Riserless Dual Drill String for Offshore Drilling
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Solution Overview
Problem
Conventional offshore drilling methods require a riser to manage pressure and fluid circulation, which can be cumbersome and lead to downtime due to formation cuttings in the wellbore annulus, and existing systems lack efficient methods for remotely replacing seal assemblies in rotating control devices.
Innovation Solution
A riserless dual drill string system with a concentric dual drill string and a rotating control device (RCD) that includes a removable seal assembly and lubrication flow paths, allowing for remote operation and replacement of the seal assembly, and independent control of crossover ports for fluid management within the wellbore annulus.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a riser is used in conventional offshore drilling, then pressure management and fluid circulation are enabled, but the system becomes cumbersome and causes downtime due to formation cuttings accumulation in the wellbore annulus
Solution Approach 1:
The patent extracts the riser from the drilling system by implementing a riserless dual drill string configuration. The inner drill string provides a dedicated flow channel for drilling fluid circulation and cuttings removal, eliminating the need for the outer riser structure while maintaining pressure management capabilities through the inner string's flow path.
Solution Approach 2:
The patent segments the drilling system into two separate drill strings - an inner drill string for fluid circulation and cuttings removal, and an outer drill string for structural support. This segmentation allows the inner string to function as a self-contained flow channel, eliminating the need for a riser and reducing overall system complexity.
2Device complexity
If a single-pipe drill string is used, then the system structure is simple, but formation cuttings accumulate in the wellbore annulus causing downtime
Solution Approach 1:
The patent divides the single drill string into two concentric drill strings - an inner string that provides a dedicated flow channel for drilling fluid and cuttings removal, and an outer string for structural support. This segmentation creates separate pathways that prevent cuttings accumulation in the wellbore annulus, thereby improving drilling efficiency without significantly complicating the overall system structure.
3Quantity of substance
If the wellbore annulus forms a flow path for drilling fluid circulation, then fluid circulation is enabled, but the fluid becomes dynamic which is not preferable for certain wellbore pressure management techniques
Solution Approach 1:
The patent extracts the fluid circulation function from the wellbore annulus by routing drilling fluid through the inner drill string's flow channel. This extraction allows the wellbore annulus to remain static for reliable pressure management while the inner string handles all fluid circulation and cuttings removal functions.
Data Source
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AI summary
A method and apparatus are disclosed for drilling a wellbore using a concentric dual drill string. Multiple individually selectively isolable crossover ports intervaled may be provided along the length of the drill string thereby facilitating pumping a well control fluid within a wellbore annulus without the need to run-in or trip-out the drill string. Multiple one way check valves may be included at various points within an inner pipe of the dual drill string to minimize settling of particulate matter during long periods of non-circulation. In an offshore arrangement, the drill string may be used without a marine riser. A rotating control device is provided, and a hydraulic power unit is located at the seafloor for controlling and lubricating the rotating control device. A pump may be located at the seafloor for managing wellbore annulus pressure via the rotating control device.