Subsurface Distribution Research Articles

Complex Vulnerabilities of the Water and Aquatic Carbon Cycles to Permafrost Thaw

The spatial distribution and depth of permafrost are changing in response to warming and landscape disturbance across northern Arctic and boreal regions. This alters the infiltration, flow, surface and subsurface distribution, and hydrologic connectivity of inland waters. Such changes in the water cycle consequently alter the source, transport, and biogeochemical cycling of aquatic carbon (C), its role in the production and emission of greenhouse gases, and C delivery to inland waters and the Arctic Ocean. Responses to permafrost thaw across heterogeneous boreal landscapes will be neither spatially uniform nor synchronous, thus giving rise to expressions of low to medium confidence in predicting hydrologic and aquatic C response despite very high confidence in projections of widespread near-surface permafrost disappearance as described in the 2019 Intergovernmental Panel on Climate Change Special Report on the Ocean and Cryosphere in a Changing Climate: Polar Regions. Here, we describe the state of the science regarding mechanisms and factors that influence aquatic C and hydrologic responses to permafrost thaw. Through synthesis of recent topical field and modeling studies and evaluation of influential landscape characteristics, we present a framework for assessing vulnerabilities of northern permafrost landscapes to specific modes of thaw affecting local to regional hydrology and aquatic C biogeochemistry and transport. Lastly, we discuss scaling challenges relevant to model prediction of these impacts in heterogeneous permafrost landscapes.

A hybrid PCG-bat algorithm for 2D gravity inversion: Applications for ore deposits exploration and interpretation of sedimentary basins

Potential field data plays a vital role in geophysical exploration especially for mineral and hydrocarbons. Inversion of such static fields, like gravity and magnetic is a proper approach to delineate the subsurface distribution of the physical property. In ore deposits prospection, studying the subsurface distributions of densities is of critical importance. A proper strategy is to subdivide the subsurface 2D model space into rectangular mesh of prisms of different densities. The problem is highly ill-posed. To solve for the unknown densities, a new hybrid scheme, using Bat algorithm (BA) with the preconditioned conjugate gradient (PCG) technique, has been applied. The scheme benefits from the advantages of both techniques. The bat algorithm acts as a rapid build-up of the model, while PCG adapts the approximated subsurface model. The new approach is applied to a free-noise synthetic data and then to data with different levels and kinds of noise. Moreover, the technique is compared with other inversion methods (stochastic and deterministic ones) to test the efficiency and efficacy. Satisfying results are achieved through the new scheme. However, the sensitivity of the problem has been studied and presented for more understanding and testing for the inverted model. The applicability and validity of this algorithm are further verified by applying it to real residual gravity anomalies in southern California, USA, and Mexico-USA border. Also, two successful applications are done, for mineral prospection in China. Results are in good agreement with those obtained by published literature.

Does the Liaoji granite represent basement in the Jiao–Liao–Ji Belt?

Lack of knowledge of the basement structure of the Paleoproterozoic Jiao–Liao–Ji Belt (JLJB) of the North China Craton has hindered understanding of the tectonic evolution of the belt and, to an extent, the entire craton. Previous studies of the JLJB were based mostly on petrological, structural, and geochemical analyses, resulting in a lack of understanding of the deep geological structure of the belt. In this study, we used a combination of geophysical and geological methods to interpret the deep geological structure of the JLJB on the basis of high-precision non-seismic geophysical data. We collected high-precision gravity, magnetic, and magnetotelluric sounding data. We also compiled data on rock physical parameters for important geological bodies, and obtained high-precision Bouguer gravity anomaly data from the China Geological Survey. We interpreted these data to visualize the subsurface distributions of geological bodies (including sedimentary and metamorphic units and intrusive rocks) in the Kuandian–Huairen area of the JLJB. We found that the Liaoji granites are developed on a large scale in the deep part of the JLJB, showing a weak gravity anomaly (−25 to −6 mGal) and high resistivity (103.5 to 106 Ω·m). These granites may have intruded along a series of normal faults at the time of the initial formation of the belt, and expanded over time. Subsequently, the low-resistivity Liaohe Group (10 to 102.5 Ω·m) was deposited on the Liaoji granite across a sedimentary contact. Therefore, the Liaoji granite forms the basement of the JLJB. The presence of extensional faults in the deep part of the JLJB suggests that the belt was also subjected to tectonic extension. The Yuejiadian–Xiaohuanggou fault to the east of Kuandian may be the boundary between the South Liaohe Group and the North Liaohe Group. The South Liaohe Group is relatively thin and tightly folded, whereas the North Liaohe Group is thicker and characterized by relatively open folds.

