Deep-water Regions Research Articles

Artificial neural networks for cloud masking of Sentinel-2 ocean images with noise and sunglint

ABSTRACTCloudy regions in optical satellite images prevent the extraction of valuable information by image processing techniques. Several threshold, multi-temporal and machine learning approaches have been developed for the separation of clouds in land and ocean applications, but this task still remains a challenge. Concerning deep water marine applications, the main difficulties are imposed in regions with high noise levels and sunglint. In this study, artificial neural networks (ANNs) with different configurations are evaluated for the detection of clouds in Sentinel-2 images depicting deep water regions with several noise levels. The ANNs are trained on a manual public dataset and on a manual dataset created for the needs of this study, which authors intend to make publicly available. Results are compared with the cloud masks produced by three state-of-the-art algorithms: Fmask, MAJA, and Sen2Cor. It was shown that the ANNs trained on the second dataset perform very favourably, in contrast to the ANNs trained on the first dataset that fails to adequately represent the spectra of the noisy Sentinel-2 images. This study further reinforces the value of the ‘cirrus’ band and indicates the bands that mitigate the influence of noisy spectra, by defining and examining an index that characterizes the importance of the bands according to the weights produced by the ANNs. Finally, the possibility of improving results by making predictions using the feature scaling parameters of the test set instead of those of the training set is also investigated in cases where the test set cannot be adequately represented by the training set.

Prediction of Favorable Carbonate Reservoirs under Extremely Thick Salts via Poststack Facies-Controlled and Prestack Zoeppritz Equation Inversions in the Santos Basin of Brazil

Subsalt carbonate rocks in Brazil’s deepwater region have broad prospects for oil and gas exploration and development. Due to the low-frequency bandwidth of the seismic data and the poor signal quality for this kind of reservoir target, there is a demand for accurate seismic prediction methods. We employ the facies-controlled inversion using a low-pass filter matrix to ensure the accuracy of the low frequency and to improve the robustness of the inversion results. We integrated the concept of adaptive regularization constraint of the Zoeppritz equation into the generalized linear inversion theory framework, which overcomes the shortcomings of the approximate equation. Making full use of the large angle prestack seismic information, Zoeppritz equation inversion improves the accuracy of the inversion results. The application of this method in carbonate reservoirs under extremely thick salts in the Santos Basin of Brazil indicates the feasibility and practicality of the proposed integrated prediction method.

ЧИСЛЕННОЕ ИССЛЕДОВАНИЕ ТЕЧЕНИЙ В ЦИМЛЯНСКОМ ВОДОХРАНИЛИЩЕ ПРИ РАЗНЫХ УРОВНЯХ НАПОЛНЕНИЯ ВОДОХРАНИЛИЩА

A description of the mathematical model of the hydrodynamics of the Tsimlyansk reservoir is given. In shallow water regions, the flows are described by the equations of shallow water, and in deep-water regions by both the equations of shallow water and the three-dimensional equations of motion of an incompressible viscous fluid. The problem is solved by finite difference methods on a uniform difference grid. The calculations were carried out at different levels of reservoir filling. A comparison of the results obtained with the surface currents scheme constructed based on the results of field work performed in the spring of 2019 is carried out. The pictures of currents were obtained at different water edges. For the period of expeditionary field work in May 2019, hydrodynamics was calculated on the near-dam site using wind data obtained for this period and compared with the results of field measurements of currents. Comparison of the obtained results of numerical modeling with the scheme of surface currents measured from the research vessel reveals a high proportion of convergence of the calculated and field data. The obtained estimates of the modeling results allow us to proceed to the problem of predicting unfavorable hydrometeorological conditions in the Tsimlyansk reservoir, which carry the risk of disrupting the operation of the water intakes of Volgodonsk located in the southern part of the near-dam site

Larval fish assemblages of myctophids in the deep water region of the southern Gulf of Mexico linked to oceanographic conditions

