Geothermal reservoir characterization by tracer and well testing

This work presents the analysis of experimental data obtained on a lab scale fractured geothermal model where matrix block sizes, fracture apertures and distributions are known. The ultimate goal is to obtain the fracture aperture which is a key parameter in determining the flow and transport characteristics of fractured media. For the tracer tests, 4,000 ppm potassium iodide solution slug was injected from the corner of the model prepared using seventy stacked marble blocks and production concentration of the tracer was monitored from the other end of the diagonal. Drawdown pressure transient tests were conducted using the same model. Results indicated that flow was mainly through a major fracture path and tracer also entered to this path from auxiliary side fractures. The apparent size of the main fracture path was calculated as average 30 microns and secondary fractures had the average size of 10 microns which was found to be in good agreement with the mechanical aperture of 13.58 microns. The apparent fracture apertures, calculated using the permeability obtained from the well test analysis, changed from 70 microns to 116 microns overestimating the mechanical fracture aperture