Numerical simulation and modeling of a poroelastic media for detection and discrimination of geo-fluids using finite difference method

Seismic numerical modeling technique provide most suitable way for the simulation of wave propagation through subsurface rocks and play an essential role in seismic interpretation, seismic inversion and in evaluating and designing a seismic survey. In order to delineate subsurface more precisely, different approaches are proposed for numerical modeling in which the solutions of Biot’s poroelastic equation are given by using reflectivity, finite element and finite difference algorithms. In current study, a finite difference forward modeling method is proposed to quantify the variation in wave properties during its propagation in a poroelastic media exhibiting mesoscopic heterogeneity due to the existence of three phase fluids. The Biot’s poroelastic wave equations are resolved and a generalized finite difference technique in time domain (FDTD) is used to examine seismic responses in a poroelastic media saturated with three phase fluids. So that the ability to detect geo-fluids through forward modeling technique can be improved. The accuracy of the simulation will lay a good foundation for the follow up work and will enhance our understandings about wave propagation through multi-phase poroelastic media and will also assist in detection and discrimination between fluids of different nature. Also, the proposed approach is of great significance for imaging and prediction of subsurface structures and distribution of fluids.

Can assimilation of satellite observations improve subsurface biological properties in a numerical model? A case study for the Gulf of Mexico

Abstract. Given current threats to ocean ecosystem health, there is a growing demand for accurate biogeochemical hindcasts, nowcasts, and predictions. Provision of such products requires data assimilation, i.e., a comprehensive strategy for incorporating observations into biogeochemical models, but current data streams of biogeochemical observations are generally considered insufficient for the operational provision of such products. This study investigates to what degree the assimilation of satellite observations in combination with a priori model calibration by sparse BGC-Argo profiles can improve subsurface biogeochemical properties. The multivariate deterministic ensemble Kalman filter (DEnKF) has been implemented to assimilate physical and biological observations into a three-dimensional coupled physical–biogeochemical model, the biogeochemical component of which has been calibrated by BGC-Argo float data for the Gulf of Mexico. Specifically, observations of sea surface height, sea surface temperature, and surface chlorophyll were assimilated, and profiles of both physical and biological variables were updated based on the surface information. We assessed whether this leads to improved subsurface distributions, especially of biological properties, using observations from five BGC-Argo floats that were not assimilated. An alternative light parameterization that was tuned a priori using BGC-Argo observations was also applied to test the sensitivity of data assimilation impact on subsurface biological properties. Results show that assimilation of the satellite data improves model representation of major circulation features, which translate into improved three-dimensional distributions of temperature and salinity. The multivariate assimilation also improves the agreement of subsurface nitrate through its tight correlation with temperature, but the improvements in subsurface chlorophyll were modest initially due to suboptimal choices of the model's optical module. Repeating the assimilation run by using the alternative light parameterization greatly improved the subsurface distribution of chlorophyll. Therefore, even sparse BGC-Argo observations can provide substantial benefits for biogeochemical prediction by enabling a priori model tuning. Given that, so far, the abundance of BGC-Argo profiles in the Gulf of Mexico and elsewhere has been insufficient for sequential assimilation, updating 3D biological properties in a model that has been well calibrated is an intermediate step toward full assimilation of the new data types.