In the Gulf of Mexico, the distribution of larval fish assemblages have been linked to continental shelf vs oceanic habitats and mesoscale structures such as cyclonic and anticyclonic eddies. Myctophids have a worldwide distribution and are one of the mesopelagic fish families with higher biomass, thus playing a key role in the trophic structure of oceanic communities. However, studies focused on their larval ecology and distribution within the gulf are limited. This study evaluated whether the formation of myctophid larval assemblages can be linked to local adult population spawning patterns and/or oceanographic conditions and surface transport. Ichthyoplankton samples were collected in August–September 2015 using standard bongo net tows. Stations extended throughout Mexico's Exclusive Economic Zone (19°N–25°N) deep water region, including the Yucatan Channel. Myctophid comprised 24.6% of the standardized total larval abundance and were present at all stations. Two dominant assemblages (out of six identified with a Bray–Curtis dissimilarity analysis) were found in stations of the central gulf and the Bay of Campeche. The high proportion of preflexion larvae coupled with differences in hydrographic parameters and surface circulation between the central gulf and the Bay of Campeche, indicated that local adult fish populations and their spawning patterns likely contribute more to the formation of these assemblages than oceanographic conditions and surface transport. Stations from the northern Yucatan Peninsula located within the region of influence of the Loop Current shared a common assemblage, which may reflect biogeographic differences in the myctophid species composition between the northern Caribbean and western gulf. These results highlight the importance of adult distribution and local spawning, providing insight into biogeographic patterns during the early life stages of mesopelagic fishes in the Gulf of Mexico.

Seismic stratigraphy of a deep water basin in the Brazilian equatorial margin: the eastern portion of Potiguar Basin and Touros High

The Brazilian Continental Margin (BEM) deep-water regions contain important geological features, although the area is poorly explored beyond the continental shelf-break. The main objective of this study is to seismically characterize syn- and post-rift sequences and certain seamounts that are part of the Fernando de Noronha Ridge (FNR) in deep-water basins and are off of the shore of northeastern Brazil. We used 2D post-stack high-resolution seismic sections to distinguish syn-rift, post-rift, and drift tectono-depositional phases. Three seismic horizons (R1 to R3) could represent, respectively, the following: an acoustic basement top, a rift top, and a highstand system tract (drift). The syn-rift stage is marked by discontinuous parallel reflectors with low amplitude and low frequency, which are offset by normal faults in half-grabens. The post-rift and drift stages are characterized by continuous parallel reflectors with low to high amplitude and frequency. Chaotic seismic reflections within the seamounts indicate their volcanic origins. Volcanic intrusions affected syn-rift, post-rift, and drift sequences and partially confine the deep-water basin deposition. The magmatic event occurred once the preexistent material and the sediment deposited after the seamount rises were partially confined by the continental slope and the seamounts. Seismic stratigraphy interpretation and its correlation with volcanic activities indicate a relative chronological control relating the emplacement of the seamounts to the Early Eocene to Late Miocene. Volcanic episodes seem to have created volcanoclastic deposits marked by a disorganized/chaotic seismic pattern with few continuous reflectors, indicating interbedded magma flows with sedimentary material. This paper provides an initial observation regarding the deep-water basin deposits on syn- and post-rift stages in the NE portion of the BEM.

Evaporite occurrence and salt tectonics in the Cretaceous Camamu-Almada Basin, northeastern Brazil

The Camamu-Almada basin is located at the South Atlantic Margin and, despite the availability of seismic data and the evidence of its hydrocarbon potential, is still considered a new exploratory frontier. In this study, the authors used fifty 2D seismic lines and twelve wells to: a) present a seismic stratigraphic interpretation of the transitional phase (i.e., the strata between the rift and the drift stages; b) investigate the distribution of evaporite deposits at the study area; b) verify the impacts of salt tectonics in the deep-water region, using basins situated in the same geotectonic context as reference. The development of the South Atlantic margin resulted in the formation of several rift basins - including the Camamu-Almada basin – and occurred through four tectonic phases: pre-rift, rift, transitional and drift. The regional deposition of evaporites marks the transitional phase, with occurrences both in Brazil and West Africa that increases in thickness and width southwardly. This work details that in the study area, the salt moved laterally and vertically, forming a highly deformed deposit that marks salt deflation and salt inflation zones, directly associated respectively with diapirs and mini-basins. Features related to salt tectonics that can be directly related to processes of migration and accumulation of hydrocarbons in the study area are also described.

