Shallow Boreholes Research Articles

Геологічна будова і перспективи нафтогазоносності ділянки Погар (Складчасті Карпати)

The Pohar plot is situated in the Skole district of the Lviv Region, 30 km south-west of Skole town, between Pohar and Kryve villages. Tectonically it is located in of junction of the Skybian (Slavske Skyba) and the Krosno covers. At the end of XIX beginning of XX centuries in the region of the village the oil-extracting enterprise was existent. There deposits of Oligocen and Eocene of the Rozluch belt of the Krosno cover and Oligocene of the scale of the Slavske skyba of the Skybian cover were exploited. During two ten-years of exploitation by exploring shafts and shallow boreholes more than 3 thousand ton of oil was extracted. Prospects of the Pohar plot should be connected with sand horizons of the Holovets suite of Oligocen (Klivsky sandstones) that are characterized by satisfactory reservoir properties. They are localized in the immersed part of the Hrosivsky scale of the Krosno cover separated by the Rozluch fault (tectonically screened deposit) from its forkball part, drilled in 1973–1974 1-Pohar borehole (well bottom 1935 m), due to deflection of its hole to the south-east, didn’t expose the Klivsky sandstones and didn’t solve its task. For complete exposition of the Klivsky sandstones of the Holovets suite of Oligocene of the Hrosivsky scale it is necessary to design vertically oriented 2-Pohar borehole of 2300 m in depth. About probable commercial oil-gas saturation of the horizon of the Klivsky sandstones testifies not only to the existence of the oil-extracting enterprise in the past, but the intensive surface oil shows in the stretched area that is controlled by the Rozluch fault. Moreover, taking the prospect of the zone of junction of the given covers in consideration, the seismic survey should be conducted at the Pohar area for the estimation of the geological structure of the deeper horizons and parametric borehole of 4000–5000 m in depth should be designed.

Cost-effective Baseline Studies for Induced Seismicity Monitoring Related to CO2 Storage Site Preparation

Induced seismicity has been identified as one of the key showstoppers for the safety of geological CO2 storage sites. The selection procedure for adequate storage sites therefore needs to include the assessment of the seismic hazard. Such studies include the mapping of active seismic faults and understanding their maximum magnitude potential. In addition, the injection and related pore pressure changes will result in stress field changes in, around and outside of the reservoir. These stress field changes can reach several kilometres outside of the field and have the potential to trigger seismicity on faults that are critically stressed, i.e. close to failure. To better assess the stress field conditions in certain regions, knowledge on the seismic activity of regional faults is important. This is generally conducted by recording a baseline of the seismicity. Having established such baseline seismicity, subsequent changes in the seismicity level can be rapidly identified during continuous monitoring. Hence, seismicity that is induced or triggered due to the injection, can be separated from the baseline seismic activity and evaluated accordingly. Based on the location, strength, mechanism and pattern of the seismicity, an estimate of both the short-term and long-term hazard can provide a decision basis on how to proceed with an injection programme. The establishing of a stable baseline-seismicity-estimate may require many years of recording within the area of interest, given a sufficiently dense deployment of seismometers. How long the actual recording time should last is dependent on the earthquake activity in the region and on the expected magnitude range that the baseline should cover. Ideally, a dense network of sensors can be deployed directly above the anticipated storage site, with sensors in shallow boreholes. In most cases of offshore CO2 storage, the deployment of a network of seismometers or geophones above the target storage site with the sole purpose of establishing a baseline is economically prohibitive. The main costs for such an offshore deployment are related to the shipping and sensor deployment, and different solutions for power consumption, which need to be properly evaluated. There is a variety of sea-floor sensors available, ranging from industry standard 4C geophones to broad-band Ocean Bottom Seismometers. Deployment methods also vary from rope installation to free-fall and pop-up to ROV operated installation. Noise from seismic interferences (shooting), platform noise and vessels also need to be considered, along with fishery/trawling routes and other offshore infrastructure. Consequently, a method to establish the baseline seismicity from land would be preferable. A very cost-effective, alternative approach to monitoring seismicity from far distances is the use of seismic arrays. By placing a number of seismometers in a certain spatial pattern, this technology takes advantage of the local coherency of the seismic wavefield while simultaneously reducing the noise. This methodology is well-known to and applied in the Comprehensive Nuclear-Test-Ban Treaty Organization, where seismic arrays are used for global monitoring. This technology is especially useful if a deployment of sensors close-by or above an area of interest is not possible. For offshore CO2 storage sites, the only cost-effective long-term installation would be onshore, which must take into account the distance to the target region, anthropogenic noise sources, property rights and other borders. To demonstrate this technology, a temporary seismic array has been installed on the Norwegian coastline with the sensor setup evaluated for both its ability for noise reduction and signal improvement. Together with single sensors along the coastline, this temporary array installation is analysed in terms of its detection capabilities and thus ability for providing an adequate seismicity baseline. Ultimately, such an array can easily be converted into a permanent installation and hence provide a continuous record of the seismic activity throughout the CO2 injection period and during the post-injection phase. The first results from a small sub-set of sensors provide encouraging results towards improved detection capabilities.

