Characteristics of paleogeomorphology and paleokarstification and the impact on natural gas accumulation: a case study of upper assemblage of Majiagou formation in central Sulige gas field, Ordos Basin, China

Zhu, Liwen; Wang, Zhenliang; Zhang, Bo; Li, Wei; Feng, Qianghan; Lei, Xun; Chen, Long

doi:10.1007/s13146-018-0434-1

Cited by 15 publications

(8 citation statements)

References 10 publications

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“…It has been found that there is a good exploration potential and development prospects in the lower Paleozoic carbonate strata, especially in the dolomite reservoirs of the upper assemblage of the Ordovician Majiagou Formation. The study area is located in the northern part of the Yishan Slope of the Ordos Basin (Figure 1), adjacent to the Jingbian gas field, where there is a transition zone of karst highland and karst slope with obvious paleokarst characteristics (Zhu et al., 2019).…”

Section: Geological Settingmentioning

confidence: 99%

Genesis of dolomite in the upper assemblage of the Ordovician Majiagou Formation in the southeastern Sulige gas field, Ordos Basin, China: Evidence from C, O, and Sr isotopes and major and trace elements

Zhu

Wang

Feng³

et al. 2020

Energy Exploration & Exploitation

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Typical dolomite reservoirs exist in the upper assemblage of the Ordovician Majiagou Formation in the southeastern Sulige gas field, Ordos Basin, however, the current understanding of dolomite genesis needs to be clarified. This study confirms the dolomitization characteristics, diagenetic environment, and genesis of dolomite through the use of core observations, thin section identification, and geochemical data (carbon and oxygen stable isotopes, strontium isotopes, and major and trace element contents). The results showed that dolomite samples from the study area includes micritic dolomite, powder crystal dolomite, and micrite to powder crystal dolomite, in which the main reservoir space consisted of intergranular pores, intercrystalline pores and various dissolved pores. The δ13C value of the dolomite samples ranged from −7.26‰ to1.28‰ with an average of −0.45‰, which is equivalent to that of seawater during the Ordovician. The δ18O value ranged from −9.94‰ to −6.32‰ with an average of −7.86‰, which is clearly more negative than that of the Ordovician seawater. The 87Sr/86Sr ratio varied from 0.70867 to 0.71033 with an average of 0.70946, which is significantly more positive than that of Ordovician seawater. The Mg/Ca ratio was lower than that of the seawater and close to 1:1. Overall, all of the samples were characterized by high Fe and Mn contents, while low Sr and Na contents. These results clearly indicate that the dolomitized fluid was closely related to seawater or a sea-source fluid. Furthermore, the restored paleosalinity, paleotemperature, and paleodepth also indicate that the dolomite was formed in a marine reducing environment. Combined with the petrological characteristics and geochemical indicators, two dolomitization models (mixed water dolomitization and burial dolomitization) were established for the upper assemblage of the Ordovician Majiagou Formation in southeastern Sulige gas field. We infer that mixed water dolomitization was dominant before the Carboniferous, whereas burial dolomitization was dominant after the Early Permian.

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Section: Geological Settingmentioning

confidence: 99%

Genesis of dolomite in the upper assemblage of the Ordovician Majiagou Formation in the southeastern Sulige gas field, Ordos Basin, China: Evidence from C, O, and Sr isotopes and major and trace elements

Zhu

Wang

Feng³

et al. 2020

Energy Exploration & Exploitation

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“…The sabkha dolostone that developed moldic pores is one of the focuses of a large number research studies since it is the most important reservoir in the Ordovician. Previous research studies focused on the geochemical characteristics and genesis of sabkha dolostone (Qin & Zeng, 1994; Wang et al, 2009), the genesis and pore evolution of sabkha dolostone reservoir (Li, Si, & Shi, 1997; Luo et al, 2020; Wei et al, 2017; Xiong et al, 2016; Yu et al, 2020; Zhu et al, 2019), and the characteristics and genesis of the moldic pore fillings (Liu, Wang, Du, & Gong, 2021; Ren, Bao, Sun, & Liu, 2012; Zhang et al, 2017; Zhang, Jin, Li, Li, & Su, 2016). Recent studies reached a consensus that the formation of the moldic pores in the sabkha dolostone was mainly related to the dissolution of gypsum concretions (Liu et al, 2021; Luo et al, 2020; Wei et al, 2017; Xiong et al, 2016; Yu et al, 2020; Zhu et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

“…fillings (Liu, Wang, Du, & Gong, 2021;Ren, Bao, Sun, & Liu, 2012;Zhang et al, 2017;Zhang, Jin, Li, Li, & Su, 2016). Recent studies reached a consensus that the formation of the moldic pores in the sabkha dolostone was mainly related to the dissolution of gypsum concretions (Liu et al, 2021;Luo et al, 2020;Wei et al, 2017;Xiong et al, 2016;Yu et al, 2020;Zhu et al, 2019). But there is a great controversy over the formation time of moldic pores and the fillings.…”

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confidence: 99%

“…But there is a great controversy over the formation time of moldic pores and the fillings. Some studies advocated that the moldic pores and the calcite fillings were formed in the epigenetic stage (Liu et al, 2021;Ren et al, 2012;Wei et al, 2017;Yu et al, 2020;Zhu et al, 2019). During the Caledonian tectonic movement, the basin was uplifted with the denudation of the Majiagou Formation.…”

