Dynamic Distribution of Multi-stage Fracturing Flow in Horizontal Well and Optimization of Fracture Spacing

摘要

Multi-stage volume fracturing in horizontal wells is the main means for efficient reforming of unconventional reservoirs.The fracture spacing is the core parameter of multi-stage fracturing in horizontal wells.In view of the previous design studies,the spacing is optimized by constant flow,resulting in large errors in stress interference.Based on the basic equations of fluid-solid coupling and the principle of damage mechanics,the finite element model of multi-stage fracturing in horizontal wells is established by extended finite element method.The dynamic distribution of each fracture injection flow is realized by ABAQUS finite element platform and FORTRAN programming of subroutine UAMP.The principle of fracture spacing optimization is given,and the law of spacing optimization under different formation conditions and construction parameters is studied.The results show that under the small fracture spacing,the intermediate fractures are short and wide due to stress interference and inhibit expansion.The fractures on both sides are long and narrow.In the middle fracture extrusion,the fractures on both sides are prone to sand plugging,which affects the fracturing effect.Injection volume and elastic modulus are the main controlling factors affecting the fracture spacing.In high elastic modulus reservoirs,it is recommended to adopt little injection volume and large spacing;conventional formations can adopt little injection volume and small spacing design patterns,which allow multiple fractures to expand evenly and effectively while ensuring construction safety.Through the secondary development of subroutine FORTRAN language programming,the flow dynamic distribution of multi-stage fracturing process in horizontal wells is realized.The main control factors of fracture spacing optimization are studied,this is useful for rationally designing multi-stage fracture spacing and improving the effect of unconventional reservoir reconstruction.