Study on shallow borehole Water blowout genesis based on geo-chemical properties from affected dug wells water

This present study aimed to investigate the shallow borehole water blowout genesis based on geochemical properties from affected dug Well. A geochemical study was performed on dug well samples at the local community houses, namely SG-01, SG-02, SG-03, located around the blowout areas. The results showed that those three respective samples clustered onto two groups of water types, namely calcium bicarbonate in SG-01 and SG-02 and mixed types for SG-03, respectively. Moreover, the dissolved metal analysis did not show high concentration anomalies, whilst cation concentrations of the three samples are dominated by calcium, which is suspected from the rock dissolution process. The dominant anion is bicarbonate for SG-01 and SG-02, while the SG-03 sample is dominated by sulfate. The cross plot between the two isotope ratios with the global meteoric water line shows the isotope values of the SG-01 and SG-02 that are right on the global meteoric water line while SG-03 falls slightly above it.

Wellbore Stability of a Deep-Water Shallow Hydrate Reservoir Based on Strain Softening Characteristics

Deep-sea hydrate has great commercial exploitation value as a new type of energy, due to huge reserves, wide distribution, cleanliness, and lack of pollution. Accurately, prediction of the mechanical properties of hydrate reservoirs is a key issue for safe and efficient exploitation of deep-sea hydrate. Although there have been some experimental and numerical simulation studies on the borehole stability of the hydrate layer, the influence of temperature and flow on the decomposition of reservoir hydrate is still not well understood. There have been few pure mechanical studies on the stress and strain state of the hydrate formation around the well, and it is impossible to intuitively understand the influence of the wellbore on the original stress state of the hydrate formation. This paper therefore uses a discrete element method to establish a deep-water shallow hydrate reservoir borehole stability model and compares the discrete element numerical model with an elastoplastic analytical model of borehole stability to verify the reliability of the numerical model. A simulation study on the influence of factors such as reservoir depth and hydrate saturation on wellbore stability is carried out. The simulation results effectively present the constitutive characteristics of strain softening of hydrate sediments. According to the different mechanical characteristics, the near-well zone can be divided into a plastic strain softening zone, a plastic strain hardening zone, and an elastic zone. Reservoir depth and hydrate saturation are found to change the stress state near the well. The greater the depth and the lower the hydrate saturation, the greater the borehole shrinkage. The diameter of the optimal horizontal well in the goaf is in the range from 0.6 to 1.2 m.

Groundwater Development and Management Practices in Lake Awassa Catchment, Southern Ethiopia

The amount of groundwater that is currently being used for domestic and non-domestic purposes in the basin is 17.8 million cubic meter. The net total amount of water that is actually available to recharge the groundwater circulation within the Lake Awassa catchment is 218.79 million cubic meter. Currently, 233 groundwater structures are found developed in different parts of the study area. Out of these 49 are non functional. Among the developed groundwater structures dominantly nonfunctional is hand dug wells, which comprises 29.55% of the total constructed hand dug wells. The hand dug wells are followed by shallow wells (25%), springs (19.75%) and boreholes (10%). Poor management of the constructed schemes, lack of awareness at community level, spare part problems, and construction problems are the major causes of the failure of the groundwater structures. Utilization of groundwater in the functional ones is not conducted on the basis of recommended values that were set based on the hydrogeological parameters during the development of the structures. Discharging hours are increased to satisfy the water demands of different users. Currently, groundwater is developed without groundwater management plan in uncoordinated manner by governmental and nongovernmental organizations and also privately.At present, the amount of natural recharge in the basin is more than the abstraction. The problem is not lack of water; it is rather absence of or poor management. This is mainly due to lack of efficient groundwater management organization at sub-basin level. Management of groundwater resources is crucial for better development and optimum utilization of the groundwater resources of the basin and to avoid any adverse effects. Therefore it is necessary to establish an efficient groundwater management organization that can conduct detailed groundwater management studies of the basin, follow the objectives of the national water resources management policy and also effectively implement. Keywords: Aquifer ; Ethiopia;Groundwater management; Hydrogeology;Lake Awsasa DOI: 10.7176/JEES/10-12-01 Publication date: December 31 st 2020

