Study On Water Base Gelled Hydrofracturing Fluid With Synthetic Polymer

Water-based fracturing fluid is the most common type of fracturing fluid that using in oil and gas well reservoir. There are three types of thickener agent mainly, which are natural polymer, surfactant and synthetic polymer. However, the poor rheological property and higher cost limit its application in oil field. Aiming at different temperature(60℃~120℃) reservoir, suitable nonionic polyacrylamide was synthesized as the fracturing fluid thickener agent. On this basis, fracturing fluid system was formed with nonionic polyacrylamide and organic zirconium. The performance of this fracturing fluid was evaluated in lab and the effect is very good.The synthesis craft of the nonionic polyacrylamide can be controlled by two temperatures. Using the acrylamide as synthesis monomer and the(NH4)2S2O8 as the initiator, the polyacrylamide was prepared by the method of the watery solution radical polymerization. The chain structure of the polyacrylamide can be controlled. The effects of reaction temperature, the adding temperature of initiator, monomer concentration, reaction time, initiator amount, on the parameters of PAM were investigated. Those parameters were characterized by molecular weight, degree of hydrolysis of PAM the and so on. The feasibility that the sample can be used as the base fluid of fracturing fluid was characterized by cross-linking capability between polyacrylamide and organic zirconium. PAM with the relative molecular of 6.5 million was selected as thickener agent. The effects of different factors on the zirconium gel is analyzed, which is shown that within the scope of the present experimental conditions, the viscosity of zirconium gel increases with the increase of molecular weight, polymer concentrations and ratio, and the viscosity decreases with the increase of polymer hydrolysis degree, temperature and salinity. The crosslinking effect is better as the pH of the system controlled between 3 and 9 and the hydrolysis degree of PAM is less than 5%. The formulations of hydrofracturing fluid which were suitable for different reservoir with different temperature were optimized by laboratory experiments: in the condition of 60℃,the formulation is 0.3%PAM+1.5%GC-1, in the condition of 90℃,the formulation is 0.35%PAM+2%GC-1, in the condition of 120 ℃, the formulation is 0.4%PAM+2%GC-1. The viscosities of formulas are over 80mPa·s after shearing for 2 hours in the condition of 170s-1 and the reservoir temperature. The filtration coefficients are less than 8.97×10-4m/min1/2. These formulations of fluid have the advantages of good rheologic behavior and strong sand carrying capacity. The gel could break within 2 hours by adjusting the concentration of ammonium persulfate. The organic zirconium gel hydrofracturing fluid has strengths such as easy preparation, strong sand carrying capacity and good filtration, good thermal stability and shear resistant properties. It shows good effect for wells fracturing on oilfield.