Vertical zonation of weathered crust ancient karst and reservoir evaluation and prediction—A case study of M 5 5 –M 5 1 sub-members of Majiagou Formation in gas fields, central Ordos Basin, NW China

He, Jiang; Shao-xian, Fang; Fang-hao, Hou; Ronghui, Yan; Zhao, Zhenjiang; Yao, Jiayi; Tang, Xiujun; Wu, Guorong

doi:10.1016/s1876-3804(13)60075-0

Cited by 51 publications

(9 citation statements)

References 6 publications

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“…The main structural units of the Ordos Basin include Yimeng uplift, Jinxi fold, northern Shaanxi sag, Yishan slope, central paleo-uplift, Tianhuan sag, western margin thrust belt and Weibei uplift (Hou et al, 2003;He et al, 2013). The basin was composed of Caledonian foreland basin and Helan rift at the same time in early Paleozoic.…”

Section: Geological Settingmentioning

confidence: 99%

“…The Ma5 member has been divided into 10 submembers. Among the 10 submembers, the Ma5 1 to Ma5 4 submembers are located in the vadose zone and horizontal phreatic zone (He et al, 2013;Sun, 2020;Xie R. C. et al, 2020;Yu et al, 2020;Xu et al, 2021), while the Ma5 5 submember is distributed in the shallow burial zone. The Ma5 5 submember is composed of dolostone and limestone.…”

Section: Introductionmentioning

confidence: 99%

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The effect of meteoric water on the very fine crystalline dolomite reservoir in the shallow burial zone: A case study of the Ma55 submember of Majiagou Formation in Ordos Basin

Lan

Guo

et al. 2023

Front. Energy Res.

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The meteoric water has obviously changed the physical properties of dolostone reservoirs in the vertical vadose zone and the horizontal phreatic zone, but its influence on the dolostone reservoirs in the shallow burial zone beneath the phreatic surface is still unclear. This study aims to reveal the effect of meteoric water on the dolostone reservoirs in the shallow burial zone through X-ray diffraction, cathodoluminescence, C, O, and Sr isotope using the sample from Majiagou Formation in the Daniudi gas field, Ordos Basin. The diagenesis and paragenesis of the Ma 55 submember were identified and interpreted through petrological study, combined with data from electron probe, X-ray diffraction analysis, and geochemical parameters of diagenetic minerals. The color of the very fine crystalline dolomite under the cathodeluminescence is dark red and red. The order degree of dolomite ranges from 0.54 to 0.91, showing the origin of early seepage-reflux dolomitization. There are a large number of different calcite cements as fills within the pores and fractures. The color of the calcite cement under the cathodoluminescence is orange-yellow, with a zonal structure. Hydrothermal fluid during late diagenesis could be identified by the authigenic fluorite filling in the fractures. According to the assembly of diagenetic minerals, the very fine crystalline dolostones have experienced the seepage-reflux dolomitization, meteoric water dissolution, shallow burial cementation and late cementation. The void spaces of the very fine crystalline dolostones are intercrystalline pores and microfractures. Although a large number of dissolved pores and caves developed in the period of meteoric water dissolution, these caves and dissolved pores has been mostly filled by multi-stages of cementation. Therefore, the effect of meteoric water on dolostone reservoirs in the shallow burial zone beneath the phreatic surface is not obvious. The main controlling factor for the quality of dolostone reservoir was dolomitization. This study provides a new understanding of the influence of meteoric water on reservoir quality in the shallow burial zone during the paleokarst period.

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Section: Geological Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The effect of meteoric water on the very fine crystalline dolomite reservoir in the shallow burial zone: A case study of the Ma55 submember of Majiagou Formation in Ordos Basin

Lan

Guo

et al. 2023

Front. Energy Res.

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“…Following deposition of the Majiagou Formation, the North China Platform was uplifted above sea level during the Caledonian Movement (Feng et al., 2003). At this time, the upper Majiagou Formation underwent 120 Myr of karstification, resulting in the dissolution of nodular gypsum (degypsification), forming gypsum mold-bearing micritic dolomites (He et al., 2013; Xiong et al., 2016). Based on the regional geology, two sedimentary environments have been proposed for this period: tidal flat (Yao et al., 2010) and restricted evaporite platform (Liu et al., 2016).…”

Section: Facies Distributionmentioning

confidence: 99%

Petrography and facies distribution of Middle Ordovician Ma 5^1 + 2 tight dolomite reservoirs in the Ordos Basin, Central China

