Fracture Propagation Mechanism of Radial Well-Guided Preflush Fluid Acid Fracturing under Injection Discharge Control

Abstract In view of the low availability of carbonate reservoirs, a radial well-assisted preflush acid fracturing technology is proposed to help communicate oil and gas reservoirs in non-principal stress directions. The acid fracturing model of the auxiliary preflush in the radial well is established by using the extended finite element and the two-scale continuous model. The mechanism of fracture directional propagation under the control of injection discharge is analyzed, and the deflection coefficient is introduced to characterize the guiding effect quantitatively. The effects of different in-situ stress differences and injection discharge on the guiding effect and guiding mechanism of radial wells are studied emphatically. The results show that the induced stress field caused by radial wells and the high-pressure gradient at the end of fractures are the main reasons for the directional propagation of fractures. Horizontal in-situ stress difference is the main factor, which influences the guiding effect by controlling the induced stress field and pressure gradient. The radial well can effectively guide fracture propagation when the local stress difference is less than 3 MPa. The preflush fluid discharge and acid discharge are important factors affecting the guiding effect. The preflush fluid discharge affects the guiding effect by controlling the induced gravitational field and pressure gradient. The preflush fluid discharge between 2.5-3.5 m 3 ·min -1 is most conducive to the directional expansion of acid fracturing cracks. The acid discharge affects the guiding effect by controlling the pressure gradient: the smaller the acid discharge, the more unfavorable the directional expansion of the acid fracture. Compared with the preflush fluid discharge, the influence of the acid discharge is smaller. The theoretical basis can be used in the field application of radial well-assisted preflush fluid acid fracturing technology through the article.