Genesis of the Ordovician fluorite and its geological significance in central uplift of the Tarim basin, China

Wang, Zhenyu; Zhang, Yunfeng; Tao, Xiayan; Zhu, Baoshan; Luo, Chenxu

doi:10.1007/s00710-014-0341-7

Cited by 5 publications

(2 citation statements)

References 7 publications

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“…silica, flints, quartz, pyroclasts, chalcedonies, and hydrothermal dolomites, see Fig. 5 g,l,m,n,o) were discovered in pores, vugs, and fractures in the Ordovician carbonates in the Huai-Fu Basin, and the δ 18 O values of these hydrothermal minerals were less than − 12 ‰ (Table 1 ), both indicating that the formation of this kind of karst was related to hydrothermal activities 4 , 5 , 29 , 30 , 67 , 68 . Moreover, some calcites were also found around the hydrothermal minerals (Fig.…”

Section: Discussionmentioning

confidence: 99%

Formation environments and mechanisms of multistage paleokarst of Ordovician carbonates in Southern North China Basin

Zhang

Liu³

et al. 2021

Sci Rep

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With the reduction of oil and gas reserves and the increase of mining difficulty in Northern China, the carbonate rocks in Southern North China Basin are becoming a significant exploration target for carbonate reservoirs. However, the development characteristics, formation stages, formation environments and mechanisms of the carbonate reservoirs in Southern North China Basin are still unclear, which caused the failures of many oil and gas exploration wells. This study focused on addressing this unsolved issue from the Ordovician carbonate paleokarst in the Huai-Fu Basin, which is located in the southeast of Southern North China Basin and one of the key areas for oil and gas exploration. Based on petrology, mineralogy and geochemical data, pore types, distribution characteristics, and formation stages of the Ordovician paleokarst were analyzed. Then, in attempt to define the origins of porosity development, the formation environments and mechanisms were illustrated. The results of this study showed that pore types of the Ordovician carbonates in the Huai-Fu Basin are mainly composed of intragranular pores, intercrystalline (intergranular) pores, dissolution pores (vugs), fractures, channels, and caves, which are usually in fault and fold zones and paleoweathering crust. Furthermore, five stages and five formation environments of the Ordovician paleokarst were identified. Syngenetic karst, eogenetic karst, and paleoweathering crust karst were all developed in a relatively open near-surface environment, and their formations are mainly related to meteoric water dissolution. Mesogenetic karst was developed in a closed buried environment, and its formation is mainly related to the diagenesis of organic matters and thermochemical sulfate reduction in the Permian-Carboniferous strata. Hydrothermal (water) karst was developed in a deep-buried and high-temperature environment, where hydrothermal fluids (waters) migrated upward through structures such as faults and fractures to dissolve carbonate rocks and simultaneously deposited hydrothermal minerals and calcites. Lastly, a paleokarst evolution model, combined with the related porosity evolution processes, nicely revealed the Ordovician carbonate reservoir development. This study provides insights and guidance for further oil and gas exploration in the Southern North China Basin, and also advances our understanding of the genesis of carbonate paleokarst around the world.

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Section: Discussionmentioning

confidence: 99%

Formation environments and mechanisms of multistage paleokarst of Ordovician carbonates in Southern North China Basin

Zhang

Liu³

et al. 2021

Sci Rep

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“…Subsequently, fluids such as the organic acid, TSR, and the hydrothermal fluid, upwelled along the lower wall of the fault and the fracture zone, causing multistage burial dissolution in the early-stage meteoric water diagenetic lenses (Wang et al, 2007;Sun et al, 2007), giving rise to non-fabric-selective dissolution fracture and cave systems with considerable scales. For example, the large hydrothermal genetic vugs at 6094.5 m in Well T45 were semifilled by subhedral-euhedral coarse crystalline sediments (Wang et al, 2015). The second-stage burial dissolution was manifested as dissolution of Hercynian vertical tensional fractures and high-angle fractures into wide and large dissolution-enhanced fractures and karst caves, which were subsequently filled by moderate-coarse crystalline calcite, fluorite, and crude oil.…”

Section: Diageneses and Porosity Evolution Of The Platform Margin Reementioning

confidence: 99%

Differences between reservoirs in the intra-platform and platform margin reef-shoal complexes of the Upper Ordovician Lianglitag Formation in the Tazhong oil field, NW China, and corresponding exploration strategies

Zhang

Tan

Sun

et al. 2018

Marine and Petroleum Geology

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The Upper Ordovician Lianglitag Formation in the Tazhong oil field, NW China, is dominantly composed of shallow marine carbonates, and it can be subdivided into five members lithologically. Unclear understanding of the reservoir evolution in the platform margin and intra-platform reef-shoal complexes resulted in difficulty in locating reservoirs and poor drilling success in the intra-platform. By comparing the basic characteristics, diagenesis, and porosity evolution of the two types of reservoirs, this study established their development patterns and proposed corresponding exploration strategies based on comprehensive analysis of core, thin-section, well-logging, three-dimensional seismic, and geochemistry data. The major difference between the platform margin and intra-platform reservoirs lied in their pore types. The platform margin reservoirs had fabric-selective intragranular dissolution pores, intergranular dissolution pores, moldic pores, and non-fabric-selective karst fractures and caves, and tectonic fractures, whereas the intra-platform ones only had tectonic fractures, intercrystalline dissolution pores, and intergranular vugs. In terms of distribution, the platform margin reservoirs were mainly distributed in the parasequence top and landform highlands of the highstand system tract in Members 3 to 1, appearing in two to six cycles, with large single layer and accumulative thicknesses and a quasi-bedded continuous distribution in the lateral. However, the distribution of the intra-platform ones was not obviously correlated with sedimentary facies and paleogeomorphology, with smaller single layer and accumulative thicknesses and poorer lateral continuity. The evolution and distribution of high-quality reservoirs in the platform margin were jointly controlled by eogenetic marine diagenetic and meteoric dissolution including karst, burial dissolution, and tectonic fractures. In comparison, eogenetic marine diagenetic and meteoric dissolution in the intra-platform reef-shoal complexes were weak, accompanied by persistent cementation. The favorable reservoirs were primarily controlled by fractures and later burial dissolution. Hence, for the exploration of the platform margin reef-shoal complex reservoirs, the priority should be given to the areas with the superimposition of eogenetic marine diagenetic and meteoric dissolution, burial dissolution, and tectonic fracturing. For the exploration of intra-platform reef-shoal complex reservoirs, more attention should be paid to areas with overlapped fractures and burial dissolution, especially where Hercynian strike-slip faults and early fractures were superimposed. Less attention should be paid to the areas with eogenetic marine diagenetic and meteoric dissolution.

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Diagenesis and origin of porosity formation of Upper Ordovician carbonate reservoir in northwestern Tazhong condensate field

Zhang

Cai

Liu

et al. 2017

Journal of Natural Gas Science and Engineering

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Genesis of the Ordovician fluorite and its geological significance in central uplift of the Tarim basin, China

Cited by 5 publications

References 7 publications

Formation environments and mechanisms of multistage paleokarst of Ordovician carbonates in Southern North China Basin

Formation environments and mechanisms of multistage paleokarst of Ordovician carbonates in Southern North China Basin

Differences between reservoirs in the intra-platform and platform margin reef-shoal complexes of the Upper Ordovician Lianglitag Formation in the Tazhong oil field, NW China, and corresponding exploration strategies

Diagenesis and origin of porosity formation of Upper Ordovician carbonate reservoir in northwestern Tazhong condensate field

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