Design of non-aqueous drilling fluid for deep water drilling operations in the black sea

Date

2025-8-27

Author

AKEL, ÖZGÜR FIRAT

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This study aims to design and develop synthetic based non aqueous drilling fluid system for deep water drilling operations in the Black Sea, which is recognized as a challenging region due to its complex geological structure, high formation pressures, and significant temperature variations. The research focuses on key fluid properties such as density, rheological behavior, High Pressure High Temperature (HPHT) fluid loss, barite sag and lubricity, with the goal of creating environmentally responsible, high-performance drilling fluids that can operate reliably between 5 and 150°C and up to 20,000 psi. These systems are intended to address important drilling issues including emulsion stability, wellbore stability, hole cleaning, barite sag, torque and drag, HPHT fluid loss, rheology at different temperatures, hydrate formation, and changes in density with temperature and pressure. In this study, oil-based drilling fluid samples were systematically formulated at different mud weights (7.2–18.0 ppg) and oil/water ratios (65/35–90/10) to reflect the range of conditions present in Black Sea wells. The selection and optimization of primary and secondary emulsifiers, rheology modifiers, and fluid loss control additives were performed according to defined performance criteria. Laboratory experiments were carried out using advanced equipment for rheological measurements, HPHT filter press for fluid loss evaluation, and lubricity testers for assessing frictional properties under simulated downhole conditions. The rheology, HPHT fluid loss, sag, lubricity and temperature & pressure dependent mud weight change test results provide a strong basis for the development of synthetic based drilling fluid system that can meet the complex operational and geological requirements of deepwater drilling in the Black Sea. The rheological evaluation demonstrated that the inclusion of specific rheology modifiers effectively mitigated thermal and pressure-induced declines in fluid properties. Optimized formulations maintained stable rheological properties across the tested temperature and pressure ranges. These rheological characteristics contributed to enhanced suspension of solids and overall fluid stability, critical for deepwater drilling operations. The findings confirm that tailored rheology control is essential for sustaining drilling fluid performance in challenging environments. Notably, successful fluid loss control was achieved even without fluid loss additives when sufficient solids were present. The compressibility behavior of NADF samples were characterized, results showed an average range, with a few exceptions, of 2.9% to 3.8% density changes under combined temperature and pressure. Lubricity results demonstrated superior performance at lower temperatures, with a decline observed as temperature increased, highlighting the influence of lubricating film integrity. Furthermore, experimental results confirmed that calcium chloride concentrations above 20 wt.% serve as efficient thermodynamic inhibitors, effectively preventing hydrate formation. Collectively, these findings offer a comprehensive and environmentally friendly drilling fluid design tailored to overcome the challenges posed by the Black Sea’s deepwater drilling environment.

Subject Keywords

Synthetic Fluid, Invert Emulsion, Drilling Fluids, Black Sea, Drilling

URI

https://hdl.handle.net/11511/115600

Collections

Graduate School of Natural and Applied Sciences, Thesis