The Establishment of a New Model for Differential Sticking Analysis

Accurate prediction of differential sticking plays an important role in minimizing and even preventing pipe sticking. Models presently in use for the prediction of differential sticking are not perfect, lacking studies on the relationship between mud cakes and pressures on the borehole wall. A new differential sticking prediction model has been established based on the studies made by other researchers, taking into account those factors such as the properties of mud cakes, differential pressure and the closed contact interface between drill string and borehole wall. Analyses of differential sticking mechanisms and calculation with drilling data indicated that the closer the permeability of an external mud cake to the permeability of a mud cake formed inside the formation, the higher the pressure exerted on the borehole wall, and this is beneficial to the prevention of differential sticking. A thin high quality external mud cake with good compressibility generates a low adhesion force at the time of differential sticking which is also easy to be unloaded, thereby fundamentally realizing the prevention of differential sticking. This study will provide theoretical guidance to the prevention of differential sticking in field operations and to drilling fluid program design.