Acta Geophysica最新文献

Talcher Coalfield is one of the most important coalfields considering thermal grade coal reserves in India; nevertheless, hardly any published geophysical study is available for mapping the subsurface coal, in-crop zone, fault location, formation boundary, etc. In the present study, a combined analysis of electrical resistivity tomography (ERT) in five profiles and high-resolution shallow seismic (HRSS) survey in two profiles was carried out in Goribandh at the northern–eastern part of the Talcher Coalfield, Odisha, India, to study the structural control of coal seams and to delineate the coal potential zone and non-coal zone. Geological core data from three boreholes were utilized to validate the ERT and HRSS results. Three ERT profiles (ERT_P1, ERT_P2, and ERT_P3) data were acquired in perpendicular to the strike direction, and two ERT profiles (ERT_P4 and ERT_P5) data were collected in the strike direction. The purpose of the acquisition of ERT data in the strike direction is to correlate the resistivity values at the cross point of dip lines and strike lines. Two HRSS profiles (HRSS_P1 and HRSS_P2) data were collected along the same two corresponding dip lines of the ERT profiles (ERT_P1 and ERT_P2). The ERT data were collected using Wenner–Schlumberger array at 10 m electrode spacing with multiple roll-along sequences to cover the desired profile length with an approximate profile line spacing of 200 m. The Res2Dinv program was used to execute the inversion of the combined data set. The HRSS data were acquired by ‘End-on-Shooting’ method using 24-fold common depth point survey at 4 m geophone spacing with multiple roll-along sequences to cover the desired profile length with approximate profile line spacing of 200 m, where near trace and far offsets trace were 88 and 276 m, respectively. HRSS data were analyzed using Paradigm 19 seismic processing software. Comprehensive analysis of five numbers of 2D ERT sections (ERT_P1-ERT_P5) and two numbers of HRSS sections (HRSS_P1 and HRSS_P2) indicates that the southern part of the study area is characterized by relatively low to moderate high resistivity (100–500 Ωm) distribution while seismic sections demonstrate multiple strong reflecting horizons, due to carbonaceous beds as identified in the boreholes, indicating Barakar formation. The northern part is characterized by high resistivity (200–1000 Ωm) distribution, while seismic sections exhibit multiple distributed minor reflectors due to boulder beds and or compact sandstone. The combined study of ERT and HRSS data delineates a prominent fault zone F4, indicating a contact boundary between the Talchir and Barakar formations.

The Axios-Thermaikos basin in northern Greece is a sedimentary composite depocenter that developed tectonically during the Neogene. It has been considered promising for hydrocarbon resources, with a proven offshore gas field. Several geological and geophysical surveys, including drilling, were conducted in previous decades. However, a complete model of the basin subsurface has yet to be constructed. This paper seeks to understand the hydrocarbon prospectivity of the onshore Axios-Thermaikos basin by analyzing various geophysical (gravity, magnetic, seismic reflection) data and integrating the geophysical model with other available data. Our approach started with a qualitative analysis of the gravity and magnetic data to extract the structural and lithological trends controlling the basin formation and development. Magnetic data were further used to map the interface between the sedimentary pile and the basement. Seismic data were interpreted using different attributes and mapped in detail the geologic contacts and the tectonic regime of the basin. The density variations in depth were investigated using two-dimensional forward modeling constrained by seismic data. As a result, the 2D gravity model displays the interfaces between the formations and the main seismic-scale faults. Based on the seismic and stratigraphic data from wells, preliminary three-dimensional models were built showing the stratigraphic and tectonic regimes, including the presence of structural hydrocarbon traps, and the different depositional environments that have acted in the basin through time. The mapped tectonic structures in the onshore Axios-Thermaikos basin might also be useful for other activities of economic importance, such as gas storage and CO₂ sequestration.

Various types of 3D sub-bottom profilers (SBPs) have been developed to widen the swath coverage of conventional single-channel SBPs. Nevertheless, the data acquisition process is frequently influenced by fluctuations in water depth, attributed to swells and tidal variations. These fluctuations, particularly pronounced during 3D sub-bottom profiling when source frequency bands reach several kHz, significantly distort the two-way travel time of seismic reflections, potentially hindering the generation of high-fidelity seismic cubes. In this study, high-precision 3D coordinates of each source and receiver channel were recorded in real-time during data acquisition and employed for pre-stack Kirchhoff depth migration to produce a static corrected seismic cube. To streamline the acquisition of positioning data for the survey system operating in coastal areas, broadcast real-time kinematics (RTK) was integrated to receive RTK correction signals via broadcast radio waves, facilitating a real-time method for generating 3D coordinates for each source and receiver channel. Additionally, a Kirchhoff migration algorithm was devised to efficiently generate the static corrected seismic cube using the 3D coordinates of the source and receiver. Field data were collected in waters near Jindo, South Korea, where tidal differences reached 4 m, resulting in the production of an ultrahigh-frequency seismic cube with a 50 cm bin size. The robustness and applicability of the automated static correction method were validated through analysis of the seismic cube.