Novel High-Efficiency Boron Crosslinkers for Low-Polymer-Loading Fracturing Fluids

Abstract

Summary Boron-based crosslinkers are used commonly to increase viscosity and to improve fluid-loss control and proppant transportability of guar and its derivative fluids. Boron crosslinkers are usually preferred because of their ability to reheal after 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 both the formation and the proppant-pack damage from polymer residues and to reduce overall fluid cost, especially with the reduced availability and higher cost of guar. Recently, we reported in paper SPE 140817 (Sun and Qu 2011( the synthesis of polyaminoboronates, bulky compounds containing multiple boron sites and capable of interacting with multiple polysaccharide strands to form more complex crosslinking networks at lower polymer loadings than conventional guar fluids. However, to improve the marketability and acceptance of the product, a lower-cost combination of raw materials is sought. In addition, a delaying mechanism to improve the control of the fluid-viscosity buildup can make the product fit into broader applications. A readily available polyamine was used as the base scaffold, and boron was incorporated by means of intermediate borate formed in the condensation reaction between boric acid and ethylene glycol to replace volatile and highly flammable trimethylborate. New chemistry was developed to produce more-controlled crosslinking. The resulting compound exhibited desired adjustable delay characteristics. This paper shows the effect of a series of new crosslinkers in terms of delay properties. The testing results of fluids with a 20%-lower polymer loading, crosslinked with the new crosslinker, are reported and compared with those of conventional fluids. Analysis and discussion of the chemistry, crosslinker performance, and economics are presented.