TECHNICAL FIELD

This disclosure relates to employing plunger lift to unload a well.

BACKGROUND

A well may be unloaded by removing a column of kill fluid from the wellbore to initiate flow from the subterranean formation (reservoir). Practices for unloading a well may include circulation of lower density fluid, nitrogen lifting, swabbing, plunger lift, and so on. The selection of the technique employed may depend on the well completion design, reservoir characteristics, and other factors. Plunger lift is an artificial lift technique for unloading a well that utilizes well energy of formation pressure to cycle a plunger (e.g., traveling piston) up the tubing or casing of a well. The plunger may serve as a solid interface between the liquid above the plunger and the fluid (e.g., primarily gas) below the plunger. The fluid below the plunger may supply the energy (via formation pressure) to propel the plunger (and the liquid slug above the plunger) to the Earth surface. Once the plunger is at the surface, the well may produce hydrocarbon from the subterranean formation. Then, when a column of liquid again accumulates in the wellbore, the well (wellbore) may be shut in to facilitate (allow) the plunger to drop back to bottom. Another cycle may begin once the well has built up sufficient pressure. Cycle frequency may vary with each well and type of production.

Plunger lift is an artificial-lift alternative applied to gas and oil wells typically having high gas-liquid ratio (GLR). Plunger lift may be an artificial-lift technique principally utilized in gas wells to unload liquid (e.g., condensate, water, etc.). However, plunger lift is also applied to oil wells with high GLR and oil wells without high GLR. Again, plunger lift is a type of gas-lift method that employs a plunger that goes up and down inside the tubing. The plunger provides an interface between the liquid phase above the plunger and the lift gas below the plunger to reduce liquid fallback.

SUMMARY

An aspect relates to a method of operating a well having a wellhead and associated wellbore in a subterranean formation. The method includes descending, via gravity, an unloading plunger from a rest position at the wellhead to a bottom portion of the wellbore. The unloading plunger has a chamber having compressed gas. The method includes ascending, via formation pressure, the unloading plunger from the bottom portion of the wellbore to the rest position at the wellhead. The method includes releasing the compressed gas from the chamber into the wellbore during the ascending to decrease hydrostatic pressure of liquid in the wellbore above the unloading plunger. The method includes unloading the liquid from the wellbore via the ascending of the unloading plunger.

Yet another aspect relates to a method of operating a well having a wellhead operationally coupled to a wellbore in a subterranean formation. The method includes closing a production valve at the wellhead to shut-in the wellbore and descending, via gravity, an unloading plunger from the wellhead through production tubing to a bottomhole of the wellbore. The unloading plunger has an internal chamber having compressed gas. The method includes opening the production valve and ascending, via formation pressure, the unloading plunger from the bottomhole through the production tubing to the wellhead. The method includes decreasing hydrostatic pressure of liquid above the unloading plunger in the production tubing during the ascending by discharging, via a timer-operated valve of the unloading plunger, the compressed gas from the internal chamber through the timer-operated valve into the liquid. The method includes unloading the liquid from the well via the ascending of the unloading plunger, wherein the unloading includes flowing the liquid from the production tubing through the production valve.

Yet another aspect relates to a method of operating a well having a wellbore in a subterranean formation and a wellhead at Earth surface adjacent to the wellbore. The method includes introducing gas into an internal chamber of an unloading plunger. The method includes setting a timer on the unloading plunger for operating position of a valve disposed at a discharge opening of the internal chamber. The operating position includes closed and open. The method includes descending the unloading plunger from the wellhead through production tubing to below liquid in the production tubing, wherein the operating position of the valve is closed during the descending. The method includes opening a production valve at the wellhead and ascending the unloading plunger through the production tubing to displace the liquid above the unloading plunger through the production valve to unload the liquid from the production tubing. The ascending includes discharging the gas from the chamber through the valve into the liquid in the production tubing above the unloading plunger to decrease hydrostatic pressure of the liquid.

Yet another aspect relates to an unloading plunger to unload liquid from a well. The unloading plunger includes a body to interface with an inside surface of production tubing in a wellbore to provide a seal in the production tubing between above the unloading plunger and below the unloading plunger. The unloading plunger includes an internal chamber to hold a compressed gas. The internal chamber has a chamber inlet to receive the compressed gas into the internal chamber and an outlet to discharge the compressed gas from the internal chamber. The unloading plunger includes a timer-operated valve disposed at the chamber outlet to prevent flow of the compressed gas through the outlet when operating position of the timer-operated valve is closed and to provide flow of the compressed gas through the outlet from the internal chamber when the operating position is open. The unloading plunger includes a nozzle in the body to receive the compressed gas from the internal chamber through the timer-operated valve and discharge the compressed gas from the unloading plunger.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