Liu

Zhang

Dong

et al. 2018

Energy Exploration & Exploitation

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The Middle Ordovician Majiagou Formation in the eastern Ordos Basin, central China, is an important area in the exploration for tight carbonate gas, especially within weathering crust layers in the first and second submembers of the fifth member of the formation (herein referred to as Ma 5 1 þ 2). However, karstification prevents a clear understanding of the petrological characteristics and facies distribution of these layers, which hinders exploration. Based on cores, thin sections, and cathodoluminescence analysis, we investigate the petrological characteristics of Ma 5 1 þ 2 , determine the nature of lateral lithological variations in the eastern and central parts of the Ordos Basin, and constrain facies distribution in the region. In addition to karst breccias with unrecognizable parent rocks, Ma 5 1 þ 2 comprises four lithologies: gypsum/halite mold-bearing micritic dolomite, micritic dolomite, grain dolomite, and microbial dolomite. We recognize three main sedimentary subfacies: restricted lagoon, grain shoal, and mound-shoal complex. Ma 5 1 þ 2 records a complete transgression-regression cycle. The Ma 5 2 2 layer was deposited during a transgression associated with enhanced water circulation and abundant mound-shoal complexes, for which their frequency is positively correlated with the thickness of the unit. The Ma 5 1 2 layer and overlying deposits correspond to a regression cycle, and the abundance of mound-shoal complexes in these units is negatively correlated with layer thickness. The Ma 5 1 3 period represents the timing of maximum regression, when a gypsum-bearing dolomitic lagoon was dominant, associated with a restricted water body. The overall facies

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“…The Middle Ordovician Majiagou Formation of the Ordos Basin, composed dominantly by dolostones, has been widely studied due to its abundant natural gas being reserved in karst-controlled and burial dissolution carbonate reservoirs (Dai, 2016). In previous studies, the favorable reservoir condition of the Majiagou Formation was mainly attributed to telogenetic karstification controlled by Caledonian tectonism (Chen et al, 2013;He et al, 2013). However, the dissolution process accompanying karstification was ignored.…”

Section: Introductionmentioning

confidence: 99%

Multiple-Stage Injection of Deep Hydrothermal Fluids in the Dolostone Reservoirs of Ordovician Majiagou Formation, Southern Ordos Basin

et al. 2022

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The Middle Ordovician Majiagou Formation in the southern Ordos Basin develops a set of sub-and peri-tidal carbonate successions that were extensively dolomitized. Diagenetic dolomitization is widely investigated because dolostones provide high-quality gas reservoirs in the southern Ordos Basin. Nonetheless, the ultimate mechanism controlling dolomitization remains enigmatic. In this study, integrated geochemical indexes including carbon and oxygen isotopes, rare earth elements, and microthermometry, coupled with U-Pb dating and lithofacies and mineralogic studies, are investigated to elucidate the periods of hydrothermal fluids involved in the formation of different types of dolomites in the studied section from Ma5 member. The results reveal that the micritic dolomite matrix was formed under the involvement of low-salinity meteoric water in the mixing zone during a shallow-burial environment. The mixing zone of paleokarst possibly provided accommodation for this dolomitization. The fine-/medium-sized dolomites were formed due to interactions between hydrothermal fluids of comparatively low temperature and matrix carbonates, which occurred during the period of the Middle Jurassic. The dolomitic microbialites were formed due to the injection of high-temperature acid fluids associated with organic matter maturing. This dolomitization occurred during the period of the Late Jurassic according to U-Pb ages. The coarse-sized dolomite cements can be furtherly classified into two types according to different U-Pb ages and carbon-oxygen isotopes, although they are very similar with respect to mineralogic features. Comprehensive geochemical evidence revealed that the dolomitizing fluids of two types of dolomite cements were derived from hydrothermal fluids associated with periodical magmatism, which occurred during the period of the Early Cretaceous. This finding provides a new insight for elucidating the diagenetic process of reservoir dolostones from the Middle Ordovician in the Ordos Basin.

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Vertical zonation of weathered crust ancient karst and reservoir evaluation and prediction—A case study of M 5 5 –M 5 1 sub-members of Majiagou Formation in gas fields, central Ordos Basin, NW China

Cited by 51 publications

References 6 publications

The effect of meteoric water on the very fine crystalline dolomite reservoir in the shallow burial zone: A case study of the Ma55 submember of Majiagou Formation in Ordos Basin

The effect of meteoric water on the very fine crystalline dolomite reservoir in the shallow burial zone: A case study of the Ma55 submember of Majiagou Formation in Ordos Basin

Petrography and facies distribution of Middle Ordovician Ma 5^1 + 2 tight dolomite reservoirs in the Ordos Basin, Central China

Multiple-Stage Injection of Deep Hydrothermal Fluids in the Dolostone Reservoirs of Ordovician Majiagou Formation, Southern Ordos Basin

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Vertical zonation of weathered crust ancient karst and reservoir evaluation and prediction—A case study of M 5 5 –M 5 1 sub-members of Majiagou Formation in gas fields, central Ordos Basin, NW China

Cited by 51 publications

References 6 publications

The effect of meteoric water on the very fine crystalline dolomite reservoir in the shallow burial zone: A case study of the Ma55 submember of Majiagou Formation in Ordos Basin

The effect of meteoric water on the very fine crystalline dolomite reservoir in the shallow burial zone: A case study of the Ma55 submember of Majiagou Formation in Ordos Basin

Petrography and facies distribution of Middle Ordovician Ma 51 + 2 tight dolomite reservoirs in the Ordos Basin, Central China

Multiple-Stage Injection of Deep Hydrothermal Fluids in the Dolostone Reservoirs of Ordovician Majiagou Formation, Southern Ordos Basin

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Petrography and facies distribution of Middle Ordovician Ma 5^1 + 2 tight dolomite reservoirs in the Ordos Basin, Central China