scholarly journals Reservoir Characteristics of the Lower Permian Marine-Continental Transitional Shales: Example from the Shanxi Formation and Taiyuan Formation in the Ordos Basin

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
H. Wang ◽  
L. Zhang ◽  
Q. Zhao ◽  
Z. Qiu ◽  
D. Liu ◽  
...  
Keyword(s):  
Pore Size ◽  
Clay Minerals ◽  
Co2 Adsorption ◽  
Ordos Basin ◽  
Lower Permian ◽  
Reservoir Properties ◽  
Taiyuan Formation ◽  
Adsorption Analysis ◽  
The Ordos Basin ◽  
Pore Types

The pore types and pore structure parameters of the heterogenetic shale will affect the percolation and reservoir properties of shale; therefore, the research on these parameters is very important for shale reservoir evaluation. We used X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), low-pressure CO2 adsorption analysis, mercury injection capillary pressure (MICP), and high-pressure methane adsorption analysis to analyze the characteristics of different pore types and their parameters of the Lower Permian Shanxi Formation and Taiyuan Formation in the Ordos Basin. The influence of different mineral contents on the porosity and pore size is also investigated. The Shanxi Formation (SF) is composed of quartz (average of 38.4%), plagioclase, siderite, Fe-dolomite, calcite, pyrite, and clay minerals (average of 50.1%), while the Taiyuan Formation (TF) is composed of calcite (average of 37%), siderite, Fe-dolomite, quartz, pyrite, and clay minerals (average of 32.3%). The most common types of pores observed in this formation are interparticle pores (InterP pores), intraparticle pores (IntraP pores), interclay pores, intercrystalline pores (InterC pores), organic matter pores (OM pores), and microfractures. CO2 adsorption analysis demonstrates the type I physisorption isotherms, showing microporous solids having comparatively small external surfaces. The similar types of isothermal shapes of the Shanxi Formation (SF) and Taiyuan Formation (TF) suggest that both types have similar pore size distribution (PSD) within the measured pore range by the low-pressure CO2 adsorption experiment. The micropore pore size of the TF is larger than that of the SF. MICP shows the larger pores (>50 nm), and most of the volume was adsorbed by macropores. Methane gas sorption capacity increases with increasing pressure. Clay minerals and quartz played an important role in providing adsorption sites for methane gas. The overall analysis of both formations shows that TF has good reservoir properties than SF.

scholarly journals Enrichment Mechanism of the Upper Carboniferous-Lower Permian Transitional Shale in the East Margin of the Ordos Basin, China: Evidence from Geochemical Proxies

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Zhifu Wei ◽  
Yongli Wang ◽  
Gen Wang ◽  
Ting Zhang ◽  
Wei He ◽  
...  
Keyword(s):  
Organic Matter ◽  
Transition Period ◽  
Sedimentary Environment ◽  
Ordos Basin ◽  
Lower Permian ◽  
Upper Carboniferous ◽  
Positive Correlation ◽  
Geochemical Proxies ◽  
Taiyuan Formation ◽  
The Ordos Basin

The organic-rich shale of the Upper Carboniferous-Lower Permian transition period in the eastern margin of the Ordos Basin, China, was formed in a marine-continental facies sedimentary environment. With a high content of total organic carbon (TOC) and a large cumulative thickness, it is considered a good source rock for shale gas development. The sedimentary environment of marine-continental transitional shale is obviously different from that of marine shale, which leads to different enrichment characteristics of organic matter. In this paper, shale samples were collected from XX# well of the Taiyuan and Shanxi Formations across the Upper Carboniferous-Lower Permian, which is typical marine-continental transitional shale. The TOC, major elements, and trace elements were measured, and the formation and preservation conditions were investigated using multiple geochemical proxies, including paleoclimate, redox parameters, paleoproductivity, and controls on the accumulation of organic matter. The TOC of Shanxi Formation is higher than that of Taiyuan Formation. In the Taiyuan Formation, TOC is positively related to the redox index (V, U, and V/Cr), indicating that the dysoxic bottom water environment is the key factor controlling organic matter accumulation. For Shanxi Formation, there is a positive correlation between TOC and paleoclimate, which indicates that the enrichment of organic matter is affected by warm and humid paleoclimate and oxic environment. In addition, the paleoproductivity is lower with a positive correlation with TOC for the marine-continental transitional organic-rich shale, suggesting that it was inferior to the gathering of organic matter.

