Study of Water Relative Permeability in Fractures Using Well Tests and Radon: Gas Bubbles Effect

Few published data are available for two‐phase flow in fractures from field studies. All measurements of relative permeability reported in the literature were done in laboratory‐scale. The in situ water saturations are normally not known for multiphase flow in natural fractures; therefore, the direct measurements of relative permeability are difficult in field‐scale. With the help of a case study before and after the 2008 Mw 5.4 Antung earthquake, groundwater radon was used as a tracer to determine the gas and water saturations in a small naturally fractured aquifer. Well tests were also conducted to estimate aquifer transmissivity before and after the 2008 Antung earthquake. Anomalous declines in both groundwater radon concentration and transmissivity were observed precursory to the 2008 Antung earthquake. Both declines are two precursory phenomena having a common effect of gas bubbles. Using the data from well tests and radon tracer, one data point of water relative permeability can be obtained for in situ fractures. This data point reveals strong phase interference between water and gas bubbles for multiphase flow in natural fractures. Both the data of well tests and radon tracer are essential to gain an improved understanding of mass transfer behavior of groundwater‐dissolved gases between water and gas phases.