Effect of Near Wellbore Condition on Electrical Submersible Pump Design

Abstract

The number of electrical submersible pumps (ESPs) used as an artificial lift process is increasing worldwide, due to their efficiency and their ability in increasing production rate substantially. Yet ESP's field implementation needs a proper design to achieve the lift efficiency needed. In case of deep and ultra deep wells, which are drilled frequently, selecting the right ESP configuration and arrangement is critical to the success of the lifting operation. The wellbore space, the rate targeted and the costs involved are among the crucial parameters for the choice of an ESP system. Reservoir conditions or at least near wellbore conditions are not taken directly into consideration while designing the ESP system. The overall ESP design -including the number of stages and motor size -is determined by pre-defined wellbore parameters, and intake and discharge pressure. The present analysis reveals the effect of skin on the targeted ESP design and the associated system characteristics. IntroductionWhen oil wells are not able to flow naturally, the well production is sustained by artificial means, known as artificial lift. Usually artificial lift is applied when the wellbore pressure drop is larger than the bottom hole flowing pressure, and therefore to overcome the pressure difference several techniques are used. The main artificial lift methods are: (i) gas lift to lower the pressure gradient in the production tubing and (ii) pumps to lower the bottomhole flowing pressure. Different types of pumps were used at the early stages of artificial lift operations. Examples include as positive displacement pumps, e.g, sucker rod pumps; and thrust pumps, e.g., electrical submersible pumps (ESP). This latest technology was possible as operators could deploy it deeper in the well and extract higher production rates (Sachdeva, et al., 1994, Macary, et al., 2003, Qahtani, 2007and Zhou & Sachdeva, 2010. A successful design of an ESP system relies on both economics and technical complications. Several authors have previously summarized the effect of each of these factors (Lea and Bearden, 1999 and Naguib, et al., 2000).Still the industry faces challenges in understanding the reasons and causes of ESP system failure, due to the complexity of the environment and the harsh media that these systems are designed for. The run life of an ESP system is shorter in some cases than the expected design life time. Near-wellbore conditions are not considered a crucial part in the design of an ESP system. Formation damage could impact substantially on the well flow performance. Therefore expected design parameters could lead to an ESP system under design for particular well scenarios. The presence of a skin in the near-wellbore region can result in additional pressure considerations. Wattenbarger and Ramey (1970) described the effect of skin on well performance and that skin was an obstruction to the flow, caused by an infinitesimaly thin damaged region around the wellbore. The present paper discusses the effect of the near-wellbore region condi...