Ultra high temperature, high pressure (uHTHP) conditions have a different definition depending on the region and the operator and 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. When bottomhole temperatures exceed 400°F, the design and engineering of drilling fluids can be challenging. Drilling fluids that destabilize can cause a variety of fluid control problems that could lead to drilling and completion issues. With Invert emulsion fluids, the major challenges encountered under these conditions are related to the thermal degradation of the emulsifier and wetting package that can lead to gelation and syneresis. Another challenge is fluid loss which is related to the emulsion stability and to the degradation of the fluid loss control additives. Finally, efficient control over the rheological properties – critical to the success of any well - can also be challenging, where effects from emulsion instability, filtration control degradation and rheology control additive degradation are coupled with increases in drilled solids, rapidly leading to rheological instability. This can manifest itself as high fluctuating rheologies and gelation, or loss of rheological properties that can give rise to sag of weight material, both 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 compares 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 temperature >500°F, demonstrating tolerance to various contaminations and showing the rheological behavior and stability to 600°F and 40,000 psi.