Ultra high-temperature, high-pressure (uHTHP) conditions have a different definition depending on the region and the operator/service company. In this paper, the definition used for uHTHP fluid performance is that of a fluid able to perform above 500° F and 30,000 psi. This paper describes the development of innovative drilling fluids specific to these well conditions.
The key fluid properties to ensure the success under these conditions are high-temperature, high-pressure (HTHP rheology and filtration control, filtercake quality, and thermal stability of the drilling fluid under extreme static conditions. When bottomhole temperatures exceed 400°F, the design and engineering of drilling fluids can become challenging. When drilling fluids destabilize, this can cause a variety of fluid control problems that could lead to drilling, logging and completion issues. With conventional invert emulsion fluids, the major challenges encountered under these conditions are related to the thermal degradation of emulsifiers and fluid-loss reducer that can lead to gelation and syneresis, as well as loss of rheological properties that can give rise to weight material sag, all potentially leading to associated well control problems.
The paper describes the development of the new fluid system designed for such uHTHP environments, highlighting the chemical differences and comparing the test data of the system with more conventional HTHP invert emulsion fluids. Data is presented showing the stability and performance of the new fluid over extended exposure to temperatures exceeding 500°F, demonstrating tolerance to various contaminations and showing the rheological behavior and stability to 600°F and 40,000 psi. Field test results will be presented as well.