This paper is not a technical paper about electric submersible pumps (ESP's), instead it traces the 20-year journey that has led to the development and successful application of multiple generations of rigless ESP conveyance systems in a commercial oilfield. The end result, after many lessons learned, is a success story in which over 300 rig interventions have been eliminated over a 20-year period, with savings of 100's of millions of dollars in intervention costs, reduced HSE exposure and many millions of barrels of additional production. Utilization of ESP technology in the West Sak viscous oil field in Alaska is challenging. The unconsolidated nature of the West Sak sands impacts the performance and reliability of conventional ESP systems due to sand production. This challenging environment causes ESP pump erosion and accumulation of sand in the tubing above the pump and in the lower completion below the ESP. The initial development of the West Sak formation was the basis for the original development of the through-tubing conveyed progressing cavity pump (TTCESPCP) in the mid 1990's. With time, the West Sak completions evolved from vertical wells to long horizontals, resulting in production capacity increasing beyond the capabilities of the 3.5 in. and 4 in. TTCESPCP systems. This led to the development of a 4.5 in. through-tubing ESP in the early 2000's. In this design, the PCP of the TTCESPCP system was replaced with a high capacity, centrifugal pump or through-tubing convenyed ESP (TTCESP). With time and successful experience utilizing the TTC systems, it became evident that although the through-tubing technology resulted in significant savings and increased production, the design was lacking in one major aspect – the ability to remove sand accumulation in the 7-5/8 in. production casing below the end of tubing. The inability to perform interventions without pulling the tubing, was leading to expensive and avoidable rig workovers not related to the ESP equipment. The resulting economics drove the development of a through-tubing, slickline (SL) deployed ESP that, when all components are removed, leaves a minimum diameter of 3.80 in. for well interventions below the end of the tubing. The wireline retrievable ESP (WRESP) system was launched in 2005 and was fully commercialized in 2014. Numerous papers have been written on this specific technology and references are provided at the end of this paper. This list does not represent a complete listing of all through-tubing technologies, as there are other systems with substantially different characteristics. This paper will focus only on the through-tubing technology development and evolution in Alaska. It will present the 20-year development history of the Alaskan through-tubing technology, how the system is deployed, answers to frequently ask questions, and as the title suggests – What went Right, What went Wrong, and What's Next? The development and successful commercial deployment of through-tubing ESP systems in Alaska has been a long journey, with many lessons learned in the evolution from conventional ESPs, to through-tubing PCP's and ESP's (TTC or Generation 1 (Gen 1)), to the wireline retrievable ESP (WRESP or Generation 2 (Gen 2)). It should be recognized that both technologies had a development phase, followed by a commercial deployment phase. There were unexpected problems and benefits that were encountered as the technology matured. The technical difficulties significantly increased while advancing from the TTC (primarily mechanical changes) to the WR technologies (which adds the electrical component of a downhole wet connect).

Electrical submersible pump (ESP) technology is a proven artificial lift method for shallow, low pressure reservoirs like 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 due to sand production. This challenging environment causes ESP pump erosion and accumulation of sand in the tubing above the pump and in the lower completion below the ESP. This paper presents a 20-year case study of the of the world’s largest, longest-running population of thru-tubing conveyed (rigless) electric submersible pumps. Conventional ESP’s require a rig to replace a pump or motor when either fails. In "rigless" systems, some of the components (pump only for Generation 1, and pump, seal, and motor for Generation 2) can be pulled and replaced using slickline (SL), coiled tubing (CT), or tractor, depending on wellbore deviation. Generation 2 systems consist of a downhole side pocket mandrel (or docking station) with a wet-connect attached to the electric cable and deployed on 4-1/2" or larger tubing. Not only do these systems allow both the pump, seal, and motor to be retrieved without a rig, they have the significant advantage of allowing 3.80" fullbore access below the pump setting depth without pulling tubing. This allows non-rig interventions such as reperforating, production profiles, CT cleanouts, CT drilling etc. to be performed after the pump, seal, and motor are pulled with conventional SL or CT. Once the desired intervention has been completed, the pump, seal, and motor can be redeployed with SL — wet-connecting to the downhole side pocket mandrel. A well with a conventional ESP would require pulling the tubing with a rig prior to and reinstalling the tubing following any well intervention below the pump setting depth. "Rigless" technology has significantly increased production uptime and reduced the cost of ESP interventions in these wells. The case study includes the analysis of the two generations of rigless ESP systems, quantifying the success rate in varying conditions in over 300 rigless ESP replacements in a high sand, high deviation environment on Alaska’s North Slope.

The Access ESP system, a Thru Tubing Conveyed Electrical Submersible Pump (TTCESP), also referred to as a rigless ESP system, was installed in a well that had a history of producing significant amounts of sand and fine solids. During production of the wellbore fluids, solids accumulate in the well bore and lower completion restricting the inflow and well performance below the ESP, requiring a clean out intervention with a coiled-tubing operation to clear the restriction and return the well to full performance. This paper records the retrieval and replacement of the rigless ESP to access the wellbore and perform a coiled-tubing clean out of the lower completion wellbore without the use of a heavy workover rig. The rigless ESP retrievable assembly components were removed through tubing, in a live well intervention, using a slickline unit, and coiled tubing unit. The application of the AccessESP system provided significant benefits and demonstrated its potential application for any ESP operation that necessitates frequent well interventions, has high rig costs, or resides in locations with limited rig availability. The rigless ESP retrievable assembly is made up of four segments that are retrieved individually. Beginning from the uphole end of the retrievable ESP assembly, the first segment is the tubing stop, next a tubing packoff with a standing valve, then the complete pump assembly from pump discharge, pump, and pump intake, and on the downhole end is the motor assembly which includes the seals, motor, downhole gauge, and plugarm wet connector assembly. When these four components of the retrievable ESP assembly have been pulled from the well thru-tubing, there is open access to the lower completion wellbore. An isolation sleeve was installed to protect the wet connector dock in the rigless ESP permanent completion from mechanical damage during the coil-tubing clean out process. After the clean out was completed the isolation sleeve was retrieved and the four components of the rigless ESP assembly were reinstalled and the well was placed back on production. The intervention and methods described herein confirms the viability of the access to the lower completion and wellbore and to perform slickline and coiled tubing well work interventions with the rigless ESP system.