Regulation Of The Net Pressure Change During Multi-cluster Fracturing In Horizontal Wells

Horizontal well combined with multi-stage slick water hydraulic fracturing has become the key technology for developing unconventional resource which has attracted more and more attention in the world in recent years.Its main characteristics are that number of fractures increases significantly while fracture spaces decrease.Previous diagnosis technology for single fracture propagation is not fully suitable for the diagnosis and evaluation of multiple fracturing propagation due to stress interference between fractures in horizontal wells,so it is necessary to investigate the fracture evaluation during multi-stage cluster fracturing in horizontal wells.In this paper,we establish the mathematical model of the net pressure by coupling the pressure drop equation,fracture width equation,material balance equation,and the fracture net pressure change over time for fracturing fluid efficiency from 0 to 1 is obtained.The mechanism of net pressure change during multi-fracture initiation has been study through combining the displacement discontinuity method,the flow distribution between multiple fractures.The model of net pressure variation during multi-fracture initiation is established by coupling calculation of fracture propagation and displacement discontinuity method.The influence factors such as injection flow rate,cluster spacing and reservoir conditions on the slope of log-log curve of net pressure and time are analyzed.Following understandings are obtained:(1)With the increase of the distance from the fracture plane,the induced stress along the direction of maximum and minimum horizontal principal stress decreases;the induced stress along the direction of minimum horizontal principal stress is greater than it on the direction of maximum horizontal principal stress;The influence area and value of force become larger when multiple fractures exist.(2)It has little effect on the slope of bi-logarithmic curve of net pressure versus time when flow rate increase,and the slope of curve could be reducing with the increase of filtration coefficient.(3)The net pressure of each cluster is higher than that of single fracture when two fractures propagation simultaneously under same flow rate;the slope of bi-logarithmic curve of net pressure versus time decline with clusters spaces increasing,similar to the filtration coefficient;the slope increases in the early period but decreases in the latter with the inject flow rate raise,even though the decrease degree is not obvious.(4)When the three fractures propagation simultaneously,the slope of the bi-logarithmic curve of net pressure versus time proportional to flow rate,but inversely to filtration coefficient and cluster spaces respectively.In this paper,the mechanism of net pressure variation in horizontal well fracturing with multiple fractures has been studied.The research conclusion has certain guiding significance for judging whether the treat pressure is normal and analyzing the net pressure accurately.