Radon Emanation And Transect Studies

Abstract

ABSTRACT Laboratory and field experiments are underway to determine the source and transport properties of radon in geothermal systems. Data are available on laboratory emanation studies and field transect experiments which are useful in studying transport and physical properties of geothermal reservoirs. The emanation studies examine the "source" term for radon transport in geothermal fluids. The emanating power of radon from radium-bearing formation rock is dependent on rock type, rock size, pore fluid density, reservoir temperature and pressure. Initial experiments have shown emanation dependence on rock structure and pore fluid density. The data also suggest that emanation in geothermal reservoirs is also controlled by annealing conditions. Experiments are being run to examine the extent of hysteresis in reservoir rock annealing processes. Radon transect experiments involve short term measurement of concentration gradients along a line of geothermal wells of known formation structure. Experiments have been conducted at The Geysers vapor-dominated reservoir. Radon concentrations along the transect are correlated to reservoir temperature and pressures. The results are used to study changes in emanation conditions in the reservoir. Fluid transport under constant emanation conditions also results in radon concentration changes due to radioactive decay. Thus the ratio of radon to stable gas component gradients along the transect provides temporal data on the reservoir transport phenomena. Constant ratios are observed in The Geysers tests.