Abstract

Engineering analysis can help avoid significant problems in deep offshore completions. Because yield-power-law fluids offer better convective heat-loss control, new algorithms have been developed that allow the modeling of convective heat transfer through such fluids. Special cases – Newtonian, Bingham Plastic, and power law – were also included in this model. This new software permits appropriate annular fluid design to avoid low-temperature-related problems such as hydrates, paraffin deposition, precipitation of salts at high pressure and casing collapse in un-vented annuli when multiple casing strings are used.

Yield-power-law fluids have viscosities that increase significantly as shear-strain rates diminish. As control over heat loss due to convection is developed, the shear-rate environment drops and viscosity of the yield-power-law fluid increases, reducing convective heat loss further. These fluids also tend to have relatively low high-shear-rate viscosity, making them easier to place and displace.

This paper explores the use of this novel engineering tool to show how changes in physical properties of the annular fluids, boundary conditions like bottomhole temperature (BHT), and fluids configurations in the wellbore result in changes in the temperature profiles in deep offshore wells – both "dry-tree" and sub-sea completions. These parametric analyses are then used to create practical general guidelines for the selection of annular fluids to meet the performance requirements in deep offshore wells and avoid the physical and chemical problems that could arise.

Introduction

A new engineering design tool, to be designated here as YPL-WTP, for "yield-power-law, wellbore-temperature-profile" program, was created to simulate wellbore temperatures during production, shut-in and injection. The program solves the energy equation for multiple casings. The solutions depend on the physical properties of the annular fluids, sea floor, wellbore geometry, and geological boundary conditions, and the fluids' configuration in the wellbore.

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