Successful Collaboration of Vendors for Detection of Micro-Leak in Corrosion Resistant Monobore Completion And Remedial Action To Restore Well Integrity
Authors: Tleulin Artur , Porretta-Serapiglia Claudia , Freeman Michael James 
Published: September 2019

This document describes the process of planning and the execution of the production tubing micro-leak’s location detection with the use of Spectral Noise-High Precision Temperature Logging and globally novel technology of multi-set bridge plug services and its isolation with an ISO 14310 V0 rated (bubble tight) Straddle Packer assembly, fully compliant to H2S service per NACE TM0177 / ISO 11960

Accurate location identification of communication between production tubing and annulus in the corrosion resistant monobore completion of a raw gas injector well with ultra-high concentration of H2S and CO2 led to intense research for optimal solutions to detect micro-leak location and its further remedial solution.

The micro leak exhibited unique behavior which occurred mainly in a gas phase with a long duration build-up of annulus pressure. This required a complex leak detection campaign, involving Spectral Noise-High Precision Temperature Logging as the primary method of determination, and pressure testing of tubing string with the multiset retrievable bridge plug, being set on an electric wireline at different depths, as the secondary method of leak and confirmation.

The most suitable method of isolation from a feasibility and reliability points of view was to manufacture specific H2S/CO2 resistant straddle packer capable of withstanding the raw gas injection requirements.

During the non-intrusive testing it was possible at an early stage to confirm the location of the leak above the downhole safety valve. The noise-temperature surface read-out mode logging tools were run down to safety valve depth in a liquid and gas phase, indicating a zone of suspicion. The zone of suspicion matched the tubing tally with a tubing connection.

In order to confirm the presence of micro-leak at suspected points a multiset retrievable bridge plug was utilised. The tool used was a new to market multiset bridge plug with a unique technology which gave the possibility to re-set the plug multiple times within one electric wireline run. Considering the unique behaviour of the leak which appeared mostly when a production tubing was containing a gas phase under a high pressure the pumping of nitrogen in the top section of the tubing string was performed. The Multi Set bridge plug confirmed the location of the leak flawlessly showing a perfect results of execution and reliability. Checking the zone of interest with multiset bridge plug installed across and pressure tested with nitrogen confirmed the presence of leak at a tubing joint connection.

The next step after the leak location had been identified was to restore the well integrity with the installation of V0 rated Straddle Packer, which was successfully installed at the first attempt. It is important to note the highest available grade of H2S/CO2 resistant materials (Inconel 718 and FFKM elastomer) was selected during the design, manufacturing and qualification of the Straddle Packer. Restoration of well integrity has been confirmed during the following start-up of the raw gas injection.

Rigorous planning and coordination of several vendors resulted in the excellent collaboration introducing the latest global technologies in an extremely corrosive well environment. The resultant success of the complex well intervention activity, when leak investigation and remedial plans were worked out in parallel, led to restoration of the well and recommencement of Raw Gas re-injection in a record time of 8 months from the problem discovery to its solution.