Crosslinked Fracturing Fluids Research Articles

Zr, N-Co-Doped Carbon Quantum Dot Crosslinking Agents for Use in Fracturing Fluids

To further improve the performance of the fracturing fluid, the Zr, N-co-doped carbon quantum dot nano-crosslinking agent was synthesized by the hydrothermal method to solve the problems of easy agglomeration, instability, and gel breaking after crosslinking of the conventional polyacrylamide fracturing fluid crosslinking agent. The crosslinking agent has good stability and multiple crosslinking sites, as well as can be crosslinked with anionic polyacrylamide (HPAM) solution to form a high-strength hydrogel fracturing fluid. Moreover, it can be used as a nano-fluorescent tracer to test the flowback rate of fracturing fluid. The fracturing fluid composed of 0.3 wt % HPAM and 0.8 wt % crosslinking agent was named as Zr-CDG. At 180 °C, the viscosity of Zr-CDG remains above 180 mPa·s after shearing for 2 h, indicating that Zr-CDG has excellent temperature tolerance and shearing resistance. The residue is only 169 mg/L after gel breaking, which means low damage to the formation. Finally, the backflow process of fracturing fluid is simulated by core displacement. According to the good luminescence of the carbon quantum dot nano-crosslinking agent, the flowback rate of the fracturing fluid is calculated. It shows that the carbon quantum dot nano-crosslinking agent also has the role of fracturing fluid tracer. The results show that the properties of the prepared carbon quantum dot nano-crosslinking agent are more stable, and the performance of the crosslinked fracturing fluid system is greatly improved, which points out a direction for the application of carbon quantum dots.

Research of a novel double cross-linking fracturing fluid

A kind of JDL-1 thickener for betaine hydrophobic association polymer was prepared by aqueous solution polymerization of mixed micelles, AM, AA, AMPS and DM16 were used as raw materials, which was synthesized by redox initiator system. Friction tester and high-temperature rheometer were used to evaluate the resistance reduction and temperature and shear resistance of the thickener. The results show that the viscosity average molecular weight of the polymer prepared with AM, AA, AMPS and DM16 mass ratio of 70∶20∶5∶5 was higher than 12 million, and the dissolution time of the polymer was less than 3 min. When the surfactant is used for physical cross-linking, the apparent viscosity of the cross-linked fracturing fluid is larger than that of 60 mPa·s at 90 °C, 170 s-1 sheared 1 h; when metal cross-linking agent is used for coordination cross-linking, the apparent viscosity is larger than that of 80 mPa·s at 120 °C, 170 s-1 sheared 1 h. The drag reduction rate was 73%, the anti-swelling rate was higher than70%, and the damage rate was less than10%. The field trial was successful and confirmed the multifunctional effect of betaine-type hydrophobic associating polymer.

Synthesis and characterization of a novel, pH-responsive, bola-based dynamic crosslinked fracturing fluid.

Fracturing fluids are important media for hydraulic fracturing. Typically, the fluids are gelled using a polymeric gelling agent. Technological improvements over the years have focused primarily on improving the rheological performance, thermal stability, and the clean-up of crosslinked gels. In this study, novel supramolecular assembly of a low-damage fracturing fluid combining an ionic polymer gel (hydroxypropyl trimethylammonium chloride guar-cationic guar) and a bola surfactant fluid (bola carboxylate polypropylene glycol) is carried out and it is reported to have improved properties and special characteristics due to the synergistic effects of the dual systems, which are different from those of polymer gels and surfactant fluids. The viscosity of the fracturing fluid shows a sudden increase upon an increase in temperature and excellent self-assembly recovery after shearing. The fracturing fluid exhibits pH-responsive viscosity changes and low permeability impairment, due to the formation of a network structure and supramolecular microspheres at different pH values.

