Plunger lift technology has been applied systematically and successfully to unload liquids from marginal tight gas and coalbed methane wells in San Juan North Basin. This article presents the recommended practices, case studies, and results of excellent plunger lift application and optimization.
A production increment of over 4 MMcfd has been achieved and sustained on about 40 plunger lift installations. Most wells that were chosen for plunger installations were either on a plug and abandon (P&A) list or on temporary abandon (TA) status. Neither gas production nor anticipated production uplift from wells could justify installation of a more costly artificial lift system such as sucker-rod pump to de-water wells. Amazingly, production uplift of more than 200 Mcfd, and/or production increment of over 300%, was realized on some wells. It important to note that many operations use the practice of surfacing plungers by auto-venting, thereby releasing greenhouse gas (GHG) into the atmosphere. Plungers were operated successfully in San Juan North operations without this practice.
All these results were achieved through applications of new plunger lift technology, efficient plunger type selection, monthly and quarterly reviews, proper maintenance, optimization and monitoring, i.e. effective utilization of plunger lift data.
The strong alliance that was formed with the plunger equipment provider was one of the important inputs to our plunger lift journey. This new approach is a significant departure from the conventional ways of operating plungers, whereby service companies traditionally supply plunger hardware to the producing companies to operate with little "service" involved. Also, the field operations' teams, with their perseverance, offered a very important contribution to this successful venture.
Introduction
Gas wells, as a result of depleting reservoir pressure, show a decrease in production over time. The liquids that are associated with the produced gas tend to accumulate in the gas well. The associated liquids could be water, oils or condensates. This liquid loading heightens and futher reduces the gas flow rate. Turner et al.1 and Coleman et al.2 models, give the minimum gas flow rates required to lift the entrained liquid droplets at certain wellhead pressure. There are a host of artificial lift methods3 available to de-liquefy gas wells, one such method being plunger lift. Given the consideration of low rates, economic feasability, well characteristics and mechanical integrity, plunger lift became the obvious choice. Plunger lift is an intermittent form of artificial lift which utilizes the natural energy of the reservoir to lift the liquids out of the wellbore. The feasibility and consideration of plunger lifts are discussed in the literature4–9.
This article brings to light success stories of wells with low flow rates that were not producing to their full potential and would at times have to be shut in to build up pressure. The operator and plunger provider tie-up coupled with vital input from the field helped establish a setup wherein regular monitoring and field input resulted in a production increment of over 4 MMcfd for about 40 wells. The wells were chosen on the basis of their plunger viability, and plunger selection was made based upon sealing, depth of down-hole stop, bottomhole pressures, line pressure, annular communication, sand and paraffin production, etc. The availablity of the SCADA system allowed dynamic monitoring of changes and their effect on the wells. In addition to conventional plunger lift, multi-stage plunger lift technology was used, and plunger enhanced chamber lift (PECLTM) 10 is being considered for the future. Details are provided in the following sub-sections.
Geology
San Juan Basin, which runs along northwestern New Mexico and southwestern Colorado (Fig. A-1), is one of the most prolific natural gas producing regions in North America. The three major reservoirs, namely upper cretaceous Dakota, Mesa Verde group and Pictured Cliffs sandstone (Fig. A-2), have produced 22 Tcf of gas as of 2004 according to Fassett et al11. The Basin and Blanco Fruitland coal, which overlies the Pictured Cliffs sand (Fig. A-2), conformably holds a resource base on the order of 50 Tcf of coal bed methane (CBM) as per Kelso et al12.
