Two-dimensional numerical calculations of streaming potential associated with hydrothermal circulation in permeable crust have been carried out. It is assumed that the streaming potential coefficient varies as temperature changes along the flow of water. Using the realistic values of the ζ-potential given by Ishido and Mizutani (1981), we showed that an observable self-potential anomaly can appear over a hot zone, where convective hot water is rising. The polarity is positive and the magnitude is 10 to 100 mV when the water flow rate is 10-8 to 10-7 m/s. Calculated selfpotential profiles are compared with recent observations at the Nigorikawa and the Hachimantai geothermal areas in Japan.
Theoretical and experimental studies are on effects of the length of impermeable portion at the top surface of the opened geothermal reservoir on a thermal convection. The reservoir is 9.2 in the reservoir aspect ratic and 2 in the heat source aspect ratio. The results obtained are as follows:(1) As the length of the impermeable portion increases, the value of stream function decreases and the convective current comes to be excel in a horizontal direction. So the convective current is influenced by the length of impermeable portion.(2) As the length of the impermeable portion increases, both temperatures within the reservoir and on the top surface rise further, which reflect the varation of the convective current mentioned above.(3) The discharge velocity of water through the top surface becomes maximum at the edge of the impermeable portion, and the discharge area of water is reflectively narrow.(4) The heat discharged through the top surface increases abruptly at the discharge area of water and the heat transported by water is above 10 times as large as the quantity transported by Newton's law of coling, and both discharges of water and heat per an unit time through the top surface decrease gradually as the length of the impermeable portion increases. These facts show that the discharged water plays an important role in a process of the discharge of heat.
This paper shows the procedure for calculating from wellhead conditions pressure and temperature changes in a geothermal well. Calculated results are compared and contrasted with available field data, and the utility and limitation of the developed numerical model are clarified.
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