The Evaluation of Polycationic, Carbohydrate-Based Surfactants as Viscoelastic (VES) Fracturing Fluids

摘要

Hydraulic fracturing plays an important role in maximizing the recovery of oil and gas in North America. Viscoelastic surfactant based fluids (VES) are an important class of fracturing fluids (Ghaithan, 2014). They are reputed to cause less formation damage during the fracturing process and break cleaner, leaving less material in the formation to impede the flow of hydrocarbons (Brown, 1996). Cationic surfactants are typically used for this application, but do not exhibit good tolerance to or solubility in the salts used to inhibit clay swelling. They are also not particularly biodegradable and have an unfavorable toxicity profile. Cationic surfactants with an improved ecotoxicity profile as well as improved tolerance to salts are needed. Improved temperature tolerance is also desired, in order to apply to a wider range of well types. Carbohydrates have the ability to react with a variety of substances and can be conveniently cross-linked to form polycationic materials. As such, molecules can be created that mimic the polymer backbones used in fracturing fluids today, potentially eliminating some of the negative side effects of those same polymers. Carbohydrate-based, polycationic molecules are created from bio-renewable re- sources such as sucrose and vegetable oils. The incorporation of ether links and short-chain components within these molecules imply a better biodegradation profile and lower toxicity than traditional long-chain cationics. Several new polycationic, carbohydrate molecules were synthesized in the lab in order to demonstrate the flexibility and range of the chemistry and explore structure-activity relationships. When formulated into viscoelastic fluids, smaller polycationics demonstrated excellent tolerance to salts, at times requiring the presence of salts in order to show viscoelasticity with enough viscosity to suspend proppant. In addition, as the number of crosslinkers per molecule increased, the resultant formulated viscosity increased, however the tolerance to salt decreased.