High-resolution Geophysical Methods Research Articles

Prediction of lamina structure and reservoir quality in shale using well logs: The Cretaceous Qingshankou Formation, Gulong Sag, Songliao Basin, China

Lamina structure is determined by composition, thickness, continuity, and mineral assemblage. Reservoir quality in oil shale reservoirs is determined by lamina structure, which controls hydrocarbon accumulation and migration. The prediction and evaluation of multi-scale lamina structures using geophysical well logs is challenging. Recent studies demonstrate that the lamina structure classification may be based on core observation and core analysis. However, there are no corresponding high-resolution geophysical logging methods to identify and categorize lamina structure continuously in a single well. Here, an experimental approach, involving an integrated analysis of cores, thin sections, well logs such as slabs and button conductivity curves of image logs (up to 5 mm vertical resolution), is used to characterize lamina structure. T1-T2 (T1, longitudinal relaxation time, and T2, transverse relaxation time) maps of nuclear magnetic resonance (NMR) logs are applied to clarify the relationships between the lamina structure, reservoir quality, and oil-bearing properties. Results demonstrate how lamina structure in shale can be divided into three types: laminated rocks, layered rocks, and massive rocks, according to observation of core at the lamina scale. The thickness of individual lamina is less than 0.01 m in the laminated rocks, and the layered rocks have bundles of genetically related laminae thickness ranging between 0.01 m and 0.1 m. In massive rocks there is no visible layering. The well log response patterns of the three types of lamina structure are established so that the distribution of lamina structure can be predicted in a single well via well logs. Results show that the oil-bearing shale intervals are dominated by laminated rocks and layered rocks, accounting for 90% of the studied Qingshankou Formation. In addition, the layered rocks play an important role in improving reservoir quality and the laminated rocks present moderate reservoir quality. The massive rocks show poor reservoir quality. Moreover, an increased proportion of felsic mineral content favors increased oil potential in oil shale reservoirs. The method is generally applicable and is of value in developing predictive indicators of subsurface reservoir sweet spots in shale oil and gas exploration and development.

Prediction of Soil Water Content and Electrical Conductivity Using Random Forest Methods with UAV Multispectral and Ground-Coupled Geophysical Data

The volumetric water content (VWC) of soil is a critical parameter in agriculture, as VWC strongly influences crop yield, provides nutrients to plants, and maintains the microbes that are needed for the biological health of the soil. Measuring VWC is difficult, as it is spatially and temporally heterogeneous, and most agricultural producers use point measurements that cannot fully capture this parameter. Electrical conductivity (EC) is another soil parameter that is useful in agriculture, since it can be used to indicate soil salinity, soil texture, and plant nutrient availability. Soil EC is also very heterogeneous; measuring EC using conventional soil sampling techniques is very time consuming and often fails to capture the variability in EC at a site. In contrast to the point-based methods used to measure VWC and EC, multispectral data acquired with unmanned aerial vehicles (UAV) can cover large areas with high resolution. In agriculture, multispectral data are often used to calculate vegetation indices (VIs). In this research UAV-acquired VIs and raw multispectral data were used to predict soil VWC and EC. High-resolution geophysical methods were used to acquire more than 41,000 measurements of VWC and 8000 measurements of EC in 18 traverses across a field that contained 56 experimental plots. The plots varied by crop type (corn, soybeans, and alfalfa) and drainage (no drainage, moderate drainage, high drainage). Machine learning was performed using the random forest method to predict VWC and EC using VIs and multispectral data. Prediction accuracy was determined for several scenarios that assumed different levels of knowledge about crop type or drainage. Results showed that multispectral data improved prediction of VWC and EC, and the best predictions occurred when both the crop type and degree of drainage were known, but drainage was a more important input than crop type. Predictions were most accurate in drier soil, which may be due to the lower overall variability of VWC and EC under these conditions. An analysis of which multispectral data were most important showed that NDRE, VARI, and blue band data improved predictions the most. The final conclusions of this study are that inexpensive UAV-based multispectral data can be used to improve estimation of heterogenous soil properties, such as VWC and EC in active agricultural fields. In this study, the best estimates of these properties were obtained when the agriculture parameters in a field were fairly homogeneous (one crop type and the same type of drainage throughout the field), although improvements were observed even when these conditions were not met. The multispectral data that were most useful for prediction were those that penetrated deeper into the soil canopy or were sensitive to bare soil.

