Palaeokarst characteristics of carbonate rocks of the Middle Permian Maokou Formation in southern Sichuan Basin:Example of strata-bound eogenetic karst in palaeo-continental settings
Xiao Di1,2, Tan Xiucheng1,3, Xi Aihua2, Liu Hong2,3, Shan Shujiao4, >Xia Jiwen5, Cheng Yao1,2, Lian Chengbo1,2
1 State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,Sichuan
2 Department of Earth Science and Technology,Southwest Petroleum University,Chengdu 610500,Sichuan
3 Branch of Deposition and Accumulation,PetroChina Key Laboratory of Carbonate Reservoir, Southwest Petroleum University,Chengdu 610500,Sichuan
4 Research Institute of Exploration and Development,PetroChina Southwest Oil and Gas Field Company,Chengdu 610051,Sichuan
5 Branch of Shunan Gas Field,PetroChina Southwest Oil and Gas Field Company,Luzhou 646100,Sichuan
By use of drilling, logging,core,and thin section data,the karst characteristics of carbonate rocks of the Middle Permian Maokou Formation in southern Sichuan Basin are studied. Maokou Formation,a deposition of open-sea platform,is characterized by the interbedding of grainstone of bank facies and micrite limestone of non-bank facies with unequal thickness. The karst is mainly developed at the upper part of Maokou Formation,with a large amount of dissolved fissures and caves overwhelmingly filled by substances from various sources including dissociated carbonate fragments,calcite crystals and carbonous clays,and no sign of karst breccia. The karstification belongs to eogenetic karst in palaeo-continental settings,which is significantly featured by the dissolution-filling controlled by its lithology and lithofacies:Micrite limestone within non-bank facies is compact,and shows little sign of dissolution-filling,while grainstone within bank facies is characterized by good karst development,and three zones of dissolution-filling can be recognized including matrix,half-dissociated and mixed-filling zones. Based on the above characteristics,it is suggested that high porosity-permeability layers of grainstone and compact ones of micrite limestone were multi-cycle superimposed vertically,and primary porosity-permeability system accompanied by faults and fissures provided sufficient channels for karst water,which resulted in the whole karst system featured by contemporaneous mult￣layer and grain￣bank facies controlled. The karst reservoir, therefore,favored to develop in both karst platform and karst slope. The research result will not only provide supplement and reference for the existing studies of the subject,but also is of meaning to the oil and gas exploration of Maokou Formation.
Xiao Di,Tan Xiucheng,Xi Aihua et al. Palaeokarst characteristics of carbonate rocks of the Middle Permian Maokou Formation in southern Sichuan Basin:Example of strata-bound eogenetic karst in palaeo-continental settings[J]. JOPC, 2015, 17(4): 457-476.
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