Experimental study on comprehensive geophysical advanced prediction of water-bearing structure of shaft

Water-bearing structures in front of coal mine shaft drivages require effective advanced prediction. Based on the characteristics of coal field logging curve carrying rich geological information, it is introduced into the advanced prediction of water-bearing bodies in mine shafts. At the same time, mine geophysical prospecting technology, such as the DC resistivity method, can accurately and effectively track and detect geological conditions during mine shaft drivage. The proposed advanced prediction method of the borehole-ground electrical method based on the detailed interpretation of logging curves was experimentally studied using physical simulations of the detailed interpretation of water-bearing rock strata in logging data and geophysical advanced detection simulations of water-bearing structures in mine shafts. By constructing a physical model of the mine shaft drivage, the change in the water content of the rock strata is simulated by adding water to sand and gravel, and the apparent resistivity logging in a borehole is simulated. The water-bearing characteristics of the model under different water content conditions are interpreted by using 3-D visualization technology, and it is concluded that the change law of the electrical characteristics of sand and gravel after adding water is a logarithmic function relationship. Then, based on the results of the detailed interpretation of the logging curves, a model experiment using the DC resistivity method of ground-borehole joint advanced detection is carried out, and the response characteristics of changes in the model water diffusion resistivity are accurately detected. In addition, a shallow geological borehole is constructed in the field. Water injection in the borehole causes anomalous changes in the electrical properties of the strata around the borehole and simulates water-bearing structures at different depths and layers, which verifies the effectiveness of the borehole-ground electrical method in detecting water-bearing structures in front of mine shaft drivages. The simulation results show that the advanced prediction method of borehole-ground electromagnetic technology based on the interpretation of logging curves enhances the effectiveness and detection efficiency of advanced detection and prediction of the water-bearing characteristics of rock strata. Based on the logging curve, the water-bearing characteristics of the strata in front of a coal mine shaft drivage in the Dongsheng coalfield in Inner Mongolia are interpreted in detail, and the provided anomalous target areas can provide reliable guidance for advanced detection using the borehole-ground electrical method in the future.

Quantifying the technical geothermal potential from shallow borehole heat exchangers at regional scale

The extraction of shallow geothermal energy using borehole heat exchangers (BHEs) is a promising approach for decarbonisation of the heating sector. However, a dense deployment of BHEs may lead to thermal interference between neighboring boreholes and thereby to over-exploitation of the heat capacity of the ground. Here we propose a novel method to estimate the technical potential of BHEs which takes into account potential thermal interference as well as the available area for BHE installations. The method combines simulation of the long-term heat extraction through BHEs for a range of borehole spacings and depths and includes an optimisation step to maximise the heat extraction. Application of the method to a case study in western Switzerland, from an available area of 284km2, yields an annual technical potential of 4.65TWh and a maximum energy density of 15.5kWh/m2. The results also suggest that, for a minimum borehole spacing of 5m and a maximum borehole depth of 200m, the cumulative installed borehole depth should not exceed 2km/ha. The estimated technical potential can be used by urban planners for the techno-economic analysis of BHE systems and by policy makers to develop strategies that encourage the use of shallow geothermal energy.

A new approach to modelling of seasonal soil temperature fluctuations and their impact on the performance of a shallow borehole heat exchanger

A borehole heat exchanger (BHE) could be used in heating and cooling systems as the ground temperature is normally higher than the average air temperature in winter and lower in summer. This difference in the temperature can be used to improve the efficiency of air conditioning systems (in summer) and heat pumps (in winter). The performance of a BHE is influenced by soil temperature that may have significant seasonal changes. These changes were largely ignored in previous BHE modelling approaches being a source for large errors in theoretical predictions. This paper presents a new internal source term approach to account for the (seasonal) fluctuation in soil temperature on a shallow BHE's performance. The proposed model is able to consider the heat flow in multi-ground-layers. The governing equations of the model are solved by using explicit finite different method. The model is validated using experimental data. The simulated soil temperatures with and without the internal heat source term showed that the maximum relative errors are 3.7% and 14% respectively. The use of high thermal conductivity grout resulted in a decrease in the borehole thermal resistance. The outlet fluid temperature under the continuous operation mode is higher than that operated under the intermittent mode.

