Sammendrag
Late-life gas-wells are often characterised by highly erratic production rates of very low average. Due to the low average well-stream velocity, liquid particles are not carried out of the well, but are dropping to the bottom of the well, and liquid accumulation will occur. Due to the hydrostatic pressure of the accumulated liquid column, the bottom-hole flowing pressure may equalise the reservoir pressure, hence killing the production.For high velocity gas-wells, the well-stream temperature may be considered isothermal and close to the reservoir temperature. For late-life gas-wells, however, heat-loss through the metal tubing may be significant. Since the tubing has a high heat conductance, the gas may efficiently be cooled by heat transport through the tubing. At large depths, the gas in the annulus will function as insulation or even a heat source, when recycling, but close to the surface, it is reasonable to assume that the tubing temperature will be governed by the surface temperature, hence varying with weather conditions, time of day, time of year and so forth.It is shown that unless the well-stream is isothermal, or ""close-to-isothermal'', the dew-point pressure of pure methane saturated with water, is below the tubing pressure at all depths, hence condensation will occur. It is also shown that recirculating dried, heated gas may shift the dew-point pressure enough so that condensation in the tubing is prevented, although seasonal surface temperature fluctuations may lead to condensation near the surface.
