Characteristics, formation and evolution of pre-salt dolomite reservoirs in the fifth member of the Ordovician Majiagou Formation, mid-east Ordos Basin, NW China

Fu, Siyi; Zhang, Chenggong; Chen, Hongde; Chen, Anqing; Zhao, Jian‐xin; Su, Zhongtang; Yang, Shuai; Guo, Wei; Mi, Wentian

doi:10.1016/s1876-3804(19)60270-3

Cited by 31 publications

(15 citation statements)

References 14 publications

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“…In addition, intense burial recrystallization can be observed in the Md2 dolomite, as shown by the relict textures of grains and overgrowths of dolomite crystals. Previous studies have suggested that the burial fluid, comprising concentrated seawater sealed in pores of contemporaneous rocks from the intracratonic depression, has had a strong influence on the petrological features of the porous Md2 dolomite (Chen et al 2018;Fu et al 2019). This highlights the influence of multiple diagenetic fluids on the formation of the Md2 dolomite.…”

Section: Md2 Dolomitementioning

confidence: 83%

“…Due to the abundant gas resources in the Ordos Basin, particularly the subsalt Majiagou Formation reservoir with proven natural gas reserves of > 200 × 10 9 m 3 (He et al 2009), numerous studies have been conducted on the Ordovician Majiagou Formation dolomites. A number of models have been proposed, including penecontemporaneous dolomitization (Han and Xin 1995;He et al 2014), burial dolomitization (Su et al 2011;Chen et al 2018;Fu et al 2019), mixed-water dolomitization (Zhao et al 2005), and localized hydrothermal dolomitization (Wang et al 2009;Huang et al 2011). These studies provide important basis for understanding the origins of dolomites in the Majiagou Formation.…”

Section: Introductionmentioning

confidence: 99%

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Dolomitization of the Ordovician subsalt Majiagou Formation in the central Ordos Basin, China: fluid origins and dolomites evolution

et al. 2020

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The Middle Ordovician subsalt Majiagou Formation in the Ordos Basin comprises pervasively dolomitized shallow marine limestone and is a major reservoir rich in natural gas resources. Four types of dolomite matrix and cement were identified based on petrographic textures: (very) finely crystalline, non-planar to planar-s matrix dolomite (Md1); finely to medium crystalline, planar-s to planar-e matrix dolomite (Md2); microbialites comprising dolomite microcrystals (Md3); and finely to coarsely crystalline dolomite cement (Cd). The Md1 and Md2 dolomites were controlled by alternating lagoon-shoal facies and have δ13C values (− 1.89 to + 1.45‰ VPDB for Md1, − 1.35 to + 0.42‰ VPDB for Md2) that fall within or are slightly higher than the coeval seawater, suggesting the dolomitizing fluid of evaporated seawater. Md2 dolomite was then subjected to penecontemporaneous karstification by meteoric water and burial recrystallization by sealed brines during diagenesis, as indicated by its relatively lower δ18O values (− 8.89 to − 5.73‰ VPDB) and higher 87Sr/86Sr ratios (0.708920–0.710199). Md3 dolomite comprises thrombolite and stromatolite and is interpreted to form by a combination of initial microbial mediation and later replacive dolomitization related to evaporated seawater. Cd dolomite was associated with early-formed karst system in the Md2 host dolomite. The lowest δ18O values (− 11.78 to − 10.18‰ VPDB) and 87Sr/86Sr ratios (0.708688–0.708725) and fluid inclusion data (Th: 123–175 °C) indicate involvement of hydrothermal fluid from which the Cd dolomite precipitated during deep burial. These results reveal the multi-stage dolomitization history of the Majiagou Formation and provide new constraints on fluid origins and dolomites evolution during deep burial in old superimposed basins, such as the Ordos Basin and elsewhere.

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Section: Md2 Dolomitementioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Dolomitization of the Ordovician subsalt Majiagou Formation in the central Ordos Basin, China: fluid origins and dolomites evolution

et al. 2020

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“…During the burial diagenesis process, the strata experienced compaction, pressure dissolution, filling, cementation, recrystallization, and metasomatism. The primary pores of dolomite are less preserved, and most of the pores are dissolution pores, caves and fractures formed in secondary process (Wei et al., 2015; Fu et al., 2019). Core observation and thin section identification in the present study revealed that dolomite samples from the upper assemblage of Majiagou Formation mainly included micritic dolomite, powder crystal dolomite, and micrite to powder crystal dolomite.…”

Section: Geological Settingmentioning

confidence: 99%

“…Accordingly, we found that the dolomite in the study area has typical characteristics of the burial dolomite. Fu et al. (2019) summarized the diagenesis and diagenetic evolution of the Ma5 member in the east–central Ordos Basin.…”

Section: Geological Analysismentioning

confidence: 99%

“…Accordingly, we found that the dolomite in the study area has typical characteristics of the burial dolomite. Fu et al (2019) summarized the diagenesis and diagenetic evolution of the Ma5 member in the east-central Ordos Basin. The authors believed that the compaction during late diagenesis period after the Carboniferous led to the release of Mg 2þ rich fluid, which resulted in a strong burial dolomitization.…”

Section: Characteristics and Geological Significance Of Major And Tramentioning

confidence: 99%

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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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Factors controlling the occurrence, distribution and physical properties of the Ordovician palaeokarstic reservoir in the Ordos Basin Daniudi gas field

et al. 2023

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The Daniudi gas field in China's Ordos Basin is located in the transitional zone between palaeo‐topographic highs and slopes, whereby dissolution‐collapse breccias are widespread within the palaeokarstic reservoir. Abundant cores, well logs and thin sections were used to study palaeo‐topography, palaeokarstic breccia types, diagenesis and reservoir pore characteristics. The results indicated that reservoir quality is controlled by lithology, palaeo‐topography and diagenesis. The extent of palaeokarstic reservoir dissolution was shown to be determined by lithologic differences, whilst only gypsiferous dolostones and finely crystalline dolostones emerged in reservoir formation. Palaeo‐topography was also found to regulate reservoir development. The reservoirs are primarily located 20 m below the Ordovician unconformity in palaeo‐topographic hills and palaeo‐topographic slopes, whilst their depth is palaeo‐topography dependent. Lithology and palaeo‐topography also coordinate the distribution of palaeokarst breccia facies. Clast‐supported and matrix‐supported chaotic breccias were found in argillaceous dolostone strata. However, crackle–mosaic breccias occurred in gypsiferous dolostones and crystalline dolostones, located in palaeogeomorphic residual hills and slopes. Reservoirs generally develop in crackle–mosaic breccias of Ma51 and Ma52 sub‐Members, the quality of such reservoirs is dependent on the development and distribution of palaeokarst breccia facies and diagenesis. Dissolution of dolomite and anhydrite nodules was found to result in moldic pores and dissolution‐enlarged pores. Overall, the most damaging effect on reservoir quality resulted from calcite cement infilling moldic pores, enlarged pores and fractures.

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Characteristics, formation and evolution of pre-salt dolomite reservoirs in the fifth member of the Ordovician Majiagou Formation, mid-east Ordos Basin, NW China

Cited by 31 publications

References 14 publications

Dolomitization of the Ordovician subsalt Majiagou Formation in the central Ordos Basin, China: fluid origins and dolomites evolution

Dolomitization of the Ordovician subsalt Majiagou Formation in the central Ordos Basin, China: fluid origins and dolomites evolution

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

Factors controlling the occurrence, distribution and physical properties of the Ordovician palaeokarstic reservoir in the Ordos Basin Daniudi gas field

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