Menjjiao Yu is associate professor of Petroleum engineering at The University of Tulsa. He also serves as associate director of Tulsa University Drilling Research Projects (TUDPR). He received his PhD degree in Petroleum Engineering and MSE degree in Electrical and Computer Engineering from University of Texas at Austin. He has authored/co-authored more than 40 technical papers, supervised more than 40 MS/PhD studies, and carried out more than 20 drilling related research projects.

Dear Friends and Members of SPE!

I would like to invite you to our next SPE Event :

Distinguished Lecture 2011-12 Lecture Season

“Modeling and Characterizing the Interactions between Drilling Fluids and Pore Fluids in Shale Formations”

Abstract:

Borehole instability in shale formations remains a major technological challenge for oil and gas industry. Wellbore instability issue often occurs when water-based mud is applied to drill shale formations. In view of the shale instability costs (>$6 billion/year), it is imperative to understand shale behavior and its interaction with different fluids. Satisfactory solutions to prevent shale instability can be approached only after the understanding of the time-dependent shale-fluid interaction is achieved. Answers to questions such as: which drilling fluid to use for drilling a particular shale, or how long can the borehole be exposed to a particular fluid without causingshale instability, can be given only after such an understanding. Most existing models assume that drilling fluid and pore fluid are ideal solutions with single solute. However, drilling fluids and pore fluids in shale formations are highly non-ideal due to the high salinity of multiple solutes presented in the system. Water activity is considered as one of the key factors in controlling shale because the imbalance of water activity between drilling fluid and pore fluid results in physical and chemical interactions which in turn cause wellbore instability. In addition, most existing shale (wellbore) stability models often involve parameters that are not readily available in labs or fields. A new model has been developed to predict the water activity in shale formations taking into account the non-ideality, multiple solutes of both drilling fluid and pore fluid. Transient water activity and pore pressure profiles can be obtained from the coupled equations developed in this study. Moreover, a new method has been developed to determine the parameters used in the model through experimental data. Initial water activity of the shale sample can be obtained using the approach developed in this study. Model prediction has been compared with existing lab data and good agreement has been achieved. Results of this study can help drilling engineers to better understand the mechanism of shalefluid interactions. The approach developed in this study can be used to help design drilling fluids that can be used to improve the stability of shale formations.