Borehole Geophysical Logs Research Articles

Improving Coal Quality Estimations with Geostatistics and Geophysical Logs

In most modern coal mines, there are many coal quality parameters that are measured on samples taken from boreholes. These data are used to generate spatial models of the coal quality parameters, typically using inverse distance as an interpolation method. At the same time, downhole geophysical logging of numerous additional boreholes is used to measure various physical properties but no coal quality samples are taken. The work presented in this paper uses two of the most important coal quality variables-ash and volatile matter-and assesses the efficacy of using a number of geostatistical interpolation methods to improve the accuracy of the interpolated models, including the use of auxiliary variables from geophysical logs. A multivariate spatial statistical analysis of ash, volatile matter and several auxiliary variables is used to establish a co-regionalization model that relates all of the variables as manifestations of an underlying geological characteristic. A case study of a coal mine in Queensland, Australia, is used to compare the interpolation methods of inverse distance to ordinary kriging, universal kriging, co-kriging, regression kriging and kriging with an external drift. The relative merits of these six methods are compared using the mean error and the root mean square error as measures of bias and accuracy. The study demonstrates that there is significant opportunity to improve the estimations of coal quality when using kriging with an external drift. The results show that when using the depth of a sample as an external drift variable there is a significant improvement in the accuracy of estimation for volatile matter, and when using wireline density logs as the drift variable there is improvement in the estimation of the in situ ash. The economic benefit of these findings is that cheaper proxies for coal quality parameters can significantly increase data density and the quality of estimations.

Application of Geophysical Borehole Logs For Aquifer Characterization in Coastal Environment of Lagos, Southwestern Nigeria

Well correlation and aquifer characterization were successfully carried out across a part of Lekki, Lagos state, Nigeria. The formation stratification sequence comprises predominantly of sand and clay with intercalations of both occurring as clayey sand and sandy clay. Three distinct fluid types (saline water, brackish water and fresh water) were delineated. The bulk resistivity (formation and fluid resistivity) ranged from 0 - 80Ωm for saline water sand and clay, 80 – 120 Ωm for the brackish water sand and clay and 120 – 620 Ωm for fresh water. Salinity occurrence was observed throughout the entire study area with depth of occurrence ranging between 14 – 152m. The depth to saline/fresh water interface range from 123 – 167m. Two aquifer types (unconfined and leaky confined aquifers) were observed in the study area. A maximum of five aquifers were delineated across the borehole sections. The depths to the delineated aquifers ranged from 163 – 249m with the aquifer thickness ranging from 10 to 56m. The maximum saline water depth extent was at about 152m (BH7 and BH5). Brackish water (the saline water interface) ranges from about 123.5 – 167m while the minimum depth to freshwater was about 163.5m (BH4) and maximum depth was about 175m (BH8) for all observed logs. The hydrogeological importance of the Coastal Plain Sand (a good aquifer unit) in the study area is under severe threat of continued seawater (saline water) intrusion on its coastal flank as observed from the vulnerability analysis of the study area. The study area is under intense stress from probably heavy abstraction as more than 80% of the observed boreholes were characterized as highly vulnerable and all of the observed boreholes already exceeded the standard range of values for some of the vulnerability parameters particularly.

Estimating Cover Thickness in the Southern Thomson Orogen – A Comparison of Applied Geophysics Estimates with Borehole Results

Potential sites for up to sixteen stratigraphic boreholes were selected to intersect the basement geology throughout the southern Thomson Orogen as part of the Southern Thomson Project. At each of these sites high resolution estimates of cover thickness were derived by applying refraction seismic, Audio-MagnetoTelluric, Targeted Magnetic Inversion and passive seismic geophysical techniques. Estimating cover thickness in this way reduced the technical risk associated with drilling and allows for the various geophysical techniques to be compared at each site. A comparison of the estimates derived from the applied geophysical techniques with the actual cover thicknesses determined from borehole geological and geophysical logs, together with an analysis of the uncertainties for each method, has highlighted the effectiveness of each geophysical technique. These new data and interpretations contribute to an Explorers’ Toolkit of techniques to help reduce the technical risk to the mineral exploration industry in searching for new mineral deposits in covered terrains in general, and in particular in the underexplored terrain of the southern Thomson Orogen. The various geophysical estimates highlight that the basement-cover interface throughout the southern Thomson Orogen can be recognised by its seismic velocity, electrical conductivity and magnetic susceptibility contrasts. However, the cover thickness estimates determined by the geophysical techniques shown here provide non-coincident estimates in some cases and, as such, it is important to take into account their unique limitations and uncertainties. When comparing results from the GSQ Eulo 1 and GSQ Eulo 2 boreholes it is clear that the refraction technique produced the most accurate estimates due to a strong contrast between the velocity structure of the Eromanga Basin sediments and the basement geology throughout the study area.

