Role of wind, mesoscale dynamics and coastal circulation in the interannual variability of South Vietnam Upwelling, South China Sea. Answers from a high resolution ocean model

The South Vietnam Upwelling (SVU) develops in the South China Sea off the Vietnamese coast under the influence of southwest monsoon winds. A very high resolution configuration (1 km at the coast) of the SYMPHONIE model was developed over the western coastal region of the South China Sea. A simulation was performed over the period 2009–2018 to study the functioning, variability and influence of oceanic circulation and hydrology in the coastal region, in particular of the SVU. The realism of the simulation in terms of representation of ocean dynamics and water masses, from daily to interannual and coastal to regional scales, is assessed here in detail by comparison with available satellite data and 4 sets of in-situ observations. The interannual variability of the SVU is examined for its 4 main development areas: the southern (SCU) and northern (NCU) coasts, the offshore area (OFU), and the Sunda Shelf area off the Mekong Delta (MKU). For the SCU and OFU, our results confirm the driving role of the summer mean wind and the summer circulation over the offshore area in the interannual variability of the upwelling intensity. They moreover reveal the impact of the spatial and temporal organization of mesoscale ocean structures and high frequency atmospheric forcing. For the NCU, the upwelling interannual variability does not seem to be related to regional scale forcing and dynamics, but is mainly determined by coastal mesoscale structures and circulation: similar summer wind conditions can be associated with very contrasting NCU intensities, and vice versa, depending on the circulation in the NCU area. Finally, our study reveals that upwelling also develops off the Mekong Delta, with an interannual variability mostly determined by the summer wind and the wind-driven circulation over the SVU region.

Distribution of oil, grease and polycyclic aromatic hydrocarbons in coastal water and sediments of Suez Bay

The permanganate index (PI), oil and grease (O&G), and 17 polycyclic aromatic hydrocarbons (PAHs) were analyzed in surface sediment and water samples collected at 13 sites along the western coast of Suez Bay (SB). PI and O&G in the SB coastal seawater ranged from 9.6 mg O2 l−1 and 17.0 mg l−1 to 16.0 mg O2 l−1 and 37.0 mg l−1, respectively. The level of polycyclic aromatic hydrocarbons (PAH) in water and sediment in the SB offshore area was determined by gas chromatography/flame ionization detection. The concentration ranged from 0.574 to 16873.2 ng g−1 in the sediment and 0.502 to 43.540 ng l−1 in water. The collected data were compared with values reported in the literature. The possible source and origin of pollution was also assessed based on the determined relative PAH levels at the study sites, the ratio of low molecular mass PAHs (LPAHs) to high molecular mass PAHs (HPAHs), and molecular indices of samples.

Atmospheric Optical Turbulence Characteristics over the Ocean Relevant to Astronomy and Atmospheric Physics

Due to the space and time constraints of turbulence measurement equipment and the experiment scene, it is difficult to obtain the atmosphere refractive index structure constant over the ocean. In this paper, the characteristics of atmospheric optical turbulence in offshore and open ocean conditions are summarized by analyzing the meteorological data obtained from two ocean atmospheric optical parameter field experiments. Because of the influence of land undersurface, the turbulence strength in offshore conditions is roughly the same as that on land and presents different characteristics in open ocean. Compared with the offshore area, the turbulence strength over the open ocean near-surface decreases during the day and increases at night, and the diurnal variation characteristics weaken. The turbulence strength profiles over the offshore area show different characteristics at different times, where the turbulence strength in the morning is higher than that in the evening. By retrieving the meteorological factors affecting the turbulence, it is found that the temperature gradient and wind shear are in good agreement with turbulence strength in both offshore and open ocean areas. Furthermore, the integrated parameters for astronomy and optical telecommunication are derived from profiles over the offshore and open ocean areas. It is of great significance to research the turbulent characteristics of ocean atmosphere for optical transmission and astronomical observations.

Wave driven Setup across the North Coast Region of West Java

Wave energy dissipation on the surf zone is compensated with the increase of mean sea level, the so-called wave setup, within the area. This study used the numerical model Delft3D to investigate the dynamics of setup across the north coast region of West Java (Losari to Indramayu) influenced by monsoon variations. The wave forcing was obtained from previous field studies on Cirebon coastal region. The waves within the region were largely dissipated far from the coastline, mainly at the area between Babakan and Karangampel, due to the gentle slope of the North coast of Java. The waves approaching the shoreline were mainly influenced by the east monsoon associated with the longer fetch from that direction. The wave setup varied from ~0.03 to 0.15 m, with the maximum setup occurred near the coastline of the east (Losari) and west (Indramayu) parts of the model domain that consisted of steeper slopes. This, potentially inducing severe coastal inundation that became a serious problem across the coastlines. Meanwhile, the setup near the coastline of the middle area of the domain (Babakan to Karangampel) was very weak, which was correlated to the larger wave dissipation within the offshore area of that region.

