Offshore Test Research Articles

Excess pore pressure observation in marine sediment based on Fiber Bragg Grating pressure sensor

Fiber Bragg Grating (FBG) technology has emerged as a relatively new sensing technology for engineering applications because of lots of advantages. In this study, a large diameter probe instrumented with FBG pressure sensors to monitor excess pore pressure in marine sediment is proposed. The principle of FBG differential pressure sensor was introduced. Laboratory tests were carried out to check the workability and stability of the FBG pressure sensor. Offshore field test was also conducted in a wharf in Qingdao of China to evaluate the feasibility of the proposed probe. The installation procedure of the probe was introduced in detail. The excess pore pressure in dissipation test, after installation and pulling process were reported. The permeability coefficient of marine sediment was calculated based on the measured data. The field data show that the proposed probe based on FBG pressure sensor has good feasibility and accuracy in monitoring the excess pore pressure of marine sediment. The generation and dissipation of excess pore pressure is closely related to the degree of soil disturbance. The variation of excess pore pressure after installation can reflect the tide well in the site.

Dilatometer and Seismic Dilatometer Testing Offshore: Available Experience and New Developments

The flat dilatometer (DMT) was first used in offshore site investigations in the late 80s. Since then, the DMT and also the seismic dilatometer (SDMT) have been increasingly used worldwide in over-water projects, mainly nearshore with limited water depth (maximum 50 m). The limitation for deep DMT testing is due to the need of a pneumatic cable, which is necessary to supply the pressure from a gas tank at the surface down to the blade at depth., The first part of this article presents the available experience of DMT and SDMT testing nearshore using the traditional pneumatic equipment. In the second part of this article, the recently developed Medusa DMT is described. This device is a self-contained cableless probe that is able to autonomously perform dilatometer tests up to a maximum pressure of 25 MPa. Hydraulic pressurization is achieved with a motorized syringe, enabling volumetric control during membrane expansion. Initially conceived only for offshore testing, the Medusa DMT also provides higher quality dilatometer data onshore, with the possibility of additional measurements not feasible with the traditional pneumatic equipment.

A leakage diagnosis testing model for gas wells with sustained casing pressure from offshore platform

Sustained casing pressure (SCP) caused by tubing leakage is mostly considered as the dangerous situation in gas wells, which is more likely to pose a serious threat to well integrity and environmental protection. In order to assess the downhole risk in early time and further provide maintenance strategies to optimize well performance, it is necessary to diagnose the source of downhole leakage accurately. This paper presents a pressure-balance-based approach for capturing two types of dynamic annulus pressure behaviors in a gas well with SCP caused by tubing leakage at different well depths. The approach includes models that take into account the influence of temperature and pressure distributions of tubing and annulus fluid, which are used to determine tubing leakage points. In addition, such an approach involves the calculation of maximum annulus pressure at the wellhead in a gas well with SCP under four main cases, representing the effects of the leakage location, bottom hole pressure, annulus liquid level and gas production rate on wellhead pressure. Afterwards, an integrated diagnostic testing system has been developed to monitor the synthetic state of annulus fluid and liquid level parameters, ultimately identifying the source of SCP correctly. In contrast to previous works, leakage diagnostic testing can be performed from an offshore platform, and it meets the requirements of offshore field testing and works without a shut-in condition, which is capable of overcoming limitations of downhole detection. A case study focused on an offshore gas well with SCP is presented to illustrate the feasibility of the proposed approach, and also to demonstrate that leakage diagnosis contributes to the mechanism investigation of SCP, as well as the design improvement of gas wells integrity.

