Preparation And Performance Evaluation Of Water In Oil Emulsion Fracturing Fluid

As the most effective way to develop low permeability reservoirs,fracturing can ensure the ideal oil recovery rate and improve recovery,then promote the use of low permeability reserves.In view of the characteristics of low permeability reservoirs such as strong water sensitivity and poor reservoir physical property.the water in oil emulsion fracturing fluid was synthesized in this paper,which have better applicability and improve the defects of the conventional fracturing fluid with serious damage and high cost.The thickener alkyl phosphate ester is synthesized by phosphorous pentoxide、triethyl phosphate and different alcohols in this paper.In order to obtain the optimal synthetic condition of thickener,the double indicator method is carried out to determine the content of thickener,the reaction time、temperature and molar ratio are analyzed by orthogonal test.The optimum synthetic conditions are polymerization time of 5h,polymerization temperature of85℃,the molar ratio of P2O5 and C6H15O4 P is 1:1.5,esterification time of 5.5h,esterification temperature of 100℃,the molar ratio of intermediate and mixed alcohol is 1:1.4.The mixed alcohol is composed of butanol、n-octanol and hexadecanol,which molar ratio is 1:1:1.The thickener DC-1 is analyzed by infrared spectrometer,the result shows the sample which contained phosphate framework is the target product.The formula of compound crosslinking agent is determined as follows:25wt% ferric sulfate + 8%wt glycol +12wt% citric acid three sodium + water.The effects of types and dosage of emulsifier、oil to water volume ratio and reaction temperature on the stability of water in oil emulsion fracturing fluid are analyzed by experiments,the remixed emulsifier formula is:90%Span80 + 5%Tween80 + 5% lauryl alcohol,the best stability condition is:emulsifier dosage of 2%,oil to water volume ratio of6:4,reaction temperature of <70;The fracturing fluid system synthesized by above formula has a good gel performance,its apparent viscosity can up to 328.9m Pa.s under the shear rate of 170s-1and temperature of 25℃.The performance of water in oil emulsion fracturing fluid are determined and evaluated,the best crosslinking ratio and the best concentration of thickener are 1:1.25 and 1.5%.The viscosity of fracturing fluid always retained at 155 m Pa.s after it sheared at 170s-1for 45 min at70℃,which confirms it has a good temperature and shear resistance.The elastic modulus and viscous modulus were tested by strain scanning,their values are larger than 1.0Pa and 0.3Pa.This water in oil emulsion fracturing fluid has good performance of suspended sand,the sedimentation rate of quartz sand is 0.0025mm/s,and when the gel breaking agent amount was 2%,demulsifier dosage was 0.8%,the apparent viscosity of fracturing fluid after gel breaking and demulsification is 4.74 m Pa.s,which meet the requirement of general standard of fracturing fluid.