Doctor of Philosophy (PhD)


Craft and Hawkins Department of Petroleum Engineering

Document Type



Drilling fluids are non-Newtonian mixtures that play a critical role in the timely and successful completion of oil and gas wells. In the particular case of offshore operations, proper design of drilling fluids is of paramount importance in the constant quest to lower break-even prices. Most downhole problems are directly or in-directly related to the rheological and physical properties of drilling fluids, thereby calling for a better understanding of the underlying changes of these properties with respect to drilling fluid composition and external conditions.

The current stance in the design of drilling fluids involves the selection of components and their concentration based on their known attributes. Surfactants and Oil:Water ratio are examples of typical parameters used in the design of drilling fluids. However, the laid emphasis on these attributes tends to overlook other effects of these components that equally affect their end rheology and physical properties, possibly to greater extents.

This project sought to assess the underlying effects of typical components used in the preparation of oil-based drilling fluids (OBM), through the investigation of oil-base complex fluids (OCF). Where OCFs refer to emulsion-suspension mixtures having oil as continuous phase. Surfactants and Oil:Water ratio were the composition variables investigated, with temperature as the external variable. The variables in the project were thus both qualitative and quantitative.

Results of experimental analysis found the underlying effects of both composition and external variables to significantly affect the flow curve, yield stress and stability of OCFs. Comparison between OCFs and OBMs showed similarities on the effect of composition and temperature on their flow and yield properties. Phenomena such as phase inversion, depletion flocculation and wall slip were equally found to affect the mechanical properties of both fluids, albeit to different extents.



Committee Chair

Akbari, Babak