Development And Application Of Low-Damage Heat-Resisting Fracturing Fluids

As an important stimulation, hydraulic fracturing is particularly important in putting into production and increasing production of low-permeability oil and gas fields.Performance of the fracturing fluid affects the effect of fracturing directly.Firstly based on a large number of theoretical analysis it is pointed out that the surfactant solution should have viscoelastic properties and active agent should have a specific molecular structure to form the micelles of rods, worms, hexagonal, lamellar and so on with the presence of adjuvants. The solution appears net structure so as to meet the requirements for fracturing fluids. We synthesized a CTCB cationic surfactant indoors, established a clean fracturing fluid system of CTCB and NaSal at50-80℃, as well as we synthesized a new Gemini surfactant indoors, optimized the fracturing fluid formulation. Its temperature resistance reaches90-120℃.Both of the systems have good performance of heat resistance and shear resistance, which broaden the application scope of clean fracturing fluid. We observed the micelle morphology and structure of the main agent CTCB as well as CTCB and NaSal at different concentrations by using a microscope and an SEM, results show that the micelle volume was increased, the mesh structure appeared with adjuvants NaSal, the system showed viscoelasticity nature of polymer solution. Experimental studies show that clean fracturing fluid has advantages including little dosage, small friction, strong sand-carrying ability, outstanding well stimulation; and it doesn’t need any cross-linking agent, breaker and other chemical additives, it has little formation damage and maintains good condition for the filling layer.Secondly, we synthesized thickener terpolymer CAMPS and cross-linking agent OB-140, optimized the synthesis condition and recipes. The viscosity of the system still maintains80mPa·s after100minute shear at180℃.The system shows good performance of heat resistance and shear resistance at120-180℃, which meets the requirements of fracturing.We synthesized organic boron, zirconium TG-401composite cross-linking agent indoors, developed and optimized high temperature stabilizers. Using CAMPS as thickener, the viscosity of the system still maintains100mPa·s after150minute shear at170s-1and200℃.Results show that the fracturing liquid system has a temperature resistant of more than200℃. Finally in order to design and use fracturing fluid more effectively, the change of reservoir and crack temperature field when fracturing was analyzed and studied, the model and programs to predict reservoir and crack temperature distribution were established and made, the cooling rate and regular pattern were forecast after pad fluid and fracturing fluid got into the reservoir.The study can provide a theoretical basis for fracturing fluid formulation design(the lowest concentration of thickening, cross-linked,gel breaking pharmacy), give full play to the properties of temperature resistance, gel breaking,hydration and flowing back.Clean fracturing fluid and high temperature resistance fracturing fluid have got very good effects when made field applications in two blocks of Daqing oilfields and Liaohe Oilfield.