Innovative Optimization of a Large-ID Sour-Service Flexible Riser for the Baobab Project in 1000m Water Depth, West of Africa
Bibliographic record
Abstract
Abstract The vast majority of flexible pipe dynamic risers installed in deep water are for sweet service application, with no or a very limited level of H2S present in the produced fluid. For the Baobab development in 960m water depth, the 11" ID flexible production risers required to be fully sour service rated to safely accommodate potential future reservoir souring. The design of such riser structure considering the standard approach proved challenging and leading to significant installation constraints. The optimization of a one length sour service flexible pipe structure to satisfactorily accommodate all loadings associated with the deep water environment (high tension at the top, high hydrostatic collapse pressure and reverse end-cap effect loading at the bottom, high installation tension, etc ..) is indeed difficult and ultimately results in a compromise solution. Through detailed engineering work, the technically optimum and most cost effective solution was identified to be a two sections riser system. Each flexible riser structure can then be optimized for the design loading pertinent to the top or bottom area respectively. This approach leads to a significant weight reduction over a one section design, bringing the top tension and installation loading to a similar level as for a sweet service riser structure. Optimization of the riser configuration, using a Deep Lazy Wave where buoyancy modules are incorporated at the touch down point area, also proved very effective to maintain large bending radius at that location in extreme storm conditions. The installation considerations are shown to be an integral part of the riser system design optimization. In particular the use of partial flooding during the critical installation stages contributed in the optimization of the riser structure design and the reduction of the risk of armour lateral buckling. The paper demonstrates that innovative design and optimization of riser configuration and installation can enable the use of large diameter flexible pipe risers for sour service production application in deep water. Introduction Deep water developments increasingly require larger diameter production risers suitable for sour service application. For flexible pipe, compatibility with sour service production fluid means using lower yield strength carbon steel wires resistant to H2S induced corrosion. This makes the design of the riser structure much more challenging to accommodate the different loading associated with deep water application, particularly so for larger diameter. Figure 1: Typical flexible riser construction (available in full paper) The paper describes the design challenges associated with such risers and the solutions selected to overcome them for the Baobab development. The benefit of splitting the riser into two separate sections is demonstrated, each section being optimized for the pertinent loading that it needs to accommodate. The optimization of the riser system configuration along with the installation measures taken are also shown to be an integral part in achieving a technically suitable and cost effective solution. Baobab field description The Baobab field is owned and operated by Canadian National Resources Limited (CNR) and is located offshore Ivory Coast, in Block CI-40, approximately 65km South West of Abidjan, in water depth ranging from 915m to 1200m.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".