Research On The Regularity Of Micro Fracture Deformation And The Dynamic Characteristics Of Profile Control For Extra Low Permeability Reservoir

The deep profile control technology of weak gel is one of the important measures for water controlling and oil increasing in the fractured ultra-low permeability reservoir,and whether the weak gel has the ability of the deep migration and the effective plugging is the two most important problem of the technology.High permeability fracture system with strong stress sensitivity is the main object of this kind of reservoir depth profile control.Therefore,it is very important to study the migration mechanism and the law of weak gel in fracture and the sealing performance of the weak gel.In this research,the characteristics of fractures and the deep profile control mechanism in the fractured ultra-low permeability reservoir have been analyzed.The experimental study on the migration of weak gel was carried out by using the physical model of fracture,and the effect of fracture width and weak gel viscosity on the migration regularity of fractures was discussed.By using artificial fractured natural core,the fracture stress sensitivity and the weak gel permeation experiment were carried out,the deformation regularity of the fracture with the fluid pressure change was clarified.Based on the theory of reservoir percolation,fluid rheology and fracture deformation theory,combined with the experimental law analysis,the dynamic model of the flow of weak gel in the fracture is established under the conditions of no fracture deformation and fracture deformation.And through finite difference and other methods,the numerical solution of the model was achieved,and the dynamic simulation of the flow of weak gel in the fracture was carried out.Otherwise,the effects of fracture width,injection pressure difference,rheological parameters of weak gel and the degree of crack deformation on the migration process of weak gel were discussed.By using the visualized crack model,the selective injectivity and plugging performance of weak gel in multi-fracture system were studied.The effect of injection pressure and fracture width on the implantation depth of weak gel was studied by using long core.The results of theoretical model were validated and the effects of weak gel injection depth on breakthrough pressure gradient and recovery were analyzed.The results show that the development of the large-scale fractures in Yanchnag ultra-low permeability reservoirs is sensitive to fluid pressure changes.As the fluid pressure increases,the crack width increases obviously.When the viscosity of the weak gel exceeds a certain critical value,the injection pressure increases significantly with the increase of the viscosity.In the experiment,when the fracture width is 0.1mm,the viscosity critical value is 600mPa·s,and the width is 0.2mm,the viscosity critical value is 1500mPa·s.In addition,the rheological parameters of weak gel have a great influence on the injection depth.When the consistency coefficient of the weak gel is less than 1000mPa?sⁿ or the flow index is less than 0.7,the weak gel pouring depth sharply decreases with the increase of the consistency coefficient or the flow index.Under the condition of constant injection pressure,the deformation of the fracture shortens the injection depth of the weak gel,and when the fracture deformation index is less than 0.1MPa^-1,which means that the fracture deformation has a significant effect on the weak gel injection.The volume ratio of the weak gel into the fracture with different width is the（2（10）_n¹）power of the ratio of slit width to width,and the more the weak gel deviates from the Newtonian fluid,the bigger the volume difference is.Weak gel is not completely blocked the cracks,but in the water injection process is injected into the water breakthrough,part of the weak gel to the deep migration,the deeper the depth of migration,the higher the recovery rate.In conclusion,the results of this paper provide theoretical basis and practical guidance for deep profile control technology in fractured ultra-low permeability reservoir.