A study on the optimal conditions for formation of complex fracture networks in fractured reservoirs

Abstract

Hydraulic fracturing is a key technology for unconventional oil reservoirs exploitation, and the formation of effective complex fracture networks is an important index to evaluate the effect of hydraulic fracturing. Pre-existing natural fractures will seriously affect the stress distribution in the reservoirs and hydraulic fractures propagation pathways. Therefore, it is very useful to investigate the interactions between hydraulic and natural fractures. In this study, the mathematical model of stress distribution at fractures intersection and the cohesive zone method (CZM) finite element simulation model are established. The effects of different fracture intersecting angles, natural fractures dip angles and horizontal stress difference (HSD) are compared and analyzed from numerical models, finite element models, and previous scholars' laboratory tests. The results show that fracture networks are most likely to be formed if the intersecting angle and natural fracture dip angle are between 30° and 60°. It can be deduced that the larger the HSD, the longer the hydraulic fracture. The research provides a reference for the formation of complex fracture networks in fractured reservoirs.