The knowledge about rheological models is critical for a drilling fluid study. Typical drilling fluids have lower rheological properties in higher temperature or increase in gel properties which is the main reason for frictional losses when circulating. Keeping the rheological properties with constant value is one of the challenges to manage ECD and its effects. Our main goal is to introduce a flat rheology water based mud in order to improve fluid stability and prevent loss circulations and robustness while drilling operation.

The newly developed flat rheology water based drilling fluid system is formulated in different mud weights 1.12 S. G – 2.15 S. G to keep the shale inhibition, temperature stability and rheological properties in the highest possible performance.

This fluid system was subjected to hot rolling for 8 hours at 250 °F and 300 °F. Rheological properties were measured before and after hot rolling in several temperatures in order to confirm the flat and stable rheology. As well, other properties like shale recovery, fluid loss and lubricity were measured. After hot rolling (250 °F and 300 °F) rheology measurements were performed with Fann Viscometer for each mud in different temperature and pressures (60 °F to 180 °F) and the results were collected to be compared with before hot rolling data in the same conditions. All rheological data (PV, YP, Gels and etc.) remained the same comparing the properties before hot rolling.

This water based mud possesses the highest shale inhibition (shale recovery ranges from 95-100%). The API-fluid loss and HPHT-Fluid Loss were sufficiently controlled. Lubricity effect provided us with a really acceptable Kf (coefficient friction factor), under 0.2, which enables applying the system in high deviated zones or directional drilling. Stability tests show that this system has no incompatibility with high salinities and is adequately resistant in presence of contaminations. Also this system is applicable in the presence of weighting agents. Finally cost comparisons and environmental evaluations introduce this system as a cost benefit and environmental friendly system.

The most striking feature of this research is to design and introduce a flat rheology water based drilling fluid replacing conventional drilling fluid systems with temperature and pressure independent rheology along with other qualified characteristics. Significantly, this system is sufficiently environmental friendly and cost effective.

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