Modeling Plunger Lift for Water Removal from Tight Gas Wells

Abstract

Many tight gas wells produce at rates below their potential, due to water loading. Plunger lift is often applied to remove produced (or condensed) water, reduce bottomhole flowing pressure, and increase both gas production rate and ultimate recovery. Previous authors have discussed dynamic models of the plunger lift process. However, these previous models considered only stabilized reservoir production. Because of the assumption that reservoir production is stabilized, these older models have only limited applicability to tight gas wells. This paper presents a study of the application of plunger lift to the problem of water removal from tight gas wells. A numerical simulation model was developed which includes gas flow in the reservoir, wellbore/annulus effects, and dynamic plunger lift cycles. Transient reservoir performance is an important feature of the new model. Transient reservoir performance is a significant factor for tight gas reservoirs, especially as average reservoir pressure decreases during the life of the reservoir. Field data from tight gas wells with plunger lift for water removal can be more thoroughly analyzed using the new simulation model. Calibration of model parameters with field cases allows the plunger lift design to be optimized for a particular well. Improved understanding of the plunger lift process for tight gas wells with water loading problems may lead to more efficient water removal, increased gas production rates and recovery, and longer well life. Introduction As gas reservoirs are depleted, the removal of produced water from the wellbores becomes less efficient. The accumulation of produced water in the wellbore (called loading) can significantly reduce gas production rates by increasing bottomhole flowing pressures. Continued accumulation of water in the wellbore can eventually cause a well to die. Plunger lift has proven to be a successful method of removing produced water from the wellbore under a variety of operating conditions.1–4 Plunger lift is an artifical lift method characterized by the cyclic travel of a plunger up and down the tubing string. The plunger reduces the fallback of liquids as the plunger and slug of liquid above the plunger are pushed to the surface by pressure below the plunger. This pressure below the plunger is supplied by reservoir production, and by the expansion of gas stored in the tubing/casing annulus. Plunger lift results in more efficient use of reservoir energy to the removal of liquids from the wellbore. However, the plunger lift process is complex and can be difficult to design and analyze. Early methods of analysis and design utilized static models.5–6 In recent years, computer modeling has provided a tool allowing the development of more useful dynamic models of the plunger lift process. Several authors have discussed dynamic numerical models developed to allow analysis and optimization of plunger lift. The assumptions made in the development of these models and the level of detail included varies. Lea7 developed an early dynamic model of the plunger rise phase of the plunger lift process, showing that plunger velocity changes as the plunger travels up the wellbore. Lea's work indicated that annular gas requirements calculated using the earlier static model of Foss and Gaul5 were up to 16% too high. Reservoir performance was modeled using the Rawlins and Schellhardt8 deliverability equation for stabilized reservoir production (considering only Darcy flow). Marcano and Chacin9 developed a dynamic model of the entire plunger lift cycle. A major contribution of this work was modeling of fallback of liquid past the plunger. However, Marcano and Chacin used an IPR equation (for stabilized reservoir production) to describe reservoir performance. Baruzzi and Alhanati10 used dynamic modeling to analyze the operation of plunger lift for oil wells. Their study showed that the minimum length buildup period that will provide just enough energy for the slug of liquid above the plunger to be lifted results in the highest possible liquid production rate. Baruzzi and Alahanati also used an IPR equation (stabilized production) to describe reservoir performance.

A Dynamic Plunger Lift Model for Shale Gas Wells

“…In 2000, Maggard et al [9] established a dynamic model of a plunger gas lift that can be used in tight gas wells. In 2008, Chava et al [10] proposed a new method to simulate the lift of the plunger, which can more accurately reflect the actual dynamics of the plunger.…”

Applicability evaluation of plunger lift technology in shale gas wells

“…In 1965, Foss and Gaul proposed the classic plunger lift model based on force balance, derived from experience in gas fields, which later influenced most subsequent research (Foss and Gaul, 1965;Lea, 1982). Maggard et al (2000) established a new dynamic model for plunger lift specifically for tight gas wells, enabling in-depth analysis of the entire gas lift process in such wells. In 2007, plunger lift was applied in 40 tight gas wells in the San Juan Basin's northern area, resulting in an increase in daily production of over 11 × 10 4 m 3 /d (Oyewole and Garg, 2007).…”

Artificial Lift and Mobility Enhancement of Heavy Oil Reservoirs Utilizing a Renewable Energy-Powered Heating Element

“…10 A similar principle can be applied when a downhole electrical heater is placed to heat hydrocarbons in close proximity to a well; compared with the steam-assisted gravity drainage (SAGD) process, this has shown some reasonable efficiency with a lower water-to-oil production ratio. 11−14 Reservoir models and simulation studies have established the feasibility of downhole electrical heating. 15,16 Laboratory work has also been conducted to experimentally study resistive heating.…”