Taking the fractured tight reservoir of the Fengcheng Formation in Mahu Depression as the research object, the RFPA software, a numerical simulation platform of real fracture process, was used to study the fracture propagation laws in fractured tight reservoirs during the fracturing process. On this basis, the influences of different factors on the fracture propagation laws in the fractured tight reservoirs were investigated, the influences of various factors on fracture propagation were quantitatively analyzed by the gray correlation method, and then the fractability calculation model for evaluating the fracturing effects was obtained by the analytic hierarchy process method. The results show that when the fracture angle is less than 70°, the natural fracture controls the hydraulic fracture propagation direction, whereas when the fracture angle is greater than 70°, the maximum horizontal principal stress controls the hydraulic fracture propagation direction. With the increase of the fracture angle, the hydraulic fracturing area firstly decreases and then increases, whereas with the increase of the fracture density, the hydraulic fracturing area gradually increases. The hydraulic fracturing area increases as the fracture compressive strength, tensile strength and elastic modulus reduction factor increase, whereas the hydraulic fracturing area decreases as the fracture Poisson's ratio reduction factor increases. Based on the gray correlation method, the ranking of the fracturing effect is clarified as fracture density > horizontal stress difference > fracture angle > elastic modulus > compressive strength > tensile strength > Poisson's ratio. Using the analytic hierarchy process, a model for calculating the reservoir fractability index is established, and has a good positive correlation with the dimensionless fracturing area.
Keywords: fractability index; hydraulic fracture; natural fracture; numerical simulation; tight reservoir.