Are You Buying Too Much Friction Reducer Because of Your Biocide?

Abstract

Slickwater fracturing is a large portion of current stimulation treatments in tight gas reservoirs. The fluids typically contain only friction reducer and biocide. They are considered incredibly simple, with little attention paid to their composition beyond the effects of water quality. In many cases, the biocides are sold and added to the fluid stream by production chemical companies while the friction reducers are added by the service company performing the fracture treatment. The paper reviews the chemical interactions between the typical anionic friction reducers and the cationic biocides such as quaternary ammonium compounds. The impact of these biocide-friction reducer interactions is that both materials are consumed and therefore prevented from performing their desired functions. During a treatment this is not obvious, but additional friction reducer eventually must be added to control pumping pressure. Further, the biocide is expected to be unavailable to control bacteria. The goal of any stimulation fluid should be that all components are compatible. As expected, some biocides complex with the oppositely charged friction reducers. This results in the formation of flocks of insoluble polymers in the fluid. Laboratory testing and a field example indicate that the quaternary ammonium biocides reduce the drag reduction seen with the common friction reducer. In comparison, nonionic biocides such as gluteraldehyde do not interact with the friction reducer. The paper also reviews studies with compatible scale inhibitors. Introduction Many key technologies have lead to the economic development of low permeability shale reservoirs (Boughal, 2008, Cramer, 2008, Palisch et. al., 2008). These include horizontal drilling, multiple fracture treatments, real time microseismic mapping, and simultaneous fracturing treatments (Daniels et. al., 2007, Fredd et. al., 2004, Penny et. al., 2006). The preferred fluid for most of these fracture treatments has been slickwater with low concentrations of proppant: usually 20/40 or smaller size sand. Slick water fracturing fluids have been unique successful due to the low leakoff present in most shale reservoirs. Shale is typically several hundred nano-darcy in permeability. Typical hydraulic fracture treatment volumes of are 715 m3 (6000 bbl) per stage with 6 to 10 stages per horizontal well. Slickwater fluids consist of friction reducer, biocide, and sometimes scale inhibitor. The friction reducer polymers are typically acrylamide co-polymers. Biocides are used to prevent souring of wells (Paulus, 2005). The most prevalent class of acrylamide friction reducers are the anionic copolymers. These polymers often contain acrylic acid which gives them their anionic nature (Sitaramaiah and Smith, 1969). Cationic friction reducers are used in acidizing, and can also be used in hydraulic fracturing fluids, but their cost is significantly higher than the common anionic types. Uncharged polysaccharide polymers like guar will give friction reduction, but the necessary concentrations are an order of magnitude greater resulting in significantly higher cost. So the industry has settled on anionic polymers as the friction reducer of choice. Friction reducer concentration is in many cases adjusted during the treatment "by feel" to try to lower pumping pressure or raise rate while staying within the working limits of the equipment. While the concentration of friction reducer is low, the cost to treat 715 m3 (6000 bbl) of fluid amounts to thousands of dollars. It appears that a large amount of this adjusting is not based on data or technical understanding. The friction reduction from an anionic polyacrylamide will be effected by the factors such as water quality and salinity of the water. It will also be affected by any other additives in the fluid which interact with the polymer.

Critical Evaluation of High Brine Tolerant Additives Used in Shale Slick Water Fracs

“…Some biocides such as THPS and quaternary amines such as ADBAC appear to have adverse effects on friction reducers (Rimassa et al, 2009) These types of chemical additives interfere with the polymer hydration mechanism, impairing viscosity gains and resulting in loss of the friction reducer emulsion's ability to invert quickly. This interaction may create a higher tubular friction pressure during pumping, which may lead to using a higher loading of friction reducer the during treatment to maintain flow rate, thereby incurring a higher cost to achieve the same friction reduction, and subsequently increasing the potential for formation damage related to polymer residue.…”

Preparation and Performance Evaluation of a Variable Viscosity Friction Reducer Suspension with High Salt Tolerance and Low Damage

“…For example, powder friction reducers suffer from slow dissolution, long mixing time, and complex mixing equipment, which restrict the supply capacity of slickwater and even affect the process of fracturing. Also, the solution of the powder product can be too viscous and stable, which makes it challenging to break. , The preparation process of a water-in-oil (W/O) emulsion friction reducer consumes a large amount of surfactants, and the existence of the oil phase causes formation damage such as a residual oil-soluble substance after gel breaking, treatment difficulty of flowback liquid, etc. − A water-in-water (W/W) emulsion friction reducer is still in the laboratory development stage, and the product exhibits a low drag reduction. In addition, it is still inevitable that polymer will swell due to the existence of the water phase, which weakens the product stability, giving it fewer advantages for long-term storage and transportation. , …”

Effect of polyacrylamide friction reducer on calcite dissolution rate at 25 °C and implication for hydraulic fracturing

“…The polymers utilised in hydraulic fracturing operations depend on the environmental conditions. Anionic PAM have a better performance in a fresh water environment (Sun 2014;Rodvelt et al, 2015), whereas cationic PAM have demonstrated an enhanced performance at high salinity scenario (Rimassa et al, 2009;Nguyen et al, 2018). The potential advantages provided by friction reducer also include reduced chemical usage, fewer environmental concerns, and decreased water consumption (Geri et al, 2019).…”