Analysis of the Main Controlling Factors of the Fractured Reservoirs Development in the Buried Hills of the Archean Metamorphic Rocks in the Bohai Sea Area

In recent years, multiple billion ton oil and gas fields have been discovered in the Precambrian metamorphic rocks of the Bozhong Depression and Liaodong Bay area, with height of oil and gas column exceeding 1 000 m, demonstrating the exploration potential of the Archean buried hills. Research has shown that the degree of reservoir development determines the oil reservoir scale of the Archean buried hill, and fractures plays a key controlling role in the reservoir. The lithology has a significant impact on the development degree of fractured reservoirs, The reservoirs with high content of plastic minerals such as biotite and hornblende are not well-developed, while fractures are developed with high content of feldspar and quartz minerals. The weathering and leaching during the epigenetic stage reduce the compressive strength of rocks, and the degree of crack development and recorded stages in the weathering crust are much higher than those in the inner zone. Experiments and thin section analysis have shown that samples with early developed fractures, although filled with minerals, have significantly reduced compressive strength, laying the foundation for later crack development. The later fractures will choose to reactivate the original crack zone, and fractures filled with clay minerals, carbonate minerals, and iron minerals are more susceptible to reactivation under the influence of later stress and fluid.Macroscopically, the Indosinian period was a critical period for the formation of fractured reservoirs due to thrust and overturning. The superimposed transformation of faults during the Yanshan and Himalayan periods played an important role in activating early fractures. The distribution of thick reservoirs was controlled by the overlapping of faults during the Indosinian, Yanshan, and Himalayan periods.