In adverse drilling environments such as high-pressure high temperature (HPHT) wells, the elevated temperatures and pressures encountered downhole by drilling fluids may degrade their chemical constituents. This may undermine the drilling fluid’s ability to carry out its functions effectively and result in problems while drilling. Some of the challenges encountered by conventional drilling fluids in HPHT environment include high temperature gelation of the drilling fluids, poor rheological control, high or severe HPHT fluid losses, sagging of weighting agents etc (Radwan and Karimi, 2017, Davoodi et al, 2018, Kakadiian et al, 2019, Ali et al, 2020, Zhong et al, 2019, Basfar et al, 2018). The main objective of this study was to evaluate the effects of temperature and pressure on fluid loss and rheological properties of novel, synthetic based drilling fluids (SBDFs) that were formulated with micronized weighting agents. Weighting additives such as 53?m barite, 25-30?m barite, 5-9?m barite, 7-9?m Ferox (Iron III Oxide) and 6-8?m Fero-Bar (blend of dual-weighted agents of Ferox and Barite) were used to formulate different mud samples to carry out rheology tests within temperature and pressure ranges of 120oF to 400oF and 14.7Psi to 12,000Psi and HPHT fluid loss tests in the laboratory. The outcome of the tests indicate that the mud samples formulated with weighting materials of ultra-fine particles sizes (5?m to 9?m) indicated a more resilient, near-flat rheological profile and lower HPHT fluid losses across elevated temperature and pressure ranges compared with mud sample from coarser particles sizes (53?m) weighting materials. Therefore, the use of micronized weighting agents of ultra-fine particles sizes to weigh up the advanced mud premix helped to bridge some of the already established challenges associated with traditional drilling fluids in HPHT drilling environments such as high temperature gelation of the drilling fluids, poor rheological control, and severe HPHT fluid losses.

Keywords: High pressure high temperature (HPHT), rheological properties, drilling fluids, weighting agents, particles sizes.