Results in Geophysical Sciences最新文献

Noise cancelation is the process done to remove out-of-range anomalies and make better edge boundaries interpretation. One of the most challenging issues in describing gravitational maps is separating the anomalies related to shallow sources from the deep ones. Furthermore, Existing noise can make it arduous to separate shallow blurred boundaries. In this study in SE Iran, gravitational surveying was carried out in shallow areas from the west of Qeshm to the Hormuz islands in a regular network with a distance of one kilometer. The range of gravitational Bouguer was -297 to -330 mGal. Modeling and determining geometrical parameters revealed five negative anomalies from salt penetration. The residual gravity was computed by deducting gravitational effects related to deep sources from measured gravitational data. Correspondingly, estimating the boundary and edge of the subsurface masses will be better than local filters, and anomalies will be highlighted with more intensity. Furthermore, three major fault systems in the Zagros basin were determined as the primary origin of activity and expansion of Hormuz salt. Sensitivity analysis was employed utilizing analytical signals and maps of tilt angle filtering, which both revealed the same satisfying results of -297 to -330 mGal. In this article, the effect of the tilt angle local phase filter on a synthetic model was accomplished through numerical coding. As a result, Total Horizontal Derivative (THDR) provides location of salt intrusion in Qeshm area; whereas the best image of salt intrusion, in terms of feature edge illumination, presented by Analytical signal of residual gravity map.

A recently proposed edge detection technique – Softsign Function (SF) filter was applied to a synthetic magnetic data to illustrate its application. It was then applied in combination with 3D Euler deconvolution and 2D magnetic modelling techniques to the low-latitude aeromagnetic data of Tafawa-Balewa Area, Northern Nigeria, aimed at subsurface geostructural mapping and tectonic analysis of the study area. This was corroborated with mapping and analysis of surface lineaments from Landsat-9 image of the study area. The SF filter depicted edges of magnetic sources from the synthetic magnetic and aeromagnetic data as distinct peaks. The 3D Euler deconvolution solutions and 2D magnetic model showed two dominant depth ranges ∼ 10 m to ∼ 400 m (D1) and ∼ 400 m to ∼ 1000 m (D2) of magnetic sources. The subsurface and surface lineaments from the aeromagnetic data and Landsat-9 image, respectively, fairly agreed in location, trends, even distribution, and density. The trends of mapped lineaments are majorly ENE – WSW direction, and the minor trends are WNW – ESE, NE – SW, NNW – SSE, NNE – SSW, and NW – SE directions. These linear structures, consistent with regional tectonics, are suspected to be strike-slip faults generated by the conjugate system of strike-slip NE – SW and NW – SE faults, including the Romanche and Chain fault systems, produced by the oceanic-continental transcurrent movements which affected the Nigerian basement complex. Explicitly, Softsign Function (SF) filter is a valuable edge detection technique in mapping geological structures from a real low-latitude aeromagnetic data reduced to the geomagnetic equator for tectonic analysis.

This paper describes research to characterize subsurface contamination caused by leaching of lead (Pb) from batteries disposed of at the surface, which has spread with groundwater movement. The contaminated soils and aquifer are located in the Matano formation (Sulawesi, Indonesia). Ground Penetrating Radar (GPR) was used to detect and delineate Pb-contaminated soils (i.e., solid-phase Pb). Lead in the solid and aqueous phase have different characteristics and responses when subjected to electromagnetic (EM) waves. Many studies have used GPR to map solid-phase Pb contamination in the subsurface. GPR uses EM as the base medium to receive subsurface images and is useful for the detection of solid-phase Pb contamination but cannot detect aqueous-phase Pb. The first step in the remediation process was to delineate solid-phase Pb contamination in the subsurface using GPR, which required a geotechnical survey to support GPR. Samples of soil and aquifer solids were then taken to quantify lead concentrations using X-ray fluorescence (XRF). We collected 15 lines of GPR measurements and 11 soil samples to quantify Pb. Frequencies of 600 MHz and 900 MHz were used for the GPR antenna. The results identified a clay layer at a depth of between 3 m and 4 m, which appears to have served as barrier to downward migration of Pb-contaminated groundwater. A shadow zone and low reflectance in the GPR subsurface section images were used to identify as the Pb contamination, which has a distinct wavelength ranging between 0.36 m and 0.45 m. We conclude from the results of this study that GPR was an effective tool for the delineation of the vertical and horizontal spread of Pb contamination eastward from the source.