Characterization and imaging of a hydrothermally active near-vertical fault zone in crystalline rocks based on hydrophone VSP data

A shallow, hydrothermally active, fault zone embedded in fractured crystalline rocks of the Central Swiss Alps has been drilled and geophysically explored in view of its potential analogies to planned petrothermal reservoirs in the Alpine Foreland. Vertical seismic profiling (VSP) experiments have been performed using a 24-channel borehole hydrophone array with a sensor spacing of 1 m in order to image the fault core and to detect hydraulically open fractures. The dense sensor spacing allows for an accurate sampling of the wavefields. This, in turn, enables their separation through standard seismic processing methodologies, thus allowing for the generation of seismic body wave VSP profiles and a tube wave corridor stack, which maps brittle deformation in the surrounding rock mass.Multiple offset hydrophone VSP data were acquired with a crooked-line survey geometry and processed with 3D methods. Hereby, a laterally changing velocity cube, representative of the vertical structural variations associated with the fault zone, is generated and utilized for Kirchhoff pre-stack-depth-migration (PSDM) imaging. The resulting seismic image delineates various vertical structures, notably the target fault zone. The interpretation of the VSP data is complemented by and corroborated through a suite of geophysical borehole logs, which characterize the fine-scale petrophysical variations in response to brittle deformation in the fault core and the surrounding damage zones.This study exemplifies typical targets of hardrock seismic exploration, where the structures are frequently near-vertical, discontinuous and where acoustic impedance contrasts are commonly associated with deformation. As such, it illustrates the benefits of using borehole seismic methods in such environments and the use of borehole hydrophone arrays for targeting fractures and shear zones.

Use of geophysical logs in hydrogeological studies and borehole designs: case study of Apapa coastal area, Lagos, Nigeria

The hydrogeological study of Apapa, a coastal part of Lagos, Nigeria, has been investigated using combined geophysical borehole logs, consisting of natural gamma and electrical resistivity components and ditch cutting samples. This study utilized data from 10 boreholes to delineate freshwater aquifer and proposes the best borehole design and construction for optimum groundwater developments in the study area. The electrical resistivity log data show that the depth to the freshwater interface varies across the study area occurring between 150 and 160 m and as shallow as 110 m in a borehole. The variations in depth of the freshwater interfaces are attributed to the extent of saline/brackish water contamination and distribution of rock types. Based on these differences and the inability to identify water quality from ditch cuttings, borehole geophysical logging is a vital tool in providing in situ subsurface information of the rock types and fluid contents in groundwater studies. This further demonstrates that geophysical borehole logs play an important part in borehole design for development of water wells.

Borehole depth determination to freshwater and well design using geophysical logs in coastal regions of Lagos, southwestern Nigeria

The determination of depth to freshwater aquifers and lack of geophysical borehole log data to help borehole developers in the design of borehole have long been identified as a problem in coastal areas. This necessitates a study of the coastal environment of Lagos, southwestern Nigeria, to determine the depth to freshwater and give recommendation on the borehole design during installation stage that can be projected to areas immediate to where geophysical logs are available. For this study, twenty geophysical log data were utilized which are spread across Ikoyi, Victoria Island and Lekki of Lagos metropolis. The study shows that the saline water extent in Ikoyi, Victoria Island and Lekki occurs to an average depth of 146, 154 and 162 m, respectively. Relative variation in quality of water across the regions is because of the differences in the thickness of clay units serving as protective units separating the polluted zones from the unpolluted zones. It is recommended that water wells in Ikoyi, Victoria Island and Lekki be drilled to an approximate depth of 240 m and the last 18 m be screened. This research work was able to develop a design model for the boreholes located in the Island. The model includes gravel packing thickness of about 50 m from the bottom of the hole and cement grouting to the surface of the borehole to avoid the contamination of the borehole.

