Subsea Barrier Valves Enable Riser Disconnection
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Solution Overview
Problem
The high operational costs and time required to complete subsea wells due to the need for expensive drilling vessels and risers, which remain in place until the completion process is finished, necessitate a method to reduce these costs and enable earlier vessel relocation.
Innovation Solution
A method involving a lower completion assembly with at least two barrier valves that can be set to form a mechanical barrier, allowing the riser and drilling vessel to be disconnected, enabling the upper completion string to be run through open water and connected to the lower assembly, thereby reducing the reliance on the riser for fluid control and allowing earlier vessel relocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the drilling vessel and riser remain in place to maintain fluid control during completion, then fluid control is ensured, but operational costs increase and completion time extends
Solution Approach 1:
The completion system is divided into two independent parts: a lower completion assembly installed through the riser with barrier valves for fluid control, and an upper completion string run through open water. This segmentation allows the drilling vessel to be disconnected and relocated after the lower assembly is installed, while fluid control is maintained by the barrier valves in the lower assembly.
Solution Approach 2:
The barrier valves are set to form mechanical barriers to fluid flow before the drilling vessel is relocated. This preliminary action ensures fluid control is established in advance, allowing the expensive drilling vessel to be moved offsite while the less expensive service vessel completes the remaining installation work.
2Reliability
If the drilling vessel and riser remain in place until completion is finished, then fluid control is maintained, but equipment costs increase
Solution Approach 1:
The completion process is segmented into two phases: first installing the lower completion assembly with barrier valves through the riser, then running the upper completion string through open water. This allows the expensive drilling vessel to be released after phase one, replacing it with a less expensive service vessel for phase two, thereby reducing overall equipment costs while maintaining fluid control through the barrier valves.
Solution Approach 2:
The barrier valves in the lower completion assembly act as intermediaries that take over the fluid control function from the riser. Once the barrier valves are set and verified, they mediate the fluid control function, allowing the riser and drilling vessel to be disconnected and relocated without compromising fluid control.
3Reliability
If traditional completion methods are used with continuous riser connection, then fluid control is ensured, but productivity decreases
Solution Approach 1:
The completion method is segmented into two independent operations: installing the lower completion assembly through the riser with barrier valves, then running the upper completion string through open water. This segmentation enables the drilling vessel to be relocated after the first operation, allowing parallel activities and reducing overall completion time, thereby improving productivity while maintaining fluid control through the barrier valves.
Data Source
AI summary
A method of completing a subsea borehole including connecting a first vessel to a subsea wellhead assembly via a riser. A borehole is drilled with a drill string communicated to the subsea wellhead assembly through the riser. A lower completion assembly is run on a service string into the borehole through the riser. At least two barrier valves of the lower completion assembly are set with the service string in order to form a mechanical barrier to fluid flow with each of the at least two barrier valves. The riser is disconnected from the subsea wellhead assembly. An upper completion string is run through open water to the borehole and connected to the lower completion assembly. An lower completion assembly for a subsea borehole is also included.