The contribution of the NEMO-SN1 seafloor observatory to improve the seismic locations in the Ionian Sea (Italy)

The Western Ionian Sea is characterised by an active and diffuse seismicity, directly related to the convergence of the European and African Plates and by gravitational sinking and rollback of the oceanic lithosphere. In this area, the location of earthquakes is characterised by considerable uncertainties due to large azimuthal gaps, resulting in notable location errors. This problem was partially overcome with the use of data recorded by NEMO-SN1 seafloor observatory (October 2002 February 2003; June 2012 - May 2013). We relocated 1130 crustal and sub-crustal earthquakes using land network and NEMO-SN1 data. As most events occurred on Mt. Etna, we focused on 358 earthquakes in the offshore area and near the coasts of Sicily and Calabria. The use of the combined land-marine networks has improved the earthquake locations in terms of azimuthal GAP, as well as in horizontal and vertical errors. The comparison between locations performed with and without NEMO-SN1 data shows that differences in latitude, longitude and depths are more evident in the Western Ionian Sea and in the coast of Sicily, where values of the differences over 5 km correspond to structural heterogeneities. The increased number of seismic stations deployed on land from 2003 to 2012 did not influence the location of events occurring offshore, where NEMO-SN1 continued to be the distinctive tool in the location process. Moreover, the new 73 focal mechanisms computed with P-wave polarities from NEMO-SN1 and land stations are in agreement with the regional structural model, showing a prevalent normal, normal/oblique, and strike-slip kinematics. The similarity of two new focal solutions with the mechanisms of the main shock and aftershock of the 1990 earthquake demonstrates that the seismic structures are still active and potentially dangerous. The P-wave travel- time residual analysis confirms the activity along the main structural alignments. A single point of observation in the Ionian Sea can significantly improve the quality of locations, giving an opportunity to focus on the seismogenic structures responsible for the occurrence of medium-to-high magnitude earthquakes.

A Crew Scheduling Model to Incrementally Optimize Workforce Assignments for Offshore Wind Farm Constructions

In the literature, different authors attribute between 15% to 30% of a wind farm’s costs to logistics during the installation, e.g., for vessels or personnel. Currently, there exist only a few approaches for crew scheduling in the offshore area. However, current approaches only satisfy subsets of the offshore construction area’s specific terms and conditions. This article first presents a literature review to identify different constraints imposed on crew scheduling for offshore installations. Afterward, it presents a new Mixed-Integer Linear Model that satisfies these crew scheduling constraints and couples it with a scheduling approach using a Model Predictive Control scheme to include weather dynamics. The evaluation of this model shows reliable scheduling of persons/teams given weather-dependent operations. Compared to a conventionally assumed full staffing of vessels and the port, the model decreases the required crews by approximately 50%. Moreover, the proposed model shows good runtime behavior, obtaining optimal solutions for realistic scenarios in under an hour.

The role of mass-transport complexes (MTCs) in the initiation and evolution of submarine canyons

The offshore area of the Otway Basin, located within the SE continental margin of Australia, is dominated by a multibranched canyon system where submarine mass-transport complexes (MTCs) are widely distributed. We integrate high-resolution multi-beam bathymetric and seismic reflection data to investigate the importance of regionally distributed MTCs in dictating the evolution of canyon systems. We interpret three regionally distributed MTCs that fail retrogressively and affect almost 70% of the study area. Within the MTCs, we observed seven canyons that initiated from the continental shelf edge and extended to the abyssal plain. Although these canyons share common regional tectonics and oceanography, the scales, morphology, and distribution are distinctly different. This is devoted to the presence of failure-related scarps (i.e. headwall and sidewall scarps) that control the initiation and formation of the canyons. The retrogressive failure mechanisms of MTCs have created a series of the headwall and lateral scarps on the continental shelf and slope regions. In the continental shelf, where terrestrial input (i.e. fluvial systems) is absent, the origin of the canyons is related to the local failure events and the contour current activities occurring near the pre-existing, massive headwall scarps (c. 120 m high, 3km long). The occurrence of these local failures has provided the necessary sediment input for subsequent gravity-driven, downslope sediment flows. In the continental slope region, the widespread scarps can capture gravity flows initiated from the continental shelf, developing an area of flow convergence, which greatly widens and deepens the canyon system. The gradual diversion and convergence through MTCs related scarps have facilitated the canyon confluence process, which has fundamentally changed the canyoning process. Thus, we conclude that the retrogressive failure mechanism of MTCs has a direct contribution to the initiation, distribution, and evolution of the canyons, especially in areas where fluvial input is missing. Moreover, the retrogressive failure mechanism is responsible for the canyon deepening and confluence process, which can greatly facilitate the delivery of sediment into deep oceans.

