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Geoscience ›› 2022, Vol. 36 ›› Issue (02): 695-708.DOI: 10.19657/j.geoscience.1000-8527.2022.193

• Oil and Gas Exploration • Previous Articles     Next Articles

Stratified Structure and Formation Mechanism of Paleokarst Cave in Carbonate Reservoir of Tahe Oilfield

CHEN Huaxing1(), KANG Zhihong1(), KANG Zhijiang2   

  1. 1. School of Energy Resources, China University of Geosciences, Key Laboratory for Marine Reservoir Evolution and Hydrocarbon Abundance Mechanism(Ministry of Education), Beijing 100083, China
    2. SINOPEC Petroleum Exploration and Production Research Institute, Beijing 100083, China
  • Received:2021-10-18 Revised:2022-03-15 Online:2022-04-10 Published:2022-06-01
  • Contact: KANG Zhihong

Abstract:

With the constantly deepening development of carbonate reservoir, the structural characteristics of stratified cave reservoir and the similar connection characteristics of fluid dynamic in same layer,has been gradually discovered and attracted by researchers. Structure, formation factors and processes of stratified paleokarst were the key to the effective development of this kind of reservoir. Based on comparison of the in-situ stratigraphic fabric and the characteristics of field karst caves, it is considered that Tahe Ordovician karst systems have better correlation marker stratums and lithology difference, which lays a material foundation for the development of stratified karst caves. Geological phenomena including multi-layer karst caves along horizontal bedding and tube-shaped ancient underground steams controlled by bedding cracks in the field verify the widespread existence of stratabound karst. On the basis of well identification, well logging correlation, well performance and seismic waveform characteristics in karst caves, such as the typical karst cave zone, three main cave layers were identified and a brand-new geological structure profile of three-layer cave reservoir was established: The caves in the first layer were mainly filled with glutenites, the caves in the second layer were large in scale and seriously filled with mud, and the caves in the third layer were small in scale and mainly developed in karst landform highlands. Formation mechanism of stratabound karst was discussed by using modern karst theory: carbonate host rock fabric was one of the material basis and main controlling factors for karstification, karst water in subsurface flow zone (full of CO2) controled the lateral development of karst caves, The karst palaeogeomorphology controled the lateral difference of caves in the same layer, The vertical migration of groundwater level controled the karst stages and stratified structure of the caves under gentle formation conditions. Finally, on the basis of research and understanding, the development model of stratabound karst reservoir was constructed by integrating all karst controlling factors.

Key words: Tahe Oilfield, carbonate reservoir, paleokarst reservoir, stratified structure, formation mechanism, karst evolutionary pattern

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