Exxon Company, U.S.A., experienced an average 100% overall penetration rate increase and a resultant 50% drilling intangible cost savings per well on three recent deep, hostile environment wells. Improved invert emulsion oil mud techniques were major factors in this success.

The oil mud program for each well was designed to provide a low viscosity and solids content drilling fluid in the hostile environment. Oil mud usage in the large protective hole intervals improved hydraulic cleaning efficiency and yielded maximum penetration rates. Hematite, a higher specific gravity weighting agent, reduced total solids content and mud viscosity. Decreasing the low gravity solids content also diminished viscosity and eliminated differential pressure sticking incidents. A high oil;water ratio optimized rheo-logical property control. A low filtrate loss reduced mud costs and stuck pipe potential. No penetration rate reduction associated with the low filtrate loss was noted. Sufficient salinity content contributed to optimum bit performance and formation stability.

This paper examines actual field results and develops a correlation between specific mud techniques and increased drilling performance. Recommendations are presented for improved oil mud performance in deep, hostile environment wells.

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