Marine Geophysical Research最新文献

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.

Heat flow measurements are a standard technique in Geophysics both onshore and offshore. Recently, such measurements became increasingly important in shallow waters. The increasing amount of offshore power installations makes it necessary to have a good knowledge about the subsurface heat flow and the thermal properties of the sediments to optimize the construction of the necessary powerlines. While the thermal properties are well studied for deep ocean sediments, only few published data exist for nearshore sediments. In this study, we investigate the sediment temperatures and thermal conductivities of nearshore sediments in the German part of the Baltic Sea. The shallow sediment temperatures reflect the interplay of the response to the seasonal cycle in connection with the sediments’ thermal conductivity. We find thermal conductivity values ranging from 0.67 to 3.34 W/(m*K) for the sediments down to ~ 4.2 m below seafloor. This variability exceeds that of conservative estimates widely used for coastal sediments and is also much higher than the variability found in the deep oceans. Sandy sediments show thermal conductivities larger than 1 W/(m*K) whereas organic-rich muds have lower values (< 1 W/(m*K)). Furthermore, the thermal conductivities seem to decrease with increasing free gas content in the sediment. The latter needs to be confirmed by further investigations.

In the recent past, an integrated analysis of predicted petrophysical properties along with acoustic impedance has emerged as an effective means of characterizing reservoirs. Model-based inversion method was applied to precisely estimate acoustic impedance (correlation: 87.9% & error: 414 m/s*g/cm³), while the multi-layer perceptron algorithm was applied to predict gamma-ray (correlation: 90.5% & error: ~ 2.5API), neutron porosity (correlation: 92.3% & error: ~ 0.01) and effective porosity (correlation: 85.8% & error: ~ 0.01) from post-stack 3D seismic data. We analyzed the entire Abenaki Formation into four parts, i.e., the Scatarie, Baccaro, Misaine shale and Artimon Members. These members have been characterized by combining the P-Imp, GR, NPHI, and PHIE responses. Well-based cross-plot study suggests that the high P-Imp, low GR and low NPHI indicate carbonate facies. In contrast, low impedance, high GR and high NPHI values indicate the shale facies from the Abenaki Formation. P-Imp, GR, and NPHI values fall in the intermediate range for the sand facies. The attribute stratal slice maps indicate the dominance of carbonate facies within the Scatarie, Baccaro, and Artimon Members, while shale facies dominate within the Misaine shale Member in the Penobscot field. The carbonate facies' hydrocarbon potentiality within different members was also accessed based on PHIE responses. The Artimon, Baccaro and Scatarie Members observed several high porosity (10–20%) zones. The current study also advocates that the integrated analysis using multi-attributes certainly minimizes the risk associated with facies discrimination in reservoir characterization for hydrocarbon exploration. Other potential prospective zones could be probed to chase the lead from well L-30 in the study area for further exploration-related works.