Liquid unloading optimization from gas wells which exploit depleted reservoirs.
Argentina Tătaru, Dan-Paul Ştefănescu, Bogdan Simescu
Vol. 31, no. 2 (2014), s. 241-251, 
One of the most important aspects in natural gas exploitation, which must be constantly monitored, is the liquid impurities loading in gas wells, mostly in depleted reservoirs. The extension of this phenomenon is observed, as the natural gas reservoirs are depleted, thus substantially reduction of the reservoir pressure. The increasing quantity of liquid impurities is a major problem in gas depleted reservoirs exploitation, which could not be naturally removed in energetical depletion conditions. In this period, to avoid liquids acumulation and afterwards flooding, wells must produce with a minimum flow, named critical flow, under whose value is not possible the unloading of accumulated liquids. Wells can produce without liquid accumulations if in the tubing is obtained a gas flow velocity, greater than the liquid drop free dowfall speed limit. The velocity and critical flow depend on bottom hole or surface dynamie pressure, flow section diameter, liquid and gas density, water superficial strength. Liquid flow inerease during gas depleted reservoir exploitation, but only a part of this quantity is naturally unloaded by gas stream, the other part tend to accumulate to the bottom hole. In this conditions, the dynamie bottom hole pressure will inerease continuosly, causing continuous dropping and pronounced gas flow rate, until the well floods and stops producing. Early recognition of signs that indicates well liquid loading and the most suitable lifting system selection can eliminate problems before the production drops and layers damage.