Development of a New Plunger-Lift Model Using Smart Plunger Data

Abstract

Abstract The problem of liquid loading, which is common to all mature gas producing wells, needs to be identified and solved in order to achieve efficient gas production. Field operators not only need to select the best possible technical solution for liquid loading, but also one that is cost effective. A popular remedial solution for liquid loading in onshore gas wells is plunger lift. However, this technology is currently designed using simplistic models with restrictive assumptions, coupled with field experience. This paper provides an overview of the various plunger lift models available in the public domain and highlights their fundamental limitations. A new approach to plunger lift modeling is then proposed, which assumes the availability of pressure and temperature data provided by smart plungers. These devices are equipped with internal gauges to record pressure and temperature with time, which can be downloaded whenever the plunger is at surface. In the proposed model, these data are coupled with the fundamental conservation equations of mass, momentum and energy that govern the dynamics of plunger lift. The main difficulties of dealing with transient flows that are typical of plunger lift operations are identified. These include the dynamic interactions between reservoir, annulus and tubing, which are particularly relevant in tight gas reservoirs. The overall objective is to develop a model capable of predicting plunger lift operations in a more realistic fashion and so optimize lift cycles. Introduction Most gas wells experience the problem of liquid loading as the reservoir pressure declines. This phenomenon occurs when the gas produced from the well loses its ability to lift the associated liquids to surface. The resulting hydrostatic head of the accumulating liquids downhole creates a backpressure on the formation and reduces gas production. This problem is tackled by removing the accumulated liquids using a variety of unloading methods depending upon the operating conditions of the well. Plunger lift is an artificial technique that uses natural energy from the reservoir and/or the energy stored in the tubing casing annulus gas to unload the liquids from the bottom of the well. The method employs a free piston, which acts as an interface between the liquid slug and gas phase, to travel up and down the tubing in a cyclic manner to lift the accumulated liquids to surface. The plunger lift cycle is usually intermittent with the well being alternatively shut-in and flowed. The former sees the well pressure to build up to a certain level that will permit the lifting of accumulated liquids to the surface, while the latter sees the accumulated liquids, followed by the gas, produced at the surface. Successful plunger lift installations strive to have the longest flowing time for increased gas production with the correspondingly shortest shut-in time.