Flow Diverting Structure for Flexible Riser Systems
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Solution Overview
Problem
Deepwater oil and gas production facilities face challenges with existing riser systems due to dynamic offshore motions, high hydrostatic pressure, and the limitations of flexible pipes, which can lead to increased costs and complexity, especially in projects requiring large inner diameters.
Innovation Solution
A riser assembly and system that includes an upper riser connected to a flow diverting structure with multiple lower bores, allowing for the connection of multiple lower risers, enabling flexible configuration and expansion, and reducing the need for multiple hang-off slots and capital expenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If flexible pipe is used for the entire riser system in deepwater, then motion accommodation is improved, but the inner diameter is limited due to increasing hydrostatic pressure resulting in collapse risk
Solution Approach 1:
The riser system is divided into multiple segments: an upper rigid riser section and lower flexible riser sections, connected through a flow diverting structure. This segmentation allows each section to be optimized for its specific function - the rigid upper section maintains large diameter for high flow capacity, while the flexible lower sections accommodate motion, avoiding the collapse issue that would occur if the entire riser were flexible.
2Area of moving object
If multiple smaller diameter risers are used instead of a single large bore riser, then the inner diameter limitation is overcome, but the riser count increases requiring multiple hang off slots and increasing capital expense
Solution Approach 1:
The flow diverting structure introduces a spatial dimension to the riser configuration by distributing flow from a single upper bore into multiple lower bores at different locations. This allows one large upper riser to serve the function of multiple smaller risers, maintaining large effective flow capacity while reducing the number of hang-off slots needed at the topside structure.
3Reliability
If FSHR systems with flexible pipe jumpers are used, then dynamic application challenges are overcome, but system complexity and installation requirements increase resulting in higher cost
Solution Approach 1:
Flexibility is applied locally only where needed - in the lower riser sections that are subjected to dynamic loads and environmental movements. The upper riser section near the topside structure remains rigid for stability and ease of connection. This localized application of flexibility achieves motion accommodation without requiring complex flexible pipe jumpers throughout the entire system.
Data Source
AI summary
Disclosed are riser assemblies for connecting a topside structure and a subsea production facility. The assembly includes an upper riser having an upper end terminating at the topside structure, a flow diverting structure having an upper interface configured to connect to the upper riser and a lower interface configured to connect to at least two lower risers such that the upper riser is in communication with the at least two lower risers. Methods of deployment of the riser assemblies are also disclosed. The method includes connecting an upper riser to the topside structure, and connecting a first lower riser to a lower bore of the flow diverting structure such that the upper riser, the flow diverting structure and the first lower riser are connected, and the upper riser is in fluid communication with the first lower riser. Additional lower risers can be installed at a later time if desired.