Abstract

Interactions between proppants and a zirconium crosslinked hydroxypropyl guar (HPG) frac fluid were examined using rheological test methods. The advantages of curable RCP over tempered RCP and sand have been well chronicIed. However, one disadvantage of curable RCP has been its effect on frac fluid viscosity and breaker activity. By definition, curable RCP is chemically reactive, and the chemistry required to form bonds between grains can interfere with a fluid's crosslinking mechanism. Using a Nordman 5002 viscometer with real-time digital data acquisition, viscosity data were gathered to quantify the rheology of crosslinked fluid exposed to uncoated sand, tempered RCP, and curable RCP. Proppant effects on oxidative breakers were studied by direct proppant / breaker consumption titrations. In addition, leachate samples of curable and tempered RCP were analyzed using Fourier Transform - Infrared Spectroscopy (FT-IR); differences in leachate provided information on which chemical species were reactive in interactive fluid chemistry.

Introduction

The use of phenol-formaldehyde resin-coated particles as propping agents in subterranean formations was first introduced in the mid seventies. In the years subsequent to its introduction, the use of resin-coated proppants (RCP) in hydraulic fracturing has grown from a tail-in material for preventing flowback of fracturing sand to a proppant which is used from fracture tip to well bore. This increase in pounds of RCP pumped per fracture treatment coupled with the higher proppant concentrations commonly used today have magnified the chemical interactions between RCP and fracturing fluids.

There are a great variety of fracturing fluids and fluid additives resulting in fluid systems with complex chemical environments. Even a single class of fluid (e.g. a borate crosslinked hydroxypropyl guar) will vary from service company to service company. As may be expected, each fluid will have particular tolerances, and it is recommended that each fluid/proppant system be understood before commencing a fracture treatment.

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