Influence Factors of Multifunctional Viscous Drag Reducers and Their Optimization for Unconventional Oil and Gas Reservoirs

Abstract

Owing to the problems of guar gum fracturing fluid and conventional slickwater fracturing fluid systems in hydraulic fracturing of tight oil reservoirs, such as bad fracture network capacity, high damage, and low sand-carrying performance, researchers are actively looking for new alternative fracturing fluids. This study takes four commonly used additives for hydraulic fracturing of tight oil and gas reservoirs in western China, including the conventional polyacrylamide friction reducer EM30S, bioglue, thickener CHS-1, and high-viscosity friction reducer HVFR-1. By testing the water solubility, rheological properties, drag reduction, sand-carrying performance, imbibition oil displacement effect, and residue content of the four additives, the best additives suitable for hydraulic fracturing of tight oil and gas reservoirs were selected, and a set of indoor evaluations and the experimental method of screening hydraulic fracturing additives for tight oil and gas reservoirs were established. The research results show that the high-viscosity slickwater system composed of CND + HVFR-1 is more suitable for hydraulic fracturing of tight oil and gas reservoirs. Compared with the other three types of additives, CND + HVFR-1 fracturing fluid has good water solubility, and the dissolution time is less than 30 s. Therefore, in order to save construction time, the CND + HVFR-1 high-viscosity slickwater system is first recommended for field application. The research results of rheological properties show that although the apparent viscosity of high-concentration HVFR-1 + CND is low, the cross value of G′ and G″ is the smallest (0.006 Hz) and the elastic modulus is the largest (4.554 Pa) corresponding to 1 Hz. HVFR-1 + CND has better sand-carrying performance when used as a sand-carrying liquid. CND + HVFR-1 not only achieves a friction reduction rate of more than 60% but also has the effect of imbibition oil displacement to improve oil recovery; it can easily break gels, and its low residue content can ensure rapid flowback after construction is completed, and the lower residue content also causes the least damage to the reservoir. At the same time, the establishment of this evaluation method provides a certain reference for other researchers who select fracturing fluids for tight oil and gas reservoirs.