ESPAC-based 2D mini-array microtremor method and its application in urban rail transit construction planning

Conventional geophysical methods face many challenges in urban areas from limited site accessibility to severe industrial interferences. With the fast-paced development in urban area and urban light rail transit system, it is highly desirable to have a high-resolution geophysical method, which is suitable for the complex urban condition with strong background noises and, at the same time, is environment-friendly.In this paper, we introduce a 2D mini-array microtremor survey method, based on the extended spatial auto-correlation (ESPAC) method. It first uses the ESPAC to extract the dispersion curve of the Rayleigh wave from the microtremor data recorded using the mini array, then reconstructs the apparent S-wave velocity (Vx) structure of the stratigraphic rock formations by the Vr–Vx transformation, and finally, the 2D Vx profile is obtained by using Vx velocity imaging. This method not only makes full use of the multi-mode Rayleigh waves of dispersion curve, but also reduces the uncertainty during inversion caused by the potential pattern misjudgment when inverting the dispersion curve directly. Since the Vx is generally sensitive to the change of rock mass density, its profile is a natural and reliable reflection of the changes in rock properties. This technique provides an accurate and cost-effective tool for mapping complex near-surface geological anomalies such as karst cavities, fractured zone, and the soil/bedrock interface, which are frequently encountered in many urban engineering projects, such as urban rail transit development. The successful application of the microtremor survey in Guangzhou Metro Line 10 project demonstrates that this method can be very effective in identifying the soil/bedrock interface, mapping the severely weathered rock formations, and detecting the abandoned underground structures.

The impact of a tear in the subducted Indian plate on the Miocene geology of the Himalayan-Tibetan orogen

Abstract The Yadong-Gulu Rift, cutting across the Gangdese belt and Himalayan terranes, is currently associated with a thermal anomaly in the mantle and crustal melting at 15–20 km depth. The rift follows the trace of a tear in the underthrusted Indian continental lithospheric slab recognized by high resolution geophysical methods. The Miocene evolution of a 400-km-wide band following the trace of the tear and the rift, records differences interpreted as indicative of a higher heat flow than its surroundings. In the Gangdese belt, this band is characterized by high-Sr/Y granitic magmatism that lasted 5 m.y. longer than elsewhere and by the highest values of εHf(i) and association with the largest porphyry Cu-Mo deposits in the Gangdese belt. Anomalously young magmatic rocks continue south along the rift in the Tethyan and Higher Himalayas. Here, a 300-km-wide belt includes some of the youngest Miocene Himalayan leucogranites; the only occurrence of mantle-derived mafic enclaves in a leucogranite; young mantle-derived lamprophyre dikes; and the youngest and hottest migmatites in the Higher Himalayas. These migmatites record a history of rapid exhumation contemporaneous with the exhumation of Miocene mafic eclogite blocks, which are unique to this region and which were both heated to >800 °C at ca. 15–13 Ma, followed by isothermal decompression. We suggest that the prominent tear in the Indian lithosphere, sub-parallel to the rift, is the most likely source for these tectono-thermal anomalies since the Miocene.

Detection of road cavities in urban cities by 3D ground-penetrating radar

Cavities under urban roads have increasingly become a great threat to traffic safety in many cities. As a quick, effective, and high-resolution geophysical method, ground-penetrating radar (GPR) has been widely used to detect and image near-surface objects. However, the interpretation of field GPR data remains challenging. For example, it is hard to distinguish reflections caused by road cavities or other urban utilities with a conventional 2D GPR survey. The superiority of 3D GPR in data interpretation is demonstrated by a laboratory experiment. Two pipes and a glass-made cavity buried in a sandpit show similar hyperbolic reflections in the 2D GPR profiles; thus, they are difficult to discriminate. In contrast, their geometric shapes and dimensions are readily identified in the 3D image reconstructed from the synthetic 3D GPR data set. Based on these ideas, we have developed a car-mounted 3D GPR system with two antenna arrays oriented in different polarization directions and have detected more than 100 cavities in three Chinese cities over the past year. The field data of two such cavities are presented. As a result, the cavity depth, horizontal size, and height can be accurately estimated from the 3D GPR data set. Laboratory and field experimental results indicate that 3D GPR possesses potential in the detection and recognition of road cavities and utilities in the complex urban environment.