Multi-Parametric Imaging of Etruscan Chamber Tombs: Grotte Di Castro Case Study (Italy)

A multi-parametric approach that involves the use of different geophysical methods coupled with geochemical data allowed us to identify undiscovered archeological burials in a funerary area of the Grotte di Castro Etruscan settlement. In particular, we tested the suitability of the capacitive resistivity method and the presence of Radon in soil for the identification of burials calibrating their outcomes over coincident survey profiles with standard geophysical techniques routinely applied for archaeological prospections. Soil Radon data were acquired both in a grid and along a profile to highlight anomalous gas concentrations, whereas electrical resistivity and ground-penetrating radar measurements were conducted on overlapping profiles to depict the electrical and electromagnetic subsurface distribution. Data integration showed a series of anomalies, suggesting the presence of multiple burials starting from a depth of approximately 1.5 m below the terrain surface. Slight anomalies of Radon in the soil were found to correspond to most of the recovered geophysical ones. Our results pointed out the effectiveness of geophysical method integration in archeological prospecting with the novelty of the joint use of Radon in soil measurements and capacitive resistivity tomography. The latter provided reliable results and can be considered as a standalone technique in archaeological surveys.

Subsurface and Infaunal Foraminifera of Kemaman-Chukai Mangrove Swamps, East Coast Peninsular Malaysia

This study analysed the distribution and abundance of dead and live (Rose Bengal stained) infaunal foraminifera from three short cores taken at three locations in the mangrove swamps of Kemaman-Chukai, Terengganu, Malaysia. Eighteen agglutinated taxa were recorded in assemblages dominated by Arenoparrella mexicana, Haplophragmoides wilberti and Miliammina fusca; and of these, only two taxa were recorded as live. The distribution of subsurface and infaunal foraminifera varied from core to core, as did their depth of occurrence. Core 1 (seaward core) was dominated by sandy deposits, relatively high salinity (32 ppt), and extensive crab mounds, displayed very low numbers of dead foraminifera inconsistently throughout the core, while no infaunal foraminifera were observed, indicating intense bioturbation by mangrove crabs. In Core 2 (middle core), even though the numbers of live foraminifera decreased down-core, the number of dead or subsurface foraminifera were inconsistent, indicating taphonomic loss of the tests. Core 3 (landward core) however, displayed ideal foraminiferal distribution patterns required in the palaeo sea-level reconstruction (with less taphonomic loss and decreasing number of infaunal foraminifera downcore). Because of the similarity displayed in the foraminiferal assemblages in the 0–1 cm and 10–11 cm intervals, the surface sample (0–1 cm) should be an acceptable basis for down-core reconstructions in this study. Live (Rose Bengal stained) infaunal foraminifera, though observed at 40–41 cm depth, are not considered abundant enough to influence the dead assemblage in the subsurface sediment and its applicability for palaeoenvironmental and sea-level reconstructions. Therefore, it is possible for palaeo sea-level to be reconstructed based on foraminiferal assemblages preserved in the Kemaman-Chukai mangrove swamps.

Petroleum geology: 3D reservoir modelling in the central Gulf of Suez, Egypt, to estimate the hydrocarbon possibility via petrophysical analysis and seismic data interpretation

October oil field is considered one of the most prolific areas in the central Gulf of Suez, which recently suffered a lack of production in some areas, in addition to some wells that have begun to deplete, which negatively affects the economic value of this field. 3D integrated reservoir model on five wells has been performed to simulate the subsurface structural setting, petrophysical modelling, and distribution of facies modelling of the Late Cretaceous Matulla Formation and Early Miocene Asl Member of Upper Rudeis Formation, which are the main oil‐bearing reservoirs in this study. Structural modelling controlled by the incorporation of explained structures, horizons, and picked zones for 3D grid express northwest–southeast to northeast–southwest fault systems, whilst facies modelling has enabled the spatial distribution of lithologic facies within the established 3D structural model reflecting two types of facies: marine carbonates and lagoon shale, and the petrophysical modelling explained a complete distribution of the petrophysical characteristic of the Matulla and Asl oil reservoirs revealed good reservoir characteristics, which are high net pay, high effective porosity, low shale content, low water saturation, and high hydrocarbon saturation. Therefore, three new commercial promising areas were identified to raise the productive value of this field according to the three‐way dip closure, petrophysical results, and the facies distribution.