Experimental Study on Particle Erosion Failure of Abrupt Pipe Contraction in Hydraulic Fracturing

Erosion damage is one of the main factors leading to failure of pipeline in oil field, especially for sudden contraction section under solid–liquid two-phase flow in hydraulic fracturing. In this article, a laboratory experiment was carried out to analyze the effects of pipe flow velocity, particle concentration and pipe inner diameter ratio on particle erosion of the reducing wall in high-viscosity liquid. The results show that the erosion rate and erosion distribution are different not only in radial direction but also in circumferential direction of the sample. The upper part of sample always has a minimum erosion rate and erosion area. Besides, the erosion rate of reducing wall is most affected by fluid flow velocity, and the erosion area is most sensitive to the change in the diameter ratio. Meanwhile, the erosion rate of reducing wall in cross-linked fracturing fluid is mainly determined by the fluid flowing state due to the high viscosity of the liquid. In general, the increase in flow velocity and diameter ratio not only causes the expansion of erosion-affected flow region in sudden contraction section, but also leads to more particles impact the wall.

Erosion of water-based fracturing fluid containing particles in a sudden contraction of horizontal pipe

A lab experiment was carried out to study the effects of pipe flow rate, particle concentration and pipe inner diameter ratio on proppant erosion of the reducing wall in hydraulic fracturing. The results show that the erosion rate and erosion distribution are different not only in radial direction but also in circumferential direction of the sample. The upper part of sample always has a minimum erosion rate and erosion area. Besides, the erosion rate of reducing wall is most affected by fluid flow velocity, and the erosion area is most sensitive to the change in the diameter ratio. Meanwhile, the erosion rate of reducing wall in crosslinked fracturing fluid is mainly determined by the fluid flowing state due to the high viscosity of the liquid. In general, the increase in flow velocity and diameter ratio not only cause the expansion of erosion-affected flow region in sudden contraction section, but also lead to more particles impact the wall.

New Insights of Formation Damage Caused by Borate Crosslinker Fracturing Fluids

Hydraulic fracturing has substantially increased the productivity of unconventional reservoirs. The most widely used one is the cross-linked fracturing fluids. Therefore this study analyzed the formation damage issues caused by borate cross-linked fracturing fluids. Results shows that permeability of formation and proppant pack conductivity are greatly affected by reside left behind. The unbroken polymer chains may be cross-linked again if favor conditions present. The residue will ultimately reduce the conductivity of sand pack and only a small amount of guar residue can be displaced with production. To minimize the formation damage problems caused by polymer residue, the concentration of breaker needs to be the optimum value. To help analyze the degradation extent of fracturing fluids, flow-back fluids can be analyzed through various chemical analysis methods, taking into account the dilution effect of produced water.

A review of crosslinked fracturing fluids prepared with produced water

Abstract The rapidly increasing implementations of oilfield technologies such as horizontal wells and multistage hydraulic fracturing, particularly in unconventional formations, have expanded the need for fresh water in many oilfield locations. In the meantime, it is costly for services companies and operators to properly dispose large volumes of produced water, generated annually at about 21 billion barrels in the United States alone. The high operating costs in obtaining fresh water and dealing with produced water have motivated scientists and engineers, especially in recent years, to use produced water in place of fresh water to formulate well treatment fluids. The objective of this brief review is to provide a summary of the up-to-date technologies of reusing oilfield produced water in preparations of a series of crosslinked fluids implemented mainly in hydraulic fracturing operations. The crosslinked fluids formulated with produced water include borate- and metal-crosslinked guar and derivatized guar fluids, as well as other types of crosslinked fluid systems such as crosslinked synthetic polymer fluids and crosslinked derivatized cellulose fluids. The borate-crosslinked guar fluids have been successfully formulated with produced water and used in oilfield operations with bottomhole temperatures up to about 250 °F. The produced water sources involved showed total dissolved solids (TDS) up to about 115,000 mg/L and hardness up to about 11,000 mg/L. The metal-crosslinked guar fluids prepared with produced water were successfully used in wells at bottomhole temperatures up to about 250 °F, with produced water TDS up to about 300,000 mg/L and hardness up to about 44,000 mg/L. The Zr-crosslinked carboxymethyl hydroxypropyl guar (CMHPG) fluids have been successfully made with produced water and implemented in operations with bottomhole temperatures at about 250+ °F, with produced water TDS up to about 280,000 mg/L and hardness up to about 91,000 mg/L. In most of the cases investigated, the produced water involved was either untreated, or the treatments were minimum such as simple filtration without significantly changing the concentrations of monovalent and divalent ions in the water. Due to the compositional similarity (high salinity and hardness) between produced water and seawater, crosslinked fluids formulated with seawater for offshore and onshore jobs were also included. The crosslinked guar and derivatized guar fluids have been successfully formulated with seawater for operations at bottomhole temperatures up to about 300 °F. Operating costs have been significantly reduced when produced water or seawater is used to formulate fracturing fluids in place of fresh water. With various challenges and limitations still existing, the paper emphasizes the needs for new developments and further expansion of produced water reuse in oilfield operations.

