Search Results (7)

With increasing global energy demand and depletion of onshore oil–gas resources, deep-sea hydrocarbon exploration and development have become strategically vital. As core subsea transportation equipment, the performance of helico-axial multiphase pumps directly determines the efficiency and economic feasibility of deep-sea extraction. However, non-uniform inflow patterns caused by uneven gas–liquid distribution in pipelines degrade pressure-boosting capability and reduce pump efficiency under actual operating conditions. To address this, an optimization method employing helical static mixers was developed. A mixer with a 180° helical angle was designed and installed upstream of the pump inlet. Numerical simulations demonstrate that the mixer enhances gas-phase distribution uniformity in stratified flow, improving efficiency and head across varying gas void fractions (GVFs). At a stratification height ratio (Ψ) of 0.32, efficiency increased by 15.41% and head rose by 15.64 m, while turbulent kinetic energy (TKE) at the impeller outlet decreased by up to 50%. For slug flow conditions, the mixer effectively suppressed gas volume fraction fluctuations, consistently improving efficiency under different slug flow coefficients (φ) with a maximum head increase of 9.82%. The optimized flow field exhibits uniform gas–liquid velocity distribution, stable pressure boosting, and significantly reduced TKE intensity within impeller passages. Full article

As terrestrial resources become increasingly scarce, the exploration and utilization of marine resources have become crucial for ensuring a stable resource supply. A maritime A-Frame is a specialized lifting mechanism mounted on the stern of a vessel, designed for deploying and retrieving heavy loads during subsea exploration. Real-time monitoring of the stress of A-Frames is essential for identifying potential failures and preventing accidents. This paper presents a stress-monitoring campaign conducted on a maritime A-Frame during a deep-sea mining project in the South China Sea. Fiber Bragg Grating (FBG) strain sensors were installed on the A-Frame to measure its stress responses throughout the deep-sea mining operation. The stress variations observed during the deployment and retrieval of a deep-sea mining vehicle were analyzed. The results indicate that the stress caused by the swinging motion of the A-Frame was significantly higher than that generated by the lifting and deployment of the mining equipment. Additionally, a finite element model (FEM) of the A-Frame was developed to estimate the stress of the hot spots by integrating the measured strain data. The analysis confirmed that the maximum stress experienced by the A-Frame was well below the allowable threshold, indicating that the structure had sufficient strength to withstand operational loads. In addition, the swing angle of the A-Frame significantly affects the stress value of the A-Frame, while lifting the mining vehicle has a very slight effect. Thus, it is advisable to accelerate the deployment and retrieval speeds of the mining vehicle and minimize the outward swing angle of the A-Frame. These findings provide valuable insights for optimizing the design and ensuring the safe operation of maritime A-Frames in deep-sea mining exploration. Full article

The research related to subsea inspection, and the prediction of corrosion is a challenging task, and the progress in this area is continuously generating exciting new developments that may be used in subsea inspection. Wall thickness monitoring is an important tool to control and predict corrosion, such as on platforms for the infrastructure of floating offshore wind power production. This study shows the results obtained in marine environments. For this experiment, a steel plate equipped with ultrasound transducers was placed in seawater to corrode naturally. The sensor test setup consisted of 15 ultrasound transducers and 1 temperature sensor, which were installed in the cassette. The data acquisition system was based on a standard industrial computer with software written in Python and MATLAB. The ultrasound signals were collected at regular intervals and processed to calculate the instantaneous wall thickness. The progress of corrosion was evaluated by trend plots of wall thickness versus time, and the change in shape of the ultrasonic back wall reflection waveform measured by each sensor. Full article

In both the industrial and scientific fields, the need for very high-resolution cartographic data is constantly increasing. With the aging of offshore subsea assets, it is very important to plan and maintain the longevity of structures, equipment, and systems. Inspection, maintenance, and repair (IMR) of subsea structures are key components of an overall integrity management system that aims to reduce the risk of failure and extend the life of installations. The acquisition of very detailed data during the inspection phase is a technological challenge, especially since offshore installations are sometimes deployed in extreme conditions (e.g., depth, hydrodynamics, visibility). After a review of high resolution mapping techniques for underwater environment, this article will focus on optical sensors that can satisfy the requirements of the offshore industry by assessing their relevance and degree of maturity. These requirements concern the resolution and accuracy but also cost, ease of implementation, and qualification. With the evolution of embedded computing resources, in-vehicle optical survey solutions are becoming increasingly important in the landscape of large-scale mapping solutions and more and more off-the-shelf systems are now available. The issues raised in this review are mainly related to the qualification of the results produced by optical systems and their limitations to cover all the needs expressed by the oil and gas industry field. Interesting qualification works of these solutions are presented in this paper as well as the use of online processing tools such as visual odometry or VSLAM to guide the data acquisition and pre-qualified survey. Finally, it seems interesting to combine acoustic and optical technologies in order to extend the field of application of these methods to low visibility conditions, which remains one of the main limiting factors in the generalization of the use of optical sensors in high resolution underwater cartography applications. Full article