Geophysical log characterization of the Flamborough Chalk Formation (Late Cretaceous, Santonian – Early Campanian), East Yorkshire, UK: implications for understanding the onshore and offshore occurrence of the Late Campanian Rowe Chalk Formation

Whilst borehole geophysical log profiles have been matched with formational subdivisions for large parts of the Chalk Group in Lincolnshire and Yorkshire, characterization of the youngest and thickest part of the outcropping succession, represented by the marl-rich and largely flint-free Flamborough Chalk Formation, has been hindered by lack of cored and geophysically logged boreholes. In the absence of optimal primary data, a stratigraphical interpretation of geophysical logs in the Flamborough Chalk has been developed by comparison of logs from deep hydrocarbons boreholes (penetrating more than 260 m of Flamborough Chalk) beneath Holderness (East Yorkshire) with generalized patterns of outcrop stratigraphy. This approach reveals geophysical log patterns that are consistent with lithology and thickness variations seen at outcrop, compatible with core and geophysical data for a deep borehole in the Flamborough Chalk at Carnaby (near Bridlington), and traceable northwards and westwards towards the margin of the Flamborough Chalk outcrop. These interpretations, and comparisons with geophysically logged offshore successions, suggest the presence of Flamborough Chalk beneath Holderness that is younger (?Late Campanian) than anything seen at outcrop, and, with the exception of possible ex-situ chalk rafts of glacial origin, cast doubt on the likely subsurface onshore extent of typically flint-rich Rowe Chalk Formation.

Borehole geophysical log signatures and stratigraphic assessment in a glacial basin, southern Ontario

Over the past two decades, the Geological Survey of Canada has used a standardized suite of slim-hole geophysical tools to log 57 polyvinyl chloride cased boreholes drilled in the glacial sediments of southern Ontario. This article documents downhole tool responses (natural gamma, apparent conductivity, magnetic susceptibility, and seismic velocity) in the context of mineralogical characteristics of the region and grain-size data from 28 of the 57 boreholes. Characteristic geophysical properties and (or) patterns are identified within the units of a regional hydrostratigraphic framework in southern Ontario. The importance of a calibrated suite of tools is emphasized, as stratigraphic units may have variable response from site to site. The use of a high-sensitivity magnetic susceptibility induction probe is shown to be an important tool in the log suite for lithostratigraphic interpretation, and more broadly, for provenance studies of source rock across the region. Ranges of compressional (P) and shear (S) wave velocities and their ratios are provided for each of the hydrostratigraphic units. Case studies are presented to demonstrate how logs may assist in the interpretation of glacial processes at lithological boundaries.

Underwater ERT surveying in water with resistivity layering with example of application to site investigation for a rock tunnel in central Stockholm

ABSTRACTWe present an approach to underwater electrical resistivity tomography surveying under conditions with several water layers with different resistivity in the water above the electrode layout. The approach is verified against a synthetic model example and tested in full scale on data from a field survey. The field survey was carried out in central Stockholm as part of pre‐investigations for a new metro train (T‐bana) tunnel planned to pass under seawater. The water passage is associated with major tectonic zones that can potentially be very difficult from a tunnel construction point of view. The aim was to identify variations in depth of the bottom sediments and variations in rock quality including the possible presence of weak zones in the rock. Survey conditions are complicated by boat traffic and electrical disturbances from the power grid and train traffic. The water depth was mapped using sonar combined with recording pressure transducers, and water resistivity as a function of water depth was recorded using geophysical borehole logging equipment. Water resistivity as a function of depth was integrated in the inversion model. The results show that the rather difficult survey conditions could be handled in a satisfactory way thanks to adequate equipment, careful planning, and attention to details. The measured data contain information that is relevant for creating coherent models of the variation in depth to rock, which corresponds well with data from drilling. The results also indicate that information in variation in rock quality that can be of critical importance for planning of underground construction can be derived from the data.

