Review of Causes and Remedial Actions of Gas-Induced ESP Downtime in Unconventional Wells
Authors: Camilleri L 
Published: August 2024

Abstract
In unconventional wells, free gas and slugging have a large negative impact on ESP production and run-lives. With depletion, GOR increases and both rates and pressures decrease, which causes an increase in gas void fraction, slugging, and repeated zero flow events. Utilizing real-time data sets, the causes of gas-induced instability are cataloged along with the recommended remedial actions for both operations and future ESP design improvements to provide field engineers with a rapid response methodology.
Well and ESP transient rates were initially modeled by Vieira and Prado (2013), who resolved partial differential equations for the entire well. Subsequently, Camilleri (2020) considered the ESP power equilibrium equation to directly measure the amplitude of ESP rate fluctuations. With the understanding of the physics provided by both authors, field data sets were reviewed to classify both causes and remedial actions into three groups: Horizontal drain slugging upstream of the ESP.Severe head degradation caused by changes in pump operating point.Insufficient lift, which is also commonly known as "gas locking".
To explain the underlying physics, data sets were identified where only one cause is present at any one time, however, in most cases, several causes coexist, which can be difficult to diagnose. To address this challenge, a multiple-parameter dashboard was used to visualize contextual data alongside directly measured data. For instance, in addition to plotting production rates and ESP gauge data versus time, key ESP-specific ratios were considered, such as pump operating point relative to the best efficiency point. It was also necessary to provide the ability to zoom in and out on the time axis as each cause can occur sequentially in time. Such visualization enables rapid diagnosis and examples of these hybrid cases were also discussed. One of the key findings is that irrespective of the cause, the best-suited pumps are those with a steeply rising head-flow curve as they dampen the impact of slugging and reduce the number of no-flow events, thereby increasing ESP run life. Finally, by integrating inflow analysis (reservoir pressure and productivity index), it was also possible to determine when and how to plan the next workover to switch to a lower flow rate ESP design, which improves drawdown and ESP gas handling.
Data signatures supported by field data sets have been identified, which enable rapid diagnostics and remedial action for field engineers managing unconventional wells in undersaturated conditions without the need for extensive modeling, although there is no escaping RTA (rate transient analysis) when planning workovers. While this has demonstrated the importance of real-time discharge pressure, the next challenge for the industry is to find a workaround where the completion precludes discharge pressure measurement. The ultimate question for the industry is whether it will be possible for artificial intelligence to automate the diagnostics and remedial action of such complex phenomena.