Guar Gum Fracturing Fluids Weighted with Formates

In fracturing formations with higher fracture pressures, high-density fracturing fluids should be used because low-density ones have difficulties fracturing these formations. Weighting agents for use in fracturing fluids should have good water solubility because the fracturing fluids will go deep into the reservoirs. Guar gum fluids, which will crosslink in weak alkaline conditions, cannot be weighted with salts of strong acids and weak bases, such as CaCl₂, ZnCl₂. Bromide salts, such as potassium bromide, calcium bromide, can be used but are expensive. By balancing the cost and performance, formates were selected to weight fracturing fluids. The density of the fracturing fluid can be adjusted between 1.0 g/cm³-1.5 g/cm³. The performance of formates was affected by the factors such as electrophicility, molecular weight, and dispersity. The tendency of reaction (both chemical and physical) between cleanup additives, clay stabilizers and formates, may lead to flocculation, separation and precipitation of the fracturing fluids. To avoid these unfavorable factors, a micro emulsion cleanup fluid ME-1 and a clay stabilizer FP-2 were selected for use in the fracturing fluid formulation. An organo-boron crosslinking agent was selected through rheology, filtration and gel-breaking experiments. This fracturing fluid, with density of 1.2 g/cm³, has been successfully applied on the well Dong-8 to fracture the formation between 5,353.70 m and 5 364.45 m, with formation temperature of 120℃. The fracturing fluid, after gel breaking, had viscosity of less than 5 mPa·s, and was 100% flowed back. This weighted fracturing fluid technology has provided valuable experiences for fracturing high closure-stress reservoirs in the future.