The development of new high-temperature drilling fluid formulations and field practice optimization is a major task worldwide. The role of divalent ions in colloidal stabilization led to the field proven Ca-muds especially under high-temperature conditions. In case of gyp-muds however Ca-tolerant dispersants, protective colloids and specialty chemicals must be used. Sulfomethylated (chemically crosslinked) lignite derivatives have been developed and used extensively for rheology and filtration control in deep and hot wells in Hungary. Optimized combination of modified lignites and selected low and high molecular weight synthetic polymers gave further improvement in temperature stability of high weight Ca-muds. Field results in several wells proved the performance of new synergistic blends at temperatures up to 490-500 K (225 °C).

Field and lab data showed the very special role of chemical equilibrium.

On theoretical basis and experience gained recently new lime mud formulation was developed. The relatively high filtrate Ca++ - inspite of high pH - combined with K-ions provides exceptional inhibitive properties.

The very special combination of synthetic polymers gives extreme temperature stability and unique performance.

Ionic and polymeric colloidal stabilization opens nwe ways in high-temperature drilling fluid formulations.

These systems have been successfully used in HPHT wells and show new promises in geothermal drilling as well.

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