A new delay agent has been developed which has hybrid functionality versus previously-reported materials. It delays viscosity development in fracturing fluids based on guar derivatives crosslinked with a variety of common zirconate and titanate crosslinkers under a wide range of pH. The viscosity development can be optimized by adjusting the concentrations of polymer, crosslinker, and delay additive to give the desired profile for a given hydraulic fracturing application. Introduction Modern hydraulic fracturing fluids are complex chemical mixtures with an imposing collection of performance requirements. They must react to generate the right level of viscosity at the right time under conditions of varying temperature, pressure, composition, and environment, and then break cleanly once the proppant is delivered. The ability to control the timing of viscosity development is especially important in fluids based on guar derivatives crosslinked with transition metals (e.g. Zr, Ti). The resulting gels tend to be shear sensitive and can perform poorly if the viscosity develops too early and the gel is exposed to high shear in pumping equipment. Uncontrolled or premature crosslinking costs the service provider in terms of higher hydraulic pumping costs and less efficient proppant delivery. This had led to the development of delayed crosslinkers affording control of the timing of the viscosity development in such systems. The chemistry involved in delayed crosslinking is conceptually straightforward (vide infra). However, the complexity and variability of the fluid formulations and use conditions makes selection of the optimum delay chemistry challenging. Having a basic understanding of the chemistry involved in guar crosslinking is critical to the successful design of a delayed fluid formulation. Also beneficial is the availability of a variety of delay chemistries during the design of new fracturing fluids. In this paper we attempt to address both of these needs. After providing an overview of the key factors affecting delayed crosslinking of guar and related polymers, we present a novel delay agent now available in commercially useful quantities. Fundamental Chemistry of Delayed Guar Crosslinking A hydraulic fracturing fluid must develop sufficient viscosity to carry proppant into fractures generated in the formation. For traditional proppants like sand, viscosities in the range of several hundred to a few thousand centipoise are required to avoid proppant settling. A common approach to generating this viscosity involves chemically crosslinking a polymer to generate higher molecular weight species having lower mobility in solution.

This paper was prepared for presentation at the 1999 SPE International Symposium on Oilfield Chemistry held in Houston, Texas, 16-19 February 1999.

Organic titanium compounds are materials having a covalent bond between titanium and another atom that is also bonded to a carbon‐based group. Titanium tetrachloride, the basic raw material from which organic titanate compounds are made, is readily converted to tetraisopropyl titanate, TYZOR TPT, by the Nelles process. This ester can be converted by alkoxy exchange (transesterification) to a wide variety of tetraalkyl titanates, which in turn react with other ligands and chelating agents to give complexes having properties significantly different from the starting materials. This article covers all aspects of the organic titanium compound, from properties, reactions, and synthesis, to uses and health and safety factors.

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