Study On Optimization Of Horizontal Well Re-Fracturing In Ultra-low Permeability Reservoirs

In the ultra-low permeability reservoir,the flow conductivity of initial fracture in the horizontal will drop to invalid due to development and geological aspects,resulting in well production cannot meet the expected requirements and need to re-fracture immediately.Compared to vertical wells re-fracturing,the previous research cannot consider the effect of fracture distribution on re-fracturing time,and had not research flow mechanism with multiple fractures.Therefore,it's necessary to research the re-fracturing time and flow mechanism of the horizontal well re-fracturing.Base on the different development patterns characteristics of horizontal wells in ultra-low permeability reservoir,carried out the research of re-fracturing time and flow mechanism.Firstly,this paper established the material balance equation,by calculating dynamic drainage volume of different fracture distribution formed a new method of judge the re-fracturing time of depleted development well.For about the re-fracture time of water-flood development,we use the dynamic parameters of reservoir to select.Secondly,based on the reservoir numerical simulation,we analyzed the stimulation mechanism of re-fracture from re-fracture the original fracture and the new fracture of horizontal well respectively.Thirdly,considering the drop of flow conductivity,established the typical geologic model of ultra-low permeability reservoir to optimize the fracturing parameter of re-fracture of these two development pattern.The results show that the re-fracturing of horizontal well with depleted development related to the initial fracturing scale,and the re-fracturing of water-flood development related to the dynamic parameters,such as water cut,pressure coefficient,flow conductivity and so on.Re-fracturing can clean the fracture,increase the stimulation volume of original reservoir and displace the remaining oil between the fracture spaces,so that it can increase the production significant.The sequence of re-fracture affecting for depleted development in actual reservoir shows,re-fracture time>fracture length>fracture conductivity>fracture space,and the optimal re-fracturing time is 3year.The sequence of re-fracture affecting for water-flood development in actual reservoir shows,re-fracture time > fracture length > fracture conductivity> diversion angle > fracture length,and the optimal re-fracturing time is water cut less 20%.