Thomas Paul Lockhart

Studies on Phenol-Formaldehyde Crosslinked Polymer Gels in Bulk and in Porous Media

The general conditions for gel formation by phenol-formaldehyde polymer solutions have been examined in studies with three acrylamide polymers. Contrary to an earlier report, polymer crosslinking is found to take place over a wide interval of pH. While the gelation time is relatively insensitive to the concentrations of phenol and formaldehyde or pH, it is strongly influenced by the temperature and the nature of the polymer. These gelants display good infectivity in corefloods and slim-tube experiments at temperatures up to 140 C. On the other hand, the partitioning of phenol into crude oil is found to be a significant issue for the propagation of these gelants. The use of a phenol pre-flush of the formation is shown by numerical modeling to be a potentially viable solution for this problem.

Zirconium additives for high-temperature rheology control of dispersed muds

Environmental considerations have stimulated new interest in the use of aqueous drilling fluids in situations where oil-based muds have previously been preferred. The least expensive and most widely used aqueous drilling fluids are dispersed muds made up with bentonite clay. These bentonite muds, however, possess limited rheological stability at elevated temperature and are also often formulated with chromium-containing thinners that are increasingly subject to environmental regulation. This paper describes a new zirconium-based rheology control additive of low toxicity that is extremely effective at extending the rheological stability of both chromium-containing and chromium-free bentonite muds at high temperature. The results of mud-aging experiments carried out between 150 and 200 C on both laboratory and field-conditioned bentonite muds illustrate the rheology-stabilizing characteristics of this additive. The low cost of drilling fluids formulated with the zirconium additive makes them attractive candidates for resolving the environmental issues and limited rheological stability of existing bentonite muds.