Subsurface fluid flow involves migration of fluids from source to surface through a wide range of geologic structures, and thus plays a crucial role in unlocking potential hydrocarbon plays. Such studies have been mainly carried out in the marine environment by means of high-resolution seismic data in unravelling the fluid flow system and remains poorly documented for on-land data. This research attempts to explore the fluid flow activity in onshore petroliferous Indo-Gangetic peripheral foreland basin of India by using high-quality 3D seismic reflection data. Several seismic attributes have been utilised for efficiently describing the patterns of subsurface fluid flow structures. The attribute-responses of fluid flow are fused into a single attribute, called the Fluid Cube meta-attribute, by designing a workflow based on artificial neural network, which has enabled to elucidate the subsurface fluid migration routes. The subsurface fluid flow features are imaged as relatively vertical mounded structure with conical vent-like morphology. Internally, these features are associated with moderately distorted reflections. The reflections at the top are vertically stacked with medium to high amplitudes. The Fluid Cube meta-attribute demonstrates that subsurface fluid vertically migrates from the Neoproterozoic strata through minute fracture networks and weaker strata of the overlying Tertiary succession. The analysis of surficial geochemical anomalies corroborates quite reasonably with these observations. Thus, the Ganga peripheral foreland basin could be considered a promising area with potential leads that can be unlocked for hydrocarbon exploration. The analysis presented through this research could be efficiently carried out over other onshore basins worldwide.

Ground magnetic surveys were carried out in the northern region of the Kashmir basin, NW Himalaya to calculate the total magnetic intensities and subsurface constraints at the Balapur fault. The susceptibility index of -0.020 SI to 0.001SI was found associated with the strike of the Balapur fault. Further, the susceptibility index of the associated Gulmarg fault was recorded as -0.01SI to 0.001 SI. The present study implies that the Balapur fault has produced well-developed magnetic constraints throughout its strike. The 3D inversion modeling implies that the Balapur fault in north Kashmir has developed enough subsurface strain features and can lead to high earthquake intensity. Little or no variation was found between the observed and predicted databases and the analysis recorded an accuracy factor of 0.002 with 20 iterations. The study suggests that ground magnetic surveys are very useful in understanding the subsurface fault characteristics based on the Magnetization factor.

Seismic velocity is considered the best attribute related to formation pressure changes. Integrating seismic attributes and well-logging data through seismic inversion predicts the reservoir characteristics across the field with the highest accuracy. This study especially presents seismic velocity for the whole south Azadegan Field in SW Iran for carbonate formations. The considered dataset includes 3D seismic data, vertical seismic profiling (VSP), logging data of 23 wells, and geological information. Here, we estimated the interval velocity using post-stack migration velocity, seismic inversion, and the relationship between the acoustic impedance (AI) model and the sonic log to predict formation pressure. As a result, the correlation coefficient of 0.71 and a high inversion accuracy (8.76% relative error) is concluded. The actual and predicted P-wave (Vp) correlation coefficient is calculated as 0.74 and all sevens as 0.79 using an AI seismic attribute. Thus, the estimated Vp agrees with the original well-log values. Inverted AI cubes in the deeper formations of the field are about 8000-15000 [(m/s)*(g/cm³)], which could be referred to as calcareous formations. The correlation of the Vp cube resulting from the Sequential Gaussian simulation (SGS) considering co-kriging with the AI, with the initial velocity cube using the inverse distance weighted (IDW) method being 0.54 is more than the same method applied with interval migration velocity trend in co-kriging. The anisotropy of the final Vp cube for the vertical variogram range is 96m, and for major and minor directions is 11850 m.

