Submarine landslides can pose a significant threat to offshore installations and coastal communities. They can strike installations far from their origin and generate destructive tsunamis. To assess and quantify this hazard, it is necessary to be able to model their dynamics in complex submarine environments with realistic rheological input parameters. Many submarine landslides involve cohesive visco-plastic soils, which can be described mathematically by rheological models such as the non-linear Herschel–Bulkley model. To model these events, accounting for complex bathymetry and rheological behavior, NGI has developed BingClaw . It incorporates buoyancy, hydrodynamic resistance and remolding, which are crucial for underwater landslide dynamics. BingClaw has been used to study the dynamics and tsunami generation of some of the largest and most complex submarine landslides in the world such as the Storegga Slide about 8000 years ago and the 1929 Grand Banks landslide and tsunami. In both cases, BingClaw provided a far more realistic description of both the landslide dynamics and the induced tsunami than other models. The link to the tsunami generation was used to better constrain the landslide dynamics. Here, we demonstrate how BingClaw is used for geohazard applications, including attempts to hindcast past landslides directly relevant to these applications, as often rheological data are sparse or not available from a given site. We first present benchmark results comparing the landslide model with results from laboratory experiments. Then, we show comparisons between simulations and observed landslide run-out for both offshore and onshore applications. The onshore application provides additional well-controlled field studies for validation, in soils with high sensitivity. We also used BingClaw in an offshore/nearshore geohazard project, namely the Bjørnafjorden project offshore western Norway. There, we linked the run-out analysis directly to static and seismic slope stability evaluations, and the predicted run-out scenarios were used in the assessment of competing bridge concepts and their foundations in the deep fjord (around 560 m water depth). These studies illustrate that this novel method, applicable for onshore and offshore geohazard assessments, can reliably reproduce field observations using realistic rheological parameters, which is important when estimating the risk posed by submarine mass movements, particularly with respect to the potential impact on infrastructure.

Slope instabilities and consequent mass gravity flows are major hazards for offshore pipelines, flowlines, cables and umbilicals crossing submarine slopes. Although several methods are available to evaluate the stability of submarine slopes, uncertainty remains over the evolution of the failed soil mass from slide initiation to complete run-out, which may lead to impact and damage of the assets even at significant distances from the initial failure. This paper is intended to apply in-situ knowledge required for the evaluation of the risk of damage and displacements of offshore pipelines caused by the impact of forecasted submarine mass transport events, typically defined as debris flows. A step-by-step methodology is proposed to define design event scenarios tied to site specific geological and geotechnical characterization, calibrate numerical models aimed to ultimately assess mass flow trajectories and impact forces on a given pipeline segment, and to drive pipeline structural response analysis. A fluid dynamics debris flow model, accounting for the seabed 3D bathymetry, has been developed to predict the propagation of debris flows from inception to runout. The model is calibrated against recent well-identified local debris flow deposits, mapped and characterized in terms of preconditioning factors, triggering mechanisms, resulting morphologies, flow dynamics and ages through the use of a combination of geophysical, geotechnical and geological tools. Specific laboratory tests are performed at relevant location and depths, to evaluate the expected rheological behavior and ranges of yield strength and viscosity of the failed soil mass. Design scenarios are then selected based on local morphology and tied to dynamic slope stability evaluations which define the likelihood of the event and initial failed volume. Model input parameters are critically evaluated based on relevant calibration cases. For each simulated scenario, results include the trajectory and run out distance of the mass flow events, along with the distribution of flow velocity and thickness in time and at each location along the flow path. Finally, the main parameters governing the effect of debris flow events on pipelines exposed on seabed are evaluated for incorporation in spatio-temporal pipeline structural response analysis. As with any engineering analysis, results are only as reliable as input. In the case of debris flow impact on pipelines, it is critical that analyses are carefully constrained with field and laboratory data. At each step in the process engineers and geologists must assess the site conditions, and insure that results are meaningful. This applies to all steps in the process, from the initial site characterization and identification of credible geohazard scenarios, selection of modeling methodology, evaluation of rheological parameters (preferably measured in the laboratory), model calibration and matching to field observations, through the final numerical modeling of the pipeline response to impact. The methodology outlined below identifies the main steps in the analysis, and highlights the need to verify engineering results with field observations.

Polymeric rotary seals used in various oilfield equipment face challenging demands, including rotation for extended periods of time while sealing high differential pressure (?P). Such seals are typically mounted in a housing and compressed radially against a rotatable shaft, and prevent fluid from escaping through the clearance between the shaft and housing. One of the damage mechanisms that limits seal life is extrusion. High ?P forces seal material to extrude into the shaft-to-housing clearance. Factors such as shaft defection and runout overstress the extruded material, causing pieces to break away. Another damage mechanism is the accelerated adhesive wear that occurs when the PV (pressure times velocity) capacity of the seal material is exceeded for conventional rotary seals, or as hydrodynamic rotary seals transition toward boundary lubrication. In static sealing, extrusion is minimized by reducing shaft-to-housing clearance. In rotary sealing, the clearance has to be large enough to accommodate shaft deflection, runout, etc. Failure to provide adequate clearance results in heavily loaded metal-to-metal contact that damages the shaft, the seal, and the housing. This paper describes an innovative sealing arrangement that dramatically increases the PV capability of rotary seals, and summarizes key results from an extensive laboratory test program. Test conditions that were varied include shaft diameter, velocity, ?P, temperature, seal material, and lubricant. In the most extreme tests, each seal was exposed to a ?P of 7,500 psi and a velocity of 240 ft/minute for 1,000 hours, and survived in excellent condition. Potential applications for the new technology include rotating control devices (RCDs), washpipe assemblies, cementing heads, and hydraulic swivels. The new high ?P sealing arrangement is based on three technical advances: The seal is lined with a plastic having excellent high pressure extrusion resistance. The seal incorporates an advanced hydrodynamic inlet geometry that is sufficiently aggressive to produce hydrodynamic interfacial lubrication when plastic seal materials are used. Hydrodynamic lubrication with plastic seals significantly increases the PV capability of the seals beyond what is achievable with elastomer seals. An axially force balanced, radially pressure balanced backup ring having a very small clearance with the shaft is interposed between the rotary seal and the shaft-to-seal housing clearance. The extrusion resistance of the hydrodynamic plastic seal, combined with the axially and radially balanced backup ring, allows this rotary sealing arrangement to reliably operate at ~5 times the PV value of conventional high pressure polymeric seals for durations in excess of 1,000 hours.