Search Results (10)

Shallow gas, with huge resources, has been confirmed using three dimensional (3D) seismic data and more than 20 drilling sites in the deep water of the LS36 gas field, the Qiongdongnan Basin, the South China Sea. The interface of sedimentary facies in the southern boundary of the basin controls the distribution within the basin of clastic sediments coming from the north and west of the land uplifted. In this study, seismic data and geophysical attributes were used to investigate the controlling effect of the interface of sedimentary facies on the distribution of shallow gas within the basin. Our study shows that the shallow gas is mainly distributed in the Quaternary Ledong Formation in the southwest of the Qiongdongnan Basin, which was observed from acoustic impedance, amplitude versus offset (AVO), and seismic interpretations. The channelized submarine fans that onlap the interface of the sedimentary facies are distributed in a vertically stacked manner and are the main reservoirs for the shallow gas. Therefore, these sedimentary studies show that the sand-rich sediments are distributed along the interface of the sedimentary facies from the southwest to the northeast and are limited to the shallow gas within the basin. The Central Canyon provides an important deep gas source, while the flank of the canyon, gas chimney, and normal faults related to basement uplift provide pathways for vertical and lateral gas migration to form the shallow gas. This study shows that shallow gas may be widely distributed in other marginal sea basins, and sedimentary systems should be further studied in the future. Full article

A 2D walkway vertical seismic profile (VSP) survey was conducted using a distributed acoustic sensing (DAS) system in southwest Utah, which is part of an enhanced geothermal system (EGS) project. The VSP was undertaken to obtain detailed structural information for a better understanding of the area’s subsurface geology and associated fracture development. By combining a 3D composite velocity model from previous studies and considering the complex geological structure beneath this region, we processed the data to create P-P depth image. We also modified the interval Q calculation using a moving window over the gauge-length corrected DAS record to generate the velocity profile and the comparable interval attenuation curve. The correlated P-P images from two DAS records successfully indicate not only the main contact between shallow unconsolidated sediments and the metamorphic basement rocks at 2650 ft (807.72 m) but also several distinct reflections related to the geological contacts. The refined velocity profiles and the depth images can provide baseline results for further seismic modeling and time-lapse imaging. Full article

Some seismo-stratigraphic evidence on the occurrence of wave-cut marine terraces in the Licosa promontory (Southern Tyrrhenian Sea, Italy) based on Sub-bottom Chirp seismic sections is herein presented. Such evidence is provided by marine terraced surfaces situated at various water depths below sea level and etched into the rocky acoustic basement, which are extensively extending in the seaward extension of the Licosa promontory. It is possible that the isotopic stratigraphy and the terraced marine surfaces are connected, so they can be attributed and dated indirectly. The geologic study of seismic profiles has pointed to the prominence of the acoustic basement, extending to the seabed close to the coast and subsiding seawards under the Quaternary marine succession. Ancient remains of marine terraces, found at a range of water depths between 5 m and 50 m, have documented the major morphological changes of the acoustic basement during the Late Quaternary. Full article

The lithological characterization of the seafloor is key information for offshore engineering, especially when it comes to pier and platform design. Undetected shallow gas pockets may cause the collapse of heavy platforms for hydrocarbon production. Unconsolidated sediments are not ideal for the basement of wind farms for electric power production. Drilling and coring can be used for local sampling, but continuous profiles or even areal coverage are far more preferable. High-resolution seismic profiles are successfully used when ports are not too busy, but otherwise, single-channel systems must be used. We show in this paper that even these simpler systems can be used to estimate parameters such as the acoustic impedance of shallow sediments directly beneath the seafloor. We exploit the amplitude decay of the multiple reflections between the seafloor and the surface, which does not depend on the source energy. If the offset between source and receiver is not too small, we can estimate the shallow P velocity and, via acoustic impedance, also the rock density. Full article

The relict (palimpsest and lowstand) deposits of the Cilento continental shelf were analyzed based on the geological interpretation of Sub-Bottom Chirp sections, calibrated with core data. A progradational unit, which is overlying the acoustic basement, is interpreted as the beach deposits of the isotopic stages 4 and 5. This unit is overlain by a seismo-stratigraphic unit, which is composed of coarse-grained organogenic sands and interpreted as relict sands. This unit consists of sandy ridges, occurring at water depths ranging between 130 and 140 m, and was interpreted as an example of submerged beach deposits, genetically related to the marine isotopic stage 2 (Last Glacial Maximum; starting date 29 ky B.P.). Full article

