Technology Focus: Drilling and Completion Fluids (November 2017)
Authors: Jan Badrul Mohamed 
Published: October 2017

Technology Focus
It is no secret that drilling in deep water is challenging. It is always associated with high pressure and high temperature (HP/HT). HP/HT is commonly used to refer to wells with pressures greater than 10,000 psi and temperatures greater than 300°F. These pressure and temperature ratings may be even higher in some cases.
Drilling in HP/HT conditions poses numerous challenges. Drilling fluid is subjected to extreme pressure and temperature, and drilling-fluid properties such as viscosity and density are affected strongly by pressure and temperature. Drilling-fluid viscosity decreases with temperature and increases with pressure. From a reservoir-fluid-behavior perspective, on many occasions, HP/HT reservoirs present fluid that is well above its critical point. In other instances, reservoir fluid may exist near its critical point. In the first case, the rheological properties of the reservoir fluid may be difficult to predict because many parameters are unknown. Fluid near its critical point usually is very sensitive. A small change in pressure and temperature changes the phase behavior of the reservoir fluids (e.g., fluid properties such as density and viscosity). On phase diagrams, the iso-volume lines of the reservoir fluid are very close to one another.
It is important to ensure that laboratory tests are conducted near the actual reservoir temperature. Unfortunately, numerous research and experimental studies are sometimes simplified and the applied test temperatures are set far below the real reservoir-fluid condition. This may be because of limitations of the equipment used such as pumps, densitometers, and viscometers. Occasionally, a binary fluid is used as a reservoir sample to ensure that operating pressures and temperatures are kept practically and relatively low.
For this feature, I have selected specific papers that present new findings related to crucial drilling parameters measured at elevated temperature. One of the papers highlights a comprehensive approach in the development of novel magnetite nanoparticles, resulting in drilling fluids with superior properties for HP/HT applications. Another paper discusses a novel high-performance brine viscosifier (polymer) for high-temperature applications. The addition of the polymer blend increases the brine suspension both before and after aging at elevated temperatures. It also shows better rheological recovery after aging at high temperatures. This is the result of additive synergies within the brine, which greatly enhance the thermal stability of the polymers in the brine.
I hope you enjoy and benefit from the selected and highlighted papers. Other interesting papers are listed as suggested additional reading. For further reading, the OnePetro online library has additional papers.
Recommended additional reading at OnePetro: www.onepetro.org.
SPE 183799 Emerging High-Temperature-Well Stimulation-Diversion Technology Leads to Significant Increases in Conductivity by Naima Bestaoui-Spurr, Baker Hughes, et al.
SPE 183872 Synergistic Effect of Thermally Stable Polymers for High-Pressure/High-Temperature Brine-Based Drill-in Fluids by Hui Zhou, Halliburton, et al.
SPE 183946 Studying the Cooling Effect of Nitrified Drilling Fluid on a Bottomhole Assembly While Drilling High-Pressure/High-Temperature Wells by Abdulrahman Alrumaidh, University of Bahrain, et al.