A Mesocyclone over the Northern Sea of Japan in February 2013

The article considers a particular event in the influence of a mesoscale cyclone (MC) on the northern Sea of Japan on February 10–11, 2013. The passage of the MC was accompanied by a sharp increase in wind to storm conditions, an almost twofold decrease in total heat transport, and a fourfold increase in the momentum flux. Perturbations of the hydrological characteristics in the wake of the MC estimated from data of two Argo floats were traced to a depth of 300 m off the west coast of Hokkaido and up to ~100 m in the deep-water region, caused by the difference in the background stability of the vertical structures. Several estimates of the contribution of various factors to the observed variability of the upper sea layer are given.

Rapid estimation of bathymetry from multispectral imagery without in situ bathymetry data.

Optimization-based semi-analytical methods (OSMs) and empirical methods (EMs) have been developed to derive bathymetry maps from satellite-based multispectral data of coral reefs, allowing for the management, monitoring, and protection of coral reefs. However, OSMs are often criticized due to the time-consuming requirements of iterative computations, yet they are praised for working without the need for in situ bathymetry data. EMs are praised for their time-saving characteristics and criticized for their need for in situ measurements. To estimate the water depth from multispectral data quickly without in situ bathymetry data, we provide a new EM that combines our previously developed OSM called the unmixing-based multispectral optimization process exemplar method (UMOPE) and an EM called Stumpf's ratio method (SRM). In the new method, reflectance values from a small number of sampled pixels and the corresponding water depths estimated by UMOPE are used to determine the regression parameters for SRM. Thus, SRM determines the upper limit of accuracy for the new method, and UMOPE determines the possibility of reaching the upper limit. The new method was evaluated using three types of imagery of Xisha Islands, namely, WorldView-2 imagery with three traditional visible bands (WV-2a), Landsat 8 imagery with four visible bands, and WV-2 imagery with six visible bands (WV-2b). The results show that the new method can perform as well as SRM for Landsat 8 data and WV-2b data with similar root mean square error values at different depths. The lack of a coastal band in WV-2a imagery may cause large errors for the new method in deep water regions, especially when the water-leaving reflectance is noise perturbed. We found that even though the depths estimated by UMOPE are not error free at different ranges of water depth, if the regression line between the depths estimated by UMOPE and the measured depths is near the 1:1 line, the new method can perform as well as SRM. The new method may facilitate the rapid estimation of bathymetry from free Landsat 8 data of optically shallow waters around the world without in situ bathymetry data.

Coupled heat and mass transfer model of gas migration during well cementing through a hydrate layer in deep-water regions

During well cementing through a hydrate layer, hydrate dissociation occurs because of the heat generated during the cement hydration reaction, which causes gas migration into the wellbore. Given the shortcomings of extant studies, the present study proposes a coupled heat and mass transfer model to investigate the gas migration occurring during well cementing through a hydrate layer. The coupled model considers the complex interactions among the cement sheath thermal model, the hydrate layer thermal model, the multiphase flow in the hydrate layer, and the gas migration model in the cement sheath. The proposed models are validated through three experiments from literature, which exhibit good agreement with the proposed model. In addition, numerical simulations are conducted using a simulation well. According to the simulation results, the heat exchange between the cement sheath and hydrate layer leads to hydrate dissociation, which is the primary cause of gas migration. Gas migration results in a high casing pressure, which poses a serious threat to the safety of the workers in the future. Conclusions and suggestions are drawn from the case study, which can assist engineers to improve the safety of workers.

