关键词: 古地貌, 岩溶模式, 碳酸盐岩潜山, 古生界, 南堡凹陷

Abstract: The Paleozoic buried hill in Nanpu Sag is an important target for oil and gas exploration and evaluation in Bohai Sea. In order to study the karst model of Paleozoic carbonate buried hill in No.2 fault zone of Nanpu Sag, based on core observation, thin section identification, logging analysis, structural evolution, karst evolution model, combined with paleogeomorphology characteristics, the differences of karst models in each block were comprehensively analyzed. The results show that: (1) the lithology of karst reservoir is limestone and dolomite, with the characteristics of dual pore medium. The connectivity of matrix pores is poor, and fractures play a key role in the reservoir space. They can communicate and dredge the micropores and dissolved pores developed along the fractures are important reservoir spaces. (2) The buried hill karst reservoir mainly experienced supergene karstification and burial cementation. The supergene karstification was affected by the Indosinian-Early Yanshanian thrust folding, forming the current structural pattern and fault system, controlling the development and distribution of karst reservoir. On the other hand, the burial cementation in the Middle-Late Yanshanian-Himalayan period is mainly manifested as the filling of the fracture cavity reservoir space formed earlier by surface water and formation water, which is the destructive effect in the process of karst reservoir formation. The intensity of karstification is controlled by paleogeomorphology and faults. According to the paleogeomorphic morphology and karstification intensity, karst Highlands, karst slope areas and karst depressions are divided. The differences in the development degree of karst reservoirs between different blocks and within the same block are mainly caused by the distance to the fault, the position of paleogeomorphology and the steep and gentle slope. (3) The intensity of karstification is controlled by paleogeomorphology and faults. According to the morphology of paleogeomorphology and the intensity of karstification, karst highlands, karst slope areas and karst depressions are divided. The differences in the development degree of karst reservoirs among the blocks are mainly caused by the location of paleogeomorphology and the steep and gentle slope. The gentle slope zone of paleogeomorphology near the faults has the strongest karstification, the best preservation conditions and the most developed karst reservoir, which is a favorable target for oil and gas exploration in the study area. The research results can provide reference for oil and gas exploration in carbonate buried hill.

Key words: paleogeomorphology, karst model, carbonate buried hill, Paleozoic, Nanpu Sag