Potential Use of Water Associated with Conventional Oil Production and Sea Water as Base Fluids for Hydraulic Fracturing Operations: Effect of Water Chemistry on Crosslinking and Breaking Behaviors of Guar Gum-Based Fracturing Fluid Formulations

Even though water consumption per hydraulic fracturing (or fracturing) job is relatively low; nearly all of the fresh water used for fracturing in California is in the regions of high water stress such as San Jouquin and Los Angeles Basins. However, water availability should not be a concern as huge volumes of water are being produced along with oil and gas from conventional formations (i.e. associated water) in the Kern County of California, a region where most of the fracturing activities take place. This associated water can potentially be used for preparing fracturing fluids in stimulating the unconventional formations. The present study reports on the relevant investigation done in this area of interest.The results suggest that associated water chemistry has limited effect on the viscosity of cross-linked formulations. However, guar gum concentration was found to affect the breaking behaviors of cross-linked fracturing fluid formulations. The new type of commercially available biodegradable breaker was found to be effective in breaking the tested cross-linked formulations at elevated temperature which was as high as 85°C (185°F). Both crosslinking and breaking behaviors of fracturing fluid formulations evaluated in this study were found comparable to the behaviors of commonly used cross-linked formulation (guar gum + 2% potassium chloride). These results suggest that both the associated water (i.e. water resulting from regional conventional oil production activites) and sea water (offshore oil fields) could serve as alternative sources of base fluid for use in fracturing jobs without putting significant burden on precious regional fresh water resources.

Experimental investigation of rheological properties of fiber-laden crosslinked fracturing fluids

Proppant settling is a critical issue in hydraulic fracturing and this is found to be a strong function of rheological properties (viscosity and elasticity) of fracturing fluids. In order to improve proppant-suspension capacity of fracturing fluids, fiber materials are often added into fracturing fluids, such as in FiberFRAC and channel fracturing. However, only few studies have currently dealt with the rheological properties of crosslinked fracturing fluids containing fiber. In this paper, a comprehensive study was performed to investigate the influence of fiber on the rheological properties (apparent viscosity and viscoelasticity) of borate crosslinked hydroxypropyl guar (HPG) gels by using a HAAKE MARS Ⅲ rheometer with different geometries (a concentric-cylinder geometry, a vane geometry and a parallel-plate geometry). It was found that the addition of fiber did not have a significant influence on the apparent viscosity of crosslinked fracturing fluid, which was due to the high viscosity of borate crosslinked fracturing fluids and low dosage of fiber. However, the addition of fiber caused an obvious increase in the elastic modulus of crosslinked fracturing fluid. Significant increment in elastic modulus was observed at high fiber concentration and long fiber length.

Technology Focus: Water Management (December 2014)

