Thermal stability of water-soluble polyacrylamide (PAM) and partially hydrolyzed polyacrylamide (HPAM) polymers under various solution conditions have been studied utilizing Quantum Mechanics Density Functional Theory (DFT) computational modeling method. The hydrolysis reaction of the amide group (AM) to form acrylic acid (AA) is significantly affected by the pH of solution and the presence of cationic species such as Ca 2+. Without catalyzed, PAM is thermally stable with transition barriers as high as 50 kcal/mol. Both acid and base can catalyze the hydrolysis reaction by lowering activation energies with more than 10 kcal/mol. Formation of the 6-membered ring transition state (TS) structure arising from the assist of a second water or an ammonia molecule yields a lower enthalpic energy, which is sufficient to overcome the entropic penalty for bring three molecular species together for reactions. Ammonia/ammonium as products of hydrolysis also catalyze the reaction, rendering an auto-accelerated amide hydrolysis kinetics. The divalent Ca +2 cation not only interacts with carboxylic groups on HPAM to alter their rheological and phase behaviors, but also catalyzes the hydrolysis reaction to increase the degree of hydrolysis of HPAM. These results provide theoretical insights for molecular modifications of PAM/HAPM for their high-temperature (HT) and highsalinity (HS) applications.

The primary purpose of stimulating shale reservoirs is to allow as much contact with the reservoir rock as possible, extend drainage radius, and maximize Stimulated Reservoir Volume. Slick water fracturing has increased significantly with the advent of horizontal shale stimulation. Technological advances, including multi-stage fracturing of horizontal wells, have brought about an increase in frac volume of up to several million gallons of slick water per well. Recent restrictions by local and state regulatory entities have put limits on fresh water usage.Concerns over the disposal and environmental impact of flowback water have created challenges for industry. To remedy some of these concerns and reduce operational cost, some operators are adopting different methods of managing large volumes of produced water by chemical and mechanical methods, in order to remove solids and iron from flowback water so it can be reused in fracturing. However, most treatments currently used do not remove dissolved salts from treated waters, therefore recycled water not only exhibits overall high salinity, but also increased multivalent ionic content.When these conditions exist, the current commercial additives perform under par, thus necessitating the development of high brine tolerant chemicals. Searches for and development of these types of chemicals began early in 2009, and were done in part to meet operational demands, while reducing chemical costs and environmental impact. These goals can be achieved by using less friction reducer per job. This paper describes friction reducer performance and other chemical selections that tolerate high salinity flowback waters.This study critically examines the performance of a newly-developed slick water system in high salt concentration brines containing mono and multivalent ions. Average water analyses of different shale reservoirs were used to determine the performance characteristics of the additives used in slick water fracturing. A friction flow loop was used as the main measurement tool in evaluating the rheological properties of the polymers, as well as the effect of other additives used in slick water fracturing.This new slick water system incorporates a high molecular weight polyacrylamide in a water internal emulsion as a friction reducer, which shows significant improvement over commercially available friction reducers of similar charge and molecular weight currently used in the industry. A ten gallon capacity friction loop was utilized to pump the fluid through one-quarter inch pipe at a Newtonian Reynolds number of 52,000. Results of this study, along with compatibility data, were used to select a polymer system that exhibits high resistance to brine. Experimental and field data illustrated in this study show significant performance improvement of slick water treatments where high brine water is used in shale fracturing.

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.

Recent studies involving the measurement of friction reducer performance with a variety of brines typical of flow back/recycled stimulation waters of the North Eastern United States have indicated a clear differentiation by specific product type. The friction reducer variances specifically studied were: product charge, charge type, charge distribution reflective of polymerization, molecular weight, inverse emulsion surfactant packages, and manipulation of the internal or external phases.Increasing environmental regulatory pressure in geographic regions sensitive to water use, stimulation flow back discharge, and an increasing need for recycled water, the Marcellus gas play for example, have created a greater demand for higher performing additives in fluid systems used for oil/gas well fracturing. One additive that is greatly influenced by brine characteristic and water quality is the friction reducer. Increasing the ionic strength as well as multivalent cation content of the water typically limits the type of friction reducer used to obtain optimum performance. Standard anionic friction reducers do not perform well in many of these recycled waters as the friction reducer's ultimate performance is decreased, but also the rate of inversion is retarded and the potential for formation damage is increased.When compared to standard friction reducers, the ultimate friction reduction of the best of the series studied achieved nearly twice the friction reduction, approaching Virk's theoretical limit, and had an inversion rate nearly four times as rapid as a standard friction reducer. The dosages of the friction reducer were from 0.25 to 1.00 gallons per thousand gallons of treatment fluid. These friction reducers were tested in a variety of brines in a 10 gallon capacity friction loop through a ½ inch pipe at a Newtonian Reynolds number of 150,000. The data was collected every second during a 10 minute run with 6 specific performance criteria used to rank the candidates. This study demonstrates it is possible to provide a friction reducer that works well in brine content typical to stimulation fluids that contain a majority of flow back water from previous well treatments. This would allow well service companies to provide quality stimulation fluids of greater brine content and also minimize fluid disposal volumes and affiliated costs. Chemical additives such as these are needed in regions where both water quality and quantity are concerns.

Rheological experiments have been conducted with commercial and experimental friction reducers indicating certain profiles are advantageous for performance. In these profiles the factors of time and concentration are important in predicting the maximum performance window. These windows become apparent without the use of sophisticated rheological instrumentation. The viscosity profile of a friction reducer is dependent on factors such as polymer charge, charge distribution, molecular weight, polymer concentration, solvent properties, specific shear rate and time. Often it is difficult to measure properties such as molecular weight and viscosity, both quite sensitive to the specific test method and many assumptions are made. In this study, the viscosity of the system depends on the shear history, concentration, and time of measurement. Most traditional viscosity methods assume a thermodynamic definition of polymer configuration. This assumption is valid for measurement of friction reduction after significant duration. However, in a hydraulic fracture, this time may not be realized during the volumetric transfer of the fluid from the pumps to the perforations. In a recirculating friction loop measurement, the friction reduction performance of an ideal candidate rapidly increases and then sometimes diminishes with recirculation time. A possible correspondence between this phenomenon can be linked to the measurement conducted in this study. Shear rate sweeps were conducted on a variety of synthetic polymers with a Couette rheometer and a microchip rheometer. Variables studied were polymer type, concentration, shear history, time, solvent, make-down procedure, and atmosphere. Both inverse emulsion and dry friction reducers were studied. Friction reduction was measured on a once through system. From this study, ideal friction reducer candidates can be selected by simply and rapidly examining the rheological profile and rheological nuances realized when conducting the measurements. When choosing an ideal friction reducer, it must perform rapidly and maintain the necessary friction reduction required for the time frame needed.