Formation And Genetic Relationship Of Different Types Carbonate Reservoirs In Lower Palaeozoic In Tazhong Area, Tarim Basin

Many kinds of carbonate reservoirs are developed in Cambrian-Ordovician in Tazhong area, and they have the traits of strong inhomogeneity, multi-influential factor, and great prediction difficulty et.al.. Based on the theories of structural geology, sequence stratigraphy, sedimentology and reservoir geology, the dissertation aims to study the distribution rule and genetic relation of different types carbonate reservoirs in Cambrian-Ordovician of Tazhong area in Tarim basin, which comprehensively uses various data such as seismic, outcrop, and well-logging data et. al.. The study result shows that origofacies, diagenesis, and tectonic movement are the homo-restriction factors of the development of different types of carbonate reservoirs. The features of sequence and system tract determine the reservoir distribution.On the basis of the establishment of Cambrian-Ordovician sequence stratigraphy framework in Tazhong area, the analysis of facies plane distribution rule and vertical development character, and the dissection of platform structure style, the author puts different carbonate reservoirs into the isochronous stratigraphy framework, and finds that the sequence has important impact on different carbonate reservoirs in Tazhong area. Eustatic sea level change and platform structure style control the development types of reef-bank and the transference of reef-bank facies. And different grade sequence borders determine the development of karst reservoir under border. The cyclicity exposure of carbonate rock caused by high-frequency sequence border and the third order sequence border has formed many periods karst intervals. With the base-level descent, the scale of karst development intervals in the top of high-frequency prograding sequences has the increase trend. So the large unconformity corresponded with the first or second order sequence border is the key control factor of the karst reservoir development in Tazhong area. Sequence stacking pattern and system tract control the development of dolomite reservoir, and the shelf margin system tract above the II type sequence border is the best favorable horizon of dolomite reservoir.Karst reservoir, reef-bank reservoir and inside dolomite reservoir in Tazhongarea have distinguished differences in distribution rule and main controlling factors, yet exist the genetic relationship. Reef-bank reservoir is developed in upper Ordovician platform-margin slope, and affected by palaeogeomorphology, tectonic action, deposition and diagenesis. Karst reservoir is generated in lower Ordovician karst slope belt, and controlled by surrounding rock type, fluid, palaeoclimate, tectoclase and diagenetic environment et.al.. Inside dolomite reservoir is created in Cambrian buried hill and slope belt of half graben, and restrained by tectonic fracture, intensity and type of dolomitization, facies belt and corrosion et.al.. Therefore, facies belt is the basement of the development of carbonate reservoir, and diagenesis is the indispensable condition of that, and then structure fracture is the key factor of that.Combinating all researches about reservoir, and applying multi-factor stacking analytic approach, the research shows that the north and the south slope belt in Tazhong area is the optimum position for reef-bank reservoir development. Moreover, the result of research reveals the best karst reservoir in upper Ordovician is grew in the area surrounding the central fault belt surrounding area and the southern area to the line well TZ48- well Z2- well TZ5-well TZ8-well TB2. And then Cambrian inside dolomite reservoir is mainly developed in the east burial hill belt surrounding area and the center slope belt of half graben in Tazhong area.