Array and spectral ratio techniques applied to seismic noise to investigate the Campi Flegrei (Italy) subsoil structure at different scales

Abstract. The purpose of this work is to study the subsoil structure of the Campi Flegrei area using both spectral ratios and array techniques applied to seismic noise. We have estimated the dispersion curves of Rayleigh waves by applying the Frequency–Wavenumber (f–k hereinafter) and Modified Spatial Autocorrelation (MSPAC) techniques to the seismic noise recorded by the underground short period seismic Array “ARF”, by the broadband stations of the UNREST experiment and by the broadband stations of the seismic monitoring network of INGV – Osservatorio Vesuviano. We have performed the inversion of a dispersion curve (obtained averaging the f–k and MSPAC dispersion curves of seismic noise and single phase velocity values of coherent transient signals) jointly with the H∕V spectral ratio of the broadband station CELG, to obtain a shear wave velocity model up to 2000 m depth. The best-fit model obtained is in a good agreement with the stratigraphic information available in the area coming from shallow boreholes and deep wells drilled for geothermal exploration. In active volcanic areas, such as Campi Flegrei, the definition of the velocity model is a crucial issue to characterize the physical parameters of the medium. Generally, a high quality characterization of the medium properties helps to separate the contributions of the volcanic source, path and site in the geophysical observables. Therefore, monitoring possible variations in time of such properties in general can help to recognize anomalies due to the volcano dynamics, i.e. fluid migration connected to the volcanic activity.

Numerical study on the heat transfer performance of coaxial shallow borehole heat exchanger

l CFD simulations on the coaxial shallow borehole heat exchanger without grouting. l Analyzing the effect of design parameters on the heat transfer performance. l Investigating the effect of thermal short-circuiting. l Providing some guidelines for the coaxial shallow borehole exchanger design. In the present work, a numerical investigation on the coaxial shallow borehole heat exchanger based on Computational Fluid Dynamics (CFD) technique in Hefei city of China has been performed. The effects of design parameters, including inlet flow rate, inlet fluid temperature, inner pipe material and outer pipe diameter, on the heat transfer performance were systematically studied. Besides, the thermal behavior along the pipe has been carefully examined with focus on the thermal short-circuiting phenomena. When the fluid inlet velocity is less than the critical value, the turbulence intensity increases and the Nusselt number increases with the inlet flow rate increasing. However, there is sufficient time for heat transfer between the fluid in inner pipe and outer pipe because of low flow rates, leading to large heat loss, i.e., thermal short-circuiting phenomenon. It is found that with the inlet flow rate increasing, the heat transfer increases first and then decreases, and the rate of reduction slows down gradually. When the inlet flow rate increases, the pumping power undergoes exponential growth. As the inlet temperature increasing, the heat transfer decreases almost linearly. Moreover, when the soil temperature at the top of the casing is lower than that of the fluid in the casing, heat is transferred from the fluid in the casing to the soil, and the heat loss increases with the increase of the inlet fluid temperature. The material of inner pipe with high heat conductivity would result in large heat loss under the influence of thermal short-circuiting. The heat load increases while the pumping power required decreases with the increasing of outer pipe diameter. This study is very beneficial for the coaxial shallow borehole exchanger designs and energy conservation of buildings.

In-situ stress measurement technology and field application based on micro-optical imaging measurement method

In-situ stress is natural stress existing in rock masses. As an important basic parameter, accurate in-situ stress is highly beneficial to the theoretical research and engineering application of rock mechanics. In-situ tests in boreholes are the most direct and effective way to obtain in-situ stress. However, the high temperature and high water pressure testing environment in boreholes limits the application scope of measurement sensors. In this study, a micro-optical imaging measurement method is proposed. On the basis of this method, an aperture measurement device is developed, and a complete set of in-situ stress measurement technology is formed. Laboratory and field application tests are carried out. The results of the temperature and pressure test in a laboratory show that the in-situ stress test technology improves service temperature and pressure and offers an extensive application range. The field test on a shallow borehole in an iron mine roadway and a deep borehole in a shale gas exploration well reveals the deformation of the test boreholes in the process of stress relief. This result proves the feasibility of the in-situ stress measurement technology. On the basis of the theory of elasticity, in-situ stress is calculated with reference to the in-situ diameter deformation of the boreholes and the mechanical parameters of the rock core. A number of in-situ stress tests are carried out under different borehole depths, and the testing times are recorded. Results show that the application of wireline coring drilling technology speeds up the test process. Hence, it can boost the operability of the in-situ stress test. In sum, the in-situ stress measurement technology based on the micro-optical imaging measurement method is feasible and operable and may thus improve the application depth of the in-situ stress measurement method based on the stress relief method.

