Marine Geophysical Research最新文献

Particle breakage at coral sands–structure interface is common in marine geological environments and is critical to the stability of geotechnical structures. However, due to the knowledge gap regarding the relationship between structure roughness and coral sand particle breakage, previous studies have not provided a clear understanding of this phenomenon. To address this gap, we conducted ring shear tests to investigate the evolution of the fractal dimension of particle breakage and its dependence on structure surface roughness and vertical stress based on fractal theory. The results show that both the roughness of the steel plate simulating the structure surface in the ring shear test and the particle size of coral sand have significant impacts on the evolutions of particle breakage and morphology at the contact interface. In detail, the particle size distributions (PSDs) of coral sands after shearing have obvious self-similarity and converge to the limit distribution state, especially when the sands contain more large particles. When the steel plate is smooth, the fractal dimension of the broken coral sand is relatively low, which indicates an early stage of fractal dimension development. Moreover, the relationship between the fractal dimension and vertical stress exerted on a rough steel plate can be approximately described using a second-order polynomial function. Moreover, there exists a critical vertical stress that corresponds to the maximum fractal dimension for each kind of coral sand in our tests. The particle breakage rates of coral sand samples on smooth steel plates are substantially lower than those on rough steel plates.

Subducted seamounts are recognized as structures that influence seismicity in subduction zones. Understanding the detailed structures of seamounts, including before and during subduction, is essential for a comprehensive grasp of their influence. Of particular importance is their competency and deformation history during subduction. To better understand seamount subduction and related processes, we analyzed seismic reflection profiles around the Daiichi-Kashima Seamount, the Katori Seamount, and a knoll situated on the oceanward slope. These three features are located at different distances from the trench axis but all fall within the hinge-line of the subducting plate. The Daiichi-Kashima Seamount is currently subducting at the junction between the Japan and northern Izu-Ogasawara trenches, while the Katori Seamount and the knoll have not yet reached the trench axis. A thick limestone layer capping the Daiichi-Kashima Seamount indicates that the core of the Seamount is at least partially intact. On the other hand, our work reveals a large number of trench-parallel or sub-parallel faults within each of the edifices. The seismic profiles also reveal sediments draping the flanks of the edifices, interpreted as turbidite and/or debris flow deposits originating from slope failures. Consequently, our findings show that seamounts and other topographic features begin brittle deformation and failure due to flexural bending of the incoming oceanic plate long before actual subduction, with implications for the strength and competency of seamounts during subduction.

This research project aims to conduct a comprehensive geophysical evaluation of the oil potential within the pre-rift Matulla Formation in the Rabeh and Edfu-Saqara fields, situated in the Gulf of Suez Basin. The investigation relies on the analysis of wireline logs from twelve wells, with eight drilled in Rabeh field (Nageh-1, South Malak-1, Tawoos-1, RE-8, RE-22, RE-25, RE-2 & RE-4) in the onshore south-western Gulf of Suez Basin, and four wells (GS323-1 A, GS323-4 A, Edfu A-3 & Edfu A-5 A) drilled in Edfu-Saqara field in the offshore central Gulf of Suez Basin. Additionally, the interpretation of twenty seismic sections covering the Rabeh field reveals the prevalence of NW–SE normal faults, supplemented by minor E–W faults. These faults play a crucial role in creating structural traps conducive to retaining oil and gas. The analysis of well logging data indicates encouraging petrophysical indicators for the Matulla sandstones, suggesting their potential as reservoirs in the studied fields. These reservoirs exhibit a moderate net pay thickness ranging from 25 to 400 feet, a fair to good net/gross ratio between 0.07 and 0.68, low shale content ranging from 0.03 to 0.20, excellent effective porosity ranging from 0.10 to 0.20, minimal water saturation ranging from 0.10 to 0.35, and high hydrocarbon saturation ranging from 0.65 to 0.90. The obtained results revealed that the Matulla Formation is being considered as a prospective hydrocarbon reservoir in addition to the widely recognized Nubia sandstones and Miocene reservoirs in both Rabeh field and Edfu-Saqara field. Moreover, the constructed iso-parametric maps for the calculated petrophysical parameters in the Rabeh field recommend a strategic focus on the eastern side of the Rabeh field for potential drilling locations, given the presence of high-quality Matulla sandstone reservoirs in that area.