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confidence: 99%

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The moldic pore evolution of the Middle Ordovician sabkha dolostone in Ordos Basin, China: A study based on the petrographic and geochemical characteristics of pore fillings

et al. 2022

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In the Ordos Basin, the sabkha dolostone reservoir with moldic pores of the fifth Member in the Middle Ordovician Majiagou Formation (M5) dominated the gas production of the Lower Palaeozoic. Recent research studies revealed the complex history of the moldic pore evolution, which intensively affected the reservoir potential evaluation. The moldic pores were formed by dissolution of the gypsum concretion and then experienced a different extent of multi‐phase filling. In order to understand the evolution of the moldic pores and explain its affection on the development of reservoirs, comprehensive petrographic and geochemical analysis including the cathodoluminescent, scanning electron microscope, trace and rare earth elements in situ, and strontium isotopes have been utilized to study the moldic pore fillings. The results reveal the moldic pore evolution: (a) the gypsum concretions were dissolved and the moldic pores were formed in the early diagenetic stage; (b) the calcite fillings formed in the vadose zone and phreatic zone during the early diagenetic stage in the sabkha environment; (c) the ferroan dolomites formed during the process of conversion of montmorillonite to illite at the burial diagenesis stage, at the burial depth of 3,500 m–4,000 m in the middle‐Late Jurassic. Significantly, filling in the late burial period is more conducive to the pore preservation compared with the filling in the early diagenetic stage, and the formation of the sabkha dolostone reservoir lies in the preservation of pores in the early diagenetic stage. Consequently, the results of this study provide a framework to differentiate the petrographic and geochemical characteristics of kinds of pore fillings and to understand the moldic pore evolution and its affection on the development of reservoirs in similar sedimentary environments.

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“…Prolonged karstification following integral platform exposure can cause disconformity, i.e., general weathering crust in carbonate reservoirs. Thus, karstification is associated with disconformity, and paleokarst reservoirs are also related to disconformity (Fritz et al, 1993;Zhu et al, 2019;Chen et al, 2022). This is highly prevalent, as 20%-30% of global oil and gas resources are subject to unconformities (Fritz et al, 1993;Burchette, 1996).…”

Section: Introductionmentioning

confidence: 99%

Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China

Zhou

Wang²,

Yang³

et al. 2022

Front. Earth Sci.

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The evaluation of reservoirs is of great importance in exploration practices, and reservoir distribution is dependent on multiple geological factors. The carbonate platform of the fourth member (Z2dn4) of the Dengying Formation (Z2dn) in the Gaoshiti-Moxi area (GMA) was uplifted above sea level during episode II of the Tongwan movement and underwent prolonged karstification by meteoric freshwater in the terminal Sinian, leading to a strong heterogeneity in reservoirs. Paleogeomorphology reflects hydraulic gradients that can affect the intensities of surface karstification and may be approximated by terrain slope gradients. Karst products (especially solution vugs and caverns) exist prevailingly in the Z2dn4; their development mirrors the extents of internal dissolution. Based on paleogeomorphological reconstruction using the elevation method, the slope angles of single boreholes were calculated through the digital elevation model (DEM). In accordance with single-borewell Fullbore Formation MicroImager (FMI) logging data, four electrofacies (host rock, vug, fracture, and cave) were identified in boreholes possessing FMI data. The identified electrofacies were matched with corresponding conventional logging curves to obtain the training data. A model generalized for other boreholes without FMI data was established with the random forest algorithm and the thicknesses of the four electrofacies in each borehole were determined to characterize the extent of karstification. Slope gradients and electrofacies thicknesses, together with multiple physical parameters of reservoirs in boreholes, were utilized for factor analysis. Four factors were obtained and fused into one comprehensive score based on their ratios of variance proportions. The favorability of reservoirs was described by the comprehensive scores of each borehole. These analyses showed that the most advantageous reservoirs are distributed in the vicinity of the platform margin in the west of the GMA, where they enjoy several benefits. Deposition of porous mound-shoal complexes occurs predominantly in the platform margin where large-scale caves are more developed in the mixing karst zone of seawater and freshwater. Meanwhile, the transmeridional lateral migration of hydrocarbons from the regional hydrocarbon-generating center abutting the west of the GMA contributes to earlier entrapment and accumulation in the mound-shoal complexes in the platform margin.

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Characteristics of paleogeomorphology and paleokarstification and the impact on natural gas accumulation: a case study of upper assemblage of Majiagou formation in central Sulige gas field, Ordos Basin, China

Cited by 15 publications

References 10 publications

Genesis of dolomite in the upper assemblage of the Ordovician Majiagou Formation in the southeastern Sulige gas field, Ordos Basin, China: Evidence from C, O, and Sr isotopes and major and trace elements

Genesis of dolomite in the upper assemblage of the Ordovician Majiagou Formation in the southeastern Sulige gas field, Ordos Basin, China: Evidence from C, O, and Sr isotopes and major and trace elements

The moldic pore evolution of the Middle Ordovician sabkha dolostone in Ordos Basin, China: A study based on the petrographic and geochemical characteristics of pore fillings

Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China

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