Pushing the Limit on Guar Loading: Treatment of a Green River Sandstone Formation by Use of a Novel Low-Polymer Crosslinked Fluid

Abstract

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.