Offshore Well Decommissioning Using Simultaneous Rig Operations
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Solution Overview
Problem
The decommissioning of offshore oil and gas wells is a time-consuming and costly process, requiring large rigs and extensive resources, with each well taking approximately 50-60 rig days to plug, and conventional methods are inefficient in reducing this timeframe.
Innovation Solution
A method involving a jack up rig with a cantilever structure and a decommissioning rig tower that can be positioned over multiple wells, supplying power and drilling mud from the rig, allowing simultaneous operations and reducing the need for a large modular rig on the platform, enabling efficient movement between wells and reducing overall footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a large modular rig structure is installed on the platform to support heavy decommissioning equipment, then the capability to perform heavy milling operations is improved, but the platform surface area required is significantly increased, occupying all or most of the surface
Solution Approach 1:
The invention extracts the heavy support functions (power supply, mud supply, accommodation) from the platform and relocates them to a separate jack-up rig. This allows the platform to retain only the essential rig tower for decommissioning operations, dramatically reducing the platform surface area occupied while maintaining full heavy milling capability.
Solution Approach 2:
The decommissioning system is segmented into two independent components: a jack-up rig providing support functions and a platform-based rig tower performing decommissioning operations. This segmentation allows each component to be optimized independently and reduces the footprint on the platform.
2Device complexity
If a single rig tower is used to decommission wells sequentially, then the equipment complexity is reduced, but the total decommissioning time increases significantly, taking a number of years to finish
Solution Approach 1:
The invention prepares the system in advance by installing multiple rig towers on the platform simultaneously, each positioned over different wells. This preliminary arrangement enables parallel decommissioning operations to begin immediately, dramatically reducing the total time required compared to sequential operations with a single tower.
Solution Approach 2:
Multiple rig towers are combined on the same platform, each independently equipped with heavy milling equipment. This merging of parallel operational capabilities allows simultaneous decommissioning of multiple wells, reducing total project duration while maintaining manageable complexity through standardized tower designs.
3Area of stationary object
If the rig tower is moved sequentially from well to well on the cantilever structure, then the equipment footprint is minimized, but the time required to reposition between wells adds to the overall decommissioning duration
Solution Approach 1:
The single moving tower is segmented into multiple stationary towers, each permanently positioned over a different well. This eliminates the need for repositioning between wells, as each tower remains fixed in its operational position throughout the decommissioning process, thereby eliminating repositioning time while maintaining a compact overall footprint.
Solution Approach 2:
The system transitions from a dynamic configuration (single tower moving between wells) to a static configuration (multiple towers fixed at different positions). This dynamic-to-static transformation eliminates the time loss associated with repositioning, as the towers are already in their final operational positions from the start.
Data Source
Figure 1
AI summary
Method and structures perform decommissioning of offshore oil and gas platforms with associated wells. By installing on a platform (1) a movable decommissioning rig tower (2) but stripping away most of the other structures and equipment on the platform (1), and specifically not providing supporting resources such as drilling mud and power, accommodation, etc. on the platform, it is possible for both the rig tower (2) and a further rig tower (28) installed on a jack up rig (20) located alongside the platform (1) to access the well bay (5) of the platform. Thereby, two wells may be accessed simultaneously through the same well bay (5) and respective decommissioning operations carried out simultaneously and independently.