Offshore oil and gas resources play a crucial role in supplementing the energy needs of human society. The crisscrossing subsea pipeline network, which serves as vital infrastructure for the storage and transportation of offshore oil and gas, requires regular inspection and maintenance to ensure safe operation and prevent ecological pollution. In-line inspection (ILI) techniques have been widely used in the detection and inspection of potential hazards within the pipeline network. This paper offers an overview of ILI techniques used in subsea pipelines, examining their advantages, limitations, applicable scenarios, and performance. It aims to provide valuable insights for the selection of ILI technologies in engineering and may be beneficial for those involved in pipeline integrity management and planning.

Clay sediments are the main component of seabed sediment. Interactions between the nano-sized, disk-shaped and charged clay particles are complicated, as they control the sediment’s rheology. In this study, we studied the rheological behavior of the clay sediment modeled by laponite and bentonite suspensions experimentally using a rotational rheometer. The yield stress decreased when water content increased. Meanwhile, the yield stress of the laponite suspension first increased and then decreased with increasing salinity. It is considered that the face-to-face repulsive electrostatic interaction between clay platelets dominated the yield behavior. A yield stress model was developed to describe the change of the yield stress with both the water content and the salinity. When the system started to flow, the viscosity decreased with increasing shear. A master curve of viscosity is was from the viscosity-stress curves at different water contents if the applied shear stress was normalized by the yield stress and the viscosity normalized by a characteristic viscosity. This study provides a preliminary understanding of the clay sediment rheology and its mechanism for the investigation on the flowing of the sediment systems with strong interparticle interaction.

Nano-water-based drilling fluids (NWBDFs) are prepared using nano-copper oxide (CuO) and multiwalled carbon nanotubes (MWCNTs) as modification materials. The effects of the temperature and concentration of the nanoparticles (NPs) on the rheological properties are studied using a rotational rheometer and viscometer. Also, the influence of two NPs on the filtration properties is studied using a low-pressure and low-temperature filtration apparatus, as well as a scanning electron microscope (SEM). It is found that MWCNTs with a concentration of $0.05 w/v\%$ have the most obvious influence on the NWBDFs, which improve the stability of the gel structure against temperature and also decrease the filtration rate. Finally, a theoretical model predicating the yield point ($\mathrm{YP}$) and the plastic viscosity (PV) as a function of the temperature considering the influence of the NPs is developed based on DLVO theory.

Seafloor mapping and vertical deformation monitoring are important for a gas hydrate exploitation. Due to the complexity of the marine environment and the difficulty of the seafloor operation, an in situ seafloor mapping and high-resolution vertical deformation monitoring simultaneously are big challenges. This paper describes an experimental research on an in situ system for a seafloor mapping and vertical deformation monitoring based on an elastic steel tape, along which an array of nine-axis microelectromechanical system (MEMS) sensors is arranged. The tape can measure both the motion of the bend and the twist. The MEMS sensor consists of an accelerometer, a gyroscope, and a magnetometer. The Euler angles obtained from the nine-axis MEMS sensor can be converted to a relative rotation matrix, showing the amount of the bend and the twist, and the curved shape of the tape can be calculated. Based on this concept, multitapes are used for the seafloor mapping and vertical deformation monitoring. To assess the monitoring system, a lab scale experiment in a water tank is carried out. The results demonstrate the feasibility of the proposed system for the seafloor mapping and deformation monitoring.