A numerical analysis of skin\u2013PPE interaction to prevent facial tissue injury

The use of close-fitting PPE is essential to prevent exposure to dispersed airborne matter, including the COVID-19 virus. The current pandemic has increased pressure on healthcare systems around the world, leading to medical professionals using high-grade PPE for prolonged durations, resulting in device-induced skin injuries. This study focuses on computationally improving the interaction between skin and PPE to reduce the likelihood of discomfort and tissue damage. A finite element model is developed to simulate the movement of PPE against the face during day-to-day tasks. Due to limited available data on skin characteristics and how these vary interpersonally between sexes, races and ages, the main objective of this study was to establish the effects and trends that mask modifications have on the resulting subsurface strain energy density distribution in the skin. These modifications include the material, geometric and interfacial properties. Overall, the results show that skin injury can be reduced by using softer mask materials, whilst friction against the skin should be minimised, e.g. through use of micro-textures, humidity control and topical creams. Furthermore, the contact area between the mask and skin should be maximised, whilst the use of soft materials with incompressible behaviour (e.g. many elastomers) should be avoided.

Correlation Among Particle Size Distribution, Subsurface Damages Distribution and Surface Roughness in Optical Polishing Process

Restricting polishing induced subsurface damage and obtaining super smooth surfaces are important in high quality laser systems. Here, experiments and theoretical simulations are combined to investigate correlations among particle size distribution, subsurface damage distribution, and surface roughness evolution in the optical polishing process. This reveals that the fraction of observable subsurface damage increases rapidly with increased particle size, which results in greater and deeper subsurface damage. In addition, control of the tail end particle size distribution is also critical for controlling polishing-induced subsurface damage. In the high surface roughness period, the surface roughness increases linearly with increased subsurface damage. In the low surface roughness period, without any polishing induced subsurface damage, optimizing pad properties to reduce microscale surface undulation could further improve surface roughness. Making sure that no observable subsurface damage is generated is the precondition for obtaining a super smooth surface. Using nanosized particles could greatly reduce the particles’ bear load and finally obtain a super smooth surface without any subsurface damages.

Molecular Dynamic Investigation of the Anisotropic Response of Aluminum Surface by Ions Beam Sputtering

Aluminum optics are widely used in modern optical systems because of their high specific stiffness and high reflectance. With the applied optical frequency band moving to visible, traditional processing technology cannot meet the processing precision. Ion beam sputtering (IBS) provides a highly deterministic technology for high-precision aluminum optics fabrication. However, the surface quality is deteriorated after IBS. The interaction between the bombard atoms and the surface morphology evolution mechanism are not clear, and systematic research is needed. Thus, in this paper, the IBS process for single crystal aluminum with different crystallographic orientations are studied by the molecular dynamics method. The ion beam sputter process is firstly demonstrated. Then, the variation of sputter yield of the three crystal faces is analyzed. The sputter yield difference of different crystal surfaces causes the appearance of the relief structure. Then, the gravel structure generates on the single crystal surfaces and dominates the morphology evolution. The state of the atom diffusion of the specific crystal surfaces will determine the form of the gravel structure. Furthermore, the form and distribution of subsurface damage and stress distribution of three different crystal surfaces are analyzed. Although there are great differences in defect distribution, no stress concentration was found in three workpieces, which verifies that the ion beam sputter is a stress-free machining method. The process of IBS and the mechanism of morphology evolution of aluminum are revealed. The regularity and mechanism will provide a guidance for the application of IBS in aluminum optics manufacture fields.

