Optimization Of Repeated Fracturing Fracture Spacing For Horizontal Wells In Low-permeability Reservoirs

In the early days,some horizontal wells in low-permeability reservoirs performed initial fracturing reforms in order to obtain economic oil flow.However,due to the influence of geological and technological factors,the fractures gradually closed,causing the fractures to lose their original conductivity and unable to meet production requirements.Repeat fracturing to restore or increase production.The fracture spacing between new fractures and old fractures during horizontal fracturing is one of the key factors that affect the design of repeated fracturing and increase production.In this paper,based on the physical properties of low-permeability reservoirs,laboratory physical simulation experiments were conducted on rock samples with different permeability to explore the stress sensitivity of low-permeability reservoirs,starting pressure gradient and the law of influence on low-permeability oil and gas reservoirs;Based on the principle of superposition and continuity,a coupling model is established—the seepage flow and wellbore tube flow in fracturing horizontal well reservoirs,and a method for solving the coupling model is given.The reservoir numerical simulation method is used to calculate the fractures based on the factors affecting the inter-fracture interference The effective fracture control distance is given between pressure and productivity;based on cluster analysis,a quantitative evaluation method for precise layer selection and selection of horizontal wells is established,and the actual block is selected for repeated fracture spacing design.The results of the study indicate that when the permeability of the rock sample decreases,the starting pressure gradient will increase accordingly.The characteristics of the power function relationship are similar to the relationship between the permeability and the starting pressure gradient.The starting pressure gradient of the oil phase measured in laboratory experiments is 2-3 times that of the starting pressure gradient of the water phase.During the development process,the damage caused by the drop in reservoir pressure on rock permeability stress sensitivity is unavoidable.As the effective stress increases,the core permeability gradually decreases.When the effective overburden is small,the core permeability decreases rapidly,while when the effective overburden is relatively high,the core permeability changes little.When the effective overpressure changes within the same range,the smaller the initial permeability,the more severe the loss of permeability under the same conditions.Comprehensive analysis shows that the four important factors affecting fracture control distance and production capacity are reservoir permeability,productionpressure difference,proposed start-up pressure gradient and stress sensitivity coefficient.The greater the reservoir permeability value,the greater the production pressure difference and the fracture The larger the control distance is;at the same permeability,when the fluctuation range of the stress sensitivity coefficient is about 10%,the fluctuation range of the fracture control distance is less than 5%;when the planned fluctuation range of the starting pressure gradient is about 25%,the fluctuation range of the fracture control distance is less than 20%.Combined with the interpretation results of logging petrophysical facies,the precise location of the fracturing position can be determined.At the same time,considering the possible types of fractures in the target block,the proportion of reservoir pore connectivity,and the starting pressure gradient,a personalized fracture spacing optimization method can be established.The research results have theoretical guiding significance for on-site repeated fracturing construction.