A Solids-Free Permeability Modifier for Application in Producing and Injection Wells

Abstract

Most currently available relative permeability modifiers (RPM) are polymers that, due to electrostatic charges, adhere to the surface of the pore spaces in a porous medium and result in a disproportionate permeability reduction (DPR) to water. However, there are a number of known limitations associated with the use of a polymer in low-permeability formations (<50 mD). The polymer may physically block the pore throats. The higher viscosity (with respect to formation water and in some cases crude) of the polymer solution will self-divert the treatment into the intervals with the highest permeability, regardless of the oil/water saturation. One solution for low permeability reservoirs is the use of solids free viscoelastic surfactant based fluid. However, core flow testing showed that the disproportionate permeability reduction to water using cationic, anionic and zwitterionic viscoelastic surfactants is markedly different. The performance of cationic and anionic surfactants varies greatly depending on mineralogy and crude oil composition, in some cases increasing the effective permeability to water. While, a zwitterionic surfactant at concentrations below the critical micelle concentration consistently results in a disproportionate permeability reduction to water, irrespective of the mineralogy or composition of the crude oil. In certain cases, the permeability to oil increases and residual oil saturation decreases significantly. An extensive study was carried out to evaluate the performance of a viscoelastic RPM. The properties of a viscoelastic RPM makes it a very versatile fluid system. In high water-cut wells, treatments have reduced the water-oil ratio, by up to 18%. While in oil-wet reservoirs, treatments have effectively stimulated oil production, by more than 10%. Another interesting application has been to treat water injection wells to reduce the residual oil saturation, improving both injection rates and sweep efficiency. These properties make the technology particularly suitable for use in increasing reserves recovery in old/mature fields.