Seasonal Sources and Cycling of Nitrogen Revealed by Stable Isotopes in the Northeastern Beibu Gulf, China

Isotope measurements were performed on dissolved nitrate (NO3−) and ammonium (NH4+) in the coastal waters of the northeastern Beibu Gulf, China, to investigate the seasonal nitrate sources and their biogeochemical processes, which are due to the rapid development of local industrialisation and urbanisation. The high N/P ratio observed in the coastal bay during both fall and spring suggests that P is a limiting nutrient, which in turn indicates that increasing P causes conditions favourable for algal blooms. Higher nutrient concentrations and δ15N-NO3− and δ15N-NH4+ values were found in the nearshore area in the fall, suggesting that nutrients originated mainly from land-based pollution. A Bayesian isotope mixing model was used to calculate the contribution of potential NO3- sources and the results showed that in the nearshore area, NO3− originated mainly from manure and sewage (58%). In the spring, however, in addition to the impact of urban sewage effluents, the exchange of sediment and water was another important factor causing higher nutrient concentrations and positive NO3− isotopes in the nearshore area. There were lower concentrations of nutrients and an increase in δ15N-NO3− and δ15N-NH4+ values in the offshore area in the fall, and the NO3− loss in the surface water was mainly caused by the process of assimilation. However, the exchange of sediment and water was the dominant factor causing higher nutrient concentrations (except for NO3−) and positive dual nitrate isotopes but lower NO3− concentration in the offshore area during the spring. Overall, isotope analysis of NO3− and NH4+ helps to illustrate the major sources of the former and their biological transformation in the northeastern Beibu Gulf.

SNB AOI Topside Design Optimization: Solution for Marginal Resources

Sisi Nubi Area of Interest (SNB AOI) is an ongoing project to develop the marginal resources located in Sisi Nubi offshore field operated by Pertamina Hulu Mahakam (PHM). As the resources being developed are small and scattered, low cost solution platform design is required to develop these marginal resources. Therefore, design optimization is a must. Fit-for-purpose design concept is used as the basis to develop process and safety facilities in new SNB AOI platforms while maintaining the compliance with government regulations and international codes and standards. Various exercises were performed in order to ensure optimized process, safety and operating philosophy requirement. Lesson learnt and benchmarking from various established platforms design including PHM's minimalist offshore/swamp platform were performed. The previous designs are reviewed, adopted and SNB AOI platform design is adjusted as per operating philosophy requirement. Based on the available basis of design and operating parameters, fully rated topside facilities design is considered feasible to be applied for new SNB AOI platforms. With this design, relief system size (i.e. vent stack and vent knock-out drum) can be further optimized. In addition, closed drain drum and LP (low pressure) vent knock-out drum is also combined in one single vessel after careful safety verification. Other optimization is externalizing equipment that could be managed with Operating Expenditure (e.g. well offloading activity by using external facility). As for process safety design, preliminary reviews based on international codes and standards showed that the following designs are considered feasible: portable Gas Detector by operator during platform visit (in lieu of permanent Gas Detection system), Fusible Plug loop installation only (instead of redundant protection using Flame Detector system), non-provision of dry fire water mains, application of Passive Fire Protection (PFP) only after confirmation from fire risk study (risk-based approach), and considering not permanently manned installation, 1 (one) stair & 1 (one) ladder combination on each platform deck (instead of dual stairs). Overall, the proposed design maintains the safety of installation with minimum impacts to future platform operation. This optimization has contributed to reduction of dimension and weight of topside installation (i.e. 32% less compared to PHM's latest Offshore Minimalist Platform design) and also weight of the structure. Design of SNB AOI project could become a good reference for other Pertamina affiliate and other companies and could open a further way forward to economically develop the "marginal resources", especially in offshore area, by implementing the "fit for purpose" design concept.

Enhancing Economics of Resources Development of Mature Mahakam Fields Through Innovation, Design Optimization, and Value Engineering

Mahakam Contract Area is located in East Kalimantan Province, Indonesia. It covers an operating area of 3,266 km2, and consists of 7 producing fields. Most of Mahakam hydrocarbon accumulations are located below body of water, with wellhead production facilities installed in the estuary of Mahakam river (referred as swamp area, 0 to 5m water depth) and the western part of Makassar Strait (referred as offshore area, 30 to 70 m water depth). Mahakam production history goes as far back as mid 1970s with production of Handil and Bekapai oil fields. Gas production started by the decade of 1990s along with emergence of LNG trading, supplying Bontang LNG plant, through production of 2 giant gas fields: Tunu and Peciko, and smaller Tambora field. In the mid 2000s, Mahakam attained its peak gas production in the level of 2,600 MMscfd and was Indonesia's biggest gas producer. Two remaining gas discoveries, Sisi Nubi and South Mahakam, were put in production respectively in 2007 and 2012. Due to absence of new discoveries and new fields brought into production, Mahakam production has entered decline phase since 2010, and by end of 2020, after 46 years of production, the production is in the level of 600 MMscfd. In 2018, along with the expiration of Mahakam production sharing contract, Pertamina Hulu Mahakam (PHM), a subsidiary of Indonesian national energy company, Pertamina, was awarded operatorship of Mahakam Block. This paper describes the efforts undertaken by PHM to fight production decline and rejuvenate development portfolio, with focus on expanding subsurface development portfolio and reserves renewal by optimizing development concept and cost through fit-for-purpose design, innovation, and full cycle value engineering.