Chemical potential related borehole (in)stabilities in the field are predominantly time-dependent. With the intention of developing a real-time wellbore (in)stability modeling capability, experimental work has been undertaken to investigate the role of chemical potential of drilling fluids on transient pore pressure and time-dependent rock property alterations of shale formations. The current work presents the concept and discusses the results of these undertakings.
The experiments using a Pore Pressure Transmission Test (PPT) apparatus expose formation (shale) cores under simulated downhole conditions to various salt solutions and drilling fluids. The uniqueness of this study comes from the fact that time-dependent alterations in the pore pressure, acoustic, static properties and strength of formations subjected to compressive tri-axial stress are recorded during the PPT experiments. This eliminates the anisotropy-associated differences obtained when different samples are used to determine the relationship between these characteristic parameters of shale formations. This comprehensive testing program will enhance our understanding of the relationship between acoustical, mechanical and chemical properties of shale as a function of time when exposed to a drilling fluid.
The main objective of this effort is to translate the results of the PPT tests to actual drilling conditions. Wherein the formation-drilling fluid chemical potential model would be validated and updated in real-time to predict borehole (in)stabilities.