An integrated numerical model for wave–soil–pipeline interactions

Laboratory experimental study of ocean waves propagating over a partially buried pipeline in a trench layer

Many countries are now using or investigating offshore geological storage of CO2 as a means to reduce atmospheric CO2 emissions. Although associated research often focuses on deep-basin geology (e.g. seismic, geomagnetics), environmental data on the seabed and shallow subseabed is also crucial to (1) detect and characterise potential indicators of fluid seeps and their potential connectivity to targeted storage reserves, (2) obtain baseline environmental data for use in future monitoring, and (3) acquire information to facilitate an improved understanding of ecosystem processes for use in impact prediction. This study reviews the environmental considerations, including potential ecological impacts, associated with subseabed geological storage of CO2. Due to natural variations in CO2 levels in seafloor sediments, baseline CO2 measurements and knowledge of physical–chemical processes affecting the regional distribution of CO2 and pH are critical for the design of appropriate monitoring strategies to assess potential impacts of CO2 seepage from subseabed storage reservoirs. Surficial geological and geophysical information, such as that acquired from multibeam sonar and sub-bottom profiling, can be used to investigate the connectivity between the deep reservoirs and the surface, which is essential in establishing the reservoir containment properties. CO2 leakage can have a pronounced effect on sediments and rocks which in turn can have carryover effects to biogeochemical cycles. The effects of elevated CO2 on marine organisms are variable and species-specific but can also have cascading effects on communities and ecosystems, with marine benthic communities at some natural analogue sites (e.g. volcanic vents) showing decreased diversity, biomass, and trophic complexity. Despite their potential applications, environmental surveys and data are still not a standard and integral part of subseabed CO2 storage projects. However, the habitat mapping and seabed characterisation methodology that underpins such surveys is well developed and has a strong record of providing information to industry and decision makers. This review provides recommendations for an integrated and interdisciplinary approach to offshore geological storage of CO2, which will benefit national programs and industry and will be valuable to researchers in a broad range of disciplines.

Environmental considerations for subseabed geological storage of CO2: a review

In this study, the multivariate adaptive regression splines (MARS) technique was applied to estimate scour depth around pipelines. To this purpose, 90 data sets related to effective dimensionless parameters on pipeline scouring phenomena were gathered from literature. A gamma test (GT) was used to define the most-effective parameters on scouring phenomena below pipelines. Performance of MARS model was compared with multilayer perceptron (MLP) neural network and empirical formulas. Results of the GT showed that e/D, τ*, and y/D are the most important parameters for scour depth. Results of MARS model with coefficient of determination (0.91) and root-mean square error (0.05) indicated that this model has suitable performance for predicting scour depth under pipelines and results of this model are more accurate compared to empirical formulas. Comparing results of MARS model and MLP showed that accuracy of MARS model is slightly lower than that of the MLP.

Prediction of River Pipeline Scour Depth Using Multivariate Adaptive Regression Splines

Scour protection of submarine pipelines using rubber plates underneath the pipes

This paper presents results from laboratory experimental model studies investigating scour by waves around a pipeline attached to a flexible rubber plate or rigid spoiler. The rubber plate was placed between the submarine pipeline and bed, while the rigid spoiler is attached to the top of the pipe. The scour around pipelines with and without a rubber plate or a rigid spoiler under regular and irregular waves was observed and measured for a range of pipe sizes, wave amplitudes and frequencies, and the length of the plate/height of the spoiler. The experiments reveal that although the rigid spoilers can enhance the scour depth and extent (thus accelerating the self-burial of the pipe), they also have significant influence on both the upstream and downstream bed topography as sand ripples and dunes are formed. On the other hand, the rubber plates cannot only significantly increase the scour depth but also have little effect on the upstream and downstream bed. The experiments show that when the length of the plate is about 1.5 times the pipe size, it provides the optimum performance in terms of the largest scour depth while restricting the impact on nearby beds for the parameters investigated in this study.

Shuyou Cao

Papers

Study of Scour around Submarine Pipeline with a Rubber Plate or Rigid Spoiler in Wave Conditions