Oil & Gas Geology ›› 2019, Vol. 40 ›› Issue (4): 738-751.doi: 10.11743/ogg20190405

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Formation of fault bend fold-controlled meteoric karst reservoir in the middle and late Himalayan movement: A case study of the Dawangou Formation carbonate rocks at Yangjikan section, Keping, northwestern Tarim Basin

Qian Yixiong1, Tian Mi1, Li Huili2, Chen Yue1, Sha Xuguang3, Li Hongquan3   

  1. 1. Wuxi Research Institute of Petroleum Geology, Petroleum Exploration and Production Research Institute, SINOPEC, Wuxi, Jiangsu 214151, China;
    2. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China;
    3. Research Institute of Exploration and Development of Northwest Oilfield Branch Company, SINOPEC, Urumqi, Xinjiang 830011, China
  • Received:2018-01-15 Revised:2018-11-08 Online:2019-08-28 Published:2019-06-01

Abstract: The karst profile at Yangjikan section, Keping, northwestern Tarim Basin, provides an excellent opportunity to evaluate the relative importance of reaction between fault bend fold-controlled uplift and meteoric water dissolution-controlled karstification during the middle and late Himalayan movement; and then the porosity caused by interlayer decollement under structural compression and dissolution was estimated, in line with the comprehensive study of petrographic, geochemical and fold disengaging analyses.The fold disengaging(simulated with VSD)facilitated the result of 0.2%-0.5% porous zones, accounting for 1/50-1/100 of the effective and actual empty-cavity rate.However, the porous zones have played a significant role in Darcy flow channel formation and karstification.The breccias related to mechanical fracture filling, calcareous tufas and megacrystalline calcites are well developed in the Yangjikan section karst reservoir.Compared to the surrounding rocks of the Dawangou Formation, the negative and linear correlation of δ18O(PDB)and δ13C(PDB)in the formation is distinct, and single-phase aqueous inclusions, typical products of meteoric water karstification, grew in the megacryst calcites within fractures and cavities.A successive tufa depositions from the lower to the upper section of karst profile, are characteristic of weakening negative depleted δ13O(PDB), δ18O(PDB) and δ34S(V-CDT).The content of Al2O3, Fe2O3, MgO, K2O, and Na2O decreases from tufas to megacrystalline calcites to(long)cylindrical scalenohedron calcites, indicating a transition in climate conditions from semi-wet to humid, to semi-humid and then to drought, as well as changes of hydrodynamic conditions.Moreover, the karst cavern of 1.5m-2.0m high can be formed within less than 5ka under a hot humid and strong hydrodynamic condition, while it may take a longer time in semi-humid and drought climate.

Key words: fold disengaging(VSD), geochemistry, karst, carbonate rock, Dawangou Formation, Middle and Late Himalayan movement, Keping-Yangjikan, Tarim Basin

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