Summary Guar-based fracturing fluids are the most commonly used fluids in reservoir stimulation. To provide high viscosity, borate-crosslinked gels are preferred for their ability to heal after mechanical shearing and their favorable environmental properties. More-efficient crosslinkers capable of crosslinking fluids with reduced polymer loading have always been of great interest to reduce formation and proppant-pack damage from polymer residues and to reduce overall fluid cost. Low permeability and the interwell connectivity of the Green River sandstone formation of the Uintah basin require hydraulic-fracturing treatment to produce oil economically. The most typical fracturing treatments use borate-crosslinked guar fluids to transport sand into wells with vertical depths of 3,500 to 6,800 ft and bottomhole temperatures of 115 to 160°F. Most operators in this region place emphasis on reduced polymer loadings for stimulation treatments, and, even with breakers present, broken polymer residues can remain in the formation at these reduced polymer loadings, resulting in damage and decreased production. Unlike conventional treatments that require a shut-in operation, stimulation treatments in this region are designed for immediate flowback to minimize filter-cake buildup and subsequent formation damage, which improves production significantly. Immediate flowback poses a challenge of a proper balance between polymer and breaker loading so that the fluid effectively transports up to 6 lbm/gal added of sand into the formation without screenout and breaks within the treatment time (20 to 30 minutes per stage) to minimize flowback of proppant. A recently developed novel poly-aminoboronate (PAB) crosslinker (Sun and Qu 2011; Legemah et al. 2013) was tested in the aforementioned formation. Multiple boron sites are available in the crosslinker, and it is capable of interacting with multiple polysaccharide strands to form more-complex crosslinking networks at lower polymer loadings than conventional guar fluids. The crosslinker, with up to an additional 15% reduced guar loading, is capable of matching or outperforming conventional crosslinked fluids in fresh water and, more impressively, in 7% potassium chloride. This paper will discuss the novel crosslinker developed, the laboratory testing, and the successful field application. Analysis and discussion of the chemistry, crosslinking performance, and economics will be reported.

Guar-based fracturing fluids are the most commonly used fluids in reservoir stimulation. To provide high viscosity, borate crosslinked gels are preferred for their ability to heal after mechanical shearing and their favorable environmental properties. More efficient crosslinkers capable of cross-linking fluids with reduced polymer loading have always been of great interest to reduce formation and proppant pack damage from polymer residues, and to reduce overall fluid cost. Low permeability and the interwell connectivity of Green River sandstone formations of the Uintah Basin require hydraulic fracturing treatment to economically produce oil. The most typical fracturing treatments use guar crosslinked borate fluids to transport sand into wells with vertical depths of 3500-6,800 feet and bottom-hole temperatures of 115-160°F. Most operators in this area place emphasis on reduced polymer loadings for stimulation treatments; and even with breakers present, broken polymer residues can remain in the formation even at these reduced polymer loadings, resulting in damage and decreased production. The stimulations for these wells are flow backed at the end of the last stage. This poses a challenge of a proper balance between polymer and breaker loading, so that the fluid effectively transports up to 6 pound per gallon added (ppa) of sand into the formation without screen out, and breaks within the treatment time (30-40 minutes per stage) to minimize flow back of proppant. Recently developed novel poly-aminoboronate crosslinker (also reported in SPE 140817 and SPE 164118) was tested in the aforementioned formation. Multiple boron sites are available in the crosslinker and it is capable of interacting with multiple polysaccharide strands to form more complex crosslinking networks at lower polymer loadings than conventional guar fluids. The crosslinker with up to additional 15% reduced guar loading is capable of matching or out performing conventional crosslinked fluids in fresh water and more impressively in 7% KCl. This paper will discuss the novel crosslinker developed, the laboratory testing and successful field application. Analysis and discussion of the chemistry, crosslinking performance and economics will be presented.

The Bakken formation is one of the largest unconventional oil plays in the United States, and large-scale hydrocarbon recovery from this formation has only recently become economically feasible as technological advancements have reduced stimulation costs. These low-permeability zones must be fracture-stimulated with large fracture networks for enhanced well production and improved economics. Guar-based fracturing fluids are the most commonly used in stimulation treatments. Cross-linked fluids with low polymer loading and high viscosity are needed to transport proppant efficiently. However, due to the tight shale formation, efficient proppant pack cleanup is critical to minimize polymer residue. The breaker systems include coated and uncoated oxidative breakers with an enzyme breaker added during the tail-in stages to break down the viscosity and aid in fracture fluid cleanup. In the field, oxidizers were found to perform inconsistently at some temperatures, and the conventional enzymes were inefficient at higher pH and temperatures. To improve reliability, a novel enzyme breaker was field-tested in early 2010 and proven to function more consistently and enhance post-stimulation productivity. In late 2012 and early 2013, this new enzyme breaker was implemented in multiple fields and consistently yielded similar results as the field trials. The enzyme breaker is a polymer-specific, thermostable mannanohydrolase, genetically modified for increased conformational stability. This enzyme breaker can be used from ambient temperatures to ≥ 250°F and functions well at an elevated pH of 11.0, whereas conventional enzymes are inefficient under these conditions. Production results from several wells were compared with offsets that had been treated with the conventional fluid system and breaker package. The wells treated with this new enzyme breaker showed higher increase in oil production. This demonstrated persistence of this new enzyme to improve breakdown of the polymer and enhance cleanup of the proppant pack which resulted in enhanced oil production.