Study On Sand Carrying Law Of Liquid CO₂/N₂ Foam Fracturing Fluid System

CO2 fracturing is very suitable for water sensitivity gas reservoirs,tight gas reservoirs and shale gas reservoirs,which shows good application prospects.CO2 fracturing of liquid CO2/N2 foam is a development form of liquid CO2 fracturing.Its rheology and sand carrying performance are the core problems of liquid CO2/N2 foam fracturing.On the basis of rheology of liquid CO2/N2 foam system,the law of sand carrying was studied.The research is of great significance for the development and application of liquid CO2/N2 foam fracturingAiming at the problem of sand carrying in liquid CO2/N2 foam fracturing process,a set of liquid CO2/N2 foam testing device has been independently developed.Screening experiment of foaming agent was carried out by means of high temperature and high pressure foam performance evaluation device.The rheological test and sand carrying performance test of liquid CO2/N2 foam fracturing fluid were carried out by using high temperature and high pressure pipe rheology and sand carrying device.Rheological properties of liquid CO2/N2 foam at different temperatures,pressures and foam qualities were studied by rheological experiments The effects of temperature,pressure and foam quality on effective viscosity and rheological parameter were obtained.It provides basic parameters for studying the sand carrying performance of liquid CO2/N2 foam fracturing fluid.The critical settling velocity and critical resuspension velocity of liquid CO2/N2 foam fracturing fluid under different conditions were determined by sand carrying experiments.The effects of sand ratio,foam quality and proppant density on the sand carrying performance of fracturing fluid are analyzed.Based on the placement experiment of proppant in visualized fractured plate,the effects of fracturing fluid velocity,foam quality,sand ratio and proppant density on the morphology of proppant sand embankment are analyzed.By comparing the shapes under the same conditions through numerical simulation,the causes of different distribution shapes are analyzedThe results show that HFE-73,as the foaming agent of the system,makes the foam solution exhibit better foaming ability.2%was selected as the experimental concentration.The liquid CO2/N2 foam fracturing fluid is non-Newtonian fluid.The effective viscosity increases with the increase of pressure and decreases with the increase of temperature.With the increase of foam quality,the effective viscosity of liquid CO2/N2 foam increases first and then decreases.In the liquid CO2/N2 foam fracturing fluid,the critical settling velocity and critical resuspension speed increase with the increase of sand ratio and proppant density.With the rising of foam quality,it first decreases and then rises.The results of laboratory experiments and numerical simulation show a high similarity.The higher the flow rate of fracturing fluid,the lower the height of sand dike,and the farther the settling position of proppant is from the entrance of fracture.The higher the proppant density is,the larger the sand ratio is,and the higher the height of the sand dike is,and it mainly concentrates on the location far from the entrance of the fracture.The effect of the foam quality of fracturing fluid on the placement of proppant is mainly reflected in the effect of fracturing fluid effective viscosity.The viscosity of fracturing fluid increases first and then decreases with the rising of foam quality,and the height of sand bank first decreases and then rises.