Features And Formation Mechanisms Of Ordovician Fractures In Tahe No.2 Oilfield

At present, China's dependence on foreign oil becoming increasingly high year by year, with the reserve reducing, of conventional porous type reservoirs, fractured reservoirs will become one of the main direction in search for hydrocarbon-bearing pool. Experts predicted that the field of marine carbonates would be a new growth point of the world's oil energy. Striking characteristic Fractures of a carbonate reservoir, exploration and development on carbonate fractured reservoir is of great importance.In this paper, under the structural settings of the study area and its adjacent regions, based on the outcrops, cores, thin sections, as well as the conventional logging, imaging logging and dynamic observation data, we conducted a comprehensive study on determining the distribution characteristics of fractures in the work area to find out the main controlling factors and analyse its causes, by using geological analysis, probability and statistics method, and analogy and other methods. The main content of this paper can be described as follows: the study on the fracture characteristics of Ordovician outcrop area and the comparison between work areas; summarizing and analyzing the main parameters of fractures in the work area; identifying features of fractures by FMI logging data and determining the predominant strike of the fractures in the work area; using conventional logging data for interpreting the intervals of interests of Ordovician and studying the distribution characteristics of fractures the study area; and finally analyzing the main controlling factors and causes of fractures in the work area.Based on the previous research on Ordovician fractures in Tahe No.2 oilfield, some achievements have been achieved: first, by comparion, we found that high-angle shear cracks is the main type fractures in the work area, which play a positive role in hydrocarbon migration and accumulating. Second, based on a comprehensive comparasion of various methods, fractures in the work area are divided into four major formative periods, the early diagenesisâ… f ractures, the Caledonianâ…¡fractures, the early Hercynianâ…¢fractures and the late Hercynianâ…£fractures. Third, the O2yj Formation and O1-2y formation is the most developed cracks in work area, the main fracture strikes are near EW, near NS, near NE, and near NE cracks are the best in oiliness. Fourth, the early Hercynian SE-NW compression stress is formed by the interaction of near SN, near EW shear fractures and near NE arched fractures. Fifth, the northern part of the Upper Ordovician erosion zones which is identical to the Upper Ordovician pinch-out line and work areas near the pinch-out line is the favorable regions for developing fractures and high-productivity wells. Sixth, rock property, tectonic stress field, local parts of structure, karstification and diagenesis are the main controlling factors of fractures in the work area.