Palaeokarst Geomorphological Restoration and Geological Significance in the Eastern Maoerxia Subsection of the Ancient Uplift in Central Sichuan
Weathering crust karst reservoirs are considered one of the important types of carbonate reservoirs,widely present in sedimentary basins in China.The Maokou Formation in the eastern part of the Leshan Longnvsi ancient uplift in central Sichuan has developed dolomite karst reservoirs,mainly distributed in the lower sub section of Mao'er.Predicting the favorable areas for dolomite karst reservoirs in the lower sub section of Mao'er plays an important indicative role in the exploration and development of the Maokou Formation in the study area.This article is based on three-dimensional seismic data,rock cores,and imaging logging data,and uses residual thickness method and impression method to finely depict the ancient karst topography of the Mao'er Lower Member.According to the restoration results of ancient karst landforms using the imprinting method,the karst landform units are divided.The atmospheric fresh water dissolution and leaching effect is the strongest and most influential in the karst slope area,and the slope area is the most favorable area for karst development.The karst highlands and depressions are the secondary favorable areas for karst development.According to the results of the residual thickness method for karst landform restoration,vertical karst zoning is carried out.The vertical seepage zone and horizontal subsurface flow zone are the main areas of karst action in the Maokou Formation in the study area.A comprehensive evaluation model for ancient karst landforms in the study area was established by combining the residual thickness method and the imprinting method.The residual thickness method characterized the pattern of vertical zoning of karst landforms,while the imprinting method characterized the strength of karst landforms by dividing them into karst geomorphic units.Based on the above two methods,it is believed that the overlapping area between karst slopes,vertical seepage zones,and horizontal subsurface flow zones is the most advantageous area for karst reservoirs,providing a basis for quantitative prediction of karst reservoirs in the next step.
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