Having a reliable backup plan is vital to ensure successful riserless light well intervention (RLWI) operations. This paper will present learnings from a subsea operation where the contingency solution was engaged to resolve a critical issue. The need for thorough back-up planning will be discussed along with the planning process, execution and lessons learned.
Crown plugs are conventionally retrieved using slickline jarring; however, high performance shifting tools on electric line are gaining foothold due to their ability to apply a focused, axial force downhole. Up to 33,000 lbs of force can be exerted through the use of a bi-directional, hydraulic ram. These electric line (e-line) stroking tools can be fitted with various shifting or pulling tools for lightweight mechanical services. For subsea interventions this is good news as space is particularly limited on vessels, which means that intervention solutions that simplify logistics by reducing equipment and crew is sought after.
The case to be presented is from a RLWI operation in the Gulf of Mexico where a crown plug had failed to release. Slickline (SL) was the first method to be put into action. On the first attempt 148 jars failed to retrieve the plug, then another 199 jars yielded the same result. It was believed that these repetitive attempts had broken the seal, resulting in saltwater inflow that had created hydrates. 25% Methanol Ethanol Glycol was pumped while jarring, but eventually the contingency plan was activated. This consisted of a hydraulic stroking tool, which successfully managed to remove the upper crown plug and thus allowed the operation to continue without further downtime.
The operator would have had six months of deferred production (being unable to open the sleeve to the upper zone) if the crown plug was not retrieved as they would have needed to wait for a riser. This underlines the importance of having an adequate contingency solution to overcome the challenges in riserless interventions. The benefits will be increased operational efficiency and reduced overhead costs.
This was the first operation where a crown plug was pulled during a RLWI operation with an e-line bi-directional stroking tool. The tool in this case was capable of 33,000 lbs of force; however, since the execution of this operation, further developments in engineering have led to a redesigned stroking tool with the ability to apply up to 60,000 lbs of force. What opportunities that opens up for RLWI operations will also be presented.