The 1980’s introduction of costly non-aqueous drilling fluids finally sent the industry a wake-up call to seriously acknowledge the significant impacts of temperature and pressure on the downhole density and rheological properties of drilling fluids. Despite notable progress since then, key issues remain, mostly related to inherent complexities and uncertainties associated with quantifying these effects.

Some issues are technical; others are procedural. Concerns are particularly critical on wells drilled under extreme HTHP (high-temperature/high pressure) conditions, in deepwater, and in Arctic and other ultra-cold locations.

The primary objective of this paper is to discuss existing issues from well-integrity and wellbore-integrity perspectives, with focus on determining hydrostatic pressures and rheological properties under downhole conditions. Also included are new representative volumetric-behavior and viscometric data measured in the laboratory under extreme HTHP conditions.

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