Measurement and validation of tsunami Eigen values for the various water wave conditions

This paper proposes the mathematical model to investigate how to compute and analyze the tsunami wave parameters and the retrieval of its early warning using remote sensing technique to improve the detection rate. The different methods available for the evaluation of the tsunami detection systems are also introduced. This research work is to compute and analyze the tsunami wave parameters such as Eigen functions in deep, intermediate and shallow water regions.The computational and algorithmic analysis of tsunami wave parameters are achieved in three steps: the first step is to calculate the earthquake fault parameters such as length, width, area and displacement from the epicenter, which corresponds to the effect of its variation with respect to the earthquake magnitude. The variation of each fault parameters have been measured and recorded out over the certain moment of magnitudes (M). This shows smaller values as compared to the earthquake magnitude M9.5 at which all the parameters shows very large response. The second step involves the measurements of water wave angular frequency in deep, intermediate and shallower region of ocean. The values of angular frequencies in deep water shows the lesser response as compared to other two water conditions because, in deep water the angular velocity of water particles travels with the lesser speed as compared to the shallower region as per Airy's wave theory. The simulation results show the angular velocity in Deep Ocean is very less, moderate in the intermediate water and very high on the coastal region. It indicates the higher impact on coastal region. The third step involves the simulation study of measurement of tsunami Eigen functions such as orbital velocity, acceleration, wave potential in deep, intermediate and shallower water regions. The simulation result shows the resultant orbital velocity and accelerations in deep, intermediate and shallow water regions provides the similar response as angular velocity due to same proportion of the water displacement from deep to coastal regions. Hence the dynamic forces are very high approximately 1 km from the beaches. Once the Tsunami waves approaches to the beach, wave height increases whereas particle acceleration decreases because near the coast, due to geological structure of the earth's surface, inertia and gravity forces increase to the extreme limits, while particle acceleration and velocity values reach close to zero. The wave potential Eigen function has also been plotted and measured with respect to the water depth condition and the similar response is obtained in the simulation result. The validation of each result has also been presented with the standard simulated data, which shows the results as less than 10% of the accuracy.

Novel micro-encapsulated phase change materials with low melting point slurry: Characterization and cementing application

The lower heat of hydration and temperature rise of slurry were required for hydrates formation cementing, the traditional experimental methods often result in a great reducing in the application performances. Therefore, the organic and inorganic composites were applied to develop a novel cement slurry, which could be used for hydrates layer in deep-water region or permafrost. Firstly, the micro-encapsulated phase change materials (MPCM) containing low melting point paraffin wax with urea formaldehyde resin shell was prepared by the method of in situ polymerization, the basic performances of MPCM, such as chemical structure, encapsulation rate and phase change properties, were studied. Secondly, the slag and fly ash were firstly added into class G oil well cement to reduced the heat of hydration and temperature profiles through chemical means. Then, the MPCM was added and applied to control the heat evolution and regulate temperature profiles, and a novel micro-encapsulated phase change materials with low melting point slurry was provided. Based on above study, a low temperature profiles and hydration heat cement slurry was developed by using organic and inorganic composites, and the developed slurry could be well applied in deep-water region or permafrost cementing to prevent the destabilization of hydrates.

Rift structures and its related unconformities on and adjacent the Dongsha Rise: insights into the nature of the high-velocity layer in the northern South China Sea

It is curious that the typical feature of high-velocity layer (HVL) underneath the crust for the magma-rich margin was found in the magma-poor margin of the South China Sea. In order to better understand the nature and age of the HVL in the South China Sea, here we provide seismic imaging on the Cenozoic structure and sedimentation using a regional seismic reflection profile combined with existing drilling data and seismic refraction lines in the northeastern South China Sea. An important finding is that the extent of erosion since Neogene is only on the Dongsha Rise and is much smaller than that of the HVL observed across the northern margin of the South China Sea, which suggests the occurrence of the HVL has no influence on the erosion on Dongsha Rise through Neogene. On the regional seismic profiles, the different structures between the deepwater rifted margins and the continental shelf were also observed. The faults in the Zhuyi Sub-basins on the continental shelf are imaged to be high-angle and bound a series of grabens and horsts. In contrast, the deepwater region is characterized by tilted fault blocks and an array of listric normal faults, which extremely thinned the crust to be ~ 5–10 km. After middle Miocene, active magmatism occurred in the deepwater region at the time of post-spreading of oceanic crust. These listric faults on the hyper-extended crust is interpreted to be conduits for magma migration to the shallower levels. This typical structure in the deepwater region changed the geophysical nature of the HVL underneath the extreme thinned crust, which should be formed before the event of hyper-extension and is likely to be associated with the subduction of the paleo-Pacific toward the Asia in the late Cretaceous. Our study will answer the question why the South China Sea with the HVL underneath the crust is a magma-poor passive margin.