The reef limestone specimens selected in this experiment can be divided into four types according to their morphologies: strongly-cemented compact-type (BM-type), weakly-cemented compact-type (M-type), weakly-cemented loose-type (BS-type), and strongly-cemented loose-type (S-type). Based on the split Hopkinson pressure bar (SHPB) test, the aims of this study were to investigate the dynamic mechanical response and energy dissipation characteristics of reef limestone under impact loads and discuss the relationships of the dynamic fragmentation fractal characteristics with the strain rate and energy dissipation of reef limestone. The results indicated that the length of the compaction section for compact-type reef limestone compared with that of the loose section, which is more significant in the case of decreasing strain rate. The fractal dimension is linearly positively correlated with the strain rate; the fractal dimension of compact-type reef limestone is lower than that of loose-type reef limestone; meanwhile, the dynamic fractal dimension of compact-type reef limestone is more sensitive to the strain rate. The fragmentation fractal dimension of reef limestone under impact loads shows exponential growth with the increase in dynamic strength. The fragmentation fractal dimension of reef limestone is linearly, and positively, correlated with energy dissipation density.

One of the main drilling challenges in the offshore deep-water Nile Delta is the overpressured Tertiary shales, which causes formation fluid influxes, kicks, and very narrow drilling window, thus contributes to non-productive times and enhanced drilling risk. Accurate understanding of pore pressure distribution is crucial for casing design, mud optimization and safe and successful drilling. This study presents first ever in-depth analysis of the pore pressure distribution within the 4500 m thick Oligocene-Pleistocene stratigraphy from the West Delta Deep Marine block in deep-water Nile Delta. Direct formation pressure measurements indicated around 0.06–0.1 PSI/ft (1.36–2.26 MPa/km) gas gradient in the Pliocene El Wastani and Kafr El Sheikh sandstone reservoirs, while the Miocene Qantara sandstones are water-bearing with a 0.42 PSI/ft (9.5 MPa/km) pressure gradient. Shale porosity distribution exhibited additional porosity retention within the montmorillonite and mixed clay-dominated Late Pliocene and deeper sediments and marks the onset of overpressure at the top Kafr El Sheikh Formation. Based on the loading trends and acoustic slowness-density relationship, we inferred compaction disequilibrium as the primary overpressure generating mechanism resulted from high sedimentation rate. Shale pore pressure was interpreted by utilizing wireline logs by utilizing compaction trendline-based approach and calibrated with drilling events and mudlog data. Qantara and Tineh formations are characterized by 0.75–0.77 PSI/ft (16.96–17.41 MPa/km) pore pressure gradient leaving a narrow drilling mud window of 1.7–2 PPG. Based on vertical effective stresses, two significant overpressure compartments were identified in the Late Pliocene and Early Miocene-Late Oligocene, which were separated by the Middle Miocene Sidi Salem Formation acting as a pressure seal.

Abstract

The northern region of the offshore southern Tanzania contains structurally controlled hydrocarbon discoveries. The Permo-Triassic, Jurassic, Cretaceous and Cenozoic source rocks are reported to have possibly charged the existing hydrocarbon reservoirs in the region. However, there is no a detailed record of possible heat sources that may have matured the reported source rocks. Additionally, focused academic research on the possibility of different petroleum traps in the area has also not been done before. This study has used conventional 2D seismic interpretation to reveal presence of several igneous intrusions in the study area. The revealed igneous intrusions include igneous dykes and sills present in the Cretaceous and Cenozoic parts of the studied stratigraphy. Together with the existing burial depth, the associated magmatic heat is interpreted to have facilitated maturation of the Cretaceous-Cenozoic source rocks in the region. This suggests that the offshore southern Tanzanian Basin contains an atypical petroleum system where source rock maturation did not entirely rely on burial temperature. The igneous intrusions have also created hydrocarbon migration pathways from different stratigraphic levels. This is reflected by fracturing of the immediate reservoir intervals and seal rocks above the mapped igneous dykes. The used seismic datasets have also allowed mapping of structural, stratigraphic and combination traps in the study area.