Extrapolated supervirtual refraction interferometry

SUMMARY Accurate picking of head-wave arrival times is an important component of first-arrival traveltime tomography. Far-offset traces in particular have low signal-to-noise ratio (SNR), but picking on these traces is necessary in order to obtain velocity information at depth. Furthermore, there is often an insufficient number of far-offset traces for obtaining reliable models at depth. We present here an extrapolation method for increasing the number of first arrivals beyond the maximum recorded offset, thereby extending the supervirtual refraction interferometry (SVI) method. We refer to the method as extrapolated SVI (ESVI). It is a novel attempt to extrapolate first arrivals using a fully data-driven method. We first test the methodology on synthetic data sets, and we then apply ESVI to two published real data sets over the Pärvie fault system in northern Sweden. These data sets were acquired along the same profile at different times with different acquisition parameters and noise levels. The results show that ESVI enhances the SNR of head waves when the noise level is high. That is the same as the conventional SVI. ESVI also increases the number of pickable first arrivals by extrapolating head waves past the original maximum offset of each shot. We also show that the significant increase in first-arrival traveltime picks is beneficial for improving resolution and penetration depth in the tomographic imaging and, consequently, better revealing the subsurface velocity distribution. The tomographic images show higher velocities in the hanging walls of the main Pärvie fault and another subsidiary fault, as interpreted relative to migrated images from previous seismic reflection processing.

Lizards and snakes from the earliest Miocene of Saint-G\xe9rand-le-Puy, France: an anatomical and histological approach of some of the oldest Neogene squamates from Europe

BackgroundThe earliest Miocene (Aquitanian) represents a crucial time interval in the evolution of European squamates (i.e., lizards and snakes), witnessing a high diversity of taxa, including an array of extinct forms but also representatives of extant genera. We here conduct a taxonomical survey along with a histological/microanatomical approach on new squamate remains from the earliest Miocene of Saint-Gérand-le-Puy, France, an area that has been well known for its fossil discoveries since the nineteenth century.ResultsWe document new occurrences of taxa, among which, the lacertid Janosikia and the anguid Ophisaurus holeci, were previously unknown from France. We provide a detailed description of the anatomical structures of the various cranial and postcranial remains of lizards and snakes from Saint-Gérand-le-Puy. By applying micro-CT scanning in the most complete cranial elements of our sample, we decipher previously unknown microanatomical features. We report in detail the subsurface distribution and 3D connectivity of vascular channels in the anguid parietal. The fine meshwork of channels and cavities or sinuses in the parietal of Ophisaurus could indicate some thermoregulatory function, as it has recently been demonstrated for other vertebrate groups, providing implications for the palaeophysiology of this earliest Miocene anguine lizard.ConclusionsA combination of anatomical and micro-anatomical/histological approach, aided by micro-CT scanning, enabled the documentation of these new earliest Miocene squamate remains. A distinct geographic expansion is provided for the extinct anguine Ophisaurus holeci and the lacertid Janosikia (the closest relative of the extant insular Gallotia from the Canary Islands).

Subsurface temperature estimation in a geothermal field based on audio-frequency magnetotelluric data

In geothermal exploration, the subsurface temperature distribution is an important parameter since it is closely related to the existing geothermal system. However, subsurface temperature information can only be obtained from boreholes, requiring a considerable cost and a limited number. A new geothermometry technique based on the relationship between temperature and resistivity has been proposed to overcome this difficulty. In order to enhance the reliability of this method, the subsurface heat condition in a different geological and geographical location was reconstructed. The temperature up to some depth beneath the surface could be estimated incorporating the back-propagation neural network using resistivity determined by high-resolution audio-magnetotelluric soundings. The temperature profiles resulting from the neural network fit with those observed from nearby boreholes, providing a satisfying evaluation result of the model’s predictive powers. Joint interpretation was then carried out following the one-dimensional resistivity inversion result and temperature cross-section. Both resistivity and temperature anomalies show an excellent agreement, so that subsurface anomaly such as altered layers, reservoir zone, and some possible faults was detected. With an appropriate training strategy, this technique can help to significantly reduce the costs at estimating the subsurface temperature.

