TABLE OF CONTENTS To effectively plan and design for gas well liquid-loading problems, it is essential to be able to predict accurately when a particular well might begin to experience excessive liquid loading. In the next chapter, Nodal Analysis ( of Macco-Schlumberger) techniques are presented that can be used to predict when liquid loading problems and well flow stability occur. This chapter presents the relatively simple "critical velocity" concept used to predict the onset of liquid loading. This technique was developed from a substantial accumulation of well data and has been shown to be reasonably accurate for vertical wells. The method of calculating a critical velocity will be shown to be applicable at any point in the well. It should be used in conjunction with methods of Nodal Analysis if possible.
The transport of liquids in near vertical wells is governed primarily by two complementing physical processes before liquid loading becomes more predominate. As the well becomes weaker, other flow regimes, such as slug flow and then bubble flow, begin to appear.
It is generally believed that liquids are lifted in the gas flow velocity regimes as individual particles and transported as a liquid film along the tubing wall by the shear stress at the interface between the gas and the liquid before the onset of severe liquid loading. These mechanisms were investigated by Turner et al., [1] who evaluated two correlations developed on the basis of the two transport...