Geomorphology of Canyon Outlets in Zrmanja River Estuary and Its Effect on the Holocene Flooding of Semi-enclosed Basins (the Novigrad and Karin Seas, Eastern Adriatic)

Detailed multi-beam bathymetry, sub-bottom acoustic, and side-scan sonar observations of submerged canyons with tufa barriers were used to characterize the Zrmanja River karst estuary on the eastern Adriatic coast, Croatia. This unique karst environment consists of two submerged karst basins (Novigrad Sea and Karin Sea) that are connected with river canyons named Novsko Ždrilo and Karinsko Ždrilo. The combined use of high-resolution geophysical data with legacy topography and bathymetry data in a GIS environment allowed for the description and interpretation of this geomorphological setting in relation to the Holocene sea-level rise. The tufa barriers had a predominant influence on the Holocene flooding dynamics of the canyons and karst basins. Here, we describe the possible river pathways from the basins during the lowstand and the formation of a lengthening estuary during the Holocene sea-level rise. Based on the analyzed morphologies and the relative sea-level curve for the Adriatic Sea, the flooding of the Novsko Ždrilo occurred 9200 years before present (BP) and Karinsko Ždrilo was flooded after 8400 years BP. The combination of high-resolution geophysical methods gave an accurate representation of the karst estuarine seafloor and the flooding of semi-isolated basins due to sea-level rise.

Detection of mineralogically accentuated biogenic structures with high-resolution geophysics: implications for ichnology and geoecology

Identification and mapping of small-scale physical and biogenic structures in sand has been a challenge to sedimentologists and ichnologists. Under natural conditions, biogenic activity (trampling tracks, burrows) alter primary sedimentary structures, but also serve as important paleoenvironmental indicators of geotechnical properties of sediments, omission surfaces, and ecosystem dynamics. Therefore, the ability to recognize such structures as anomalies in shallow subsurface, especially when using indirect non-invasive methods, such as geophysical imaging, is an important aspect of assessing their relative contribution to the overall erosional-depositional record. This study presents experimental evidence of the viability of two highresolution geophysical methods in detecting sediment deformation that mimics shallow animal traces. High-frequency (800 MHz) ground-penetrating radar (GPR) imaging aided in visualizing a buried depression produced by a deer hoofprint cast indenter, with high-amplitude reflection return enhanced by a heavy-mineral concentration (HMC). Bulk in situ low-frequency (930 Hz), low-field magnetic susceptibility (MS) experiment supported the theoretical pattern of a decrease in MS over the thickest cover sand (maximum indentation depth) to ~0 mSI and the highest values over raised HMC horizon (marginal ridge; >8 mSI). Because both methods are affected by the presence and relative abundance of heavy minerals, the present approach can be applied in most siliciclastic settings. This study demonstrates the promise of extending the 2D visualization of subsurface targets to 3D datasets, with potential implications for sedimentological, ichnological, archaeological, and geoecological research that involves animal-sediment interaction at different scales.

Studying the Construction of Floor Mosaics in the Roman Villa of Pisões (Portugal) Using Noninvasive Methods: High-Resolution 3D GPR and Photogrammetry

Over the past decade, high-resolution noninvasive sensors have been widely used in explorations of the first few meters underground at archaeological sites. However, remote sensing actions aimed at the study of structural elements that require a very high resolution are rare. In this study, layer characterization of the floor mosaic substrate of the Pisões Roman archaeological site was carried out. This work was performed with two noninvasive techniques: 3D ground penetrating radar (3D GPR) operating with a 1.6 GHz central frequency antenna, which is a very high-resolution geophysical method, and photogrammetry with imagery obtained by an unmanned aerial vehicle (UAV), which is a very high-resolution optical method. The first method allows penetration up to 30–40 cm depth and 3D models can be obtained, and with the second method, very high detail surface images and digital surface models can be obtained. In this study, we analyze a combination of data from both sensors to study a portion of the floor mosaic of the Pisões Roman Villa (Beja, Portugal) to obtain evidence of the inner structure. In this context, we have detected the main structural levels of the Roman mosaic and some internal characteristics, such as etched guides, internal cracking, and detection of higher humidity areas. The methodology that we introduce in this work can be referenced for the documentation of ancient pavements and may be used prior to carrying out preservation activities. Additionally, we intend to show that a Roman mosaic, understood as an archaeological structure, does not consist of only beautiful superficial drawings defined by the tesserae, but these mosaics are much more complex elements that must be considered in their entirety for preservation.

