Restoring Critical Well Integrity in A High-Pressure Gas Well Via Coiled Tubing in the Sultanate of Oman

Abstract

Abstract A high-pressure gas exploration well was drilled in May 2018. The main objective of the well was to explore for gas in three different formations. The well underwent a successful fracturing intervention which increased the total gas production, however, at a later stage, a leak point was observed at the tie-back seal followed by repetitive isolation plug failures. The criticality of the well status was due to the integrity failure while having above 9,000 psi of tubing head pressure. The objective of the paper is to describe the successful method of restoring well integrity in a high pressure well by retrieving the failed isolation barriers. Prior to the intervention and due to the failed integrity of the high pressure well, a work cycle was developed to ensure the successful intervention was executed in a controlled manner. Due to the complexity of the restoration process, contingencies were aligned as part of the retrieval and isolation intervention. Restoring the well took place in a sequence initiated firstly by the retrieval of a failed junk catcher and the top retrievable plug using the coiled tubing. This was followed by pushing the bottom failed retrievable plug to TD successfully without collapsing the Coiled Tubing string, at the live conditions of the well. The final restoration step included the utilization of a mechanical plug to be set followed by 300 m of cement, to ensure well isolation for next workover stage. The most pivotal challenge was the intervention in a high pressure well of above 9,000 psi in the presence of a failed integrity issue. The strategy of well restoration was a complex combined intervention of utilizing multiple downhole tools to retrieve the well barrier, clean the unexpected debris accumulated and successfully control the leak that has resulted in the integrity failure of the well. Although controlling the failed retrievable plugs was difficult, due to the high pressure pushing the unset plugs shallower, manipulating the status of the well between opening the returns and shutting-in during the intervention was observed a secondary control parameter throughout the job. The combined approach of Coiled Tubing's tubing force analysis, downhole tool configuration, well condition and contingency management throughout the intervention resulted in the successful restoration of a high-pressure gas well. The paper presented highlights the successful restoration of a complex intervention executed through Coiled Tubing. This case helps to present the value, challenges, lessons learnt and opportunities existing in well restoration that would have previously been deployed through a costlier mean of workover operation.