Comparison of Various Offshore Industrial Gas Technologies

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27939, “Application of Gas Industrial Technologies Offshore,” by Carlos G. Saavedra, Saavco International, prepared for the 2017 Offshore Technology Conference, Houston, 1–4 May. The paper has not been peer reviewed. Copyright 2017 Offshore Technology Conference. Reproduced by permission. Offshore oil-exploration drilling and testing are key for the production of oil; however, a number of associated challenges, particularly the handling of associated gas, must be overcome. This paper discusses the alternatives for processing the associated gas and transporting it to markets. The technologies described in this paper are applicable to nonassociated-gas projects as well. Fig. 1 provides a description of gas-handling value chains for some of the alternatives. Floating Liquefied Natural Gas (FLNG) Liquefied natural gas (LNG) is natural gas that has been converted to liquid form for ease of storage or transport. It is a gas cooled to −162°C and has a volume that is 1/600 that of the gas at room temperature. The gas has to be processed at both ends of the shipping chain in order for LNG to be produced and used. It can be transported by specially designed cryogenic seagoing vessels (LNG carriers). At the destination, the LNG is offloaded to a receiving terminal that stores it and revaporizes it into a pipeline that takes the natural-gas product to the end users. Floating Compressed Natural Gas (FCNG) Compressed natural gas (CNG) is a concept for gas transport over intermediate distances. The FCNG technology involves storing natural gas at high pressure in a carrier ship to transport it from an offshore location to a typically onshore location. The high pressure and possibly reduced temperature increase the density of the gas, making it more economical to transport. CNG is stored and distributed in cylindrical or spherical vessels at pressures up to 275 bar and at ambient or sub ambient temperatures. Higher pressures and lower temperatures allow more gas to be contained per unit volume. The typical volume reduction is 1/300. An FCNG production vessel is a traditional gas floating production and operation unit (FPO) with a high-pressure gas-transfer system, instead of a subsea pipeline, to load CNG shuttle ships. The CNG is transferred at near-ambient temperatures, so the hoses and transfer systems are the same high-pressure hoses and systems used to transfer high-pressure gas and well fluids onto an FPO. The CNG shuttle carriers provide both storage and transport, thus avoiding the necessity for storage on board the FCNG vessel. Any CNG-delivery-system technology should offer a continuous-flow process without interruption or discontinuity (like a pipeline). Gas should flow continuously with high reliability through the CNG shuttle ships. Major buoy-system suppliers have reviewed CNG transfer and found that their systems can be adapted to CNG transfer without developing new technology. CNG appears to be a potentially suitable and promising technology for deployment despite not having been deployed commercially to date. It has no technical barriers. The principal commercial barrier stems from CNG being a solution that lies between a pipeline for shorter distances and LNG for longer distances. FCNG technology has existed in a design state for several years, with numerous studies having been conducted; however, no facilities have been built yet.

Corrigendum to Overview and introduction: Pressure core-sampling and analyses in the 2012–2013 MH21 offshore test of gas production from methane hydrates in the eastern Nankai Trough JMPG 66 (Sep 2015); Pages 296-309

Corrigendum to Overview and introduction: Pressure core-sampling and analyses in the 2012–2013 MH21 offshore test of gas production from methane hydrates in the eastern Nankai Trough JMPG 66 (Sep 2015); Pages 296-309

Comparisons of the dynamical characteristics of a semi-submersible floating offshore wind turbine based on two different blade concepts

Scaled model tests are important for the development and validation of floating offshore wind turbines. However, it has been found that Reynolds number dissimilitude between scales deteriorates the aerodynamic performance of floating offshore wind turbines when using model test investigation methodologies. To overcome this challenge, a semi-submersible floating offshore wind turbine model test with two different solutions, namely a geometrically matched blade model and a performance-matched blade model, was conducted in a wind/wave basin. Subsequently, a series of comparisons of the dynamical characteristics of these two models were made to clarify the respective validity of the two models and provide references for future floating offshore wind turbine model optimization. It is found that both model methods are capable of reflecting the essential dynamical characteristics but there are some differences in system eigenfrequencies and response amplitudes. Compared with the geometrically matched blade model, the performance-matched blade model has enhanced aerodynamic performance. Nevertheless, the overweight blades within the performance-matched blade model yields inevitable discrepancies compared with the original design.

Characterization of a Wind Generation System for Use in Offshore Wind Turbine Development

Environmental conditions created by winds blowing oblique to the direction of the waves are necessary to conduct some survivability tests of offshore wind turbines. However, some facilities lack the capability to generate quality waves at a wide range of angles. Thus, having a wind generation system that can be rotated makes generating winds that blow oblique to the waves possible during survivability tests. Rotating the wind generation system may disrupt the flow generated by the fans because of the effect of adjacent walls. Closed or semiclosed wind tunnels may eliminate the issue of wall effects, but these types of wind tunnels could be difficult to position within a wave basin. In this work, a prototype wind generation system that can be adapted for offshore wind turbine testing is investigated. The wind generation system presented in this work has a return that minimizes the effect that the walls could potentially have on the fans. This study characterizes the configuration of a wind generation system using measurements of the velocity field, detailing mean velocities, flow directionality, and turbulence intensities. Measurements were taken downstream to evaluate the expected area of turbine operation and the shear zone. The dataset has aided in the identification of conditions that could potentially prevent the production of the desired flows. Therefore, this work provides a useful dataset that could be used in the design of wind generation systems and in the evaluation of the benefits of recirculating wind generation systems for offshore wind turbine research.

