As the scope of deepwater operations increases, the need for cost-effective well servicing is paramount, particularly because of the continued challenges associated with current volatile commodity pricing. One of the first requirements on any subsea deepwater intervention with a horizontal wellhead production tree is pulling the subsea horizontal tree isolation lock mandrel plugs, commonly referred to wellhead or crown plugs. This can be a "show stopper" event if not planned correctly. Because of the critical nature of this action, the majority of operators follow a two-prong approach, with a primary plan of action and a contingency procedure, to help ensure barrier removal proceeds as planned. Although successful removal of the crown plugs is the principal concern, it needs to be completed cost-effectively for the intervention to obtain approval.
The advent of digital slickline (DSL) allows surface readout (SRO) monitoring during the removal and installation of these barriers to provide an increased level of confidence during this important phase of the operation. This paper outlines case studies of the real-time sensors available with the RF communication DSL system that was highlighted previously (
Additionally, the straight pull battery operated extended-stroke downhole power unit highlighted in
New developments as the downhole power generator was ported to DSL are discussed, notably on- command motor controls and SRO, which was traditionally only available in memory. A downhole anchor was added to the toolbox, which can be run in combination with the downhole power generator to expand effectiveness, as new production trees might not allow for a no-go landing shoulder. To address the increased water depths, the 3.59-in. extended-stroke downhole power generator was upgraded to 80,000 lbf pulling force.
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.