Abstract: Waterflooding-induced fractures are the by-products during long-term water-injection in low-permeability reservoirs,seriously affecting the performance of oil reservoir.We study the major factors controlling the formation and development of these factures in Chang 6 reservoir in Ansai oilfield,Ordos Basin,using geological,logging,testing and production performance data.The formation of these fractures is mainly controlled by both geological and engineering factors.The geological factors refer to natural fractures,current in-situ stress,reservoir architecture and rock mechanical properties,and the engineering factors mainly include artificial fractures and injection-production parameters (such as injection time and volume,injection-production ratio or injection-production volume,etc.).Natural and artificial fractures serve as physical stimuli to the formation of waterflooding-induced fractures; current in-situ stress controls the dominant direction of the fractures,and indirectly affects their propagation; architecture units and architecture interfaces of various levels control the scale and propagation extent respectively; reservoir rock mechanical parameters constrain,to a certain extent,the propagation routes; and injection-production parameters control the formation and propagation speed to the most.

Key words: waterflooding-induced fracture, waterflood development, low-permeability reservoir, Ansai oilfield, Ordos Basin