Preparation and properties of A Guanidine Gel Fracturing Fluid System for Wellbore Reconstruction

In reconstructing wellbores by refracturing of the reservoirs, several problems such as high cost of the fracturing fluids as well as difficulties in controlling friction and adding sands into the fracturing fluids, need to be solved. In this study a guar gum modified by graft and a multilevel chelating crosslinking agent are synthesized and are used to formulate a guar gum fracturing fluid for reconstructing wellbores through refracturing. This fracturing fluid has good swelling property, its 3 min viscosity can be as high as 87% of its maximum viscosity. The viscosifying capacity of this new guar gum is better than that of the conventional guar gum; A fracturing fluid treated with 3.8 g/L of this new guar gum has viscosity that is the same as the fracturing fluid treated with 6 g/L conventional guar gums. This new guar gum reduces the friction of fracturing fluids by at least 70% and the content of residues left in a used fracturing fluid is less than 70 mg/L. After shearing at 150 °C for 2 h, the viscosity of the fracturing fluid is 50 mPa∙s or higher. The fracturing fluid has good sand carrying capacity, almost no settling of proppants is found after 2 h of standing of the fracturing fluid. This fracturing fluid has been applied on the first well fractured with equipment and facilities that are all homemade. In the fracturing operation, the flowrate of the fracturing fluid was 16 m³/min, the highest sand/fluid ratio was 30%, and the sand used in one fracturing segment was averaged at 220 m³, solving the difficulty of adding sand into the fracturing fluid. Good application results are achieved in this operation.