Physical simulation test of multi-stage staged fracturing for shale horizontal wells

Abstract

In order to clarify the influence of in-situ stress difference, displacement and fracturing series on the propagation of staged fractures in shale horizontal wells, we do the research based on a true triaxial hydraulic fracturing test system, using outcrop shale samples (300 mm × 300 mm × 300 mm) as the research object, combined with the new method of fracture-induced stress detection of staged fracturing and the three-dimensional morphological structure of specimens after hydraulic fracturing test. On the condition of maximum horizontal stress > vertical stress > minimum horizontal stress, we carry out the page multi-stage fracturing test study of horizontal wells in rock outcrops, to explore the influence of in-situ stress difference, pumping displacement and fracturing series on the fracture propagation of staged multi-stage fracturing in shale horizontal wells. The research results show that: because the overburden stress is lower than the maximum horizontal principal stress, the horizontal stress difference (the value is equal to the maximum horizontal stress minus the minimum horizontal stress) remains unchanged, and the reduction of the overburden stress easily leads to the opening of the bedding joints; the greater the horizontal stress difference is, the farther the propagation distance of the cross-cutting wellbore hydraulic fracture is; the net pressure is low under small displacement, the fracturing fluid is easy to filter out, and it is not easy to produce deep-penetrating main fractures; the interference between fractures with fewer fracturing stages is weak and can open hydraulic fractures of the corresponding series; the state of in-situ stress affects the compaction of bedding fractures and rock samples. When the overlying stress is low, the fracturing fluid is easy to penetrate into the bedding fractures, and the induced stress value is small and fluctuates greatly. Combined with the pump injection pressure curve and the induced stress curve, we can more accurately undersand the process of hydraulic fracturing fracture propagation. The research results of this article can promote the in-depth study of the fracture propagation law of multi-stage staged fracturing in horizontal wells.