC-C are composed of mudstone with an HI < 400 mg/g, with biomarkers characterized by a Pr/Ph ratio higher than 0.8, a Gam/C30H ratio lower than 0.2, a C19/C23TT ratio higher than 0.6, and a sterane/hopane ratio lower than 0.4. Dolomitic mudstone belonging to organic facies A-B is mainly developed in the BNAN, WLHs, and Anan sag and is characterized by a fault-controlled distribution in the sag, a right-declined rare earth element pattern, and an enrichment in the elements of Ba, Cu, Zn, Fe, and Ni. The genesis of high HI dolomitic mudstone is associated with hydrothermal and volcanic activity because the hydrothermal fluid or hydrolysis of volcanic ash result in increasing input of reducing gas and soluble nutrient ions, thus promoting the formation of anoxic and saline Cretaceous lakes with high primary productivity.

Dataset Information

Pore types, genesis, and evolution model of lacustrine oil-prone shale: a case study of the Cretaceous Qingshankou Formation, Songliao Basin, NE China.

Publications

Pore types, genesis, and evolution model of lacustrine oil-prone shale: a case study of the Cretaceous Qingshankou Formation, Songliao Basin, NE China.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets