Application of a Novel Hyperbranched-Polymer Fracturing-Fluid System in a Low-Permeability Heavy-Oil Reservoir

Abstract

Summary Hydraulic fracturing can be used for stimulating low-permeability heavy-oil reservoirs. It is challenging to achieve a high degree of fracturing-fluid flowback, as well as a low degree of formation damage, in low-permeability heavy-oil reservoirs. This research investigates the application of a novel hyperbranched-polymer fracturing fluid in low-permeability heavy-oil reservoirs. Such hyperbranched polymer is characterized by Fourier-transform infrared (FTIR) spectrophotometry. It has numerous end groups and possesses a 3D spherical molecular structure with many branches. Laboratory tests are conducted to evaluate the thermal stability and shearing resistance, reversible-crosslinking performance, salinity tolerance, static-filtration performance, gel-breaking performance, and sand-carrying performance. The degrees of core damage are evaluated through conducting coreflooding experiments, where the cores are treated with two kinds of gel-breaking fluids formed by hyperbranched-polymer fracturing fluid and guar fracturing fluid, respectively. Laboratory tests show that the hyperbranched-polymer fracturing fluid has good rheological characteristics, a high swelling ratio, a high proppant-carrying performance, and good thermal stability and shearing resistance. After being sheared for 90 minutes under 170 s−1 at 150°C, it can still reverse to gel with high strength because of its good reversible-crosslinking performance. This fracturing fluid exhibits a high-salinity tolerance. Furthermore, the hyperbranched polymer has a high swelling ratio. Field applications in some wells in China show that the friction loss of this fracturing fluid during fracturing is approximately 30 to 50% of that of the normal guar fracturing fluid. Thus, it has an ultralow friction-loss feature. As for the same reservoir, hyperbranched-polymer fracturing fluid has a higher flowback ratio compared with the guar fracturing fluid. Besides, its cost is approximately 75% of that of normal guar fracturing fluid, making it a clean and cost-effective system. The fracturing fluid prepared with hyperbranched polymer possesses outstanding technical advantages and good cost effectiveness, implying a promising application in the large-scale fracturing stimulation of low-permeability heavy-oil reservoirs.