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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. |
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