Aquifer configuration and geostructural links control the groundwater quality in thin-bedded carbonate–siliciclastic alternations of the Hainich CZE, central Germany

Abstract. The quality of near-surface groundwater reservoirs is controlled, but also threatened, by manifold surface–subsurface interactions. Vulnerability studies typically evaluate the variable interplay of surface factors (land management, infiltration patterns) and subsurface factors (hydrostratigraphy, flow properties) in a thorough way, but disregard the resulting groundwater quality. Conversely, hydrogeochemical case studies that address the chemical evolution of groundwater often lack a comprehensive analysis of the structural buildup. In this study, we aim to reconstruct the actual spatial groundwater quality pattern from a synoptic analysis of the hydrostratigraphy, lithostratigraphy, pedology and land use in the Hainich Critical Zone Exploratory (Hainich CZE). This CZE represents a widely distributed yet scarcely described setting of thin-bedded mixed carbonate–siliciclastic strata in hillslope terrains. At the eastern Hainich low-mountain hillslope, bedrock is mainly formed by alternated marine sedimentary rocks of the Upper Muschelkalk (Middle Triassic) that partly host productive groundwater resources. Spatial patterns of the groundwater quality of a 5.4 km long well transect are derived by principal component analysis and hierarchical cluster analysis. Aquifer stratigraphy and geostructural links were deduced from lithological drill core analysis, mineralogical analysis, geophysical borehole logs and mapping data. Maps of preferential recharge zones and recharge potential were deduced from digital (soil) mapping, soil survey data and field measurements of soil hydraulic conductivities (Ks). By attributing spatially variable surface and subsurface conditions, we were able to reconstruct groundwater quality clusters that reflect the type of land management in their preferential recharge areas, aquifer hydraulic conditions and cross-formational exchange via caprock sinkholes or ascending flow. Generally, the aquifer configuration (spatial arrangement of strata, valley incision/outcrops) and related geostructural links (enhanced recharge areas, karst phenomena) control the role of surface factors (input quality and locations) vs. subsurface factors (water–rock interaction, cross-formational flow) for groundwater quality in the multi-layered aquifer system. Our investigation reveals general properties of alternating sequences in hillslope terrains that are prone to forming multi-layered aquifer systems. This synoptic analysis is fundamental and indispensable for a mechanistic understanding of ecological functioning, sustainable resource management and protection.

Microstructure and composition of brittle faults in claystones of the Mont Terri rock laboratory (Switzerland): New data from petrographic studies, geophysical borehole logging and permeability tests

Claystones are considered as a geological barrier. However, the properties of claystone may be modified if these are cut by brittle faults and fractures. Investigations of fault rocks are therefore crucial to evaluate the barrier properties of clay rich formations.The present study is dealing with the characterization of naturally and artificially deformed Opalinus Clay of the Mont Terri rock laboratory in NW Switzerland. Complete core sections, covering the artificially excavation damaged zone (EDZ) and several tectonic fault zones, have been studied using a multidisciplinary approach consisting of geophysical, geotechnical, mineralogical/geochemical and lithological/structural data.The fault zones encountered are characterized by a high density of planar discontinuities, which often show slickenside striations. Under the microscope, the fault zones turned out to be pervasively deformed resulting in open veins and pore space, now filled with calcite and celestine. Fault zone reactivation led to very fine-grained, cohesionless fault gouge and fragmentation of the previously formed calcite veins.Packer tests in boreholes reveal excavation induced, enhanced permeabilities up to 3m borehole depth (1.9m ┴ to gallery floor). Seismic borehole measurements indicate that seismic attributes, which are typical for undisturbed Opalinus Clay, are not reached until 7.5m borehole depth (4.8m ┴ to gallery floor), which is larger than in the usual gallery configuration.We interpret the anomalies in geophysical measurements as well as the elevated permeabilities, measured in the Main Fault (3.6m to 4.2m ┴ to gallery floor), to result from an enlarged EDZ, influenced by the presence of the brittle fault structures. The up to two orders of magnitude higher permeability (compared to the intact claystone) most probably results from excavation induced stress and a local reactivation of fault planes.The results suggest that the presence of a fault zone can alter the extent of the EDZ significantly, and thereby affect the rock integrity, at least in the near field of a repository tunnel.

