Viscoelastic Nanomaterials and Surfactants for High-Performance Well Enhancement

Abstract

Well-stimulation and treatments are necessary for high-efficiency oil and gas production. Control of formation damage is one of the primary aims. Although polymer-based fluids and viscosifiers (namely gels based on polymers like natural guar and synthetic polyacrylamides) have been primarily used, other alternatives have been explored. Viscoelastic surfactants (VES) as part of fracturing fluids and proppant transport fluids compositions during a fracture treatment is a departure from the use of polymer viscosifiers. A VES fluid's viscosity is created by self-assembling surfactant small molecules in solution to create spherical, rod-shaped, and bicontinuous structures of lyotropic liquid crystalline order micelles.(Yang 2002)(Olsson 1986) Entanglement of these flexible and higher-order micelles imparts increased viscosity to the solution (Fischer 1997). Hydraulic fracturing (HF) has been used for many years for the completion phase of drilling. Various stimulation fluids have been developed to withstand high pump rates, shear stresses, and high temperatures and pressures in the bore hole. In the completion stage of drilling (exploration and production), retained permeability and leak-off (fluid loss) control are two of the most important requirements. The main goal eventually is to achieve high conductivity pathways that do not damage or lower the productivity of completed wells. With VES fluids, elasticity, and micellar structure rather than fluid viscosity are the leading property drivers. A significant advantage is that VES fluids can efficiently stimulate at lower viscosities with reduced friction pressure and thus reduce the energy for pumping fluids downhole towards more extraordinary fracture lengths (horizontal), enabling better fracture geometry control and deeper formations. Other possible uses of VES technology include filter cake removal, selective matrix diversion, permeability preservation, and coiled tubing cleanout. Yet, VES has some disadvantages: 1) Poor stability at high concentrations and temperatures, 2) poor stability with complex brine conditions or highly salt-saturated environments, 3) lack of viscosity-elastic control once deployed with other chemical components and additives, and 4) cost. Besides HF applications, VES for well-stimulation and completion applications are also important. The availability of various VES fluid systems is an advantage for working with different formation characteristics, base lithology, mineral compositions, formation fluids (brine chemistry), and operations (e.g., different pumping configurations) (Samuel 2000). Tight gas wells, unconventional wells, shale, coal beds, and wells with adverse capillary effects, including sub-irreducible water saturation and hydrocarbon saturation, necessitate oilfield chemicals optimized for a specific well condition. The low productivity of both old and new wells can be boosted by stimulation and completion procedures, e.g., acid stimulation and diverters. Herein, VES stimulation fluids can have advantages: 1) employment of complementing surfactant systems, 2) benign to the formation (no polymer residue or formation damage), 3) lower surface tension, 4) does not require biocides or clay control agents, 5) insensitive to salinity, and 6) the flow back fluid can be reused. Using diversion methods, it is possible to focus treatment on the areas that require more stimulation. To be effective, the diversion effect should be temporary to restore the full productivity of the well when the treatment is completed.