Study of methane migration in the shallow subsurface from a gas pipe leak

With the increased use of natural gas, safety and environmental concerns from underground leaking natural gas pipelines are becoming more widespread. What is not well understood in leakage incidents is how the soil conditions affect gas migration behavior, making it difficult to estimate the gas distribution. To shed light on these concerns, an increased understanding of subsurface methane migration after gas release is required to support efficient leak response and effective use of available technologies. In this study, three field-scale experiments were performed at the Methane Emission Technology Evaluation Center in Colorado State University to investigate the effect of soil textural heterogeneity, soil moisture, and leak rate (0.5 and 0.85 kg/h) on methane migration caused by leaking pipelines. Subsurface methane concentrations, in addition to soil moisture and meteorological data, were collected over time. A previously validated numerical model was modified and used to understand the observed methane distribution behavior. Results of this study illustrate that the influence of soil texture, leak rate, and moisture on subsurface methane distribution is determined by the relative contribution of advection and diffusion and closely related to the distance to the leak source. Advection dominates gas transport within 1–1.5 m of the leak source, driving the migration of high concentration contours. Beyond this distance, diffusion dominates migration of lower concentration contours to the far-field. Although large leak rates initially result in faster and further gas migration, the leak rate has little influence on the diffusion dominated migration farther from the leak source. Soil moisture and texture complicate gas behavior with texture variations and elevated soil moisture conditions playing a dominant role in locally increasing methane concentrations. Scenarios highlight the importance of understanding the effects of soil moisture, texture, and leak rate on gas migration behavior in an attempt to unravel their contribution to the gas concentration within the soil environment.

An electrical conductivity model of a coastal geothermal field in southeastern China based on 3D magnetotelluric imaging

The hydrology and geology of the Xinzhou geothermal field in South China and its surrounding area have been well studied. Previous studies have indicated that mantle heat, granite radioactive heat, and partial melting are the likely key thermal sources. However, neither the geometry of the geothermal reservoir nor the groundwater circulation pattern has been fully characterized. Toward that aim, a grid of magnetotelluric (MT) data has been acquired to reveal the subsurface distribution of electrical conductivity and to detect the geothermal reservoir. An analysis of the phase tensors suggests that 3D MT inversion is essential for accurate interpretation of the data. We perform a 3D full-impedance MT inversion and observe pronounced low electrical conductivity zones in the inverse model. We interpret these materials as widely developed granites that form the bedrock, which is cut by a crisscross of faults. The cracks in the bedrock provide pathways for the vertical and lateral movement of the hydrothermal fluid. The geothermal reservoir appears as a prominent high electrical conductivity anomaly beneath the hot spring. A northwest-dipping zone of enhanced electrical conductivity reaching approximately 6–7 km in depth is found in the southeast part of the study area, and it is interpreted as the geothermal reservoir recharge channel. We develop an inferred underground fluid circulation model, informed by the electrical conductivity of the area, in combination with hydrologic data. We suggest that the water supply of the Xinzhou geothermal field mainly comes from meteoric water, which is mixed with the invading seawater and shallow cold groundwater as it rises along the fault. The results of our MT study confirm earlier inferences that the Xinzhou geothermal field belongs to an intraplate deep-circulation type originated from the mantle heat flow.

Hydrogeophysical Investigation and Aquifer Evaluation of the Formations in Nsukka Area, Southeastern Nigeria

The study targeted the aquiferous Ajali Sandstone and Nsukka Formations that underlies the Nsukka metropolis and its environs (within Latitudes 6 o 80 1 N and 6 o 89 1 N; Longitudes 7 o 21 1 E and 7 o 30 1 E), covering an area of about 210 square kilometres. Thirty four (34) cross array Vertical Electrical Sounding (using the Schlumberger electrode configuration) and records from four (4) selected boreholes have been used to investigate the subsurface distribution of electrical resistivity and to delineate hydraulic properties of aquifers in Nsukka area, Southeastern, Nigeria.The electrical surveys of the area show high values of permeability, ranging from 0.0075 to 0.015cm 2 , hydraulic conductivity, ranging from 8.29 to 16.64m/s, transmissivity, between 455.87 and 1002.48m 2 s -1 , and specific yield, ranging from 2.35 to 4.76m 3 . A tie with the results of borehole logs analysis reveals the presence of at least four layers of contrasting hydraulic conductivity. Analyses, however, suggests that the Nsukka Formation (which overlies the Ajali Sandstone) is thick and poorly conductive while the Ajali Sandstone unit is homogenous and anisotropic and has higher conductivity (especially beyond the depth of 100 m), suggesting a prolific water-bearing formation at such depth and beyond. The Ajali Sandstone aquifer in the area is thick and prolific. The distribution of major geological units, well log data, static water level data were shown to have influence on the groundwater occurrence and flow pattern in the area. Keywords: Ajali Sandstone Aquifer, Nsukka Metropolis, Resistivity measurements, Well data DOI: 10.7176/JEES/11-7-04 Publication date: July 31 st 2021