The Makoure's newly discovered iron deposit belongs to Nyong group. It is yet to be documented. Detailled field mapping, petrographic study, and ground magnetic geophysical surveys were used to characterize Makouré iron prospect. The lithology of Makouré is made up of gneiss, amphibolite, micaschist, orthogneiss, quartzite, iron formations and duricruts. The Makouré’s iron formations is a typical Banded Iron Formation (BIF). The rock is highly magnetic, weakly metamorphosed, with well expressed centimetric dark bands of magnetite alternating with light bands of silica. Magnetites are subhedral coarse grained (0.5 to 1.5 mm), while silica crystal are the smallest (less than 0.5 mm). The foliation of the Banded Iron Formation avreagely strikes N065°E and dips 70° toward the SSE. The rock exposures experienced brittle deformation, the fractures are sub-vertical and perpendicular to the foliation, in some place they form chlorites/sulphides veins. The recorded magnetic values vary from 32,000 to 34,000 nT. The dipole values higher than 33,100 nT are related to iron formations. The magnetic susceptibility vary from 0.0001 to 0.05 m³/kg. The strongly magnetic body is open at depth and along strike. The ore body is steeply dipping towards the East and seems to be structurally controlled, mostly when getting close to the surface. Drilling results should also be integrated in the remodelling of magnetic susceptibility to put constraints on the model.

The Korek and Pirat mountains are two outstanding geomorphic features in the Iraqi Kurdistan Region (IKR), forming two anticlines. The two anticlines are separated by the Gulley Ali Beg stream. Both anticlines form right-hand en-echelon plunging as the Korek anticlines is concerned. The oldest exposed rocks in the core of both anticlines belong to the Lower Jurassic formations, whereas the Bekhme formation forms the bulk of both anticlines. The Korek anticline includes three domes and its southeastern plunge forms left-hand en-echelon plunge with the Ranya anticline. Whereas, the Pirat anticline includes two long domes with very faint indication. We have interpreted satellite images to indicate different geomorphological forms which are good indication for the lateral growth of the anticlines. Moreover, we have measured different geomorphological and structural aspects; accordingly, we have determined that both anticlines are Detachment Folds.

This research was administered to spatially predict the soil loss rate of the kaffa zone using a model estimate and GIS. Revised Universal Soil Loss Equation (RUSLE) adapted to Ethiopian conditions was accustomed estimate potential soil losses by utilizing information on rainfall erosivity (R) using interpolation of rainfall data, soil erodibility (K) using DSMW soil map, vegetation cover (C) using spot6 images, topography (LS) using Digital Elevation Model (DEM) and conservation practices (P) using DEM and satellite images. supported the analysis, the mean and total annual soil loss potential of the study area was 30 tons ha-1 year-1 and 36,264.5tons ha-1 year-1, respectively. The results also showed that about 2.89, 8.02, 15.31 and 73.78% of the study area were classified as slight, moderate, high, and very high with values ranging from 0 to 15,15 to50,50 to 200, and >200 tons ha-1 year-1, respectively. The study demonstrates that the RUSLE using GIS and RS provides a great advantage to spatially analyzing multi-layer of knowledge. The expected amount of soil loss and its spatial distribution could facilitate sustainable land use and management.

A robust evaluation of the casing-cement sheath-rock formation system is foundational in ensuring wellbore integrity throughout a well's lifecycle. Analytical theory for a multi-layer, thick-walled cylinder is used to evaluate the aggregate stress distributions within the casing-cement sheath-rock formation system, honoring boundary conditions of radial stress and displacement continuity. These stress distributions are adjusted for scenarios that a well may experience in its lifetime. Each layer of the casing-cement sheath-rock formation system is evaluated separately against various possible mechanical failure mechanisms, all of which can compromise wellbore integrity.

A blowout scenario after a mismanaged loss-of-well-control situation induces high stress loads in the casing-cement sheath-rock formation system, with the wellbore pressure rapidly decreasing during post-blowout discharge, followed by a rapid increase following successful well capping. Casing and cement sheath failures can expose the surrounding rock formation to the pressurized fluid inside the wellbore, risking hydrocarbons broaching the surface, or the seafloor. The aggregate stress distribution model is applied on a case study performed using parameters from the MC 252–1 “Macondo Well” blowout from April 20, 2010 in the deepwater Gulf of Mexico. The stress evolution suggests stability against mechanical failure mechanisms within the casing (collapse/burst and tensile/compressive), cement-sheath (inner or outer debonding, and shear cracking), and rock-formation layers (longitudinal or transverse tensile fracture initiation, along with shear-slippage along pre-existing faults in the near-well vicinity), throughout the blowout aftermath. Nevertheless, tendencies towards radial cracking and disking (tensile) failures were indicated for the cement-sheath layer as the system reaches radial stress and displacement continuity, after cement setting.