Access is a key aspect of any deepwater operation. For instance, a large-scope operation can be delayed or aborted if the crown plug isolating the wellbore from the riser cannot be retrieved. Subsea trees are generally equipped with upper and lower crown plugs.
The top crown plug is usually easily retrieved if the fishing neck is accessible, and pressure is applied between the top and lower plug to assist in extraction. However, the lower crown plug is generally more difficult to extract because of either a residual differential pressure from the bottom of the riser or excessive friction after years of seal installation.
After the upper crown plug was successfully pulled, the braided line and upward jarring action failed to extract the lower crown plug. Thus, Talos required well intervention to extract the lower crown plug.
SLB recommended the anchor-linear actuator of the ReSOLVE™ instrumented wireline intervention service connected to a GS pulling tool. This high-force mechanical actuator can pull or push up to 40,000 lbm for a 12-in total stroke.
The bottomhole assembly was optimized to meet the specific requirements of the intervention riser system (IRS). The anchor point must be located above the BOP in the riser to avoid damaging any critical components. Therefore, a long spacer must be installed between the pulling tool and the anchor-linear actuator. Additionally, the string must include shearable tubes facing the shear rams or valves to make sure the rig can disconnect from the IRS at any time. SLB provides an extra safety measure with two additional release devices. The first release device is right above the pulling tool, and the second is at the head. The three redundant release mechanisms vastly improve the safety of the operation.
After anchoring the ReSOLVE Family™ anchor-linear actuator, a 40,000-lbm upward pull was applied. Unfortunately, the force was not sufficient to extract the lower crown plug. After about 20 relaxations and straight pulls were applied, and the rig was pressure cycled to exercise the seal in both directions, the plug remained intact.
Following an in-depth review, SLB lightened the riser column to the maximum axial force that the actuator could hold to combine the pull force from the stroking tool and the force resulting from the differential pressure. A 2,300-psi differential pressure was applied across the plug while the ReSOLVE Family anchor-linear actuator stroked up. When the plug came free, the anchor-linear actuator retracted quickly under the thrust from the plug. Such a technique would have been impossible in slickline as the plug would have been ejected with the slickline BHA, but the ReSOLVE Family anchor-linear actuator prevents ejections while attempting to retrieve the plug. After pulling out of hole, the GS pulling tool was sheared off, which was expected. Then the braided line rigged up to scoop the dislodged plug.
