Environmental constraints have led to the development of an invert mud system which has excellent toxicity, health and safety aspects, and is biodegradable. This system is particularly suitable for North Sea use where discharges from drilling with mineral oil-base drilling fluids are limited. Based on a synthetic material as the continuous phase, this mud system gives the same high performance as that of mineral oil-base systems. This paper describes this novel mud system and focuses on the impact of its use in environmentally sensitive areas.

The ratio of synthetic liquid continuous phase and aqueous phase (S/W ratio) can vary from 90/10 to 50/50 with mud weights ranging from unweighted to 18.0 ppg. The rheology parameters can be altered with rheology modifiers to give increased low-shear-rate viscosities for enhanced hole cleaning capabilities. Huxley-Bertram HTHP viscometer data shows good stability of the system under downhole conditions. Additional work indicates this system has reduced gas solubility, better lubricity, and lower retention on cuttings when compared to mineral oil-base muds.

Favorable toxicity data, bioaccumulation studies, and biodegradation work have been compiled for both the synthetic material and mud system. U.K. toxicity tests give highly acceptable values. These results, along with the bioaccumulation data, have led the U.K. Department of Energy (DEn) to assign the system a Category 0 classification under its Chemical Notification Scheme. Likewise, the Norwegian government agency (SFT) has agreed to permit this system to be used on a field trial basis. Currently, the U.S. Environmental Protection Agency (EPA) is considering its use, and subsequent discharge of cuttings, for Gulf of Mexico drilling.

You can access this article if you purchase or spend a download.