Thermal field of the Donbas

We estimate results of the study of deep heat flow of Donbas. Anomalies of different nature have been distinguished. Their interpretation has been conducted. The thermal model of the crust and upper mantle has been plotted.Self-constructed electrical thermometers have been applied. It was also shown, that the used drilling technology (without washing fluid circulation) and the short time of drilling provided a very short borehole “rest”. Already in several hours after finishing drilling stable bottom borehole T were observed during several 24h terms.The main part of heat flow determinations were made by using the results of the borehole bottom Т measurements made by standard logging thermometers in the geophysical borehole logging . As a rule, the boreholes “rest” was from several hours to several days. Instrumental errors of this operation were repeatedly estimated and made the first tenth of a degree centigrade. The main error is clearly due to Т distortions.The data collected generally enable plotting heat flow HF and interior temperature maps scaled at 1: 2 500 000 — 1: 5 000 000. More detailed maps of the Donbas territory where the network density is well above the average one of the Ukraine have also been shown. The HF and deep temperature data are supplemented with the geothermal resource maps of the Donbas.

Remedial investigations of karst aquifers: a case study at former Marietta Air Force Station, Lancaster County, Pennsylvania

A phased multi-disciplinary approach was used to investigate potential environmental impact on the overburden aquifer and karst (bedrock) aquifer from the historic use of a suspected fire training pit at the former Marietta Air Force Station in Lancaster County, Pennsylvania. Investigation techniques have included direct push technology, real-time sample analysis via use of a mobile laboratory, earth resistivity imaging/induced polarization, geophysical borehole logging, packer testing, installation of one multi-port well with five sampling ports set in the karst aquifer, installation of multiple conventional monitoring wells, and completion of multiple rounds of groundwater sampling and data analysis. Both the vertical and lateral extents of groundwater contamination by chlorinated volatile organic compounds were delineated in the overburden and karst aquifer. The pathway-focused human health risk assessment has indicated that groundwater remediation is required to meet the federal and state health standards for volatile organic compounds. Based on the hydrogeological conditions and the nature and extent of the delineated contamination, plumes in both the overburden and karst aquifers, chemical oxidation (in the karst aquifer), and enhanced bioremediation (in the overburden aquifer) have been selected as the preferred alternatives for groundwater remediation, with monitored natural attenuation included as a common component of both alternatives.

Structurally coupled inversion of ERT and refraction seismic data combined with cluster-based model integration

Electrical resistivity tomography (ERT) and refraction seismics are among the most frequently used geophysical methods for site-investigations and the combined results can be very helpful to fill in the gaps between the point measurements made by traditional geotechnical methods such as Cone Penetration Test (CPT), core-drilling and geophysical borehole logging. The interpretation of the results from a geophysical investigation constituting a single method often yields ambiguous results. Hence, an approach utilizing multiple techniques is often necessary. To facilitate interpretation of such a combined dataset, we propose a more controlled and objective approach and present a method for a structurally coupled inversion of 2D electrical resistivity and refraction seismic data using unstructured meshes. Mean shift clustering is used to combine the two images and to compare the separate and coupled inversion methodologies. Two synthetic examples are used to demonstrate the method, and a field-data example is included as a proof of concept. In all cases a significant improvement by the coupling is visible. The methodology can be used as a tool for improved data interpretation and for obtaining a more comprehensive and complete picture of the subsurface by combining geophysical methods.

Critical pore pressure assessment for CO2 geological storage in Gyeongsang Basin, Korea, from a geomechanics perspective

We use a relatively simple analytic model incorporating two primary geomechanical factors–in situ stress and frictional coefficient of discontinuity–to assess the critical pore pressure increase associated with CO2 geological storage that initiates shear activation of pre-existing fractures and faults. Shear activation of fractures/faults can break the sealing integrity along the discontinuities, providing possible CO2 leakage channels. With an example of Gyeongsang Basin, Korea, which is considered a potential onshore geological storage site, the available in situ stress measurement data are analyzed to infer the stress states at an assumed storage depth of 1 km. The stress magnitudes in the basin are characterized by their spatial heterogeneity, implying that the critical pore pressure may vary depending on locations. As another primary factor for the analysis, frictional coefficient is shown to be possibly correlated with clay content in the host rocks encompassing the discontinuities, and in the infillings within the discontinuities, which demonstrates the possibility of estimating the frictional property from the clay content measurable using borehole geophysical logs. Based on the in situ stress conditions coupled with pore pressure change and assumed frictional coefficient of 0.6, the critical pore pressure is estimated, which would induce shear activation along well-orientated discontinuities for slip under the given stress states and consequently provide potential CO2 leakage pathways. The estimated critical pore pressure as an upper bound of allowable pore pressure is 4–8 MPa above the hydrostatic pore pressure in most of the basin, whereas the same is 0–4 MPa in the southern part of the basin. These results may be useful in the site selection stage for CO2 geological storage project.

