Study Of Cambrian-Ordovician Carbonate In Nanpu Sag Peripheral Of Bohaiwan Basin

Because of the serious heterogeneity, carbonate reservoir has been the challenge to the petroleum geology, and the further research is always making just for the great petroleum reserves.The exploration started from 60's of last century in peripheral of Nanpu sag, but the extent of exploration and knowledge are low at present. However in recent years many important discoveries show the great oil & gas exploration potential. Taking the Paleozoic Cambrian-Ordovician carbonate reservoir in peripheral of Nanpu sag as the study object, based on traditional thin section, cast thin section, mercury intrusion analysis, scanning electron microscope, X-ray diffraction, full chemical analyses, physical analysis, the rock type, chemical constituent, mineral composition, texture and structure, sedimentary characteristics and sedimentary environment, reserving property, reserving space type and its feature, distribution, genesis, law and influence factors to fracture are studied under the guidance of petrology, sedimentology, reservoir prediction, buried-hill accumulation by the means of field investigation and core observation. At the same time the comprehensive analysis of influencing and controlling factors and synthetical evaluation to carbonate reservoir, the study of Paleozoic buried-hill accumulation mode are done, and the potential exploration target are determined.Thin section, X-ray diffraction, full chemical analyses are employed to identification the main rock type, mineral composition, texture and structure. The main rock types of Cambrian-Ordovician carbonate, which is characterized by mud-crystal structure or powder-crystal structure, fine crystalline structure for a little, are composed of limestone, dolomitic limestone, argillaceous limestone, calcareous dolomite, argillaceous dolomite, dolomite. The main mineral compositions are: calcite, dolomite, and little of argillaceous, pyrite, siliceous and gypsum.Cambrian-Ordovician carbonate reservoir is evaluated synthetically. And the result shows that it can be classified into four types. The first class is fracture-corrosion pore reservoir, which reservoir space includes fine dissolved pore, large-medium size hole, small fracture or big dissolved pore, large-medium size hole, medium-size fracture. The second class is cavity-fracture reservoir, which reservoir space includes large-medium size hole, small fracture, or large-medium size hole, medium size fracture. The third class is dissolved pore and fracture reservoir, which reservoir space includes fine pore, small fracture or fine pore, medium size fracture. The forth class is compact reservoir, which reservoir space consists of micro-pore, micro-crack, and micro-fissure. According to the above reservoir class, each formation of Cambrian-Ordovician reservoir is evaluated, and the new favorable formations are put forward, it provides a direction for the future exploration.It discusses the influence factor to Cambrian-Ordovician carbonate reservoir, such as petrology, diagenesis, tectonic, paleokarst, etc. And it is put forward firstly that there exists the late burial organic dissolution, which overprints the early paleokarst, improves the reservoir, and is one of the important factors to improve store-permeability conditions and reservoir formation.It establishes the hydrocarbon accumulation mode of Cambrian-Ordovician carbonate ancient buried-hill, summarizes the key control factors of hydrocarbon accumulation and oil & gas distributing rule. Ancient buried-hill accumulation is mainly controlled by fault and weathering crust, which are also the hydrocarbon migration pathway. From the view of stratum, oil & gas is distributed mainly in the formation of Fujunshan, Xiamajiagou, Mantou, Liangjiashan, Maozhuang. From the view of lithology, oil & gas is distributed mainly in limestone and dolomitic limestone. There exist two types of hydrocarbon reservoir, including structural-massive hydrocarbon reservoir and buried-hill unconformity hydrocarbon reservoir. The key factors, which control the accumulation, consist of valid reservoir, migration pathway, lateral joint, and the spatial relationship between reservoir and hydrocarbon generation sag.Based on the research results of carbonate reservoir and previous research, combine the accumulation mode of buried-hill, the prospective sites are put forwarded and evaluated. In Xinanzhuang-baigezhuang uplift, Cambrian buried-hill reservoir is the potential target. In Laowangzhuang-luochaowan uplift, Cambrian-Ordovician reservoir is the exploration object. Upper tertiary low amplitude tectonic reservoir is the favorable exploration direction in the area of Matouying uplift.