Numerical simulation of the stability of hydrate layer during well cementing in deep-water region

Well cementing aids in enhancing wellbore stability and provides zonal isolation during the exploration of oil, gas, and hydrate energy. However, cementing a well through hydrate layer is problematic. The heat generation from cement hydration leads to the dissociation of the hydrate around the wellbore, resulting in cementing operation failure or serious safety accidents. Current studies seldom focused on the stability of the hydrate layer during well cementing. Therefore, a transient thermal model of cement column is established in this study on the basis of cement hydration kinetics model. On this foundation, a coupled model between the cement column and hydrate layer is established given the interactions between temperature field, hydrate layer, and cement hydration reaction. The transient thermal model of cement column is verified through a field test and the thermal model of hydrate layer is verified by an experiment, which exhibit good agreement. Based on the simulation results conducted in this paper, the total heat generation during cement hydration reaches 198,247 kJ/m, which leads to the dissociation of 9.84×104kg hydrate. The hydrate dissociation is a significantly longer process when compared with the cement hydration process. Thus, the safety threats posed by hydrate dissociation exist during well cementing and also for a long time after well cementing. Additionally, the results suggest that the use of a casing with a higher diameter significantly reduces the hydrate dissociation. The conclusions and suggestions of the study can aid in troubleshooting problems and optimizing the cement operation in the hydrate layer.

Pliocene integrated chronostratigraphy from the Anno Formation, Awa Group, Boso Peninsula, central Japan, and its paleoceanographic implications

The Pliocene climate is one of the best analogs for the climate of a globally warmer future. Here, we present a new Pliocene integrated chronostratigraphy from the Anno Formation in the uppermost Awa Group, which is distributed throughout the Boso Peninsula, central Japan, based on paleomagnetic and benthic foraminiferal oxygen isotope records. This new chronostratigraphy provides valuable constraints for paleoceanographic and paleoclimatic studies in the northwestern Pacific Ocean, where the number of paleoceanographic records is limited due to the lack of calcareous microfossils from deep-sea sediment cores, with the exception of some plateaus at water depths above the calcite compensation depth (CCD). Paleomagnetic results indicate that the Anno Formation corresponds to the period extending from the Nunivak normal polarity subchronozone (4.493–4.631 Ma) to Chron C2An.2n (3.116–3.207 Ma), which is just above the Mammoth reversed polarity subchronozone. Although foraminifera are not found in the middle Anno Formation, our oxygen isotope records from the upper and lower Anno Formation demonstrate the recording of glacial–interglacial cycles. However, the amplitude of our δ18O profile is much larger than that of the LR04 stack, with similar to slightly lower glacial values and much lower interglacial values. This observation implies that the bottom water had lower δ18O values and/or a warmer water mass during interglacials compared with global average deep-water regions.

Sediment accumulation patterns on the slopes and abyssal plain of the southern Gulf of Mexico

