Case Study: Safe Thru-Tubing ESP Installation in Pressurized Well through Novel Killing Techniques

Abstract

Cable Deployed ESPs (CD-ESPs) are foreseen as the future of ESP installations as they eliminate the need for full-fledge rig on location to perform ESP change out. One of the main challenges of performing ESP installation riglessly is the lack of mud circulation system which is used to monitor increase in fluid loss rate, indicate possible well kick and bring the well back to control in case of such emergencies. With the lack of this line of defense, there is a need to develop alternative method to ensure safe rigless ESP installation particularly when ESP components are being made-up and lowered down the well. The first high H2S vertical well CD-ESP worldwide was trial tested in a pressurized onshore well in Saudi Arabia. The candidate well had a shut-in pressure of 390psi, H2S concentration of 1.12% and fluid loss rate of 18-24 bbl per hour (bph) for 71 pound per cubic foot (pcf) kill fluid. Kill fluid has to be continuously supplied at a rate equivalent to the varying loss rate of the well. For this, the surface well testing equipment (required for well flow-back after ESP installation) was modified to monitor and store excess kill fluid return. The new modification allows pumping of kill fluid to continue while Blow-Out Preventer (BOP) equipment are open on top of the Christmas tree. The density of the kill fluid was monitored and maintained during the whole operation. The operation started by bullheading with one and a half wellbore volume. The well performance was monitored and then kill fluid rate was increased gradually to measure the loss rate of the well. Pumping of kill fluid was highly coordinated during the main installation phases of the CD-ESP: surface make-up of ESP assembly in sections, run in hole with cable to target depth and the final make-up of the cable hanger. The returns of any excess kill fluid could be measured by the modified surface testing package. Pumping rate of kill fluid was highly correlated with Tubing Casing Annulus (TCA) pressure since the volume of fluid in the annulus changed (due to the small contraction/expansion of the seal bore assembly). While the pump was inside the well, pumping kill fluid caused significant increase of weight reading. The pump (5.62") acted like a piston inside the (6.275") ID of the 7" tubing causing high weight values. At one point during the operation, the loss rate of the well increased dramatically. This caused negative readings on pressure gauges of the wellhead (loss rate was higher than maximum pump supply). The paper presents a novel comprehensive well killing measures for rig-less CD-ESP installation. To assure the safe conduct of future operations, the paper also shows lessons learnt and contingency measures for unexpected events during the operation.