Stefano Carminati

How do Anions in Water-Based Muds Affect Shale Stability?

The effect of different anions on shale behavior has been studied. Viscosity effects, pore blocking mechanisms and osmotic phenomena have been evaluated by pressure transmission tests under high pressure and high temperature conditions. Parallel to this short tenn experiments, mechanical (indentation) tests on cuttings aged for 12 days at 80°C have been run. In addition to organic and inorganic sodium and potassium salts, two commercial glycols (with and without Cloud Point) have been selected and analyzed. All the experiments have been carried out at alkaline pH. It is shown that different anions induce different shale hardening and different unbalance (related to osmotic phenomena) between pore and drilling fluid pressures. Besides that, some conclusions on the role of glycols have been drawn.

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.