Combined use of Total Dissolved Gas Pressure (P_tdg) and water pressure (P_H20) to optimize pumping from gassy aquifers

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When wells are pumped, the decreased water level in the well extends into the formation that the well is screened in. In wells that are screened in groundwater aquifers with high groundwater gas concentrations (i.e. high total dissolved gas pressures) production can be impeded by gas exsolution in the aquifer when the decreased hydraulic head in the aquifer is lower than the total dissolved gas pressure. Gas exsolution in aquifers reduces their permeability rapidly. This phenomena, known as 'gas-locking' is recognized in domestic water wells in regions with gas-charged aquifers. It is more recently a problem in water-supply and dewatering wells being drilled within the energy industry. The same phenomena (rapid gas pressure release by bubble formation in aquifers) can result in well-blowouts, and is responsible for geyser eruptions. The best way to manage pumping in aquifers is to maintain the 'bubbling pressure' (P_bub, which is equal to the water pressure plus atmospheric pressure, and can be represented as gauge 'water pressure' (P_w) so that it is greater than the total dissolved gas pressure (P_tdg). The P_tdg is the gas pressure that would be exerted by a mixture of gases in equilibrium with the water phase, and is equal to the sum of partial pressures of individual gases. Although a relatively new groundwater tool, the P_tdg measurement is relatively simple, inexpensive, and can be employed continuously. This project seeks to combine continuous gas and water pressure monitoring to optimize groundwater pumping from gassy wells by maximizing pumping (i.e. drawing the water table down, decreasing P_w) as much as possible without allowing the P_w to decrease below the P_tdg. To our knowledge this approach has never been conducted.