Multidimensional Investigation of Bedrock Heterogeneity/Unconformities at a DNAPL-Impacted Site.

Organic solvent (i.e., dense nonaqueous phase liquid, DNAPL) migration in the subsurface is known to be extremely sensitive to geologic heterogeneity. There is often a focus on heterogeneity that results from changing depositional conditions over short spatial scales. Similar or even more extreme spatial heterogeneity can result postdeposition due to erosional processes. This study applies a synergistic approach based on a combination of high-resolution lithologic logs of continuous cores, borehole geophysical logs, surface electrical resistivity, and seismic refraction tomography models to assess spatial heterogeneity in a shallow bedrock sequence subject to multiple unconformities and contaminated with a mixture of organic chemicals. The persistence of DNAPL in the source zone and an associated dissolved-phase plume led to variable impacts on formation resistivity across the study site. Seismic refraction in combination with electrical resistivity tomography improved interpretation of highly irregular erosional boundaries by delineating sharp lateral transitions in lithologic composition near the source zone and across the dissolved-phase plume. Electrical resistivity was effective at differentiating between clean and mud-rich sandstones and their unconformable contact with an underlying dolostone. Geophysical measurements revealed eroded dolostone mounds encased by a network of younger mud-rich sandstones channelized by clean semi-lithified sand, all of which was buried beneath variable glacial drift. Our synergistic multidimensional approach resulted in the development of a detailed three-dimensional shallow bedrock geospatial model, which has led to an improved understanding of DNAPL migration and contaminant plume heterogeneity.

Geotechnical evaluation of coal deposits based on the Geophysical Strata Rating

In exploration programs for coal mining, geophysical logging of boreholes is mainly undertaken to reveal seam locations and the basic lithological section. Through the introduction of the Geophysical Strata Rating (GSR), this paper develops new geotechnical applications for geophysical logs. The GSR is an empirical rating scheme based on P-wave velocity data from sonic logs and estimates of the clay content and porosity derived from natural gamma and density logs. In coal measure strata, GSR values range between 0 and 100, with values of <15 indicating very poor rock and values over 80 representing extremely good rock.Given that geophysical logging data are obtained at closely spaced intervals within boreholes and that coal measure strata are usually laterally persistent between boreholes, geophysical results such as the clay content and the GSR can be modelled in two- and three-dimensions. This allows geotechnical information to be viewed in a geological context. Examples are provided of the log analysis and modelling. Geotechnical applications in risk identification, hazard assessment and design optimisation are also discussed. These applications exist in both underground and open cut mining.

Combining high resolution vertical gradients and sequence stratigraphy to delineate hydrogeologic units for a contaminated sedimentary rock aquifer system