A rock physics modelling algorithm for simulating the elastic parameters of shale using well logging data

As a high-resolution geophysical method employed by the oil and gas industry, well logging can be used to accurately investigate reservoirs. Challenges associated with shale gas reservoir exploration increase the importance of applying elastic parameters or velocity at the logging scale. An efficient shale rock physics model is the foundation for the successful application of this method. We propose a procedure for modelling shale rock physics in which an appropriate modelling method is applied for different compositions of shale rock. The stiffnesses of the kerogen and fluid (oil, gas or water) mixture are obtained with the Kuster-Toksöz model, which assumes that the fluid is included in the kerogen matrix. A self-consistent approximation method is used to model clay, where the clay pores are filled with formation water. The Backus averaging model is then used to simulate the influence of laminated clay and laminated kerogen. Elastic parameter simulations using well logging data show the importance of treating the volume fractions of laminated clay and kerogen carefully. A comparison of the measured compressional slowness and modelled compressional slowness shows the efficiency of the proposed modelling procedure.

Investigation Geological structural morphology of Quaternary sediment on coastal Bac Lieu

Georadar is a high-resolution near-surface geophysical method which employ radio waves, typically in the 1 to 1000 MHz frequency range tomap structure and features buried in the ground (or in man-made structures). Georadar method with Pulse EKKO 1 OOA instrument offers the highest resolution and rapidly provides continuous graphicformat which permits rapid semi-quantitative interpretation for in-field analysis. VLF method with Wadi instrument records the ratio of the strengths of the vertical and horizontal fields at the ground surface. Then this method can be used to reveal steeply dipping structures with large cross-sections and low resistivities as fructure/ conductivity zones.This paper is presented the result of using Georadar, VLF and electrical profiling methods for geological structural morphology of quaternarysediment investigation on coastal Baclieu. The structural cross-section of morphology of quaternary sediment is established by nine layers of georadar data for shallow structure and several interfaces of conductivity for deeper structure.

Spatially Averaged, Flow‐Weighted Concentrations – A More Relevant Regulatory Metric for Groundwater Cleanup

Spatially Averaged, Flow‐Weighted Concentrations – A More Relevant Regulatory Metric for Groundwater Cleanup

Hydrogeophysical exploration for estimating groundwater reservoirs areas in Southern Rhodes through ERT (Electrical Resistivity Tomography) method.

The present study deals with the groundwater investigation of hydrogeological conditions of Southern Rhodes, in the search for additional groundwater supplies to support the water needs of the area. An extensive Hydrogeological – Geophysical research was conducted, aimed to identify exploitable groundwater zones. Thisgeophysical survey was carried out along alluvial basins, looking for more permeable geological formations within the sequence of the Neogene and Quarternary deposits. The use of a high resolution geophysical method (ERT) was selected for targeting the shallow geological structures and hydrostratigraphy. Thirteen ERT sections of total length of approximately 34000m were measured, laid out primarily at the south eastern part of the island. The geophysical survey revealed that alluvial sediments have an average thickness of about 30m while nearby the coastal zone increase locally up to 50m. The hydrostratigraphical structure is characterized by three distinct sections, the overlying alluvial deposits, the intermediate clay-marls and the underlying coarse formations. Moreover, almost all fault zones which are reflected in the surface geological map are revealed ingreater depths. Result of vertical tectonic movements is the uplift of geological formations with increased resistivity. Finally, the target areas were selected based on hydrogeological criteria and specifically taking into account the increased possibility of groundwater reservoirs within the alluvial aquifer.

