Riserless Drilling System with Flexible Choke Lines
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Solution Overview
Problem
Offshore drilling from floating MODUs faces challenges in achieving prolonged service life and reduced pollution, with existing systems experiencing equipment overloading, pollution risks, and high operational costs due to the use of heavy and complex marine risers.
Innovation Solution
A riserless drilling system utilizing a lightweight subsea BOP with flexible choke and kill lines, a drilling fluid recovery funnel, and a subsea booster pump to manage drilling fluids and seawater, eliminating the need for a marine riser and reducing stress on wellheads, while ensuring controlled fluid handling and minimal pollution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a marine riser is used to connect the MODU with the subsea BOP, then well control and drilling fluid management are achieved, but equipment weight and wellhead stress increase significantly
Solution Approach 1:
The patent removes the marine riser from the drilling system, extracting the problematic component that caused excessive weight and stress. The well control function is maintained through alternative means (subsea BOP with flexible hoses and mud return system) that do not require the heavy rigid riser structure, thereby resolving the contradiction between reliability and weight.
Solution Approach 2:
The subsea BOP is designed to perform multiple functions previously distributed across separate components (riser, choke manifold, kill manifold). By integrating these functions into a single subsea unit, the system eliminates the need for heavy marine riser while maintaining well control capability, addressing both reliability and weight concerns.
2Reliability
If a marine riser is used to connect the MODU with the subsea BOP, then drilling operations can be controlled, but bending stress and strains on wellhead housings increase to maximum levels
Solution Approach 1:
The marine riser is removed from the system, eliminating the source of horizontal and lateral forces that caused excessive bending stress on wellhead housings. The drilling control function is maintained through the subsea BOP system with flexible connections that do not impose rigid stress constraints on the wellhead.
Solution Approach 2:
The patent employs flexible hoses and flexible connections between the subsea BOP and surface equipment, replacing the rigid marine riser structure. These flexible elements can accommodate movement and stress without transmitting excessive bending forces to the wellhead, thereby reducing stress while maintaining operational control.
3Reliability
If oil based mud is used with a marine riser system, then drilling fluid management is achieved, but pollution occurs through seawater contamination of the mud system
Solution Approach 1:
The marine riser is removed, eliminating the interface zone where seawater contamination of drilling mud occurred. The alternative system uses a subsea BOP with flexible hose connections and a dedicated mud return system that prevents seawater ingress into the drilling fluid, thereby maintaining fluid management capability while eliminating pollution.
Solution Approach 2:
The patent introduces a mud return system with a subsea pump and flexible hose as an intermediary pathway for drilling fluid return. This controlled return path prevents uncontrolled mixing of seawater and drilling mud at the riser interface, eliminating pollution while maintaining effective drilling fluid management.
4Reliability
If heavier BOPs with more closure rams are installed to reduce downtime risk, then well control reliability improves, but equipment weight and wellhead loading increase
Solution Approach 1:
The subsea BOP is designed as a multi-functional unit that integrates well control functions, choke and kill line connections, and mud return capabilities. This integration allows for reliable well control with adequate closure rams while avoiding the excessive weight that would result from adding multiple redundant systems, as the single integrated unit performs all necessary functions.
Solution Approach 2:
The use of flexible hose connections and the integrated subsea BOP design with the riserless system reduces the overall weight and dimensional constraints. This flexibility allows for optimized BOP configuration with necessary closure rams for reliability without the penalty of excessive weight and wellhead loading that would result from traditional rigid riser-connected heavy BOP systems.
Data Source
AI summary
The invention provides a drilling system for drilling subsea wells from a floating mobile offshore drilling unit (MODU), the system comprising a subsea BOP. The system is distinctive in that the subsea BOP has relative small weight and size, the system includes no marine riser but the system comprises: flexible choke and kill lines arranged between the subsea BOP and the MODU, means for drill string guidance and cleaning, for guiding when inserting or taking out a drill string from the BOP and for drill string cleaning when pulling the drill string out from the BOP, means for controlled leakage of seawater into a recovery funnel arranged below the means for drill string cleaning but above the BOP, and means for return from the recovery funnel to the MODU of drilling fluid and seawater leaked into the recovery funnel.