Technology Focus The demands for fresh water used in hydraulic-fracturing operations are placing constraints on water resources in some regions of the United States. Because of the high volumes of fresh water needed for hydraulic fracturing, the competing demand driven by industrial, municipal, and agricultural users has decreased the availability of fresh water and increased associated costs. Along with higher acquisition costs for fresh water, produced-water-disposal costs also have increased. To overcome these challenges, operators are using alternative methods of water management, including recycling and reusing produced water, to help reduce the total amount of fresh water required for their fracturing operations and, at the same time, reduce the amount of produced water that must be transported, treated, and disposed of. If the produced water is not recycled, the water is pumped into disposal wells. This practice has become a topic of public concern after reports of earthquakes began approximately 4 years ago in the central United States, where disposal wells are heavily used. Research conducted by the US Geological Survey and universities suggests that the increased injection of produced water from oil and gas operations near fault zones may be inducing earthquakes. Reclaiming produced water as a base fluid for hydraulic fracturing not only helps alleviate the oil and gas industry’s dependence on fresh water but also lowers the overall cost of fracturing. Produced water is usually composed of formation water and injected fluids from previous fracturing treatments. It can contain hydrocarbon and high levels of total dissolved solids (TDS), along with suspended solids and residual production chemicals. To reuse high-TDS produced water effectively in crosslinked-gel- based hydraulic-fracturing fluids, the water must first be treated. The goal of treatment is to control ions that hinder the development of the stable crosslinked fluid or that cause scale buildup in the wellbore. In response, a growing group of chemical suppliers, researchers, and service companies is on a mission to develop chemicals that will enable guar to hydrate and crosslink with boron crosslinker in untreated, high- TDS produced waters and yield a stable crosslinked fracturing fluid. The papers featured this month deal with water management and produced-water- treatment technologies. I urge you to look at OnePetro, the SPE online library, and download papers. You will find updates on best practices, case studies, new treatment technologies, and much more. JPT Recommended additional reading at OnePetro: www.onepetro.org. SPE 168520 One Company’s Upstream- Water-Resources-Management Guide by Stuart R.D. Lunn, Imperial Oil, et al. SPE 168401 Chevron San Ardo Facility Unit Beneficial Produced-Water Reuse for Irrigation by James E. Myers, Chevron SPE 168568 Appalachia Shale-Gas- Water Management Best Practices by Sean Beecroft, Chevron, et al. SPE 168469 Water Worth Waiting for: Smart Water Management Reduces Environmental Impact by S. Monroe, Baker Hughes, et al. SPE 165138 Produced-Water- Reinjection Design and Uncertainties Assessment by Jalel Ochi, Total, et al.

Advanced Degradable Alloys for Multi-Stage Fracturing Applications

New aluminum alloys with unique mechanical and electrochemical properties have been developed in response to a strong demand for new technologies tailored to the expanding hydrocarbon multi-stage fracturing market. The novel alloys disclosed in this paper purposely possess an augmented degradability in water-based oilfield fluids, an unusually high hardness and high compressive strength following proper processing while withstanding thermal aging in wellbore environments. In highlighting major findings from years of research in developing new alloys, this paper overviews major characteristics of these novel alloys from microstructural development, processing, mechanical properties, and electrochemical response in oilfield fluids such as salinated water (brine), acids, and cross-linked fracturing fluids.

Performance of a New Thermostable Mannanase in Breaking Guar-Based Fracturing Fluids at High Temperatures with Little Premature Degradation

A new thermostable β-1,4-mannanase (DtManB) cloned from Dictyoglomus thermophilum CGMCC 7283 showed the maximum activity towards hydroxypropyl guar gum at 80 °C, with a half-life of 46 h. DtManB exhibited good compatibility with various additives of fracturing fluid, retaining more than 50 % activity in all the cases tested. More importantly, premature degradation could be alleviated significantly when using DtManB as breaker, because at 27 and 50 °C it displayed merely 3.7 and 18.5 % activities compared to those at 80 °C. In a static test, 0.48 mg DtManB could break 200 mL borax cross-linked fracturing fluid dramatically at 80 °C, and merely 18 mPa s of the viscosity was detected even after the broken fluid was cooled down and only 161.4 mg L(-1) of the residue was left after the enzymatic reaction. All these positive features demonstrate the great potential of this mannanase as a new enzyme breaker for application in enhanced recovery of petroleum oil.

