The flow field and pressure field of low-permeability reservoirs are changed by dynamic fractures

significantly affecting the swept volume of water flooding. Comprehensively using the data of imaging logging

core analysis

rock mechanics experiments

production performance

and dynamic monitoring

the paper analyzes the characteristics and controlling factors of dynamic fractures in four typical ultra-low permeability reservoirs in the Ordos Basin

including Jing’an

Ansai

Xifeng

and Huaqing. Based on their geneses

dynamic fractures can be classified into two types

i.e.

being formed by exceeding the rock formation’s fracture pressure and activated by natural fractures. According to impacts on the water cut of oil wells

they can be divided into unidirectional and multidirectional dynamic fractures. The evolution of dynamic fractures undergoes four stages:rapid growth to a certain scale

a fixed length

and a maximum length

and contraction stage; the extension direction of fractures is primarily controlled by the current maximum horizontal principal stress direction. The development intensity of dynamic fractures is influenced by factors such as matrix permeability

natural fractures

rock brittleness index

as well as development technology policies. The lower matrix permeability

more developed natural fractures

higher brittleness index

and stronger water injection development technology policies are easier for the formation of dynamic fractures

and the transition from unidirectional to multidirectional fractures. Dynamic fractures significantly affect the water cut increase regularity of oil wells and the distribution of remaining oil.