Study On Rheological Characteristics And Sand Carrying Law Of Nano Clean Fracturing Fluid

The fracturing fluid in the fracturing of coalbed methane reservoirs is the key to forming a large-scale effective stimulation volume and obtaining a fracture network system with sufficient conductivity.In the process of fracturing coalbed methane wells,compared with ordinary water fracturing fluids,clean fracturing fluids not only have the advantages of low residue,easy flowback,less damage to the reservoir,better rheology,and high fluid efficiency,but also The good sand-carrying performance can make the proppant migrate to the depth of the fracture and achieve better laying effect,but the high cost and high consumption of clean fracturing fluid limit its application in coalbed methane production.In addition,the mechanism of clean fracturing fluid carrying sand in fractures is still unclear.Therefore,it is of great significance to develop a new clean fracturing fluid system and study its sand-carrying law in fractures.Taking the clean fracturing fluid composed of nano particle（Si O₂）modified cetyltrimethylammonium chloride（CTAC）and sodium salicylate（Na Sal）as the research object,this paper has carried out a series of studies on the performance of nano clean fracturing fluid system and its sand carrying law in the fracture by using the combination of experiment and numerical simulation.The conclusions are as follows:（1）The rheological experiment of fracturing fluid was carried out,a new nano clean fracturing fluid system was optimized,and the performance of the fracturing fluid system was evaluated.The experiment shows that the stability of micellar solution is further improved after nano Si O2 is used to modify the clean fracturing fluid,which increases the viscosity of the system and greatly reduces the economic cost.The prepared nano clean fracturing fluid system has good rheology and viscoelasticity,and maintains high viscosity at high temperature and high shear rate,which can meet the needs of downhole fracturing and sand carrying.Carreau constitutive model with good fitting was selected to characterize the rheology of the modified nano clean fracturing fluid.（3）Considering the shear thinning and viscoelasticity of nano clean fracturing fluid,the free settlement velocity model of proppant in nano clean fracturing fluid is established,and the reliability of the model is verified by proppant settlement experiment.In addition,considering the impact of particle collision,wall block and fracturing fluid filtration on the settlement,the correction coefficient is used to modify the settlement model to make the settlement of proppant more in line with the actual situation.（4）Based on Euler multiphase flow model and particle dynamics model,considering the collision between solid particles,the slip between solid and liquid phases and the rheology of fracturing fluid,a single fracture model is established.The sand carrying law of nano clean fracturing fluid in single fracture is studied by using fluent numerical simulation software,and the pump discharge,proppant particle size,proppant density,sand ratio Finally,the grey correlation analysis method is used to rank the influencing factors of nano clean fracturing fluid sand carrying.The results show that the influencing factors of equilibrium height and sand embankment placement rate are relatively consistent,and the influencing degrees from high to low are proppant particle size,proppant density,fracturing fluid property,sand ratio and displacement,The influence degree of each parameter of equilibrium time from high to low is proppant density,sand ratio,displacement,fracturing fluid property and proppant particle size.（5）A multi angle and multi size geometric model of complex fractures is constructed,and the numerical simulation experiment of nano clean fracturing fluid carrying sand in complex fractures is carried out.The experimental results of clean water fracturing fluid and nano clean fracturing fluid are compared and analyzed;The increase of the angle of the branch fracture in the complex fracture is not conducive to the sand carrying of the fracturing fluid.Similarly,with the deepening of the complexity of the fracture,the flow speed of the fracturing fluid will be reduced,making it difficult for the proppant to enter the branch fracture.However,in general,the sand carrying performance of the nano clean fracturing fluid in the established complex fracture is better than that of the ordinary clean fracturing fluid.This paper has 36 figures,18 tables,and 63 references.