Study and Application of Fracture Development Patterns and Injection-Production Connectivity Based on Structural Evolution Analysis

The Jinzhou South Oilfield in the Bohai Sea is a typical fractured reservoir in a metamorphic rock basement. It has now entered the medium to high water cut stage, with complex water breakthrough patterns in oil wells and unclear understanding of remaining oil distribution. The difficulty of stabilizing oil production and controlling water production is increasing, making it urgent to conduct research on the classification of fractured reservoirs and the distribution of remaining oil. The results show that the orientation, density, aperture of fractures, and the distance between oil and water wells have a significant control effect on the water cut increase in oil wells and the distribution of remaining oil. Therefore, based on the understanding of the fracture development pattern throughout the oilfield, the fractured reservoirs are further classified into three types: anticline type, semi-anticline type, and slop type. Numerical simulation techniques are used to study the distribution patterns of remaining oil in different types of reservoirs. The anticline type reservoir mainly develops tensile fractures in the core of the anticline and conjugate compressive-torsional fractures in the wings. The connection between oil and water wells is poor, the water-free production period is long, and the remaining oil is mainly concentrated in the matrix system. The semi-anticline type reservoir, in addition to tensile fractures in the core and compressive-torsional conjugate fractures in the wings, also develops a set of tensile fractures caused by faults. This set of fractures controls the direction of water breakthrough, and the remaining oil is concentrated in the direction where this set of tensile fractures is not developed. The uplifted anticline type reservoir mainly develops one set of conjugate fractures and one set of tensile fractures. The connection between oil and water wells is good, and the oil wells are prone to water breakthrough. A large amount of remaining oil is concentrated in the fracture system and the matrix system. This research result has guiding significance for improving the development effect of metamorphic rock basement fractured reservoirs in the middle and late stages.