Crosslinking of Guar and Guar Derivatives

SummaryCrosslinking of guar and guar derivatives has played a major role in improving stimulation of oil and gas wells. While crosslinking has been used for a number of years, many facets of crosslinked systems are still not well understood. Part of the problem is that the traditional methods of determining the properties of crosslinked fluids work well for obtaining the data necessary for treatment design, but yield little insight into the nature of the crosslinked system. A good example of this is found in the development of low polymer concentration crosslinked gels. These gels are important because they lower costs and help to minimize formation damage. In this paper, methods for predicting crosslinkability at low concentrations are reported.The polymer literature is filled with methods for characterizing polymer solutions almost none of which find wide use in the development of crosslinked fracturing fluids. Dawson et al. (2000) first reported that the concentration at which a polymer solution transitions from dilute to semidilute could be used as a method for determining the potential for low concentration crosslinking in guar or guar-derivative solutions. To test this assertion, we have conducted a series of experiments that not only shows that the dilute-semidilute transition concentration is an important indicator for the polymers used in this study, but also presents a framework for exploring the potential of other polymer systems. These experiments show conclusively that low-polymer concentration crosslinking is strongly related to the value of the critical overlap concentration, c*. Both the critical overlap concentration and the critical crosslinking concentration increase in the order guar-3 < CMG < CMHPG < guar < HPG. In addition, we show that the critical crosslinking concentration for the range of polymer-crosslinking systems studied is correlated to the critical overlap concentration (ccc = 1.8(c*)0.77). A strong case is presented for the ability to crosslink at low concentrations is a strong function of the polymer type and a weak function of the crosslinker type.

Advanced Rheological Techniques for Optimizing Borate-Crosslinked Fracturing Fluid Selection and Performance

Summary The complex rheological behavior of crosslinked fracturing fluids is a function of shear history, temperature, and chemistry. Understanding the relationship between these variables and the downhole properties of the fracturing fluid is a challenging task. Rheological measurement techniques are presented that unravel some of the mystery associated with crosslinked fracturing fluids. The concept of a physical gel-point for fluids undergoing crosslinking is introduced and shown to correlate strongly with the proppantcarrying ability of the fluid. The gel-point variation with temperature and chemistry is discussed. This variation can be studied in the laboratory to provide an in-situ field performance evaluation without the need for expensive proppant-transport flow loops. The limitations for newly developed, low-concentration polymer fluids are also discussed. The fluid system chosen for analysis was the pH-activated, borate-crosslinked hydroxypropylguar (HPG) fluid.

Applications of a New, Efficient Hydraulic Fracturing Fluid System

Summary This paper discusses low-temperature applications for an optimized low-gel borate fluid system that does not rely on a separate component to maintain system pH. This fluid system's viscosity, fluid loss, static proppant settling, and dynamic proppant transport were tested; experimental procedures and results are described. Case studies from Argentina, Ecuador, the Texas Panhandle, and Permian Basin are also included. A new, borate-crosslinked hydraulic fracturing fluid system has been developed. This new, optimized fluid system provides higher viscosity with lower gelling-agent concentrations compared to conventional, borate-crosslinked fluids. Application of the optimized low-gel borate (OLGB) fluid system at low temperatures is discussed. Viscosity, proppant transport, and fluid-loss data of the OLGB fluid system are compared to conventional, borate- crosslinked fracturing fluids. Treatment designs are also presented.

Impact of Fluid Selection on High-Permeability Fracturing

Summary High permeability fracturing has become a major well completion technique both for production rate increase and, especially, for pressure drawdown decrease. Today, this type of treatment is the main means of sand control in some petroleum regions. Several of these treatments which are characterized by short lengths and, often, disproportionate widths, have been reported to exhibit positive post-treatment skin effects. This can only be the result of fracture face damage. This paper indicates that if the extent of fracturing fluid invasion is minimized, the degree of damage (i.e., permeability impairment due to filter cake or polymer invasion) is of secondary importance. Thus, if the fluid leak-off penetration is small, even severe permeability impairments can be tolerated without exhibiting positive skin effects. While the first priority in designing fracture treatments should be to maximize the fracture conductivity, it is recommended that in high permeability fracturing, high polymer concentration cross-linked fracturing fluids with fluid loss additives and breakers should be used. Experimental work corroborates these contentions.

