A Non-Damaging Fracturing Fluid System for High-Temperature Unconventional Formations

Abstract

Abstract Many fracturing fluids are based on guar and guar derivatives, primarily because of their abundance and capability to operate at relatively high temperatures when formulated at high pH. However, insoluble residue in guar can damage permeability especially in unconventional formations. Another issue for applying guar-based fluids at high pH is the tendency to form scales with divalent ions. The fluid cost can also be strongly influenced by the volatility of the guar price. A third disadvantage is their low thermal stability when the temperature exceeds around 350 ° F. To mitigate these operating issues, a low- or non-damaging, high-temperature fluid system without elevated fluid pH is therefore highly desirable. Thermally stable synthetic polymers such as acrylamide-based polymers and copolymers are considered to be low-residue to residue-free. However, acrylamide polymers at high doses may still cause formation damage in circumstances like incomplete degradation. This paper demonstrates the successful application of a specific acrylamide copolymer to formulate a novel low-loading, non-damaging fracturing fluid system that fulfilled high viscosity requirements over a temperature range from 280 to 450°F. The fracturing fluid system based on the novel acrylamide copolymer demonstrated superior viscosity performance and excellent thermal stability at high temperatures at 450°F or higher. In one example, at the polymer loading as low as 20 lbm/1,000 gallons, the fluid viscosity stayed above 500cP (at 40 s−1 shear rate) at 300°F for about 2.5 hours. In another example, at a polymer loading of 30 pptg, the fluid viscosity stayed above 500cP (at 40 s−1 shear rate) at 400°F for about 1.5 hours. This data indicates that the fluid system has sufficient proppant suspension capability. The fluids could be efficiently broken to allow for good cleanup using oxidative breakers. Proppant-pack conductivity tests showed good regained permeability of over 90% at 300°F, proving the low- to non-damaging potential of the fluid system to formations treated. Moreover, the low-loading fluid system also reduced the fluid cost by about 50% when compared with the commercially available systems with similar viscosity performance. Using the novel low-loading, residue-free acrylamide copolymer has therefore rendered better cleanup, reduced formation damage, lowered operating cost, and enhanced production rates. The fracturing fluid system based on the novel acrylamide copolymer has demonstrated the unprecedented combination of a number of advantages including low polymer loading, robust high-temperature performance, high regained permeability, low scaling tendency, and reduced operating cost.