Research and practice of offshore wind turbine model test platform and technology

The abundance of offshore wind energy resources has promoted the development of offshore wind turbine. With the increase of wind turbine power, the fixed foundation for shallow sea area no longer meets the design requirements, and the floating foundation for deep sea area has been developed rapidly. In this paper, the development process, types and particularity are introduced, and it demonstrates that the model experiment is indispensable in the development of floating offshore wind turbine (FOWT). Firstly, key technologies of basin model test are concluded, such as similarity criteria, scale ratio determination technology, model blade design technology, mooring system processing technology and environmental conditions simulation technology. Then object of 6 MW SPAR-type FOWT proposed by Shanghai JiaoTong University is researched, and production process of model is summarized, including model blade, model nacelle and model tower. Finally, the construction of the deep water test tank of marine engineering of Shanghai JiaoTong University is introduced, and the test results of the new multi-column TLP FOWT model test in the test tank are shown. The test results have great agreement with software simulation results. The results show that the deep water test tank of marine engineering of Shanghai JiaoTong University can be well developed as basin model test of FOWT. This paper supplies some guidance for the following model test and provides a theoretical basis for the development of the FOWT.

Offshore and onsite placement testing for English pathway programmes

English language programmes provide established pathways for international students seeking university admission in countries such as Australia and the United Kingdom. In order to refer international applicants to appropriate levels and durations of English language support prior to matriculation into their main course of study, pathway providers need effective and efficient language assessment tools. This report evaluates the effectiveness of an online vocabulary knowledge test as an index of English proficiency for university English pathway programme applicants (N = 177). The Timed Yes/No (TYN) test measures vocabulary recognition size and speed in a time- and resource-effective format. Test results were correlated with performance on a comprehensive placement test consisting of speaking, writing, reading and listening components. The predictive validity of word recognition accuracy (a proxy for size) and response time (a measure of efficiency) for placement test outcomes were examined independently and in combination. The TYN test scores’ sensitivity at predicting comprehensive placement test scores were assessed using a cut-score analysis resulting in an identification accuracy rate ranging from 76 to 86% for five critical band scores. The potential use of the online vocabulary-screening test for measuring international students’ English language proficiency is discussed in terms of reliability, validity, speed, usability and cost-effectiveness in onsite and offshore testing conditions.

Investigation Into the Performance of a Dual-Layer Thin-Film Organic Coating During Accelerated Low-Temperature Offshore Testing

The application of thin-film coatings is a method to protect armatures, accessories, and control elements on offshore facilities against corrosion and mechanical damages. The performance of a dual-layer thin-film (30 μm) coating system under simulated Arctic offshore exposure was investigated. The coating system consisted of polyamide-based primer and molybdenum-disulfide (MoS2)/polytetrafluoroethylene (PTFE)—modified topcoat. The investigations involved the following tests: accelerated corrosion protection/aging tests, coating adhesion tests, scanning electron microscopy (SEM)/energy-dispersive X-ray (EDX) inspections, static contact angle measurements, specific surface energy measurements, hoarfrost accretion, and abrasion resistance tests. The test conditions were adapted to Arctic offshore conditions. Effects of accelerated offshore aging on surface morphology, surface chemistry, and hoarfrost accretion were also investigated.

Horizontal Pendulum Performance Analysis with Multilevel Model Plate on Ocean Wave Electric Power Plant (PLTGL)

- With the times and the industry, the energy sources such as fossil fuels dwindling. It encourages all parties to be more advanced and developed by creating solutions to renewable energy generation with the latest innovations, one of which is the sea wave power plant - pendulum system. Ponton who uses pendulum system is one tool used to convert from ocean wave energy into electrical energy. In this study using the test conditions without using ballast onshore and off-shore testing with the ballasts. Obtained from testing the many rounds that can be generated pendulum pie plate thickness and the angle of the pontoon. To test the largest on-shore power obtained on the test using arc angle 30 °, 3 mm thick, the angle of 60o power produced 0036 watts. For testing offshore in the ballasts 12 cm, 15 cm, 17.5 cm, the largest power generated at 15 cm ballasts with 0041 watts power on pie, thick, and a tilt angle equal to the on-shore testing. Number of rounds with time, the on-shore testing that produces the greatest value in the segment with an angle of 30 °, a thickness of 3 mm the angle of 60o value obtained 0.938 rad / s. In the off-shore pengjuain is greatest in the ballasts 15 with 0847 rad / s.

