A NOTE ON A METHOD FOR MEASURING THE TRANSPORT-PROPERTIES OF A FORMATION USING A SINGLE WELL

For some subsurface investigations of contaminant transport, particula rly those conducted in consolidated material, the costs related to wel l construction prohibit the installation of a comprehensive field of m onitoring wells. To alleviate this problem for fractured, low-porosity formations, a method for measuring transport properties using a singl e well was developed. The method involves the injection of fluid and t racer over a short duration which establishes a radial source conditio n in the formation. Following this the ambient how is allowed to carry the tracer back through the injection well where tracer concentration is monitored passively, in situ. To interpret the experimental result s, a numerical model was adapted to account for the mass balance of so lute in the source/monitoring well during the injection and monitoring periods. The model accommodates advection-dispersion, adsorption, dec ay, and matrix diffusion in a framework of fractures having a variety of geometries. To illustrate the use of the method, a field experiment was conducted using a single well which is intersected by a discrete horizontal fracture in a flat-lying shale and limestone formation. Int erpretation of the results agreed well with the interpretation of othe r tracer experiments conducted previously in the same fracture plane. This suggests that the method may yield defensible estimates of transp ort properties such as matrix porosity and groundwater velocity in geo logical formations that are expensive and difficult to characterize.