Modeling of Combined Effects of Water, Solute, and Heat Flows on Pore Pressure Profile near a Wellbore Drilled in Shale Formation

A general coupled model for the transport of solute, solvent, and heat is presented. The optimization of drilling fluid concentration, weight, etc. is crucial for wellbore stability analysis particularly in high pressure and high temperature environments, and thus the convenient selection of these parameters can be obtained from a clear understanding of the shaledrilling fluid interactions. The coupled effects of chemical potential (chemicalosmosis) and temperature gradients (thermalosmosis) on fluid flow significantly change the pore pressure and thereby causeing the redistribution of stress around a borehole. The model presented here considers both electrolytic solutions, drilling fluid and pore fluid, as nonideal. The assumption of nonideality of the solutions must be taken into account to accurately model the flow of solute and water through shale membranes. Due to chemical potential gradients between the solutions, water can flow from low salt concentration to high salt concentration and an osmotic pressure is created which can significantly influence the flow of both solute and water through shale. The impacts of thermal effects on wellbore stability are especially important for offshore high temperature, high pressure, and deep wells, where a small amount of temperature change in wellbore wall can cause various instability problems. Because of these reasons, the impacts of coupled chemical and thermal effects on water flow have been studied here.