Understanding Sliding Mudmat Behavior using Eulerian-Lagrangian Simulations
- M. Kabir Hossain (Bryant Consultants, Inc) | Jean M. Audibert (Independent Consultant) | John T. Bryant (Bryant Consultants, Inc)
- Document ID
- Offshore Technology Conference
- Offshore Technology Conference, 4-7 May, Houston, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2020. Offshore Technology Conference
- flowline-jumper-mudmat-seabed system, Deepwater soft clay sites, Sliding mudmat, Coupled Elerian-Lagrangian FEA, 3-D simulation
- 8 in the last 30 days
- 72 since 2007
- Show more detail
- View rights & permissions
At deepwater sites, skirted mudmats with a sliding mechanism have been the preferred choice to support pipeline or flowline end terminations (PLET or FLET) on soft clay seafloor to accommodate line expansions and contractions that occur during shutdown and restart cycles. The sliding mechanisms can experience line expansions of up to 4 m, or if it were to lock-up, horizontal forces in excess of 2,000 kN. The design and fabrication of sliding mechanisms for such large movements can often become challenging and costly. As an alternative, the industry is now designing mudmats that do not utilize sliding mechanism but rather slide directly on the seafloor, if necessary. While it is an attractive alternative and is gaining popularity, all aspects of direct sliding mudmat design are not sufficiently understood because of the complexity that arises from the interactions among the various components, i.e., flowline/pipeline, mudmat, jumpers, and the supporting soft seafloor behaving as one system. The design must ensure that the mudmat will not unduly sink, rotate or dig into the seafloor in the course of the back and forth sliding caused by many shutdown and startup cycles during the field's operating life. Therefore, it is essential to sufficiently understand the characteristics of the sliding motions and estimate as accurately as possible the resulting interaction forces in the flowline-mudmat-jumper-seabed system. This will allow the designer to avoid the risk of any system instability from incoherent component motions, or potential overstressing of connections.
This paper investigates the direct sliding behavior of the mudmat motions using realistic simulations of the flowline-mudmat-jumper-seabed system. The simulations rely on coupled Eulerian (soft seabed) and Lagrangian (flowline, mudmat and jumpers) finite element analysis (FEA) method. The simulations yield insight into the complex mudmat sliding behavior interacting with the jumper, the hydrocarbon line and the supporting seafloor. The simulations show that merely modeling the mudmat alone fails to capture the actual behavior of a real-life PLET/FLET's back and forth cycling on the seafloor, because for example, the restraints (and attendant stresses) at the flowline and jumper connections are not accounted for, or that slanting the sides of the mudmat reduces its tendency to self-embed decreasing connection stresses. The paper demonstrates that realistic simulations allow important visualization of mudmat interactions with flowline, jumper, and the seabed during the shutdown-startup cycles, and provide accurate determination of the associated critical responses.
|File Size||1 MB||Number of Pages||13|
Audibert, J.M., Hossain, M.K. and Bryant, J.T, 2020. Sliding Mudmats Design - Current State of Practice and Realistic 3D Simulations, 4th International Symposium on Frontiers in Offshore Geotechnics, ISFOG 2020, AT&T Conference Center - University of Texas At Austin, August 16-19, Austin, Texas, USA.
Blanc, M., Thorel, L., Wallerand, R., and Stuyts, B., 2016. Effect of Soil Profile on The Response of a Sliding Subsea Foundation. Institut Francais des Sciences et Technologies des Transports, de PAménagement et des Réseaux - EUROFUGE 2016, 3rd European Conference on Physical Modelling in Geotechnics, NANTES, France, pp 295–300.
Bretelle, S., and Wallerand, R., 2013. Foundations Superficielles Glissantes pour l'Offshore Profond-Methodologie de Dimesionnement / Deep Offshore Sliding Footings-Design Methodology. Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris, France, P. Delage, J. Descrues, R. Frank, A. Peuch and F. Schlosser, Editors, Presses des Ponts (in French), pp. 2331–2334.
Hossain, M.K., Banneyake, R., Abdalla, B., Bell, G., Eltaher, A., and Jukes, P., 2011. Ice Keel-Seabed-Pipeline Interaction Simulation-Ice Pipe JIP Extracts, Coupled Eulerian-Lagrangian (CEL) FEA handles severe soil deformation modeling smoothly and hence is a robust tool for offshore arctic pipe-ice gouging analysis. The Journal of Pipeline Engineering, 2nd Quarter, pp. 105–114.