Analysis of technological parameters of selected lightweight cement slurries used for sealing shallow boreholes with a downhole temperature of up to 45°C

Analysis of technological parameters of selected lightweight cement slurries used for sealing shallow boreholes with a downhole temperature of up to 45°C

Comparison between Distributed Acoustic Sensing and Geophones: Downhole Microseismic Monitoring of the FORGE Geothermal Experiment

AbstractWe compare the performance of a downhole distributed acoustic sensing (DAS) fiber-optic array with that of conventional geophones. The downhole collocated arrays are part of the Frontier Observatory for Research in Geothermal Energy (FORGE) geothermal experiment, in which stimulation of the rock volume in an enhanced geothermal system (EGS) causes microseismic events. The DAS acquisition system yields data sampled at every 1 m at 2000 samples per second for the entire length of the well, spanning to a depth of 985 m from the surface. Whereas single DAS channels are substantially noisier than geophones at the same location, their large number and spatial coherency allow for the application of effective array processing techniques. We follow a complete workflow for the fiber-optic array: velocity model building, event detection, event location, and magnitude estimation. Estimated velocity models agree well with sonic logging in a nearby well and map a granitic contact accurately. Detection performance is somewhat worse than geophones and yields magnitude completeness of −1.4 compared to −1.7 for geophones. Using a single vertical fiber array, we cannot retrieve the azimuth of the events relative to the well. However, we can very accurately estimate their depth and horizontal distance from the array. Magnitude estimation with DAS approaches geophone results to within a standard deviation of M=0.115 and negligible mean difference. The DAS processing results outperform a regional and local surface array, consolidated with a shallow borehole sensor. Although downhole geophones in the FORGE experimental layout performed better, DAS holds several critical practical benefits that were not demonstrated. Thanks to its heat resistance, it can be deployed much closer to the reservoir; fibers can be deployed along cased active wells, eliminating the need for a dedicated monitoring well; the permanently installed fiber can be used for years or decades. Therefore, we argue that DAS holds vast potential for long-term monitoring of EGS projects.

THE LITHOSTRATIGRAPHY OF THE NEAR-SURFACE IN PART OF SEDIMENTARY KOLMANI FIELD IN NORTHERN BENUE TROUGH, NIGERIA, USING SOIL CORE AND SEISMIC REFRACTION DATA

Soil samples from 31 shallow boreholes were acquired at depths 0m, 1m, 2m, 3m, 4m, 5m, 7m, 10m, 15m, 20m, 25m, 30m, 35m, 40m, 45m, 50m, 55m, and 60m in Pingida (Kolmani Field) in Ako LGA, Gombe State, Nigeria. Using the same boreholes, seismic refraction data was also acquired. The aim of the survey was to delineate the near-surface lithology and velocity layering. The boreholes were drilled using rotary drilling rig and the core samples acquired and described using Wentworth Scale. Seismic refraction data acquired using a single trace Stratavisor NZXP portable digital recorder. The recording spread consisted of a single SM4- 10Hz geophone positioned at depths where the soil samples were taken. A hammer was used as the energy source and placed 3m away from the hole to obtain the first breaks. The refraction data was interpreted using UDISYS Version 1.0.0.0 software. The soil layers in the Kolmani Field have three distinct layers specified as follows, namely, top weathered and sub-consolidated layers made up of intercalation of sandstone, gravel ash clay and muddy coal shale. The lithologic strata do not correlate throughout the field resulting from the highly variable elevation which ranged from 317m and 524m with average of 389.16m. The top weathered layer of laterite intercalated with cobblestones with compressional wave velocity ranging from 342 ms-1 to 517 ms-1 with an average of 405.03 ms-1. Beneath the weathered layer is the sub-consolidated Clay layer intercalated with silt and laterite of compressional wave velocity ranging from 440 ms-1 to 1854 ms-1 of average of 826 ms-1. The underlying consolidated layer is the shale and coal layer having compressional wave velocity ranging from 1518 ms-1 to 4201 ms-1 with an average of 2162.65 ms-1. The dominant lithologic sequences encountered are laterite, clay, silt, sand, gravel, coal and shale. The results of this work can be used for static corrections in seismic reflection processing, planning and assessing risk for engineering structures, and for groundwater exploration. The laterite, clay, silt, sand, gravel, coal and shale can be utilized in agriculture, construction, process industries, and environmental remediation.

