Study on diagnosis method of fracture network complexity after fracturing in deep ultra-deep reservoir

The post fracturing production of deep and ultra-deep reservoir layers is closely related to the complexity of fracture formation. Diagnosing the complexity of the fracture network after fracturing is of great significance for analyzing the effectiveness of fracturing transformation and optimizing fracturing design. At present, direct monitoring methods such as microseismic and wide area electromagnetic methods are limited in their application in deep and ultra deep reservoirs. How to fully utilize fracturing construction curves to diagnose the complexity of fracture networks has gradually become a research hotspot. Therefore, based on the principle of conservation of mass and equivalent fracture theory, this article couples the filtration of fracturing fluid in matrix multi-stage fractures, establishes a pump stop pressure drop model, and forms a fracture network complexity diagnosis method based on the main fracturing pump stop pressure drop. The effectiveness of this model and method is verified and analyzed by combining field well data. The results show that: (1) the natural fracture level is an important factor affecting the pressure drop of fractured reservoirs. The larger the fracture level, the more complex the post compression fracture network and the higher the post compression production; (2) For wells with multi-level natural fractures, due to the effect of diversion, the expansion of the main fracture is limited, resulting in an approximately negative correlation between the length and area of the main fracture and the open flow rate under this condition. However, the multi-level fracture network space formed under this condition can control more oil and gas reservoir volumes, resulting in higher fracturing fluid efficiency, more effective proppant paving, and higher post fracturing production.The diagnostic method established in this article can quickly determine the fracturing construction effect of deep and ultra deep reservoirs, analyze the fracture network morphology after fracturing, and provide guidance for subsequent fracturing optimization design.