Study On Sedimentary Characteristics And Reservoir Distribution Of Ordovician Inter - Housing In The Central And Western

Based on plenty of document study, using methods of combination of macroscopy and microcosmos, and under the guidance of new theory and methods, such as carbonate sedimentology, paleobiology and reservoir geology, and under the foundation of core observation and thin slices analysis, and efficiently making use of well drilling data, logging data, well logging and seismic data, this paper discusses those following aspects of Yijianfang formation Upper Ordovician in Tazhong western area:stratum distributing laws, main types of sedimentary facies and their distribution, reservoir characteristics description, reservoir evaluation, reservoir property controlling factors and prediction of favorable reservoir distribution areas etc.By the analysis of guide fossil, it is believed that the lower section of the former Lianglitage formation is the Yijianfang formation of Middle Ordovician, then a pressing problem of research on sedimentary feature and reservoir distribution comes into our eyes which needs to be solved quickly. According to the new regional stratigraphic classification plan, stratigraphic division and comparison are done, and combing with seismic data and structural feature, the thickness and distribution of Yijianfang formation is analyzed. Under the identification of various facies symbol, we find that the facies in study area is mainly open platform, including intraplatform bank subfacies and interbank sea subfacies, vertically displaying cyclic assemblages of intraplatform bank and interbank sea. Horizontally, intraplatform bank is thick and continuous, and interbank sea is relatively less, mainly distribution in the lower-middle part of Yijianfang formation.With the analysis of reservoir property and reservoir space types in bank reservoir of Yijianfang formation in study area, it comes to a conclusion that the main reservoir type is hole-type reservoir, followed by fractured and porous reservoir, and fractured reservoir is relatively less, and a certain amount of cave reservoir distribute in the upper part of Yijianfang formation. According to the reservoir evaluation criterion, the type III reservoir is the main reservoir type, type Ⅰ and type Ⅱ are less developed and take a small part. Efficient reservoir mainly develop in the middle-upper part of Yijianfang formation, which is horizontally continuous and can be compared with adjacent wells, while, there are less reservoir developed in the lower part of Yijianfang formation.Reservoir distribution in study area is affected by many factors, for example, lithological association and facies, weathering karst, buried karst and multi-episodic activity of faults. Among those factors, the lithological association and facies forms the material basis, which is benefit for reservoir development. Weathering karst is the primary cause of high quality reservoir formation, during the process, plenty of solution pore and cavity was formed, the most developed reservoir zone lies in Horizontal undercurrent belt. Buried karst improved reservoir property by reconstructing the former holes and fractures. Faults and fractures improve the performance of reservoir seepage and accelerating the process of karst. Based on the analysis of many controlling factors, a prediction of favorable reservoir developing areas is made, which shows that favorable reservoir development areas mainly distribute along the direction of faults, while the area with less faults is bad for reservoir development. And those achievement can be used in the exploration and development process of Yijianfang formation.