A New Extreme-HP/HT Viscometer for New Drilling-Fluid Challenges

Abstract

Summary Growing demand for natural gas in North America is driving the exploration and production industry to look for new resources in previously unexplored areas, and the deep Gulf of Mexico (GOM) continental shelf is currently attracting substantial attention. Several current deep-shelf high-pressure/high-temperature (HP/HT) wells have anticipated bottomhole temperatures that significantly exceed the operating limits of existing measuring-while-drilling and logging-while-drilling (MWD/LWD) tools; therefore, down-hole annular-pressure measurements will not be available for pressure management. This leaves temperature and hydraulic models as the best, if not the only, source of downhole-pressure information for these wells. These models depend on accurate surface inputs and laboratory-measured fluid properties under downhole conditions. Unfortunately, these anticipated temperatures and pressures also exceed the operating limits of conventional HP/HT viscometers. This lack of measured fluid properties under these extreme conditions will severely limit the ability of hydraulic models to predict downhole pressures. A new extreme-HP/HT (XHP/HT) concentric-cylinder viscometer was designed and built to fill this important technology gap for GOM deep-shelf HP/HT wells. The instrument is capable of measuring typical drilling-fluid viscosities up to 600°F (316°C) and 40,000 psig (276.0 MPa) and is capable of accurate property measurements for drilling fluids containing ferromagnetic materials. Subsequent verification and validation proved that the new viscometer compares favorably to commercially available field viscometers and more-sophisticated laboratory rheometers and therefore lends itself to widespread industry use. This paper reviews the development of the instrument and associated automated control system and explores health, safety, and environment (HSE) issues related to testing drilling fluids at these extreme conditions. The paper also presents results of verification and validation testing on invert-emulsion drilling fluids.