Eogenetic Karst in Interbedded Carbonates and Evaporites and Its Impact on Hydrocarbon Reservoir: A New Case from Middle Triassic Leikoupo Formation in Sichuan Basin, Southwest China  

作　　者：Hong Liu Xiucheng Tan Ling Li Xiong Ding Jian Cao Guang Yang Teng Ma 

机构地区：[1]State Key Laboratory of Oil and Gas Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China [2]School of Earth Sciences and Technology, Branch of Sedimentology and Hydrocarbon Accumulation, CNPC Key Laboratory of Carbonate Reservoir, Southwest Petroleum University, Chengdu 610500, China [3]Department of Earth Sciences, Nanjing University, Nanjing 210023, China [4]Institute of Petroleum Exploration and Exploitation, PetroChina Southwest Oil and Gas Field Company, Chengdu 610051, China

出　　处：《Journal of Earth Science》2019年第5期908-923,共16页地球科学学刊（英文版）

基　　金：funded by the “13th Five-Year Plan” National Science and Technology Major Project of China(No.2016ZX05004002)

摘　　要：Karst in interbedded carbonates and evaporites has been reported to have important and complex impacts on reservoir. It is significant for exploration and karst geology. Here, we report such a new case from Middle Triassic Leikoupo Formation of Sichuan Basin, Southwest China. Stratigraphic incompleteness and the occurrence of unconformity provide evidence for the presence of eogenetic karst. Under the impact of this eogenetic karst, residual weathered and solution-collapse breccia, solution pores and silicification and dedolomitization have been observed. Classic stratigraphic zonation of karst is not readily distinguishable, which is ascribed to the stratigraphic collapse of carbonate rocks resulting from the dissolution of evaporites by lateral subsurface fluid flow. In terms of impact on reservoir quality, karst can generally improve the initial physical property of the porous layers in theory. However, subsurface fluid flow dissolved the evarporitic beds and facilitated the collapse of overlying strata. As a consequence, the lateral continuity of the reservoirs would be destroyed, and relatively high-quality reservoirs can only be developed with little collapse of overlying strata, reflecting reservoir heterogeneities. This may be a general feature of reservoir formation under the impact of karst in interbedded carbonates and evaporites.Karst in interbedded carbonates and evaporites has been reported to have important and complex impacts on reservoir. It is significant for exploration and karst geology. Here, we report such a new case from Middle Triassic Leikoupo Formation of Sichuan Basin, Southwest China. Stratigraphic incompleteness and the occurrence of unconformity provide evidence for the presence of eogenetic karst. Under the impact of this eogenetic karst, residual weathered and solution-collapse breccia, solution pores and silicification and dedolomitization have been observed. Classic stratigraphic zonation of karst is not readily distinguishable, which is ascribed to the stratigraphic collapse of carbonate rocks resulting from the dissolution of evaporites by lateral subsurface fluid flow. In terms of impact on reservoir quality, karst can generally improve the initial physical property of the porous layers in theory. However, subsurface fluid flow dissolved the evarporitic beds and facilitated the collapse of overlying strata. As a consequence, the lateral continuity of the reservoirs would be destroyed, and relatively high-quality reservoirs can only be developed with little collapse of overlying strata, reflecting reservoir heterogeneities. This may be a general feature of reservoir formation under the impact of karst in interbedded carbonates and evaporites.

关 键 词：KARST carbonate reservoir EVAPORITE Middle TRIASSIC Leikoupo Formation Sichuan Basin 

分 类 号：P[天文地球]