Characteristics and major controlling factors of the fractures in igneous buried hill reservoirs in Huizhou Oilfield

To clarify the reservoir quality and development potential of the igneous buried hill reservoir in Huizhou Oilfield, the characteristics, spatial distribution, and key controlling factors of fractures were studied comprehensively by using the data of core, imaging logging, and thin section. Results show that three groups of NW-, NE-, and EW-trending fracture systems are developed in the buried hill reservoirs, of which the NW-trending fracture system is dominant. The main frequency of the fracture dip angle is 49°～60°. Three types of fractures were distinguished, i.e., structural fractures, dissolution fractures, and diagenetic fractures. The structural fractures are major types, followed by dissolution fractures, and diagenetic fractures are isolated and contributing little to the reservoir properties. The development of fracture was controlled by tectonic, lithologic, and fault and fluid action. Multi-stage tectonic movement was the mechanical basis of the fracture formation in the buried hill rock. Granite and diorite were conducive to the formation of fractures. The trap-control fault affected the fracture development in range of about 150 m, and the influence range of the secondary faults was about 80 m. Based on quantitative characterization of main controlling factors of fracture development, the dominant region of fractures in the buried hill was predicted by PR multiple information probability fusion method. In addition, four dominant fracture zones were recognized in the weathering zone in the buried-hill. This research provided an important reference for reservoir evaluation and development of the buried hill reservoir in Huizhou oilfield.