The installation of subsea equipment is a critical step in offshore oil and gas development. A dynamic model to evaluate the lowering process is proposed. The cable–payload system is discretized as a series of spring dampers with the lumped-mass method. For the first time, not only the lowering velocity but also the rope’s structural damping and the nonlinear loads, such as drag force and snap load, are considered. The lowering velocity of the cable is considered through a variable-domain technique. Snap loads are considered by setting the internal forces in the elements to be zero when the cable slacks. A series of simulations reveals that the lowering velocity has great effects on the dynamic force in the cable. However, the structural damping of the cable has little effect on the system response. The snap load may occur in the cable when subjected to rapid downward heave motion, and decreases with the lowered depth increasing. The cable stiffness affects the system’s resonance depth, but has little effect on the peak dynamic force. The present work should be a valuable reference for future subsea equipment installation analysis. Full article

The subsea tree is one of the critical pieces of equipment in the subsea production system, and its installation is related to the safe production of offshore oil and gas. Due to the differences in the form of the structures, the speed of entering the water, the marine environment, and other factors, the process of the structure entering the water is exceedingly complicated. During the engineering installation, the most dangerous phase involves the structure passing through the splash zone. Based on the theory of the movement of the subsea tree passing through the splash zone, Lingshui 17-2 subsea tree installation was analyzed with the marine engineering software OrcaFlex, and a sensitivity analysis of the lowering of the subsea tree was performed. During the splash zone phase, the wave height had the highest impact on the subsea tree, affecting the horizontal offset and cable load, which may lead to the oil tree capsizing and cable breakage. Furthermore, the velocity only affected the horizontal offset, and the overall effect was not noticeable. The operational safety window for the subsea tree installation was established according to the operational safety standards. Therefore, the recommended lowering speed was 0.50 m/s, while the flow velocity should not exceed 1.50 m/s, and the wave height should not be higher than 4.5 m. Full article

In recent years, many oil and gas fields have been discovered in ultra-deep sea (UDS). Some of these fields are evaluated to have no commercial value if existing oil field development approaches are used, especially while the oil prices remain low. A new alternative field development solution, termed as Subsurface Well Completion (SWC) system, is proposed with the aim to produce oil and gas in a cost-effective manner in UDS. This system primarily consists of four parts: a tethered subsurface platform, the rigid riser, SWC equipment and flexible jumper. Obviously, central to the evaluation and application of the new SWC technology is the inherent risk relative to acceptance level. In particular, an uncontrolled release of hydrocarbons to sea, which may lead to catastrophical consequences involving personnel risk, environmental damage and economic losses, is a main contributor to the total risk and of great concern to the offshore petroleum industry. As for the new SWC system, any failure will not be a direct source of risk for the personnel on the surface installation due to its offset feature. In this context, this paper proposes a quantitative risk assessment (QRA) framework to assess such uncontrolled releases to sea with regard to the SWC system for an oil field in the production phase based on the new Subsurface Tension Leg Production (STLP) facility. According to the QRA results presented in this paper, the identified scenarios representing uncontrolled releases to sea are subsea wellhead leaks, rigid riser leaks, subsurface wellhead leaks, releases from X-mas tree and flexible jumper leaks. Among these scenarios, subsea wellhead is found to be the high-risk area. Compared with the established risk acceptance criteria (RAC), the environmental risk levels for the subsea wellhead’s leak lie within the As Low As Reasonably Practicable (ALARP) region while other risks are all below ALARP limits, which means that there is a need for improved consideration of the existing design with regard to the subsea wellhead area, and the corresponding risk reduction measures are proposed. Furthermore, the sources and effects of uncertainties are reviewed and sensitivity studies are carried out to illustrate the effect of some of the important assumptions in the risk model. It can be found that some assumptions made are conservative or optimistic while others are unknown. However, the final QRA results can be regarded as somewhat conservative. This paper concludes that the new SWC technology has a distinct advantage with respect to the leakage duration time in UDS, and thus mitigates the environmental and commercial impacts to a large extent. Besides, relaxed design requirements for the X-mas tree and flexible jumper can be accepted. It is also concluded that there are no serious and major commercial losses for all the identified accidental release scenarios, which is of great importance and attractiveness to oil producers. Full article