Here we present new results on the spatial distribution patterns of lithogenic and biogenic components and sedimentation processes in the deep-water region (966–3741 m) of the southern Gulf of Mexico (sGM). A collection of 44 cores retrieved from the continental slopes and the abyssal plain were dated with the aid of accelerator mass spectrometry (AMS) 14C determinations on planktic foraminifera. We applied a mixing box model (MBM) to estimate the mixed layer age (TML), the mean sediment accumulation rate (Sm), and the mixing depth (XML) for each core. Observed ranges for these variables were Sm (3.4–17.7 cm/kyr), TML (393–6021 yr) and XML (2.4–24.3 cm). Deep-sea sediments in the study region fall into three main groups, which reflect the importance of the main sediment components, lithogenic and biogenic, and sedimentation processes at depth in the sGM. Cores clustered in Group 1 include most of the stations in the abyssal plain, show the oldest TML, relatively low Sm, and a relatively higher ratio between the carbonate and terrigenous components (mostly silt and clay). Group 2 cores were collected from stations in the transitional region, between the abyssal plain and the continental slopes, show relatively higher Sm, a younger TML and a relatively lower ratio between the carbonate and the terrigenous content than cores from G1. Group 3 cores were collected from different water depths on the continental slopes, show the highest Sm, younger TML, and the highest terrigenous content. These distinct groupings enabled us to recognize anomalous properties in certain cores, with implications on the local processes that alter their sedimentation processes at those sites. Our results highlight the importance of the terrigenous input to this basin, as one of the main controls of the burial rates with important implications on the possible fate of anthropogenic inputs and its sequestration in the deep-sea sediments of the sGM.

Space and Time Variations of Organic Matter in Caspian Sea Water

The analysis of data on the space and time variations of the concentrations and element composition of organic matter dissolved in Caspian Sea water over 2010–2015 showed that the average concentrations of Corg and Norg did not changed over the last 5 years of sea level drop relative to the period of level rise, while the concentrations of Porg decreased more than three times, i.e., qualitative changes had taken place in the organic matter. According to the average data, the concentrations of Corg, Norg, and Porg in the southern waters were slightly higher than those in the Northern and Middle Caspian waters. In deep-water regions, the concentrations of Сorg, Norg, and Рorg increase at the boundary of hydrogen sulfide appearance. The presence of hydrogen sulfide in deep waters of the Derbentskaya and Southern Caspian depressions, accompanied by an increase in OM, suggests that no radical increase in vertical seawater mixing took place in these regions during the eight-year regression. The distribution of carbohydrates demonstrates a considerable contribution of petroleum hydrocarbon OM to the total pool.

Resource Growth Through Petroleum Exploration in PNG

Mesozoic and Tertiary clastic and carbonate reservoirs are prolific producers of high quality liquid-rich gas onshore PNG. LNG projects are among the lowest cost and most profitable globally. Accordingly there has been a recent resurgence of petroleum exploration in PNG.In 2015 Oil Search undertook a country-wide petroleum Common Risk Segment analysis that highlighted potential for giant new oil and gas fields of sufficient scale to support future LNG projects. It also concluded that 40 trillion cubic feet of gas plus 550 million barrels of oil resources remain to be found (representing approximately 60% of PNG’s total petroleum resource).In 2016 Oil Search completed an ambitious integrated structural, stratigraphic, burial, maturation, migration, uplift and erosion model of PNG’s total petroleum system to quantify the locations for highly prospective under-explored regions.Tectonic events at plate and basin scales were re-assessed and correlated within a new country-wide PNG Chrono-stratigraphy of regionally mappable sequences and flooding events, some of Global extent.A Base Tertiary Mega-Sequence Boundary is mappable over the entire onshore to deepwater regions. 130 1D burial models combined with restored 2D structural and stratigraphic cross sections, have contributed to a new regional petroleum charge model of the Foldbelts, Foreland and Offshore regions.It is concluded that petroleum was generated pre- foldbelt during Late Cretaceous times in interior PNG while petroleum is currently being generated at the present day mountain front.A holistic 4D charge model explains why very young foldbelt traps are petroleum charged.

