Currently, guar-based fluid systems are the preferred choice for hydraulic fracturing operations, primarily because the fluid formulations can be widely varied depending on reservoir conditions and operational needs. However, fluids prepared with guar are inherently dirty and contain water-insoluble residues, which can significantly reduce the permeability of the proppant pack when flowing back and producing the well. This can result in a possible reduction in overall hydrocarbon production. Herein, a new, residue-free, hydraulic fracturing fluid system has been developed that provides excellent performance during the fracturing process and includes superior cleanup characteristics.The "res-free" fluid is a premium fracturing fluid with comparable, or improved, properties compared to a typical guar/borate crosslinked system. First, because the fluid does not generate insoluble residue on breaking, excellent regained conductivity and core permeability can be achieved, which has been demonstrated both in laboratory testing and in the field by measuring well productivity. Second, the fluid is robust, allowing for precise viscosity and breaker control. Third, the fluid is salt tolerant and is usable up to temperatures of 275°F. Finally, it is capable of providing excellent proppant-carrying characteristics. The proppant-transport characteristics of this fluid are comparable to other fluids in use, as measured by a slurry viscometer. This paper highlights regained conductivity and core permeability, rheological performance, and proppanttransport characteristics of the new fluid and provides comparative guar-based fluid data. This new, residue-free fluid is applicable to fracturing a wide variety of reservoirs, including unconventional reservoirs, and has been used successfully in over 180 wells (>2,250 stages/zones) at temperatures up to 300°F bottomhole static temperature (BHST). Future papers will present case studies of jobs and will provide production and well performance results.
Enzyme breakers have been widely used in water-based fracturing fluids for more than three decades. Enzyme breakers have several significant advantages compared to traditional oxidizer chemical breakers. First, enzymes specifically break long-chain polymers without causing undesirable damage to the wellbore, formation, or fracturing equipment. Second, because of the catalytic nature of the enzyme, they are not consumed, thereby requiring minimal amounts. Third, enzymes are non-toxic compared to oxidant breakers. However, enzymes operate under a narrow pH range and often become inactive at high pH values. In addition, at elevated temperatures, their activity decreases or completely diminishes as a result of denaturing. This paper discusses a new method to extend the breaker activity of a mannanase enzyme to higher pH and temperatures by the addition of lignin-based additives. Results show that the addition of lignosulfonates stabilizes the enzyme at an elevated temperature and pH, thereby extending enzymes breaker performance beyond what was previously achievable. Another aspect of fracturing fluid breakers that is difficult to control is break time. Generally, varying the amount of breaker provides customizable break times. For example, if a faster break time is required, then a larger amount of breaker is added to the fluid. However, enzymes are highly expensive, and the use of greater amounts to achieve a faster break adds significant cost. On the other hand, if lesser amounts of enzyme are used, extended break times are achievable, but the polymer breakdown becomes incomplete, which could lead to formation or propped fracture permeability damage. In this study, it was possible to modulate the break times of guar-based fluids by varying the amount of lignosulfonate and keeping the enzyme loading constant. The higher loading of the less-expensive lignosulfonate aids in faster breaking of the fluid viscosity. Consequently, this approach is more economical as it requires less enzyme loading. Additionally, the polymer breakdown is complete despite the low amounts of the enzyme used. The effects of different structural types of sulfonated lignins on enzyme activity are also discussed. To the best of the authors' knowledge, there are no mannanase enzyme stabilizer additives available in the oilfield industry. Introduction of these new additives will aid in improving higher temperature and pH tolerance of mannanase enzyme breakers.
Well stimulation flowback water generally contains the chemicals and/or byproducts of a hydraulic fracturing process used on a specific well. Produced water is a different category, which is naturally occurring formation brine that is produced along with the hydrocarbons from the well, and can contain large quantities of dissolved salts, dispersed hydrocarbons, and other materials. Both of these waters are considered waste by-products of oil and gas production and typically present logistical difficulties for operators. Some of the challenges include transportation of waste water over long distances as well as local government and environmental regulations related to the safe disposal of the water from oil fields.The ability to recycle flowback and produced water provides great opportunities for service providers and producers to help reduce the total amount of fresh water that is used in their operations. By reducing the volumes of fresh water that are used in hydraulic fracturing and, at the same time, reducing the amount of flowback and produced water that has to be transported and disposed, operators are able to show their commitment to the community, the environment and can potentially minimize logistics. These benefits, however, can come with difficulty. For example, the cost of purifying flowback and produced water to near potable quality might not be financially feasible, while bypassing treatment entirely can pose difficulties in using the water effectively for fracturing fluids. In this paper, new and customized fluid compositions that can be used effectively with recycled waters are discussed, as well as successful case studies.
Crosslinked polymer hydrogels are commonly used in hydraulic fracturing to provide enhanced fracture width and length, while providing the ability to suspend and transport high concentrations of proppant deep into the generated fractures. Then, during post-fracture cleanup, the gel viscosity must be reduced and the broken fluid flowed back through the proppant to the wellbore. This process should occur with minimal damage to the proppant pack so as not to restrict hydrocarbon production from the reservoir. Significant permeability damage to the proppant pack occurs if insoluble residue from the fluid becomes trapped within the pores of the proppant pack. Consequently, it is of prime importance to ensure the fluid breaks cleanly and any insoluble residue is minimized. A new nearly residue-free (res-free) fracturing fluid was developed for use in crosslinked fluid applications. This fluid system was found to be very clean, leaving little to no residue (< 1%) upon breaking, leading to improvements in well cleanup and increased hydrocarbon production. This new fluid is a polysaccharide-based material that can be formulated to provide the necessary fluid performance parameters expected from traditional guar-based systems, but without the damaging insoluble characteristic of guar-based fluid systems. A number of successful treatments using the res-free fluid have been performed, resulting in superior production. This paper describes the fluid system, laboratory testing and results, field operation best practices, and production data from a series of wells stimulated with the nearly res-free fluid compared to offset wells.
One of the properties of guar borate complexed gel systems is the ability to recover dynamic viscosity after being subjected to high shear. This phenomenon is typically referred to as shear rehealing; and the ease of use of guar borate fluids during hydraulic fracturing operations can be partly attributed to this property. While many metal crosslinked fracturing fluid systems exist, and many provide higher proppant pack permeability after well cleanup, their overall use is lower because of higher cost, operational complexity, and perceived higher screenout rates. This paper examines laboratory and operational data to help parse the primary influences of screenouts for different fracturing fluid systems.Extensive laboratory experiments investigating low to moderate shear viscosity tendencies of fluids as well as the low shear proppant transport properties of various fracturing fluid systems were performed to determine if there is a strong correlation between fluid flow properties and proppant transport under shear. The operational data reviewed includes wells with similar completion methods, such as completion tools and well construction methods, and the performance of the tested fluids in the field. Experimental data shows proppant transport under low to moderate shear is possible with all of the fluids investigated, and screenout rates did not show significant correlation to the type of fluid used. The decreased ability for shear rehealing is typically associated with higher bottom hole treating pressure and screenout rates of metal crosslinked fluid systems.In many cases, operators are choosing simplicity of operations over the benefits of using higher quality fracturing fluids. This paper also discusses some of the factors that can help promote surface efficiency, while using the optimal fracturing fluids for the specific well.
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