Forward Modelling and Detection of Gpr in Urban Road Base Disease

Ground penetrating radar is a high-resolution engineering geophysical method which has better detection effect to disengaging, cavities and leakiness in urban road base. This paper is based on the principle of ray tracing through the forward modelling of urban road base hollow, empty and not dense disease, analyses waveform, frequency, wave propagation characteristics of primary disease forward image simulation. The paper summarizes the urban road base diseases in ground penetrating radar profile feature of signal, and analyses field exploration radar profile and further research on primary diseases of urban road ground penetrating radar fingerprint for urban road base disease detection of ground penetrating radar data interpretation to provide the reference.

Image-guided inversion of electrical resistivity data

Electrical resistivity tomography (ERT) is based on solving a Poisson equation for the electrical potential and is characterized by a good sensitivity only in the vicinity of the electrodes used to gather the data. To provide more information to ERT, we propose an image-guided or structure-constrained inversion of the apparent resistivity data. This approach uses structural information obtained directly from a guiding image. This guiding image can be drawn from a high resolution geophysical method based on the propagation equation (e.g. migrated seismic or ground penetrating radar images) or possibly from a geological cross-section of the subsurface based on some prior geological expertise. The locations and orientations of the structural features can be extracted by image processing methods to determine the structure tensor and the semblances of the guiding image at a set of pixel. Then, we introduce these structural constraints into the inversion of the apparent resistivity data by weighting the four-direction smoothing matrix to smooth along, but not across, structural features. This approach allows preserving both discontinuities and coherences in the inversion of the resistivity data. The image-guided inversion is also combined with an image-guided interpolation approach used to focus a smooth resistivity image. This yields structurally-appealing resistivity tomograms, while the whole process remains computationally efficient. Such a procedure generates a more realistic resistivity distribution (closer to the true ones), which can be, in turn, used quantitatively using appropriate petrophysical transforms, to obtain parameters of interest such as porosity and saturation. We check the validity of this approach using two synthetic case studies as well as two real datasets. For the field data, the image used to guide the inversion of the electrical resistivity data is a GPR section in the first case and a combination of seismic and structural information in the second case, which corresponds to a geothermal site at Pagosa Springs, in Colorado.

Karst cavity detection in carbonate rocks by integration of high resolution geophysical methods

Combined surveys using Ground Penetrating Radar (GPR) and Electrical Resistivity
 Tomography (ERT) are deployed to provide a cost effective characterization of the
 subsurface karst environments. A total of 12 GPR traverses and 4 ERT lines with lengths
 from 140 to 710 m are conducted at Sulaimani governorate, NE Iraq (45o 04' E and 35o 35'
 N). The area represents a broad syncline of limestone rocks, which is covered by a thin
 layer of recent sediments. Great anomaly depicting crest (high) like pattern was noticed on
 GPR records. A plausible interpretation for this anomaly was a cavity filled either by
 groundwater or by residual products of karstification. The presence of this cavity was
 confirmed also by electrical resistivity tomography. An excellent correlation exists
 between GPR signatures and ERT layers. The extension and the depth to the top of the
 cavity were determined from both GPR data and 2D inversion interpretation. A huge cave
 was discovered. It is located at depth of 25.0 meters. It has an elongated shape that extends
 from southeast to northwest direction. The geophysical survey results show this cave with
 approximate dimensions of 150.0 m long, 35.0 m wide and 24.0 m high.

Interdisciplinary characterization of subsurface hydrocarbon contamination on a test site in Hungary

Pesticides, chlorinated organic compounds and hydrocarbons are among the most threatening soil and groundwater contaminants because of their mobility and persistence in the subsurface, their widespread use, and their health effects. Hazardous chemicals getting into underground medium can be especially dangerous because they may remain persistently hidden from human eyes for a long time and their harmful impact on health may appear much later than their emission time and spatially far from the source of contamination. Development and combination of reliable and accurate geophysical methods and hydrogeological transport models with the traditional chemical analytics are greatly needed to assess the risk posed by the contamination plumes of these compounds to the subsurface. The paper presents the successful cooperation of these three disciplines in detailed characterization of subsurface hydrocarbon contaminants in a test site of Hungary. Combining the chemical analysis with high resolution geophysical methods and hydrogeological transport modeling the 4 dimensional characteristics of the contamination can be produced. The interdisciplinary research produced new developments and results in all participating fields of sciences.

