One of the critical factors in the deepwater exploration and development is the temperature during the drilling process. Temperature in the wellbore will induce the wellbore instability, which means the bottom hole pressure will change according to the accumulated thermal effects on the density, viscosity of the fluid during the circulation. Unpredicted bottom hole pressure will lead to unknown well control risks, which make the deepwater drilling is in great danger and unacceptable for the engineers.
In the casing design, the thermal effects were ignored in the past but with drilling deeper subsea wells, the thermal effects will exist inevitably. The extreme values observed at the seafloor could be as low as 40°F and as high as 150∼200°F at the wellbore annulus. Unfortunately, deepwater environments combine low temperatures, high pressures, gas and water that can induce hydrate formation. Hydrates can lead to drillpipe blockages and affect BOP operation. The low temperatures due to the hydrate or ocean current affect the properties of cement, which indicates to redesign cement slurry composition required.
Except the effects on the density and viscosity of fluid, the rising temperature in the annulus between the drill pipe and casing will make the trapped pressure increase in the annulus between outside casings. If the annulus build-up pressure can’t be released without rapture disks, otherwise the trapped pressure is beyond the initial design pressure, and the potential damage will happen.
This paper provides a simplified method to predict the circulation temperature under steady-state heat transfer in the deepwater rissssserswellbore, and a simulator is developed.
