Research on optimization crack monitoring technology for construction parameters of coalbed methane well seam reconstruction

Coal reservoir has the characteristics of low pressure, low permeability and low saturation, and rock mechanical properties are characterized by low Young's Modulus, large variation of anisotropy and small stress difference between upper and lower compartments. In the early stage, large displacement and large-scale active water fracturing technology were widely used, and the fracture height was easy to get out of control. It was difficult to form fracture net volume in coal seam fracturing, and the fracturing effect was not ideal. In order to release coalbed methane to the greatest extent and improve the volume of reservoir reconstruction, the relationship between fracturing fracture morphology and construction parameters is studied qualitatively or quantitatively under different geological conditions by means of effective fracture monitoring technology, and the fracturing construction parameters and fracturing design were optimized. Through the above technology, the graphical characterization of fracturing cracks can be realized, which is helpful to judge the fracture morphology of coal seam fracturing. The results show that stress difference coefficient is the key factor of fracture morphology. Coal seam with stress difference coefficient less than 0.3 is favorable for the formation of network cracks in coal seam; coal seam with stress coefficient greater than 0.3 is not easy to form network cracks. Under the condition that the difference of maximum and minimum horizontal principal stress is small, the small-displacement and high-viscosity silicone fracturing fluid construction process can form a network crack; under the condition that the maximum and minimum horizontal principal stress difference is large. In the composite fracturing fluid system, the low-viscosity liquid is used to form the network crack in the pre-liquid phase, but the low-viscosity liquid displacement needs to determine the range of the fracturing displacement according to the stress difference of the interlayer to prevent the pressure layer and the sand-carrying stage. The use of high-viscosity liquids improves the conductivity of the fractures, and finally forms an ideal network crack in the coal seam.