Summary Hydrogeologic units (HGUs), representing subsurface contrasts in hydraulic conductivity, form the basis for all conceptual and numerical models of groundwater flow. However, conventionally, delineation of these units relies heavily on data sets indirect with respect to hydraulic properties. Here, we use the spatial and temporal characteristics of the vertical component of hydraulic gradient (i.e., vertical gradient) as the primary line of evidence for delineating HGUs for Cambrian–Ordovician sedimentary rocks at a site in Dane County, Wisconsin. The site includes a 16 km2 area encompassing a 3 km long mixed organic contaminants plume. The vertical gradients are derived from hydraulic head profiles obtained using high resolution Westbay multilevel systems installed at 7 locations along two, orthogonal 4 km long cross-sections and monitoring to depths between 90 and 146 m with an average of 3–4 monitoring zones per 10 m. These vertical gradient cross-sections reveal 11 laterally extensive HGUs with contrasting vertical hydraulic conductivity (Kv). The position and thickness of the Kv contrasts are consistently associated with sequence stratigraphic features (maximum flooding intervals and sequence boundaries) distinguished at the site using cores and borehole geophysical logs. The same sequence stratigraphic features are also traceable across much of the Cambrian–Ordovician aquifer system of the Midwest US. The vertical gradients and sequence stratigraphy were arrived at independently and when combined provide a hydraulically calibrated sequence stratigraphic framework for the site. This framework provides increased confidence in the precise delineation and description of the nature of HGU contacts in each borehole, reduced uncertainty in interpolation of the HGUs between boreholes, and some capability to predict HGU boundaries and thickness in offsite areas where high resolution hydraulic data sets are not available. Consequently, this HGU conceptual model will serve as a better basis for numerical simulations of groundwater flow and contaminant transport needed for continued risk assessment and to evaluate potential remedial technologies for the site. More broadly, the association between Kv contrasts and sequence stratigraphy demonstrated at this site provides valuable insight into the relationship between geology and hydraulic contrasts that can be transferred to other areas of the upper Midwest US and perhaps elsewhere to strata deposited in similar settings.

An investigation of the hidden precious water resources of Dampier Peninsula using airborne electromagnetic method

SUMMARY An airborne electromagnetic (AEM) survey was carried out over the Dampier Peninsula, North of Broome, WA during September-October, 2012. The key objectives of this geophysical survey funded by the Department of Water was (i) to obtain a better understanding of the nature of the contact between the base of the Broome Sandstone and the underlying siltstone; (ii) to identify areas of water retentive clay layers in the near surface, (iii) to create a map of the water table; (iv) to study the detailed geometry of the near shore saline intrusion; and thus (v) assist the conceptualisation of the hydrogeology and determine the quantity and quality of available groundwater resources for the benefit of local communities, government and industry. The survey was conducted using SkyTEM, a helicopter-borne time domain AEM system. The processed AEM data for each of the survey lines were examined and inverted using the industry standard inversion techniques. The results were then compared with available bore-hole geophysical logging as well as the regional geophysical, geological and hydrogeological data. Apart from successfully mapping the depth to water table for the whole project area, this survey has clearly delineated the thickness of Broome Sandstone, shallow impermeable layers within the Broome Sandstone and areas of possible saline sea water intrusions. The survey has also successfully identified a WNW-ESE trending lineament (a basement high) and couple of NW-SE trending structural features (such as fault structures) from the central part of the survey region. The regional geophysical data images obtained from Department of Mines & Petroleum supports this finding.

Fill to spill stratigraphic evolution of a confined turbidite mini-basin succession, and its likely well bore expression: The Castagnola Fm, NW Italy

This study documents the stratigraphic evolution of the Castagnola ponded turbidite mini-basin through analysis of a detailed base-to-top section measured in the central part of the basin. Vertical variations in facies characteristics, thickness ratio of mud cap vs. sandstone of event beds and net/gross are argued to be good proxies for pinpointing the stratigraphic transition from dominantly ponded deposition, where most of the flow is trapped by the confining topography, to a flow-stripping – dominated phase in which an increasingly large part of incoming flows can escape the basin by spilling over the enclosing topography. Thickness statistics of sandstones and mud caps of event beds from the case study show that in the initial stage of turbidite deposition only part of the mud of exceptionally large volume flows escaped the confining topography; as the basin was progressively infilled, nearly all inbound flows were affected by flow stripping, with part of the sand and most of the mud escaping the basin. In the latest recorded stage of deposition the abundance of by-pass features coupled with significant modification of the sandstone bed thickness population suggests that the turbidite system was no longer obstructed frontally, and could step forward onto a healed topography. In order to assess whether the documented trends of turbidite bed characteristics indicative of the ‘fill to spill’ transition could be recognised from wireline log data alone, synthetic logs were prepared by up-scaling the field data to resolutions typical of borehole geophysical log data. Vertical trends of average bed thickness and net/gross recognisable in the synthetic data suggest that the transition from ponded to spill-dominated situations should be resolvable in geophysical log data.