Field Study Examines Wellhead-Penetrator Problems, Solutions in SAGD Operations
Authors: Carpenter Chris 
Published: November 2021

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201167, “Wellhead-Penetrator Problems and Best Practices in ESP Thermal SAGD Applications,” by Pat Keough, SPE, Jesus Chacin, SPE, and Kyle Ehman, SPE, ConocoPhillips, prepared for the 2020 SPE Virtual Artificial Lift Conference and Exhibition–Americas, 10–12 November. The paper has not been peer reviewed.

Wellhead penetrators are a critical component in electrical submersible pump (ESP) systems. Harsh steam-assisted gravity-drive (SAGD) conditions impose an even higher level of stress on penetrators. Recently, a sudden increase in wellhead-penetrator failures in the Surmont SAGD ESP operation in Canada led to an enhanced fieldwide root-cause analysis (RCA). The complete paper is a field case study that describes the findings of this RCA and the mitigation measures taken.

Introduction

Fig. 1 shows a wellhead-penetrator assembly typically used in SAGD operations. This assembly consists of two main parts: a mandrel that seals against the wellhead while carrying power from the surface facilities through the tubing hanger and the lower field-attachable connector that splices the ESP cable and threads into the mandrel below the tubing hanger.

Because of the design of the ESP, when an electrical-system failure is detected through traditional means, accurate determination of which electrical component has failed is impossible without first sending a rig, killing the well, removing a portion of the wellhead, disconnecting or cutting the penetrator or cable, and completing further resistance testing on the cable components.

At Surmont, 230°C-rated penetrators had proved reliable and electrical failures were almost exclusively caused by a failed downhole component. The produced fluid temperature typically is below 230°C, somewhere between 180 and 220°C during normal operating conditions. However, approximately 12 months after a large installation campaign that almost quadrupled the Surmont ESP population, a sudden increase in penetrator failures was observed. Between late 2017 and early 2019, 18 penetrator failures occurred. These failures accounted for approximately 25% of the ESP-related events in Surmont during this period.

These penetrator failures occurred at different runtimes, varying from 148 to almost 900 days, with most occurring 12 to 18 months after being installed. In all instances, penetrator failures occurred at runtimes shorter than the expected ESP mean time to failure (MTTF) of the ESP population.

Failure Investigations: Approach, Results, and Recommendations

At the end of Q1 2018, the first five failures occurred in succession, which prompted a failure investigation on this group of wells. Nearly all field measurements pointed to a short circuit in the field-attachable connector.

Given the special nature of the penetrator design and construction, it was thought necessary to send failed specimens to the manufacturer. Dismantles showed that, in all cases, the high- modulus tape was missing. Without the tape in place, rubbing of leads, development of wear, and an eventual short were all possible when considering excessive thermal expansion.

RCA techniques were conducted and identified the potential contributing causes described in this subsection.