Improved Friction Reducer for Hydraulic Fracturing

Abstract

Abstract An improved polyacrylamide friction reducer delivered in an inverse emulsion form has been developed for use in fresh water up to 2% KCl. The main benefits realized were an increased level of friction reduction along with an enhanced rate of inversion. These benefits were obtained without compromising the emulsion storage stability. These improvements were gained primarily by optimizing the breaker surfactant package used to release the polymer from its delivered form into the aqueous based treatment fluid. Friction reducers are often a significant portion of the aqueous based chemical stimulation package used in either the stimulation and/or completion of oil/gas wells. Common friction reducers used for fresh water operations typically have a decline in performance when exposed to aqueous based fluids of increased salt content. The performance decline is not solely due to the nature of the polymer, but rather the mechanism of polymer release from its inverse emulsion state. The presence of salt not only affects the polymer configuration but also the ability of the inverse emulsion to release the polymer from its water internal phase into the water continuous stimulation fluid. The new friction reducer was developed by examination of various surfactants by way of simple additions to ternary mixture designed experiments. A variety of bench top performance tests were used to narrow the selection yielding a final surfactant package. The final candidates were then screened using an in-house friction loop. The improved friction reducer dosed at 0.5gpt had a 29% increase in ultimate friction reduction in fresh water and a 119% increased performance in 2% KCl when compared to a standard friction reducer of similar charge and molecular weight. Ultimate performance enhancement was gained within reasonable raw material costs and stability limits. With the increased ultimate friction reduction and superior inversion rate, this new product will reduce the energy required to deliver a specific volume at a set rate or increase the rate of the delivered volume at the same power for water based systems containing up to 2% KCl for stimulations and/or completions. Introduction Friction reducers used in the stimulation of petroleum bearing strata often do not perform to the potential theorized by the practitioner. Because the active ingredient of the friction reducer is often not correctly matched to the fluid and other additives contained within the fluid. However, quite often the active ingredient may not have a chance to fully participate as a friction reducer because it not fully or properly released into the stimulation fluid. This occurs when the friction reducing product is delivered in a form which requires full destabilization when introduced to the stimulation fluid to maximize its performance. This is particularly true of inverse emulsion based friction reducing products. These problems are often amplified when the stimulation water is a brine solution. For the active ingredient in the product to fully participate as a friction reducer, it must be delivered to the site in a usable form. If the product has turned from a freely flowing emulsion to a solid state it will not be able to function as a friction reducer. If the product has localized gelatinous masses within it, these masses can impede the flow of the product to the blend tank. The product must be both useable and stable whereas these factors are usually diametrically opposed. Typically, products that invert at rapid rates are inherently unstable and conversely, stable products do not invert rapidly. In reality a compromise must be achieved to have a functional friction reducer with acceptable product stability. A solution has been arrived at through careful selection of surfactants of an inverse emulsion polymer that both performs as a friction reducer in 2% KCl and has proven stability. By performance and stability testing various surfactant candidates identified and examined. Details are presented later in this paper.