Effects of Thermal Osmosis on Shale Instability

ABSTRACT: Optimization of drilling fluid parameters such as mud weight, salt concentration, and temperature is essential to alleviating instability problems when drilling through shale sections, particularly in hot environments. This paper describes the development of a solution for stress and pore pressure distribution around a borehole when considering significant thermal-and chemo-mechanical processes involved in shale-drilling fluid interactions. Phenomena related to thermal and chemical osmosis are included within the framework of linear thermoporoelasticity. The solution is one of generalized plane strain, therefore, it is suitable for investigating the impact of shale membrane characteristics, mud chemistry, and mud temperature on the stability of inclined well bores in shale. Application of the solution to a typical field operational situation has demonstrated that thermal osmosis can significantly impact fluid flux into the formation, thereby reducing stability. Also presented is new thermoporoelastic formulation for chemically-active rocks. Preliminary analysis suggests that mud temperature should be optimized in order to maximize the efficacy of chemical osmosis in stabilizing the borehole.