Development Of Recyclable Clean Fracturing Fluid Formulation System For Tight Reservoirs In Southern Ordos

With the decreasing of conventional oil and gas reserves in China,people gradually turn their attention to the exploitation of unconventional oil and gas.The tight oil reservoirs in southern Ordos are abundant;fracturing is the main way to increase production and the Guar gum fracturing fluid is the main fracturing fluid,which accounts for more than 90%.However,there are many problems in the use of the Guar gum fracturing fluid system,for example,the fracturing fluid system is basically alkaline cross-linking,which is difficult to be compatible with carbon dioxide.Besides,Guar gum residue and incomplete gel-breaking will greatly affect the construction effect.In addition,requirements of environmental protection are becoming more and more strict,which makes the reuse of fracturing fluid more and more important.Based on the evaluation of the basic characteristics of the tight oil reservoirs in southern Ordos,a new type of surfactant(GCF-3)is synthesized for the problem of on-site fracturing,which is used as the main agent to develop a recyclable clean fracturing fluid system,and the optimum formulation of the fracturing fluid system is optimized through experiments.The viscosity of the fracturing fluid system is related to the p H value.The back flow can be recycled by simple sedimentation and filtration,which has some advantages,such as little damage to the formation and compatibility with carbon dioxide.The properties of this fracturing fluids were measured by some experiments,including the compatibility experiment between the fracturing fluid system and the formation water in southern Ordos as well as carbon dioxide,the visco-temperature experiment,the sand-carrying experiment,the core damage experiment,the friction experiment,the filtration experiment and the recyclability experiment.The results show that the fracturing fluid system has great properties.Firstly,it has good compatibility with formation water and carbon dioxide and has good temperature shear resistance(up to 100°C,shearing 120 min,viscosity > 30 m Pa·s).Secondly,it has good sand-carrying performance(The sedimentation rate of proppant is less than 0.8cm/s).Thirdly,the core damage of it is low(less than 15%);the friction loss of it is small(the friction loss is 40% of clean water at an average flow rate of 4.21 m/s)and the fluid loss coefficient of it is low(Less than 9×10-3m/min1/2).Finally,the fracturing fluid can be reused at least 6 times.The use of the fracturing fluid can greatly reduce the environmental pressure of on-site fracturing and lower the development cost of tight oil in southern Ordos,which has better social and economic benefits.