Abstract
The overall objective of this research was to study the combined influence of pressure and temperature on the complex viscous behaviour of two oil-based drilling fluids. The oil-based fluids were formulated by dispersing selected organobentonites in mineral oil, using a high-shear mixer, at room temperature. Drilling fluid viscous flow characterization was performed with a controlled-stress rheometer, using both conventional coaxial cylinder and non-conventional geometries for High Pressure/High Temperature (HPHT) measurements. The rheological data obtained confirm that a helical ribbon geometry is a very useful tool to characterise the complex viscous flow behaviour of these fluids under extreme conditions.The different viscous flow behaviours encountered for both all-oil drilling fluids, as a function of temperature, are related to changes in polymer-oil pair solvency and oil viscosity. Hence, the resulting structures have been principally attributed to changes in the effective volume fraction of disperse phase due to thermally induced processes. Bingham’s and Herschel-Bulkley’s models describe the rheological properties of these drilling fluids, at different pressures and temperatures, fairly well. It was found that Herschel-Bulkley’s model fits much better B34-based oil drilling fluid viscous flow behaviour under HPHT conditions.Yield stress values increase linearly with pressure in the range of temperature studied. The pressure influence on yielding behaviour has been associated with the compression effect of different resulting organoclay microstructures. A factorial WLF-Barus model fitted the combined effect of temperature and pressure on the plastic viscosity of both drilling fluids fairly well, being this effect mainly influenced by the piezo-viscous properties of the continuous phase.
Highlights
The oil industry is increasingly drilling more technically challenging and difficult wells
The low yield stress values for B34-based drilling fluid suggest a short-range attractive force between the particles, which develop a network of aggregates weakly interconnected (Moraru, 2001)
High Pressure/High Temperature (HPHT) viscous flow characterization of oil drilling fluids formulated with two different organoclays was performed by using a non-conventional geometry coupled to a rheometer
Summary
The oil industry is increasingly drilling more technically challenging and difficult wells. Drilling of deeper wells worldwide requires a constant searching for adequate drilling muds to overcome extreme conditions (Williams et al, 2011). The successful completion of an oil well and its cost depend, on a considerable extent, on the properties of drilling fluids. The proper selection of the drilling fluid during rotatory drilling process is essential for dealing with the wide range of challenges encountered, in high angle drilling, completion and workover operations. Non aqueous drilling fluids (oil based and synthetic based), owing to their excellent lubricity, high rate of penetration and outstanding thermal stability, are often used to drill difficult wells, such as long sections of high angle and/or HPHT wells (Ghalambor et al, 2008)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
