Fully Coupled Chemico-Geomechanics Model and Applications to Wellbore Stability in Shale Formation in an Underbalanced Field Conditions

摘要

Time-dependent wellbore stability has been observed in thernfield. Yet, a combined effect of pore fluid advection, swellingrnshale, and thermal diffusion may not be sufficient to explainrnand simulate this process adaquately. A coupled chemicogeomechanicsrnconstitutive model combined with a model withrnan ion-concentration dependent strength is developed in thisrnpaper. Strength reduction due to water hydration seems torndominate the time-dependent process in wellbore collapse.rnThe ultimate borehole instability is proposed to be determinedrnby the damage radius not the onset of wellbore wall mechanicsrnfailure, the latter is usually practiced. A field case is analyzed,rnand from experimental testing and simulations, it is concludedrnthat the time-dependent nature is dominated both by the timedependentrnstrength reduction and damage zone propagation.