Analysis of water flow in rock by a Tracer-aided X-ray CT

A new scheme named the Tracer Density Time-integration Method (TDTIM) is proposed to evaluate the ununiformity of a steady water flow in rock by means of the X-ray CT. Transport diffusion phenomenon of a tracer is analyzed to determine the distribution of flow rate. Tracer mainly composed of potassium iodide is utilized, preparing the viscosity of water-tracer mixture to be equivalent to pure water in a wide range of the tracer density. The CT images subtraction technique is applied to evaluate the tracer density at points within a rock specimen. Subsequent time-integration of the tracer density provides the simultaneous linear equation for the pore-water pressure, and the flow rate of water is determined, basing upon the Darcy law. Case examples clarify that the present method is a promising tool available for evaluating the fluctuation of water flow deeply influenced by heterogeneities in rock.