A Helmholtz resonator (HR) with an embedded aperture is an effective acoustic metamaterial for noise reduction in the low-frequency range. Its sound absorption property is significantly affected by the aperture shape. Sound absorption properties of HRs with the embedded aperture for various tangent sectional shapes were studied by a two-dimensional acoustic finite element simulation. The sequence of resonance frequency from low to high was olive, common trapeziform, reverse trapeziform, dumbbell and rectangle. Meanwhile, those HRs for various cross-sectional shapes were investigated by a three-dimensional acoustic finite element simulation. The sequence of resonance frequency from low to high were round, regular hexagon, square, regular triangle and regular pentagon. Moreover, the reason for these phenomena was analyzed by the distributions of sound pressure, acoustic velocity and temperature. Furthermore, on the basement of the optimum tangent and cross-sectional shape, the sound absorption property of parallel-connection Helmholtz resonators was optimized. The experimental sample with optimal parameters was fabricated, and its average sound absorption coefficient reached 0.7821 in 500–820 Hz with a limited thickness of 30 mm. The research achievements proved the significance of aperture shape, which provided guidance for the development of sound absorbers in the low-frequency range. Full article

The purpose of this study is to describe a methodology for assessing the geotechnical stability of agricultural facilities, enabling prediction of the state of the geotechnical system, taking into account the influence of external factors and combinations of reactions of the geotechnical system under study. According to the methodology, the heterogeneous geotechnical monitoring data obtained are used in an adjusted geotechnical system model, allowing a bifurcation analysis to be carried out. The bifurcation analysis determines critical values of influencing factors, and the limits of stability of the geotechnical system studied parameters are adjusted. The developed methodology was used to assess and predict the geotechnical stability of agricultural facilities during the processing of geoelectric, resistive acoustic, accelerometric and strain-gauge control data obtained in the period from 2016 to 2021. A feature of the geotechnical system under study is the periodic flooding of the building basement caused by the processes of reclamation and irrigation, leading to changes in the groundwater level. The results show that the permissible calculated elastic limit of the foundation elements (32.2–35.1 MPa) before the loss of stability should be significantly reduced with a change in the water content coefficient (W) of the soil base: at W = 0.15 Eb = 30.7–32.0 MPa; at W = 0.35 Eb = 26.8–28.2 MPa; at W = 0.55 Eb = 24.9–25.3 MPa. Full article

The depositional environments offshore of the Cilento Promontory have been reconstructed based on the geological studies performed in the frame of the marine geological mapping of the geological sheet n. 502 “Agropoli”. The littoral environment (toe-of-coastal cliff deposits and submerged beach deposits), the inner continental shelf environment (inner shelf deposits and bioclastic deposits), the outer continental shelf environment (outer shelf deposits and bioclastic deposits), the lowstand system tract and the Pleistocene relict marine units have been singled out. The littoral, inner shelf and outer shelf environments have been interpreted as the highstand system tract of the Late Quaternary depositional sequence. This sequence overlies the Cenozoic substratum (ssi unit), composed of Cenozoic siliciclastic rocks, genetically related with the Cilento Flysch. On the inner shelf four main seismo-stratigraphic units, overlying the undifferentiated acoustic basement have been recognized based on the geological interpretation of seismic profiles. On the outer shelf, palimpsest deposits of emerged to submerged beach and forming elongated dunes have been recognized on sub-bottom profiles and calibrated with gravity core data collected in previous papers. The sedimentological analysis of sea bottom samples has shown the occurrence of several grain sizes occurring in this portion of the Cilento offshore. Full article

An autonomous surface vehicle, known as a wave glider, was used to record refracted and reflected signals from a seismic source penetrating the shallow subsurface. An integrated survey system consisting of a wave gilder and a human-operated source vessel was deployed. These survey systems are used to acquire wide-offset seismic survey data from specific areas, such as offshore structures. The wave gliders can collect seismic refraction and reflection data, which can be used to estimate subsurface information, e.g., acoustic wave velocity and subsurface structure. We processed raw data collected by a receiver equipped with the wave glider and used the relationship between travel time and offset distance to calculate the velocities of shallow sedimentary deposits and the acoustic basement. The velocities of the sedimentary deposits and basement were estimated to be 1557 and 3507 m/s, respectively. We then overlaid the velocities on subsurface data measured using a single-channel streamer. Our results indicate that unmanned equipment can be used for ocean exploration to aid offshore energy development. Full article

Ship type classification with radiated noise helps monitor the noise of shipping around the hydrophone deployment site. This paper introduces a convolutional neural network with several auditory-like mechanisms for ship type classification. The proposed model mainly includes a cochlea model and an auditory center model. In cochlea model, acoustic signal decomposition at basement membrane is implemented by time convolutional layer with auditory filters and dilated convolutions. The transformation of neural patterns at hair cells is modeled by a time frequency conversion layer to extract auditory features. In the auditory center model, auditory features are first selectively emphasized in a supervised manner. Then, spectro-temporal patterns are extracted by deep architecture with multistage auditory mechanisms. The whole model is optimized with an objective function of ship type classification to form the plasticity of the auditory system. The contributions compared with an auditory inspired convolutional neural network include the improvements in dilated convolutions, deep architecture and target layer. The proposed model can extract auditory features from a raw hydrophone signal and identify types of ships under different working conditions. The model achieved a classification accuracy of 87.2% on four ship types and ocean background noise. Full article