Multiphase gas mechanisms in groundwater

Abstract

Numerous groundwater springs bubble, yet the flow and transport of gases are not well understood in hydrogeology. An understanding of the processes by which gases enter, migrate, and are liberated from groundwater is required. A quantitative conceptual model of gas migration in groundwater will allow an understanding of what informative aquifer signals may be present in gas data, as well as what information signals may be masked or diminished by phase changes. Through analysis of existing published literature, seven facies of groundwater bubbles were developed to provide a framework for research in these specific categories of gas transport. In order to better understand these multiphase bubbling springs, an instrument was designed and deployed over the discharge of a spring in southern Oklahoma that measured the total gas flux, ebullative and diffusive. By measuring the water discharge from the spring too, a hydropneumograph of gas and water mass flux over time can be produced. In addition to the mass flow rates of the two phases provided by the hydropneumograph, water and gas samples were collected for compositional analysis. By combining the compositional data of exsolved and dissolved gas with the mass flow rates from the hydropneumograph, estimation of the quantity of light noble gases is radically changed (60% for He, 45% for Ne) which provides improvements in the calculation of recharge temperature of 4 to 25% depending on the model selected. These improvements in the understanding of the physical hydrogeology of bubbling springs provide an additional avenue for researchers to explore aquifer dynamics that is largely ignored in the extant literature.