Multi-Valued Problems Associated with Liquid-Assisted Gas-Lift Processes and its Implication for Production Enhancement

Abstract

Liquid-assisted gas-lift process (LAGL), a variation of conventional gas lift, is a relatively new technique to improve the productivity of existing wells suffering from liquid loading. Its versatility is especially attractive because modern wells tend to be deeper, often with long horizontal sections, as shown by the examples from offshore and unconventional resources developments. By conducting transient computer simulations in various scenarios (i.e., a wide range of injection conditions for shallow and deep wells), this study aims to gain the fundamental knowledges associated with LAGL and learn how to apply them optimally in the field applications - unloading liquids in the producing wells and, at the same time, reducing the maximum injection pressure (Pinj-max) required. After determining model parameters from the simulation fit to experimental data and extending the simulations into a wide range of conditions, this study shows the following major findings. First, adding water in the injection stream during LAGL process does not always guarantee a reduction in Pinj-max. Instead, the results support that there is a certain range of injection-condition window (in terms of gas and liquid flowrates (Qg and Qw)) within which the process can effectively reduce the maximum injection pressure (Pinj-max). Second, the presence of such a window associated with a multi-valued problem is caused by the complex multiphase flow behavior, which coincides with the change in flow regimes (i.e., transitioning from mist/annular flow to slug flow). Third, applying the injection condition within the window in field-scale trials may not be necessarily straight forward because the pressure and liquid holdup responses sometimes show oscillatory behaviors (whether cyclic or chaotic) during the process. These oscillatory behaviors occur more easily in deeper wells in which the system allows more time for the injected gas and liquid mixture to get segregated during the downward flow in the annulus. The use of pressure and liquid holdup contours, as implemented in this study, is believed to be a useful means of planning for the LAGL treatments in the field.