Effects of ageing on the hydraulics of water wells and the influence of non-Darcy flow | Effets du vieillissement sur l'hydraulique des puits et influence de l'écoulement non-Darcéen Efectos del envejecimiento sobre la hidráulica de los pozos de agua y la influencia del flujo no Darciano 老化对水井水力学的影响以及非达西水流的影响 Efeitos do envelhecimento na hidráulicas de poços de abastecimento e a influência do fluxo não Darciano
2018
Houben, GeorgJ. | Wachenhausen, Julia | Guevara Morel, CarlosR.
Well ageing is mostly caused by mechanical and biogeochemical clogging processes, which affect the gravel pack, screen slots and casing. Clogging deposits increase head losses due to a constriction of the hydraulically effective area. For this study, clogging is mimicked by systematically reducing the gravel pack porosity, the screen open area and the nominal inner casing diameter. Groundwater flow velocity strongly increases close to the well, inducing inertial and turbulent flow components. Therefore, gravel pack head losses were calculated using the Forchheimer-Engelund equation, in conjunction with the Kozeny-Carman equation, which relates gravel pack porosity and hydraulic conductivity. Screen losses were assessed using the Orifice equation and turbulent casing losses with the Darcy-Weisbach equation. For the settings chosen here, a dramatic increase of head losses occurs when the clogging has reduced the effective porosity in the gravel pack by ~65%, the open area of the screen by ≥98%, and the casing diameter by ~50%. Since the latter two conditions are rarely reached in actual wells, the clogging of the gravel pack is the decisive parameter that controls well ageing. Regular monitoring of the well yield is therefore needed, since processes in the gravel pack are difficult to track directly. Unlike the deposits on the casing and in the screen slots, obstructions in the gravel pack are much more difficult to remove.
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