A medium pH range water base mud system designed as a result of high temperature high pressure studies on various clays and polymers has been laboratory developed and field tested. This type of system has proven to have advantages over water base mud systems previously used.

After detailed laboratory studies of attapulgite, bentonite, sepiolite and saponite clays in conjunction with polymers and various salts, a system using a mixture of saponite/sepiolite for the primary viscosifier has been developed.

The rheology of most clay slurries can be controlled by high molecular weight and low molecular weight temperature stable polymers. Potassium salts such as potassium bicarbonate and potassium carbonate are used instead of the sodium salts to control the alkalinity and chemical base exchange of clays. Potassium salts of the polymers are also used instead of sodium salts in order to maximize the potassium availability and minimize the sodium content.

These systems can be used in almost any type of make-up water and can be increased in density for control of high pressure-high temperature environments. They have been used for drilling in both shallow and deep wells, including wells of total depths below 17,000 ft. In addition to small diameter holes; these systems also show excellent hole cleaning ability and borehole stability in large diameter holes drilled for mine shafts.

These systems have temperature stability above the 500°F (254°C) range and with correctly chosen chemicals, show inhibition to water sensitive clays when run at intermediate pH range. They are easy to test and maintain and can result in faster drilling rates, improve hole cleaning, better cement jobs and minimal formation damage; and, add a more economical approach to drilling fluids. In addition, the environmental aspect is extremely appealing.

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