Specialty drilling fluids, described by mud companies as rheologically flat, constant, or continuous, were introduced for drilling in deepwater less than 10 years ago. As used, the terms describe a rheological profile which is relatively flat or continuous only when compared to that of a conventional non-aqueous fluid. These specialty fluids have been shown to reduce plastic viscosity by 50-70% at seabed temperature and provide more consistent yield point, 6, and 3 rpm rheological values across a broad range of temperature. The properties are maintained primarily by use of temperature sensitive associative polymers.First generation associative polymers are efficient but have limited temperature stability. Controlled 16 hour dynamic exposure shows that the temperature stability of the highest quality associative polymer in use by most mud companies is less than 210°F. This modest temperature stability and resulting thermal degradation of the polymer and mud properties has begun to limit application in hot wells. It has been claimed that early generation polymers can be used when bottom hole temperature exceeds 250°F However, it has been necessary in some cases, before logging or completing a well, to spot 50-100 barrels of drilling fluid supplemented with organoclay as a "pill" in the open hole. This is needed if thermal damage and loss of rheological properties are expected to occur due to extended exposure to bottom hole temperature beyond the thermal stability of the associative polymer selected.When a deeper higher angle well with bottom hole temperature of 250-350°F is considered, the probability for rapid thermal degradation increases and a more stable polymer chemistry is preferred. In 2010 a second generation associative polymer with claimed temperature stability of 350°F was introduced for use in the field.Laboratory tests confirm significantly improved temperature performance by the novel second generation associative polymer. Field experience has shown that the new polymer is essentially interchangeable with an earlier version without significant change in rheological properties at lower temperature. A detailed study and discussion documents how the new second generation polymer compares to the original polymer in terms of indicative cost, performance, and potential for application in hotter environments.
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