Non-linear waves of fluid pressure and contaminant density in swelling shales

The control of drilling parameters, such as salt concentration, mud percentage and temperature is of fundamental importance for maintaining borehole stability when drilling through shale sections. For this purpose, a non-linear model of mechanic and chemo-poroelastic interactions between fluids, contaminants and solid matrix is presented. For the binary case we obtain a system of two non-linear coupled equations describing the isothermal evolution of fluid pressure and contaminant density in shales. In addition to the usual diffusive solutions obtained in linear analyses, a novel process is found. Indeed we show the presence of intense transient phenomena, i.e. quick non-linear shock waves of both pressure and contaminant. We apply this model first to a simple, homogeneous shale, then to more realistic cases, and finally to a non-compressive filter cake buildup. All these waves exhibit a Burgers solitary wave dynamics and can give destructive instabilities in deep drilling oil in shales. ► Transient quick non-linear waves of pressure and contaminant in swelling shales. ► Mathematical structure of Burgers solitary shock waves. ► Effect on these transients of a fine particulate migration. ► Build up of a filtering cake on the surface of the rock.