Application of high-resolution geophysical methods in submarine pipeline inspection

High-resolution marine geophysical equipment employed includes single beam echo sounder (SBES), multi-beam echo sounder (MBES), sub-bottom profiler (SBP) and side scan sonar (SSS). By employing SBES, the reflection curve in shallow water reveals the real condition of pipeline; while in deep water, the reflection or diffraction curve can’t reveal the real condition. Compared with SBES, MBES is characterised by intuition, efficiency and high resolution. But the same as SBES, the beam angle affects its detecting ability seriously. As for the SBP, system employing Chirp technology can detect the buried conditions of pipelines. Ship speed and water depth can affect the detection. The SSS can detect the plane position, exposed height, spanning state and pipeline trench, but buried pipelines. In order to understand the whole in-situ conditions of submarine pipeline, multiple geophysical methods should be employed.

Exploration of Tunnel Alignment using Geophysical Methods to Increase Safety for Planning and Minimizing Risk

Engineering geophysics provides valuable and continuous information for the planning and execution of tunnel construction projects. For geotechnical purposes special high-resolution geophysical methods have been developed during the last decades. The importance of applying geophysical methods in addition to usually used geological and geotechnical exploration techniques is increasing. The main goal is to achieve an accurate and continuous model of the subsurface in a relative short period of operation time. The routine application of engineering geophysical methods will increase in the coming years. Due to the high acceptance of engineering geophysics at construction sites, much wider application of geophysical investigations is expected. The combination of different methods—geophysics, geology, and geotechnics as well as the so-called joint interpretation techniques—will be of essential importance. Engineering geophysics will play an important role during the three phases: geological investigation, tunnel planning, and execution of tunnel construction. If hazards are well known in advance of a tunnel project the safety of workers will essentially be increased and geological risks will be minimized by means of successful and interdisciplinary cooperation.

The Portland Hills Fault: uncovering a hidden fault in Portland, Oregon using high-resolution geophysical methods

The Portland metropolitan area historically is the most seismically active region in Oregon. At least three potentially active faults are located in the immediate vicinity of downtown Portland, with the Portland Hills Fault (PHF) extending directly beneath downtown Portland. The faults are poorly understood, and the surface geologic record does not provide the information required to assess the seismic hazards associated with them. The limited geologic information stems from a surface topography that has not maintained a cumulative geologic record of faulting, in part, due to rapid erosion and deposition from late Pleistocene catastrophic flood events and a possible strike-slip component of the faults. We integrated multiple high-resolution geophysical techniques, including seismic reflection, ground penetrating radar (GPR), and magnetic methods, with regional geological and geophysical surveys to determine that the Portland Hills Fault is presently active with a zone of deformation that extends at least 400 m. The style of deformation is consistent with at least two major earthquakes in the last 12–15 ka, as confirmed by a sidehill excavation trench. High-resolution geophysical methods provide detailed images of the upper 100 m across the active fault zone. The geophysical images are critical to characterizing the structural style within the zone of deformation, and when integrated with a paleoseismic trench, can accurately record the seismic history of a region with little surface geologic exposure.

Selected radar images of man-made underground galleries

Ground-penetrating radar (GPR), as a high-resolution geophysical prospecting method, has proved to be a very useful tool in archaeological site investigations, especially in the detection and identification of tunnels and galleries. This work shows seven selected profiles collected at four different archaeological sites in Spain and Mexico, with a wide variety of targets, not only in terms of their size (from 1 × 1 m to 3 × 4 m) but also in their depth (from 0.5 to 7 m). In all, 14 galleries and/or tunnels were detected. The approach to these studies was organized in two ways: firstly the presence of a known subsoil was used to compare the response of different antennae looking for these kinds of targets; secondly, GPR was used to find unknown historical galleries before any excavation took place. The equipment used in these studies were the SIR-8, with 120 and 500 MHz monostatic antennae, and PulseEkko IV, with 100 MHz bistatic antennae. Copyright © 2002 John Wiley & Sons, Ltd.