Offshore Gas Well Flow and Orifice Metering System: An Overview

This research presents a concise account of offshore surface well test from objective, organization, to practical approach and in relation to orifice metering system of natural gas; against the perspective of regulatory standards. With reference to reliability, availability, affordability and including control measures governing the design, the orifice meter sometimes called a head loss flow meter is chosen most often because of its reputation in the oil and gas industry. Alternative metering system of natural gas, including robust and cost effective innovations within the industry which addressed some key limitations of orifice meter was examined. The advanced flow computer with transducers suited for orifice measurement installations is a cost effective electronic flow real time measurement system. It has telemetry features and improved accuracy under fluctuating flow conditions based on functional differential pressure root mean squared volume calculation principles. These new developments and their capabilities have reduced the market share of the mechanical orifice chart meters. Except that Electronic flow meters has environmental limitations; thus, the proven mechanical orifice metering systems are still an effective solution for many flow measurement applications.

Experimental analysis of buoyancy battery energy storage system

Buoyancy battery underwater energy storage is an emerging area of research relating to the storage of energy generated by renewable resources such as offshore wind and solar. This study presents an experimental analysis of a basic buoyancy system. Tests were performed on a container with minimal ambient fluid volume, as well as in a large offshore testing tank. Development and integration of fundamental system components is discussed in terms of experimental apparatus and larger application. Discharge cycling was performed with variables relating to discharge voltage, power, and discharge velocity obtained. Energy losses to kinetic energy and hydrodynamic drag are estimated for completed trails. The effect of pulley friction is evaluated for no-load discharge testing. Conclusions are drawn as to the observed operation of the system as designed, primary areas for performance improvements, and next steps for system development.

A Review and Comparison of Floating Offshore Wind Turbine Model Experiments

Floating offshore wind turbines provide more access to deeper water than conventional fixed-bottom wind turbines, which expands the viable area for wind energy development, reduces visibility from shore, and can potentially be located in areas with a higher and steadier wind characteristic. However, since floating turbines are in the early prototype stage of development, there are very limited data to use for validating computer models of these machines. This lack of validation increases uncertainty and risk for future installations. In lieu of large scale test turbines, which are expensive to build and operate, a few institutions have conducted small scale experiments in wave basins. This paper will present a review of the past and planned model-scale floating offshore wind turbine experiments, with a focus on types of data collected and challenges encountered by these tests.The objective of this review is to provide a background for the Integrated Research Program on Wind Energy (IRPWind), specifically for Work Packages 6.1 and 6.2. The goal of these work packages is to create a database of both fixed-bottom and floating offshore wind turbine test cases that can be accessed by researchers to verify and validate computer-aided engineering codes. The database will consist of a number of benchmarks that will validate different parts of a given design code. This review will discuss two model experiments that are likely to be included in the IRPWind database.

Load extrapolations based on measurements from an offshore wind turbine at alpha ventus

Statistical extrapolations of loads can be used to estimate the extreme loads that are supposed to occur on average once in a given return period. Load extrapolations of extreme loads recorded for a period of three years at different measurement positions of an offshore wind turbine at the alpha ventus offshore test field have been performed. The difficulties that arise when using measured instead of simulated extreme loads in order to determine 50-year return loads will be discussed in detail. The main challenge are outliers in the databases that have a significant influence on the extrapolated extreme loads. Results of the short- and longterm extreme load extrapolations, comprising different methods for the extreme load extraction, the choice of the statistical distribution function as well as the fitting method are presented. Generally, load extrapolation with measurement data is possible, but care should be taken in terms of the selection of the database and the choice of the distribution function and fitting method.

Validation of Uncertainty in IEC Damage Calculations Based on Measurements from Alpha Ventus

The aim of this paper is to validate environmental assumptions used in the design of offshore wind turbines. This is done by comparing the load uncertainty (load variation) resulting from assumptions to full scale measurement data from a Senvion 5M turbine on a jacket substructure positioned in the offshore test field Alpha Ventus in the North Sea. The focus is put on fatigue loads occurring during power production. Sensors at the tower base and tower top of the turbine are evaluated. Simulations are performed by using the coupled simulation tool Flex5-Poseidon. Measurements over a period of 10 months are selected so that a high quality of reference data is ensured. Uncertainty from both measurements and simulations are determined by Monte Carlo experiments and evaluated by Bootstrap methods. Results show that a variation of damage from simulations is significant and that the presented method could be used for evaluation of assumptions used in the design process.

