Guar-borate crosslinked fluids have been successfully used in hydraulic fracturing operations for decades. These fluids are often preferred because of cost, ease of use, and robustness. Additionally, borate fluids are renowned for their ability to recover viscosity after exposure to high shear, a process commonly referred to as “rehealing.” With the prevalence and reputation of these fluids, it is easy to become complacent and rely on the assumption of rehealability when pushing borate fluids to their operational limits. This is particularly true in the current climate of cost minimization. However, there are situations in which borate fluids might not reheal, or the rehealing process is significantly retarded. Because common assumptions about borate fluids cannot be assured in all situations, understanding the variables that affect performance is imperative.
This paper explores the properties of instant and delayed borate crosslinked fluids under different shear rates, shear histories, and a range of pH values. Various experiments were conducted to investigate the viscosity and the ability of viscosity to recover under different shear histories, temperatures, and pH values. This paper focuses on optimizing the fluid chemistry to provide the desired viscosities from the surface to deep within the fracture.
The work completed demonstrates how several borate fluid formulations can generate nearly identical viscosity profiles under a single shear rate, but vastly different profiles after exposure to high shear. If shear history is not considered in fluid design, some formulations could appear feasible during initial testing but fail to provide the desired viscosity in the near-wellbore (NWB) region during field operations. Assuming borates will simply reheal without consideration of pH and shear history on rehealing time could give rise to premature screenouts.
Borate crosslinked fluids are viewed as simple and forgiving. This is true to a point, but there are limitations that can be overlooked if the appropriate testing is not performed and formulations are stretched to their limits. The information presented in this paper demonstrates where assumptions about borate fluids' ability to reheal fail, while providing recommendations that can help ensure the desired viscosity is maintained throughout the treatment.
This paper compares the operational performance of a newly developed low friction, nearly residue-free (LF-RF) fluid system to a conventional derivatized guar-based fluid system and an existing nearly residue-free (RF) fluid system. The RF system has provided increased well production in numerous applications; however, the system requires lower treating rates due to increased friction. During recent field operations, the LF-RF system surpassed previous treating rates, which were previously unattainable, while maintaining maximum fluid cleanup.
The friction responses between the RF, LF-RF, and derivatized guar-based fluids were assessed through quantitative analysis of surface treating pressures. All comparisons between fluid systems were made between wells on the same pad with the same completion method. The wells used in this study were all located in the Denver/Julesburg (DJ) basin and pumped using the same hybrid treatment design. Along with field data, laboratory testing was conducted to compare the viscosity profiles of the LF-RF and derivatized guar-based fluid, which were used in the field.
Guar-based fracturing fluids have long been the industry standard. However, these fluids produce insoluble residue on breaking, which can reduce proppant pack conductivity and adversely affect well production. The RF fluid is an ultraclean, proven system, which has been successfully pumped in more than 16,000 stages. This fluid leaves virtually no insoluble residue, which has led to increased production from unconventional reservoirs. Yet, the RF fluid tends to exhibit increased treating pressures compared to guar-based fluids, which might require lower treating rates during operations. Additionally, a higher gel loading is necessary with the RF fluid to achieve comparable viscosities to the guar-based fluids. The new LF-RF fluid system retains all the beneficial cleanup properties of the RF system, while providing improved friction reduction. Intervals pumped with the LF-RF fluid provided lower treating pressures compared to those pumped with RF fluid, even at increased treating rates. With the improved friction reduction verified, the LF-RF fluid was pumped alongside a derivatized guar-based system at 80 bbl/min; a rate well beyond that which the RF fluid is generally pumped. The LF-RF fluid successfully placed all proppant and had similar treating pressures to the derivatized guar-based system toward the heel of the well. The LF-RF fluid was also able to accomplish this using a gel loading comparable to the derivatized guar-based system.
Through quantitative analysis of the surface treating pressures, the LF-RF system has demonstrated increased friction reduction compared to the existing RF system. The improved friction reduction allows the LF-RF fluid to be pumped at high rates, expanding the range of possible well and treatment designs which this fluid system can accommodate.
Conventional guar borate systems have historically been preferred for hydraulic fracturing applications because of the lower cost of the base polymer and crosslinker. Additionally, the fluid formulations can be easily tailored based on reservoir conditions and operational needs and the favorable tubular friction reducing characteristics of guar-based fluid systems makes them a desirable option for fracturing fluid systems. However, water insoluble residue resulting from guar-based systems may significantly impact the permeability of the proppant pack when flowing back and producing the well. A recently developed, nearly residue-free (RF) fluid system offers excellent cleanup properties and, as a result, has provided significantly improved production of hydrocarbons compared to typical guar-borate systems. While offering excellent performance and production, the RF fluid demonstrated significantly less friction reduction than comparable guar-based systems. This paper introduces a newly developed fluid system offering equivalent cleanup properties and performance, but with significantly enhanced friction reduction. The lower friction of the (LF)-RF system helps lower wellhead pressures to allow maintaining pump rate, adhering to the job design, to place the desired amount of proppant in the fracture.
This newly developed LF-RF fluid is a high performance fracturing fluid with improved regained conductivity and core permeability cleanup compared to typical guar-borate crosslinked systems. It is applicable within a wide variety of reservoirs, including unconventional reservoirs, and to-date has been successfully used in more than 1,100 stages since its introduction in early 2014. The LF-RF fluid system is applicable from 100 to 275°F bottomhole static temperature (BHST) and offers excellent operational versatility and proppant transport. This paper compares fluid performance and friction response of a conventional guar-borate fluid and the existing RF system with the newly developed LF-RF fracturing fluid.
This work examines how the use of high salt content waters (i.e., produced and flowback water) in conjunction with a recently developed, virtually residue free (res-free) hydraulic fracturing fluid affects the cleanup properties of the system. The res-free fluid system is designed around a naturally low residue polymer that, upon breaking, causes significantly less damage to the formation and proppant pack compared with conventional, guar-based fracturing fluids.
Since its introduction, guar-based fluid technology has grown to dominate the hydraulic fracturing industry due to its reliability and cost-effectiveness. However, guar gum contains a significant amount of insoluble residue that is not removed during its processing. The residue can cause damage to both the proppant pack and the hydrocarbon-bearing formation when the broken fluid is flowed back following the fracturing treatment. This damage can impair hydrocarbon flow from the formation and through the propped fracture, resulting in lower production over time. The res-free fluid offers better cleanup upon breaking than guar-based fluids and therefore significantly higher proppant pack conductivity and formation permeability in laboratory testing.
The res-free polymer exhibits sensitivity to certain ions present in solution, both in terms of gel hydration and crosslinking behavior. Depending on the ions present in the water and their respective concentrations, manipulation of the chemical formulation of the crosslinked res-free fluid system can mitigate these effects and achieve a stable, highly viscous fluid suitable for hydraulic fracturing. This work investigates whether the necessary reformulations impact the regained permeability and conductivity of the fluid system. Rheological data demonstrating how the reformulated fluid compares to standard formulations is presented. Additionally, test results are presented highlighting the effects of the alternative water sources on the res-free fluid regained permeability and conductivity data.
The use of produced and flowback waters for fracturing operations can substantially reduce both the economic and environmental impact of fracturing operations. The combination of the res-free fluid’s ability to utilize these water sources and its excellent damage reducing properties provides a system with significant advantages over conventional technologies in many applications.