Research on Calcium Chloride Weighted Polymer Fracturing Fluid for Ultra Deep and High Stress Reservoirs

Abstract

To enhance fracture and conversion effects in deep and ultra-deep oil and gas reservoirs, a low-cost polymer-weighted fracturing fluid technique was developed using industrial calcium chloride as a weighting agent and synthesizing a polyacrylamide polymer, FA-31, with a molecular weight of 4-6 million, as a thickening agent. In addition, we have developed an amphoteric metal crosslinker capable of forming multiple hydroxyl bridges with crosslinked groups, a novel XG160 high-efficiency gel breaker, and a complete set of stress corrosion inhibitors. The optimal concentration for the use of calcium chloride dihydrate is 46% and the density of aqueous solution is 1.35 g/cm3. The developed highly salt-resistant polymer dissolves rapidly in a high-density calcium chloride salt solution. The industrial calcium chloride gel formed by polymer has a maximum temperature resistance of 170 °C, a shear rate of 170 s-1 for 120 min, and a viscosity of more than 100 mPa·s. It also performs well in high-temperature suspension sand conditions. The viscosity of the gel breaker is less than 5 mPa·s. Laboratory tests have shown a core damage rate of about 20% and no stress corrosion cracking. The on-site application of liquid preparation and construction has been smooth, achieving the desired effect of reducing construction pressure. For example, when refurbishing a 7500 m reservoir, the building pressure can be reduced by 10-20 MPa. On-site testing of calcium chloride-weighted frac fluids has confirmed their effectiveness as a cost-effective alternative to conventional weighted frac fluids, providing a viable solution for the conversion of deep, ultra-deep, high-stress oil and gas reservoirs.