Convection due to hot well casings affecting shallow groundwater as ubiquitous phenomenon

Wells and their casings (rising pipes) pumping gas and or fluids from several kilometers depth or hot (e.g. 70C-100C), due to the high temperatures present at such depths. Hot well casings heat up adjacent groundwater which becomes less viscous and lighter by thermal expansion. The reduced groundwater density triggers convection flow of groundwater in aquifers they pass. Convection transports water from the bottom of the aquifer upward along the casing and spreads it near the top of the aquifer. Salinity and other chemicals in the deeper groundwater, including natural methane will thus show up in the top of the aquifer affecting the quality of nearby drinking water wells. In this example the salinity of the groundwater in the aquifer increases linearly downward between 0 and 35 g/L and so does the associated density. The density counteracts the convection reducing the spreading of hot water near the top of the aquifer, instead circulating it in the stable mount that appears in the lower part of the aquifer. The density distribution here is extreme. The more uniform the natural groundwater density, the more will the deeper groundwater be convected to the top of the aquifer where it will spread sideways, likely affecting nearby drinking water wells. Methane gas, often naturally present and dissolved in the deeper groundwater likely comes out of solution due to the large pressure drop associated with the convection flow from the bottom of the top of the aquifer. The formed methane bubbles decrease the density further, which may even speed up the convection, as does the low viscosity of the heated groundwater next to the well casing. Given these general and unavoidable phenomena associated with hot well casings, one should not wonder when methane starts escaping from home taps connected with local drinking water wells, as was recently shown in the documentary Gasland. This phenomenon is general and has nothing to do with leakage of oil or gas wells, it is due to the heating of the groundwater next to the casing and expected to become ubiquitous as hundreds of thousands of shale gas wells will be rolled out over states and countries during the coming decades.

Category:

Science & Technology

Tags:

• mflab
• groundwater
• theo
• olsthoorn
• oil well
• shale gas
• drinking water
• well
• tap
• methane
• convection
• tempereature
• viscosity
• density
• flow
• Gasland
• TUDelft
• hydrology
• SEAWAT