Gas lift operations in toe-down gas wells are usually dictated by convenience or knowledge based on previous experience. Parameters such as end of tubing location and packer placement are vital in determining efficacy of gas lift operations, alongside injection rate and injection location. The aim of this study is to quantify the effects of these parameters. The scope of this study is to provide guidelines to help assist design of gas lift systems for toe down gas wells.
A large scale experimental facility was constructed to study gas lift operations in toe-down gas wells. Air and water were used as test fluids, and the flow rates studied were those typically seen in toe down gas wells, resulting in slug flow being the dominant flow regime. Three end of tubing locations were studied, and in two of these locations the effect of a packer was quantified. Two different injection locations were studied as part of this study. Flow parameters such as pressure drop, holdup and slug characteristics were measured along the test facility.
Experimental results indicated that gas lift operations do not significantly affect the behavior of flow parameters such as holdup and pressure, upstream of the point of injection. The most significant effect of gas lift is observed to be a reduction of pressure drop fluctuations downstream of the point of injection. Packer placement also significantly affects gas lift performance, and it was observed that packered configurations are more efficient. Also, for a given end of tubing location, gas lift injection at the deepest point is observed to be the most effective in reducing pressure drop fluctuations.
This is the first experimental study conducted on the effect of end of tubing location and packer placement on gas lift operations on a large-scale test facility with field scale diameters for casing and tubing. Packer placement is currently dictated by mechanical concerns and depth limitations. This study addresses potential risks and benefits of running a packer as deep as possible, from a hydrodynamic standpoint.