Abstract

Understanding subterranean reservoirs, geological characteristics, fluid composition, and hydrocarbon potential strongly relies on precise reservoir characterization. Seismic inversion is a key method in reservoir characterization to approximate the acoustic impedance and porosity of underlying rock formations using seismic and well-log data. A sparse layer reflectivity (SLR) post-stack inversion method approach is used in this study to make thin layers more visible. To generate an impedance volume, it uses a predetermined wavelet library, an objective function, and a regularization parameter, the regularization parameter is a tunable parameter used to control the balance between fitting the data closely (minimizing the misfit) and ensuring a smooth and stable model for and sparseness computed coefficients. This study uses Blackfoot data to estimate the density, velocity, impedance, and porosity of a particular region using the SLR and Radial Basis Function Neural Network (RBFNN). According to the interpretation of the impedance section, a low impedance anomaly zone with an impedance range of (8500–9000) m/s*g/cc is present at a time of (1040–1065) ms. The low impedance zone is classified as a clastic glauconitic sand channel (reservoir zone) based on the correlation between seismic and borehole data. Further, a Radial Basis Function Neural Network (RBFNN) has been applied to the data to estimate porosity volume and to conduct a more thorough examination of the reservoir zone and cross-validate inverted results. The research demonstrates that the high porosity zone, low velocity, and density zone are discovered by the RBFNN technique, and the low impedance zone interpreted in inversion findings are correlating, which confirms the existence of the glauconitic sand channel. This research is crucial for understanding how well SLR, RBFNN, and multi-attribute analysis work to define sand channels.

Abstract

The Black Sea, situated between Türkiye, Bulgaria, Romania, Ukraine, and Russia, is tectonically separated into two different sub-basins: Eastern and Western Black Sea. These two sub-basins have been a target of interest for oil and gas exploration for several decades. Although the participation of the Black Sea Basin in the global oil market is very small compared to the Caspian Sea, this basin is considered a potential hydrocarbon deposit since both areas have similar characteristics in terms of source rock. In this study, satellite-derived Bouguer and free-air gravity data were interpreted to disclose the prospective hydrocarbon reservoirs and gas hydrate deposits within the Western Black Sea Basin. The locations of the maxima identified in the I₂ invariants map were assessed as five substantial hydrocarbon prospective zones three of which are in the Turkish Exclusive Economic Zone. Numerous oil and gas seeps are evidence of lateral and vertical hydrocarbon migration from the source rock through major faults in the WBSB where the maximum I₂ anomalies are observed.

Recently, subsidence at the coast of Pingtung alluvial plain (SW Taiwan) considerably accelerated, mainly caused by excessive groundwater exploitation from shallow aquifers. To better understand the subsidence pattern and groundwater flow, investigating the structural setting of the Pingtung Basin is essential. The present investigation has revealed that the shallow-marine region off the most rapidly subsiding area of Linbian estuary and Dapeng Bay is characterised by extensive fault and fracture networks, along with a buried syncline, as evidenced by the seismic records. Nearshore, seismic records reveal tectonic fault blocks situated only a few meters beneath the modern seafloor, within the upper 200 m of the seafloor sediments corresponding to the upper interval of the syncline’s infill. This syncline has the same width as the Pingtung basin on land and likely represents its marine extension. Seaward of the most rapidly subsiding area, namely the Linbian estuary, a depression developed on the modern seafloor by both sagging above the syncline centre towards the western flank and extensional faults, which are indicative of recent sinking (= reactivation) of the syncline underneath. The faults, the submarine depression and the coastal subsidence are primarily manifest above the western flank and the centre of the syncline, possibly due to asymmetric reactivation prograding from the syncline's centre towards its western flank. The western flank is intersected by the Liuchu Hsu mud-diapir ridge, which started to rise further and thus, likely triggered the formation of a series of extensional faults above the syncline, followed by minor fault inversions. Previous studies have described freshwater leakage from land aquifers to the seafloor near the subsiding area and at the locations of faults. In fact, these aquifers extend to the adjacent seafloor. Furthermore, faults and fractures in the sub-seafloor deposits in vicinity to the subsiding land areas likely act as conduits in two ways: (1) saline water can infiltrate into the aquifers or (2) freshwater flows out of them. Therefore, these conduits facilitate flow of water from land towards the sea and vice versa. Consequently, the human-induced groundwater overdraft at the Pingtung coast represents a primary factor, which causes seawater to intrude inland whereas tectonic subsidence of the Pingtung Basin is of subordinate importance. The extensive fault and fracture networks, however, have the potential to amplify seawater intrusion inland or seaward freshwater leakage by providing pathways, as highlighted by this study results.