Neodrill Wellhead Support System
Main purpose is to protect the permanently installed wellhead from fatigue life reduction during the drilling process of the well.
· High load capacity to withstand drive/drift-off loads
· Wellhead fatigue protection
· Highly efficient compared to alternative WLR (Well Load Relieve = Tethered BOP)
o Less equipment cost
o Less logistic cost (installation and retrieval of system)
The Neodrill WSS is literally “based” on the CAN technology, where the CAN provides a stable subsea foundation for the support elements that relieve the loads coming from the BOP.
In simple terms the WSS is a structural element that is placed between the wellhead and the BOP. It consists of a (high capacity) mandrel, an adapter plate, and a conventional connector in the axial direction (top to bottom) and a support frame in the lateral direction. Hydraulic jacks/tension struts warrant the installation and prevent tight manufacturing tolerances.
Wellhead Fatigue Mitigation
BOP loads are taken up by the WSS to a high degree and diverted into the CAN before they reach the wellhead system. This substantially reduces fatigue damage of the wellhead system during the drilling phase. Once the drilling phase is completed the WSS can be taken off, making room for the SPS equipment (such as flow base, x-mas tree, etc.).
The degree of fatigue relieve depends on the relative stiffness between the well and the WSS system. This means:
· The stiffer the WSS system, the lower fatigue damage inflicted into the wellhead
· The more flexible the wellhead, the lower fatigue damage inflicted into the wellhead
The table below shows the improvement for three different scenarios. The dimension (diameter, wall thickness) of the conductor is the main contributor to wellhead stiffness. One can see that the “more flexible” the conductor is, the higher the fatigue life factor for the wellhead system. This is of course a a relative measurement, as the absolute fatigue life of a 36"x2” conductor is higher than that of a 30"x1.5” conductor.
For cases where the conductor is not selected yet (new wells), one has the freedom to choose the appropriate conductor size. However, for existing wells (see below, P&A case) this behavior is in fact good news as the WSS system can divert more than 90 % of the loads coming from the BOP.
Application Case (A) – Fatigue Protection for Production Wells with CAN/WSS
For wells being drilled by a CAN-ductor the implementation of the WSS is straight forward.
· The CAN-ductor is installed by a CSV or AHTS vessel
· The rig drills and cements the surface casing
o A slim hole well program is enabled by the CAN-ductor, the 20” section may be dropped and replaced by the 13-3/8” section
· The rig runs the WSS, which is connected to the CAN by ROV
· The rig installes the BOP on top of the WSS and executes the drilling phase as per conventional drilling program
o This phase is the main contributor of fatigue damage due to the high loads coming from the BOP
o The WSS can prevent at least 80 % of the loads, which translates to fatigue life increase of a factor of 100 (or more), due to the non-linear (cubic) behavior of fatigue damage (e.g., 50 % reduction of load translates to a fatigue damage of 50%^3 = 12.5% fatigue damage)
· Once the completion is installed, the BOP is removed, making room for SPS equipment
· For cases where work-over operations are required, or for cases where the P&A activities need to be carried out while the tree is still on place an extended version of the WSS can be supplied
Application Case (A) – Fatigue Protection for Existing Wells (P&A Activities)
The CAN/WSS combination may also be used for P&A activities of existing wells.
The process for this is shown below, and causes less cost for equipment and logistics compared to the teathered BOP method.
· The x-mas tree is removed, and a guide frame is installed
o This guide frame enables Neodrill to install a CAN over the existing well
· Once the CAN is in place the process continues by installing the WSS system, connecting it the the wellhead and to the CAN
o All operations up to this stage are done from a crane vessel, no rig time is required
· With the WSS in place it is now safe to connect a modern BOP to the well, as most of the loads of said BOP are diverted via the WSS directly into the CAN
o The remaining load going into the original wellhead is less than 10 % compared to a direct connection of the BOP to the original well
· Once the P&A activities are completed the well is cut below seabed
o This may be done by the rig, but can also be done by wire from a crane vessel by using the Terminator tool of BakerHughes
o Neodrill cooperates with BakerHughes and has done several wellhead cutting operations in joint operations during CAN retrieval campaigns
· The CAN and guide frame are recovered and may be used on the next well
Application Case (C) – Drive/Drift-Off Protection for Production Wells with CAN/WSS
For wells where drive/drift-off loads present a structural problem to drill a well, the WSS offers a unique possibility to utilize high-capacity connector system without changing the standard H4 connection profile between wellhead system and SPS equipment.
The order of sequence is similar to Application Case (A), we will therefore only point out the small changes that are required to utilize high capacity wellhead connector system during the drilling phase.
· For this case the wellhead mandrel on top of the WSS structure is replaced to a high capacity profile, e.g., DrilQuip EXeTM system
· The wellhead system used on the well remains the same “old trusted” H4 profile with 27” outer diameter
· By utilizing the CAN-ductor the conductor is already in place when the rig arrives
· The first rig operation is to spud the well with a 26” BHA for a 20” surface casing (or 17-1/2” for 13-3/8” casing), that is cemented in place
· Before the BOP (fitted with a high capacity connector) is run, the WSS (fitted with a high capacity wellhead to match the BOP) is run and connected to the CAN
· The well is drilled, utilizing the structural capacity of the high capacity wellhead connector to cope with the high loads of a potential drive/drift-off scenario
o The weak point for such a setup is often in the riser or flex joint, therefore above the BOP. This adds additional safety in case of a critical well control event
· Once the drilling phase is completed, the BOP is disconnected and the WSS is recovered, revealing the “original” wellhead with the 27” H4 profile
· The SPS equipment is then run and connected to the wellhead and the well can be set into production
Key advantages for all presented cases
· Substantially decreases fatigue damage for exploration and production wells, increased fatigue life (depending on wellhead stiffness) of a factor of 100 and far beyond
· Enables safe and efficient P&A activities of existing wells with unknown remaining fatigue life
· Allows utilization of high capacity wellhead connector systems without the need to deviate from established standard connectors on the wellhead system or the SPS equipment
· No need to change BOP connector during drilling campaign from high capacity to standard capacity
· Avoids cost and complex logistics to use the teathered BOP system
· Lowers overall well cost by saving rig time for conductor installation
· Moves a good amount of rig time to less costly crane vessel time
Please contact us at www.neodrill.com for further information, I’m sure we can contribute to your challenges.