FIG. 1 is an overview of an open water workover system 1 according to prior art. The system 1 is a set of equipment which is installed on top of a Christmas tree (XT) 2 and allows safe intervention operations in a hydrocarbon containing well (not shown). A well control package (WCP) 3 also named lower riser package (LRP) is connected to the top of Christmas tree 2. At the top of the lower riser package (LRP) 3, an emergency disconnect package (EDP) 4 is attached. A workover riser 5 is extending from a drilling rig 6 on the sea level 7 down to the emergency disconnect package 4.
FIG. 2 shows a typical setup for a prior art horizontal Christmas tree 10 with a monobore workover system 11. In this setup a monobore or workover riser 12 extends from the rig (only the lower part of the riser is shown) down to a monobore emergency disconnect package (EDP) 13 and lower riser package (LRP) 14. The lower riser package 14 is connected to the horizontal Christmas tree 10 through a Christmas tree adaptor connector (XTAC) 15. The Christmas tree 10 is in the other end connected to a wellhead 16 and a tubing hanger 17 sits in the Christmas tree in conventional manner for horizontal Christmas trees 10. The emergency disconnect package 13, the lower riser package 14 and the Christmas tree adaptor connector 15 are constituting the monobore workover system 11. The system is referred to as monobore due to a single, straight main bore 18a that runs down the centre of the system and is adapted to correspond with a main bore 18b in the horizontal Christmas tree 10. An annulus bore 26 encloses the main bore 18b in the horizontal Christmas tree 10. The horizontal Christmas tree 10 has a horizontal production outlet 19 where the production flow is routed. This outlet 19 is closed during the workover process by valves 20. When the workover system 11 is attached to the Christmas tree 10, tools (not shown) can be lowered and hoisted through the riser 12 and main bore 18a, 18b in order to perform different tasks in the well.
In FIG. 2 an annulus line 21 is arranged beside the main bore 18a in the workover system 11. The annulus line 21 starts as a hose (not shown) from topside and enters the emergency disconnect package at the top part 22 before taking a varied path down through the system and into the Christmas tree 10. There are several valves in the annulus line 21 and several crossover points 23 from the annulus line 21 into the main bore 18a, creating circulation paths that can be used for various operations. The line 21, valves 24 and crossover points 23 can together with valves 25 in the main bore 18a for instance be used for flushing of hydrocarbons from the riser 12.
FIG. 3 shows a typical setup for a prior art vertical Christmas tree 31 with a similar monobore workover system 11 as in FIG. 2, but includes a passive bore selector 32. The vertical Christmas tree has a configuration with a production bore 33 and annulus bore 34. When using a monobore workover system on the vertical Christmas tree 31 it is therefore required to use a bore selector technology, either a passive or an active bore selector, to match the configuration of the vertical Christmas tree. The workover system 30 in FIG. 3 has a similar structure than the monobore workover system 11 in FIG. 2, except that there is arranged a passive bore selector 32 between the lower riser package and the vertical Christmas tree 31. The main bore 18a in the lower riser package 14 is adapted to correspond with the production bore 33 in the vertical Christmas tree 31 through the passive bore selector 32. The same applies to the annulus line 21 in the lower riser package 14 which is adapted to correspond to the annulus bore 34 in the vertical Christmas tree 31. The Christmas tree 31 is in the lower end connected to a tubing hanger 35 and a wellhead 36 in a conventional manner for vertical Christmas trees 31
With use of the passive bore selector 32 the whole riser system must be pulled to the surface in order to change bore selector.
The present invention is applicable both on Vertical Christmas Trees (VXT) as well as other types of Christmas trees. In the Figures illustrating the invention there are shown a vertical Christmas tree and the invention will be further described for this use, but the invention is not limited only to vertical Christmas tree, but is also applicable for other types of Christmas trees, such as hybrid Christmas trees, horizontal Christmas trees or other possible types of Christmas trees.
To retrieve or deploy a Vertical XT, it is required to set plugs in the Tubing Hanger—one plug in the main bore and one plug in the annulus bore.
Traditionally this has been done using either a dual bore workover system or a monobore workover system with active or passive bore selectors, as described in FIG. 3.
A dual bore work over system has several limitations—especially on the Emergency Disconnect Package (EDP) and Lower Riser Package (LRP) design. The two bores need to be straight to allow straight access to the Christmas tree and the tubing Hanger. Different bore configurations in the XT will require the same corresponding bore configuration in the EDP/LRP, hence making standardization of the EDP/LRP design difficult. A dual bore system also requires an extra 2″ riser in addition to the normal main bore riser—something that can lead to a reduced operational window along with increased wellhead fatigue. Some special joints, like a safety joint or a heave eliminator are very complex to make for a dual bore system.
Using a monobore workover system requires the use of bore selector technology. A passive bore selector is an alternative connector assembly that can be used that offsets the whole lower workover riser package (WRP) stack, i.e. EDP and LRP to align the main bore over the annulus bore to give the required access. A passive bore selector has traditionally been chosen due to the reliability and the small size, but the operational efficiency is greatly reduced since the whole riser stack must be pulled to the surface in order to change the bore to be intervened.
An active bore selector allows wireline tools to be re-directed from the main bore in the EDP to either the main or the annulus bores in the LRP, with a path that is straight enough for the wireline tools to navigate. Using an active bore selector has shown to add complexity to an already complex system, and it is required to use a flexible jarring tool for setting of the annulus plug due to the “dog leg” going from main to annulus bore. The risk for getting stuck with the jarring tool, or failing with the jarring due to lack of force transfer is greatly increased through a “dog leg”. In addition, an active bore selector will typically add weight and height to a system that is already above the weight/height limitations stated in commonly used standards.
With both of the above arrangements, this creates a heavier, more complicated and more expensive system design. Therefore, the invention proposed is aimed to solve this problem by creating a separate tool that can be deployed to perform the annulus plugging/removal operation when necessary.