Sedimentary characteristics and sand body distributions in the Lower Permian He 8 member, Ordos Basin, China

2021 ◽  
pp. 1-50
Author(s):  
Zhiyuan Lu ◽  
Zhiliang He ◽  
Shizhong Ma ◽  
Yu He
Keyword(s):  
Ordos Basin ◽  
Lower Permian ◽  
Braided River ◽  
River Sand ◽  
Meandering River ◽  
Sedimentary Characteristics ◽  
Fluvial Deposits ◽  
Sand Body ◽  
The Ordos Basin ◽  
Sand Bodies

The Lower Permian He 8 Member (P1h8) in the Ordos Basin is a typical producing zone of tight lithologic gas reservoirs. Analyses of sedimentary characteristics, electrofacies, and sand-body distributions of P1h8, conducted on modern fluvial deposits, outcrops, cores, and well logs, revealed that braided rivers that developed in the Lower P1h8 and Upper P1h8 are characterized by meandering river. Within these fluvial deposits, the procedure consists of analyzing high-resolution sequence stratigraphy and sedimentary dynamics defined from calibrated logging curve signatures and depositional studies. According to modern and ancient fluvial deposits, we have developed a process-based sedimentary conceptual model for interpreting and predicting the distribution and geometries of sand bodies in braided and meandering deposits. The main sand body of the braided river system was bars and channel fill deposits. The braided river sand bodies are distributed over multiple vertical superimpositions and overlapping horizontal connections. The meandering river sand bodies are mainly point-bar deposits, which are bead-shaped and exhibit scattered development in the vertical direction. This comparison indicates that there were significant differences between braided and meandering deposystems. The sand bodies in the Lower P1h8 were multidirectionally connected and primarily distributed in a stacked pattern. In contrast, the sand bodies in the Upper P1h8 were distributed in an isolated manner, and fine grains (mud and silt) were deposited between the sand bodies with poor connectivity. We interpreted the fluvial deposits that control the distributions of the sand body of the He8 Member in the eastern Sulige gas field and constructed a corresponding prediction model of a braided-meandering reservoir. This model will promote understanding of the extent of fluvial deposits and sand-body distribution of P1h8, thus elucidating hydrocarbon-bearing sand units of the Ordos Basin for future exploration.

Characteristics and origin of desorption gas of a transitional shale: A case study from the Lower Permian Taiyuan Formation shale, Ordos Basin, northern China

2017 ◽  
Vol 35 (24) ◽  
pp. 2262-2268 ◽  
Author(s):  
Liang Xu ◽  
Yongli Wang ◽  
Zhifu Wei ◽  
Baoxiang Wu ◽  
Mingfeng Zhang ◽  
...  
Keyword(s):  
Ordos Basin ◽  
Northern China ◽  
Lower Permian ◽  
Taiyuan Formation

scholarly journals Pore Structures of the Lower Permian Taiyuan Shale and Limestone in the Ordos Basin and the Significance to Unconventional Natural Gas Generation and Storage

Geofluids ◽  
2022 ◽  
Vol 2022 ◽  
pp. 1-16
Author(s):  
L. Zhang ◽  
Q. Zhao ◽  
C. Wu ◽  
Z. Qiu ◽  
Q. Zhang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Natural Gas ◽  
Shale Gas ◽  
Pore Volume ◽  
Ordos Basin ◽  
Source Rocks ◽  
Taiyuan Formation ◽  
Oil Generation ◽  
Unconventional Natural Gas ◽  
The Ordos Basin