Moment Analysis for Modeling Soil Water Distribution in Furrow Irrigation: Variable vs. Constant Ponding Depths

Despite increasing use of pressurized irrigation methods, most irrigation projects worldwide still involve surface systems. Accurate estimation of the amount of infiltrating water and its spatial distribution in the soil is of great importance in the design and management of furrow irrigation systems. Moment analysis has previously been applied to describe the subsurface water distribution using input data from numerical simulations rather than field measured data, and assuming a constant ponding depth in the furrow. A field experiment was conducted in a blocked-end level furrow at Maricopa Agricultural Center, Arizona, USA, to study the effect of time-variable ponding depths on soil water distribution and the resulting wetting bulb under real conditions in the field using moment analysis. The simulated volumetric soil water contents run with variable and constant (average) ponding depths using HYDRUS 2D/3D were almost identical, and both compared favorably with the field data. Hence, only the simulated soil water contents with variable ponding depths were used to calculate the moments. It was concluded that the fluctuating flow depth had no significant influence on the resulting time-evolving ellipses. This was related to the negligible 10-cm variation in ponding depths compared to the high negative matric potential of the unsaturated soil.

An integrated approach to evaluate the unconventional hydrocarbon generation potential of the Lower Goru Formation (Cretaceous) in Southern Lower Indus basin, Pakistan

Southern Lower Indus basin is an oil and gas prone basin, which is important for producing hydrocarbon in Pakistan. Due to limited Rock-Eval pyrolysis data availability in the prospective shale gas basin, the organic facies geochemical characteristics study is a challenging task for researchers. The primary objective of this study is an evaluation of the Lower Goru Formation organic facies hydrocarbon potential by geochemical data and its subsurface facies distribution study by well tops and seismic data. The study area is situated at the Southern Lower Indus basin of Pakistan that is considering the prospective shale gas basin with immense unconventional hydrocarbon potential. In the present study, Rock-Eval pyrolysis data analysis along with the integration of both seismic and well tops data were conducted for investigation of source rock generation potential of organic facies variability within the Lower Goru Formation. The geochemical approaches used in the current study show that the Lower Goru Formation encountered in, bears fair to excellent total organic carbon (TOC) content values of 0.50–3.60% in Well-A and 0.10–4.69% in Well-B. Additionally, the results of Rock-Eval pyrolysis data show that interbedded shales of the Lower Goru Formation contain different types of kerogen (III, II–III, and II) with variable generation potential of oil and gas.

Integrated Interpretation of Magnetic and ERT Data to Characterize a Landfill in the North-West of Cologne, Germany

Electrical resistivity tomography (ERT) and ground magnetic surveys were applied to characterize an old uncontrolled landfill in a former exploited sand and gravel quarry in an area to the north-west of the city of Cologne, Germany. The total magnetic field and its vertical gradient were recorded using a proton precession magnetometer to cover an area of about 43,250 m2. The magnetic data were transferred to the frequency domain and then reduced to the north magnetic pole. The amplitude of the analytical signal was calculated to define the magnetic materials within and outside the landfill. Eight ERT profiles were constructed based on the results of the magnetic survey using different electrode arrays (Wenner, dipole–dipole, and Schlumberger). In order to increase both data coverage and sensitivity and to decrease uncertainty, a non-conventional mixed array was used. The subsurface resistivity distributions were imaged using the robust (L1-norm) inversion method. The resultant inverted subsurface true resistivity data were presented in the form of 2D cross sections and 3D fence diagram. These non-invasive geophysical tools helped us to portray the covering soil, the spatial limits of the landfill, and the depth of the waste body. We also successfully detected low resistivity zones at deeper depths than expected, which probably be associated with migration pathways of the leachate plumes. The findings of the present study provide valuable information for decision makers with regards to environmental monitoring and assessment.