Through-Tubing-Conveyed ESP Technology Overcomes North Slope Challenges

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 193783, “Through-Tubing-Conveyed Wireless ESP Technology: A 20-Year Case History of Wireline-Retrievable ESPs,” by John Patterson, Patterson Consulting; Grant Dornan and Gary Targac, SPE, ConocoPhillips; David Malone and Samer Cheblak, AccessSEP; Jennifer Julian, SPE, BP; and Matthew Walker, AccessESP, prepared for the 2018 SPE International Heavy Oil Conference and Exhibition, Kuwait City, Kuwait, 10–12 December. The paper has not been peer reviewed. Electrical-submersible-pump (ESP) technology is a proven artificial-lift method for shallow, low-pressure reservoirs such as those found in the West Sak viscous oil field in Alaska. However, the unconsolidated nature of the West Sak sands challenges the long-term lifting performance and reliability of conventional ESP systems. The case study in this paper includes the analysis of the two generations of rigless ESP systems, quantifying the success rate in varying conditions in more than 300 rigless ESP replacements in a high-sand, high-deviation environment on Alaska’s North Slope. Through-Tubing (Rigless) ESP Technology: Generation 1 and Generation 2 In 1998, the operator developed through-tubing-conveyed (TTC) ESP (TTCESP)/TTC progressive-cavity-pump (PCP) (TTCPCP) technology to allow failed pumps (ESP or PCP) to be replaced quickly and economically using conventional equipment without a rig. In this first-generation rigless ESP system, a rig deploys conventionally, on tubing, the electric cable, motor, and seal sections, with a special latching device that allows the pump (only the pump, not the motor or seal) to be pulled and replaced by use of slickline (SL) or coiled tubing (CT), without a rig. In 2014, a second-generation rigless ESP system was introduced that added the ability to deploy and retrieve the motor and seal using conventional SL equipment, leaving fullbore access to the lower completion and producing zone. In addition to the ability to replace a failed pump or motor, this fully  retrievable ESP system brought additional value by al-lowing simple, low-cost SL, electric-line, and CT access to the lower completion once the ESP was retrieved without the need for a rig. Fig. 1 shows the progression of through-tubing development from the conventional tubing-conveyed ESP to the TTCESP and, finally, to the Generation 2 wireline-retrievable ESP (WRESP).  Completion Designs A range of completion designs has been implemented over the 20-year history of rigless ESP deployments in Alaska. The earliest wells were 7⅝-in. cased, S-shaped trajectory designs in which the well deviation returned to vertical to facilitate running the completion. As horizontal (and later, multilateral) completions were implemented, well trajectories became even more challenging, with deviations increasing to 80° with either 7⅝- or 9⅝-in. casing. Both Generation 1 and Generation 2 systems have been able to pass through dogleg severity of 12°/100 ft and inclinations of 65° with SL, relying on weight and gravity to deploy the equipment to the pump setting depth. When the equipment cannot be deployed because of high deviation, it can be pumped down to the setting depth. CT has been used to run equipment in wellbores with angles greater than 65°.