In the Ordos Basin, multiple sets of coal seams, organic-rich shale, and limestone are well developed in the Permian Taiyuan Formation, which are favorable targets for collaborative exploration of various types of unconventional natural gas resources, including coalbed methane, shale gas, and tight gas. In this study, core samples from the Permian Taiyuan Formation in the eastern margin of the Ordos Basin were used to carry out a series of testing and analysis, such as the organic matter characteristics, the mineral composition, and the pore development characteristics. In the shale of the Taiyuan Formation, the total organic carbon (TOC) content is relatively high, with an average of 5.38%. A thin layer of black shale is developed on the top of the Taiyuan Formation, which is relatively high in TOC content, with an average of 9.72%. The limestone in the Taiyuan Formation is also relatively high in organic matter abundance, with an average of 1.36%, reaching the lower limit of effective source rocks (>1%), being good source rocks. In the shale of the Taiyuan Formation, various types of pores are well developed, with relatively high overall pore volume and pore-specific surface area, averaging 0.028 ml/g and 13.28 m2/g, respectively. The pore types are mainly mineral intergranular pores and clay mineral interlayer fractures, while organic matter-hosted pores are poorly developed. The limestone of the Taiyuan Formation is relatively tight, with lower pore volume and pore-specific surface area than those of shale, averaging 0.0106 ml/g and 2.72 m2/g, respectively. There are mainly two types of pores, namely, organic matter-hosted pores and carbonate mineral dissolution pores, with a high surface pore rate. The organic matter in the limestone belongs to the oil-generation kerogen. During thermal evolution, the organic matter has gone through the oil-generation window, generating a large number of liquid hydrocarbons, which were cracked into a large number of gaseous hydrocarbons at the higher mature stage. As a result, a large number of organic matter-hosted pores were generated. The study results show that in the Ordos Basin, the shale and limestone of the Permian Taiyuan Formation have great potential in terms of unconventional natural gas resources, providing a good geological basis for the collaborative development of coal-bearing shale gas and tight limestone gas in the Taiyuan Formation.

scholarly journals Pore structure and its control on reservoir quality in tight sandstones: a case study of the Chang 6 member of the Upper Triassic Yanchang Formation in the Jingbian oilfield in the Ordos Basin, China

2020 ◽  
Author(s):  
Yubin Bai ◽  
Jingzhou Zhao ◽  
Delin Zhao ◽  
Hai Zhang ◽  
Yong Fu
Keyword(s):  
Physical Properties ◽  
Pore Structure ◽  
Clay Minerals ◽  
Mercury Porosimetry ◽  
Ordos Basin ◽  
Reservoir Quality ◽  
Overburden Pressure ◽  
Thin Sections ◽  
The Ordos Basin ◽  
Sandstone Reservoir

AbstractThis study applied vacuum-impregnated casting thin sections, fluorescence slices, scanning electron microscopy (SEM), pressure-controlled mercury porosimetry (PCP), rate-controlled mercury porosimetry (RCP), X-ray diffraction of clay minerals, overburden pressure, and conventional physical property strategies to determine the microscopic characteristics of the Chang 6 member, a typical tight sandstone reservoir in the Jingbian oilfield in the Ordos Basin, China. We also analyzed the controlling effects of pore structure on reservoir quality and oiliness. The results showed that the pore types of the Chang 6 sandstone reservoir can be divided into four categories: residual intergranular pores, dissolution pores, intercrystalline pores between clay minerals, and microfractures. The pore size of the Chang 6 sandstone reservoir ranged from 20 to 50 μm. We employed PCP and RCP strategies to characterize the pore structure of the Chang 6 reservoir. The pore radius was less than 2 μm, and on average, the throat radius was less than 0.3 μm. The reservoir physical properties were affected by diagenesis, particularly compaction, and the average porosity failure rate was 56.3%. Cementation made the reservoir more compact, dissolution improved the physical properties of the reservoir locally, and fracturing effectively improved the reservoir seepage ability; however, its influence on porosity was limited. The pore structure controlled the quality of the reservoir. The physical properties of the reservoir were closely related to the oil-bearing properties. The lower limits of porosity and permeability of industrial oil flow in the reservoir were 7.5% and 0.15 mD, respectively. These results provide an additional resource for the exploration and development of tight oil in the Ordos Basin.

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