Compiled potential field data and seismic surveys across the Eastern Brazilian continental margin integrated with new magnetometric profiles and stratigraphic configuration for Trindade Island, South Atlantic, Brazil

ABSTRACTThis work discusses the regional geological and geophysical datasets (potential field data coupled with seismic lines) available across the Eastern Brazilian Continental Margin and addresses tectonic models that have been applied to the geological interpretation of the Vitória-Trindade Chain (VTC). New magnetic data acquired in the Trindade Island is combined with compiled petrological data and geological maps to propose a stratigraphic column with radiometric control for the volcanic sequences. The gravity and magnetic anomaly maps were integrated with regional seismic profiles extending from the continental platform towards the oceanic crust, showing the geomorphology of the Abrolhos Volcanic Complex (AVC) and the VTC. A detailed geological mapping of the Trindade Island was complemented by magnetometric profiles acquired on the island. The magmatic episodes identified in the Trindade Island within different volcano-stratigraphic sequences are, geochronologically, dated by 40Ar/39Ar method as Late Neogene to Quaternary (Pliocene/Upper Pleistocene) and indicate intrusive and extrusive igneous rocks formed on the Mesozoic (Cretaceous) oceanic crust. Models for the emplacement of these volcanic rocks on much older oceanic crust include hotspots and leaking fracture zones. The presence of flat tops as observed in the volcanic banks and seamounts along the Vitória-Trindade volcanic chain indicate abrasion of much higher volcanic edifices that now form the isolated islands in the Trindade-Martin Vaz Archipelago. Geological mapping and detailed magnetometric surveys suggest different rock properties for distinct volcanic episodes that formed the Trindade Island. The remarkable pattern of magnetic anomalies trending NE-SW in the deep-water region of the Espírito Santo Basin, eastwards of the AVC, suggests that the linear chain of volcanic edifices in the VTC may be associated with mantle anomalies caused by a hotspot or plume that was influenced by the E-W direction of leaking transform fracture zones.Abbreviation: Abrolhos Volcanic Complex (AVC); Vitória-Trindade Chain (VTC)

Prediction of hydrocarbon depth for seabed logging (SBL) application using Gaussian process

Seabed Logging (SBL) is an application of marine Controlled-Source Electromagnetic (CSEM) technique to characterize hydrocarbon-filled layers underneath the seabed remotely in deep water regions. This technique maps structure of subsurface electrical resistivity in the offshore environment. Basically, exploration of offshore hydrocarbon is based on the contrast of electrical resistivity between hydrocarbon reservoir and its surrounding sea sediments. Modelling offshore hydrocarbon is a core analysis and time consuming task. Current numerical modelling techniques used in SBL application involve meshes and complicated mathematical equations. Thus, a simple supervised learning method which is Gaussian Process (GP) is proposed to process synthetic SBL data which are generated through Computer Simulation Technology (CST) software to predict the depth of hydrocarbon. This statistical model is able to provide additional hydrocarbon information by utilizing the prior information. 1-dimensional (1-D) forward GP models have successfully been developed to predict the presence of hydrocarbon and as the continuation work, 2-dimensional (2-D) forward GP model is then developed to be used as the standard profile in order to predict the depth of hydrocarbon. This shall give indication that GP can be used as the methodology to predict the depth of hydrocarbon reservoir underneath the seabed.

Geoacoustic inversion for bottom parameters in the deep-water area of the South China Sea

The properties of bottom acoustic parameters are greatly influenced on sound field prediction. Acoustic parameters in deep water are not well understood. We will discuss experience with geoacoustic inversion of transmission-loss (TL) data from 100 to 600 Hz from deep water regions. Bottom acoustic parameters are sensitive to the TL data in the shadow zone of deep water. Multiple steps TL inversion method is proposed to invertsound speed, density and attenuation in deep water. Both a uniform liquid half-space and a two-layer geoacoustic profile are assumed. Sound speeds of bottom are inverted by using TL data in the shadow zones at low frequency obtained in an acoustic propagation experiment conducted in the South China Sea (SCS) in summer 2014. Meanwhile, bottom densities are estimated combining with the Hamilton sediment empirical relationship. Attenuation coefficients at different frequencies are then estimated from the long range TL data by using the known sound speeds and densities as a constraint condition. The nonlinear relationship between attenuation coefficient and frequency is given in the end. The inverted bottom parameters can be used to forecast the transmission loss in deep water area of SCS very well.