Fracturing fluids

Abstract

Hydraulic fracturing is a technique to stimulate the productivity of a well. A hydraulic fracture is a superimposed structure that remains undisturbed outside the fracture. Thus the effective permeability of a reservoir remains unchanged by this process. The increased productivity results from the increased wellbore radius, because in the course of hydraulic fracturing, a large contact surface between the well and the reservoir is created.The literature from 2004 to 2014, more than 100 references concerning waterbased fracturing fluids for fracturing ultralow-to moderate-permeability reservoirs has been reviewed [1].Guar-based polymers are still used in fracturing at temperatures less than 150 • C. To minimize the damage associated with this class of polymers, several approaches are known. These include the use of a lower polymer concentration in formulating these fluids and the use of different crosslinking agents. Higher viscosities with lower polymer loadings can be achieved. In addition, cleaner guar-based polymers are used now, because commercial guar contains some 5% of residues, which may cause a damage of proppant packs.It has been found that shear and pressure effects on the rheological behavior of borate crosslinked gels are important. Although these fluids recover their viscosity after shear, they have been observed to lose a significant portion of their viscosity under high pressures.When fracturing is done in deeper wells, i.e., in hotter reservoirs, a new class of thermally stable polymers became relevant. These are poly(acrylamide)-based polymers. These synthetic polymers show a sufficient viscosity at temperatures up to 230 • C [1]. Examples are 2-acrylamido-2-methylpropanesulfonic acid and copolymers of partially hydrolyzed acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, and vinyl phosphonate. High-density brines have been used to increase the hydrostatic pressure by 30% for high-pressure pumping.Also, new breaker materials emerged [1]. These breakers destroy the gel by a reaction with the crosslinking agent. They form ligands with the metallic crosslinking agents and displace them from the crosslinking moieties of the guar-based polymers. Examples of these breakers include poly(succinimide) derivates and lignosulfonate derivates.To minimize the environmental impact of using massive amounts of fresh water and to minimize costs associated with treating produced water, the use of produced water in hydraulic fracturing treatments has been reported. Petroleum Engineer's Guide to Oil Field Chemicals and Fluids. http://dx.567 568 CHAPTER 17 Fracturing fluids B HO 17.3 Types of hydraulic fracturing fluids 571 TYPES OF HYDRAULIC FRACTURING FLUIDSGenerally, a hydraulic fracturing treatment involves pumping a proppant-free viscous fluid, or pad, usually water with some fluid additives to generate high viscosity, into a well faster than the fluid can escape into the formation so that the pressure rises and the rock breaks, creating artificial fractures or enlarging existing fractures.After fracturing...