Design and test of 1/5th scale horizontal axis tidal current turbine

Tidal current energy is prominent and renewable. Great progress has been made in the exploitation technology of tidal current energy all over the world in recent years, and the large scale device has become the trend of tidal current turbine (TCT) for its economies. Instead of the similarity to the wind turbine, the tidal turbine has the characteristics of high hydrodynamic efficiency, big thrust, reliable sealing system, tight power transmission structure, etc. In this paper, a 1/5th scale horizontal axis tidal current turbine has been designed, manufactured and tested before the full scale device design. Firstly, the three-blade horizontal axis rotor was designed based on traditional blade element momentum theory and its hydrodynamic performance was predicted in numerical model. Then the power train system and stand-alone electrical control unit of tidal current turbine, whose performances were accessed through the bench test carried out in workshop, were designed and presented. Finally, offshore tests were carried out and the power performance of the rotor was obtained and compared with the published literatures, and the results showed that the power coefficient was satisfactory, which agrees with the theoretical predictions.

Numerical simulation on gas production from hydrate reservoir at the 1st offshore test site in the eastern Nankai Trough

According to the available geological data of hydrate reservoir at the 1st offshore production site in the Eastern Nankai Trough in 2013, a simulation model matching the production test scheme was established to investigate a relatively long-term production performance and the effect of perforated interval on gas production by comparing the short simulation results and the field test data (6 days). The verification results indicate that the simulated gas production rate is consistent with the measured field value but a certain deviation of corresponding water production rates occurs. The relatively long-term simulation performed reveal that both gas released rate in the sediment and gas production rate in the well increase before complete dissociation of hydrates between bottom hole and underburden. After that, they convert to decreasing and the water production rate increases sharply. Meanwhile, the slight secondary hydrates are observed in the dissociation front. Additionally, the sensitivity analysis of completion interval indicates that the perforated interval design for candidate hydrate reservoir like this site should avoid the low-permeability hydrate layer and take the lower hydrate layers as the water blocking zones when using depressurization method, and that the optimum completion interval should be determined by together considering the production period and the expected production rate.

Developing an automated risk management tool to minimize bird and bat mortality at wind facilities.

A scarcity of baseline data is a significant barrier to understanding and mitigating potential impacts of offshore development on birds and bats. Difficult and sometimes unpredictable conditions coupled with high expense make gathering such data a challenge. The Acoustic and Thermographic Offshore Monitoring (ATOM) system combines thermal imaging with acoustic and ultrasound sensors to continuously monitor bird and bat abundance, flight height, direction, and speed. ATOM’s development and potential capabilities are discussed, and illustrated using onshore and offshore test data obtained over 16 months in the eastern USA. Offshore deployment demonstrated birds tending to fly into winds and activity declining sharply in winds >10 km h−1. Passerines showed distinct seasonal changes in flight bearing and flew higher than non-passerines. ATOM data could be used to automatically shut down wind turbines to minimize collision mortality while simultaneously providing information for modeling activity in relation to weather and season. Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-015-0707-z) contains supplementary material, which is available to authorized users.

A seafloor electromagnetic receiver for marine magnetotellurics and marine controlled-source electromagnetic sounding

In planning and executing marine controlled-source electromagnetic methods, seafloor electromagnetic receivers must overcome the problems of noise, clock drift, and power consumption. To design a receiver that performs well and overcomes the abovementioned problems, we performed forward modeling of the E-field abnormal response and established the receiver’s characteristics. We describe the design optimization and the properties of each component, that is, low-noise induction coil sensor, low-noise Ag/AgCl electrode, low-noise chopper amplifier, digital temperature-compensated crystal oscillator module, acoustic telemetry modem, and burn wire system. Finally, we discuss the results of onshore and offshore field tests to show the effectiveness of the developed seafloor electromagnetic receiver and its performance: typical E-field noise of 0.12 nV/m/rt(Hz) at 0.5 Hz, dynamic range higher than 120 dB, clock drift lower than 1 ms/day, and continuous operation of at least 21 days.