Drilling-fluid densities vary significantly over wide ranges of temperature and pressure, a concern that is particularly critical in deepwater, Arctic, and high-pressure/high-temperature. The variations can affect well integrity, well design, regulatory compliance, and drilling efficiency.

Drilling-fluid densities depend on the compressibility and thermal expansion of the fluids (liquids) and solids used in their formulation. Suitable pressure/volume/temperature (PVT) correlations for these fluids previously have been fairly inaccessible, primarily because of continually changing base fluids and blends, and the lack of readily available test equipment.

This study was conducted to measure the volumetric behavior under extreme temperatures and pressures of a broad range of the oils, synthetics, and brines currently used in industry to prepare oil-, synthetic-, and water-based drilling fluids. It follows a recent study that successfully qualified the commercially available test equipment.

For the most part, tests for this study were run at temperatures from 36 to 600°F and pressures from atmospheric to 30,000 psi, ranges that generally exceed those provided in other published studies. Correlation coefficients are provided for reference and to demonstrate their use in a compositional, material-balance model to accurately predict drilling-fluid density as a function of temperature and pressure. Tests run on field drilling fluids are included to demonstrate how these data can be used in procedures and software to predict equivalent static density and hydrostatic pressure during drilling operations.

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