Use of Volumetric-Average Shear Rate To Test Crosslinked Fluids With the Fann 50 Viscometer

Summary We describe a method where laboratory tests of delayed, cross-linked fracturing fluids can be conducted, using different size bobs, to generate consistent, reproducible measurements of viscosity.

Viscoelasticity of Crosslinked Fracturing Fluids and Proppant Transport

Summary In hydraulic fracturing treatments, the success of the treatment strongly depends on the proper placement of proppant particles in the fracture. "Proper placement" means the packing of the fracture to achieve maximum conductivity of gas/oil through the fracture into the wellbore. The placement of the proppants along the fracture is based on design equations where sand transport velocity is related to the rheological parameters of the fracturing fluid and characteristics of the proppant particle, such as size and density. The present work describes the theoretical transport equations that take into account the elasticity of the fluid in predicting proppant settling rate in the fracture. It presents the rheological data of commonly used fracturing fluids (titanate and borate crosslinked), including viscous and elastic parameter measurements made with a Rheometrics Pressure Rheometer™ (RPR) and Rheometrics Mechanical Spectrometer™ (RMS-800). These data show some important differences between borate crosslinked gels and titanate crosslinked gels. The paper also presents experimental data of proppant settling rates in various fracturing fluids and how these can be correlated with rheological parameters obtained in this work. The difference in rheology between borate and titanate gels was correlated with the difference in settling rates of proppants in these two gels. The theoretical and experimental work presented here led to the conclusion that the model for proppant placement in a hydraulic fracture should include: (1) proppant characteristics, (2) viscous rheological parameters (K and n), (3) elastic parameters (complex dynamic viscosity) from linear viscoelastic constitutive equation, and (4) normal stress difference from nonlinear viscoelastic constitutive equation. The influence of crosslinked-polymer-gel network structure on proppant transport is also discussed.

Alternatives to the Power-Law Fluid Model for Crosslinked Fluids

Abstract Measuring the rheological properties of crosslinked fracturing fluids is difficult but important. Fluid properties play a key role in the determination of the final geometry of die created fracture and in the distribution of proppant within the fracture; therefore, an accurate knowledge of these parameters is necessary for optimum treatment design. The first paper1 in this series described a method to measure accurately and reproducibly the rheological properties of crosslinked fracturing fluids. The technique is the first that applies long-accepted mathematical methods to correct the measurements for the deviations in shear rate caused by the non-Newtonian nature of the fluids. This, in turn, allows the rigorous examination of mathematical fluid models to determine which, if any, best describes the flow properties of the fluids.

Chemical Evolution of a High-Temperature Fracturing Fluid

Abstract Reservoirs with bottomhole temperatures (BHT's) in excess of 250°F [121 °C] and permeabilities of less than 1.0 md are commonly encountered in drilling and completing geothermal and deep gas wells. Successful stimulation of these wells often requires the use of massive hydraulic fracturing (MHF) treatments. Fracturing fluids chosen for these large treatments must possess shear and thermal stability at high BHT's. The use of conventional fracturing fluids has been limited traditionally to wells with BHT's of 250°F [121 °C] or less. Above 250°F [121 °C], high polymer concentrations and/or large fluid volumes are required to maintain effective fluid viscosities in the fracture. However, high polymer concentrations lead to high friction pressures, high costs, and high gel residue levels. The large fluid volumes also increase significantly the cost of the treatment. Greater understanding of fracturing fluid properties has led to the development of a crosslinked fracturing fluid designed specifically for wells with BHT's above 250°F [121 °C]. The specialized chemistry of this fluid combines a high-pH hydroxypropyl guar gum (HPG) solution with a high-temperature gel stabilizer and a proprietary crosslinker. The 6fluid remains stable at 250 to 350°F [121 to 177°C] for extended periods of time under shear. This paper describes the rheological evaluations used in the systematic development of this fracturing fluid. In field applications, this fracturing fluid has been used to stimulate successfully wells with BHT's ranging from 250 to 540°F [121 to 282°C]. Case histories that include pretreatment and posttreatment production data are presented.