Shallow subsurface thermal structure onshore Denmark: temperature, thermal conductivity and heat flow

Available measured temperatures and thermal conductivities covering Danish onshore areas to a depth of about 300 m have been compiled and analysed. Temperature data from 236 borehole sites, including 56 boreholes with detailed temperature profiles, are applied together with thermal conductivities mea- sured on samples collected at 34 well-characterised outcrops and on core material from 20 boreholes. Significant thermal variations in the shallow subsurface are observed. At a depth of 50 m, a mean temperature of 8.9 ± 0.8°C is found, close to the mean annual surface temperature. Higher mean values of 9.7 ± 1.1°C found at 100 m and 11.6 ± 2.2°C at 200 m reflect a general increase of temperatures with depth. In contrast to the assumption commonly held, we observe significant lateral variations both lo- cally and regionally. At a depth of 100 m, temperatures vary between 7.3 and 13.0°C across Denmark, and at 250 m between 9.6 and 17.9°C. Mean values of the thermal conductivities lie within a range of 0.6–6 W/(m·K) measured water- saturated at laboratory conditions. The majority of values are within the interval of 1–3 W/(m·K) and show a strong correlation with lithology. The content of quartz and the rock porosity (the content of water) are found to be two main factors controlling the observed variations. Characteristic temperature gradients are in the range 1–4°C/100 m. Following Fourier’s law of heat conduction, a clear correlation is observed between temperature gradients and thermal conductivities of different lithologies. Intervals of quartz-rich sand deposits with high thermal conductivity show low temperature gradients, chalk and limestone intervals with intermediate conductivity display intermediate gradients, while sections with fine grained clay deposits of low thermal conductivity show high gradient values. A correlation analysis provides an estimate of regional shallow heat flow of 37 ± 5 mW/m2, consistent with local, classically determined heat-flow values from shallow borehole data. However, it is significantly below deep background heat flow, and this is believed to be caused by long-term paleoclimatic effects. The shallow subsurface thermal regime across the Danish area is largely controlled by thermal conduction. Only locally, and in rare cases, do we observe temperature perturbations due to ground- water migration. In addition to general geoscientific purposes, our results are important for several applications including exploitation of shallow geothermal energy and the use of the subsurface for heat storage and cooling purposes.

Infiltration efficiency and subsurface water processes of a sustainable drainage system and consequences to flood management

AbstractWith increased intensity rainfall events globally and urban expansion decreasing permeable surfaces, there is an increasing problem of urban flooding. This study aims to better understand rainfall infiltration into a Sustainable Drainage System (SuDS) permeable pavement, compared with an adjacent Green Area of made ground, in relationship to groundwater levels below both areas. Both areas were instrumented with soil water content and matric potential sensors and four shallow boreholes were instrumented with groundwater level sensors. Surface infiltration rates were measured using a double‐ring infiltrometer. Results showed that average infiltration rates of the SuDS (1,925 mm/hr) were significantly higher than the Green Area (56 mm/hr). The SuDS was well designed to transfer rainfall rapidly to the aquifer below, where groundwater levels rapidly rose within 1 hr of a 1 in 30 year event (32.8 mm/hr). In comparison, soil compaction of the made ground Green Area decreased infiltration rates, but still enabled the majority of rainfall events to infiltrate. The aquifer below the Green Area responded more slowly, as lower matrix potentials facilitated water retention in the soil profile, slowing water draining to the aquifer. This work reiterates the importance of ensuring a 1 m separation depth between the base of the SuDS infiltration zone and aquifer depth.

New <i>Chikyu</i> Shallow Core Program (SCORE): exploring mass transport deposits and the subseafloor biosphere off Cape Erimo, northern Japan

Abstract. The Chikyu Shallow Core Program (SCORE) has been started to provide more opportunities for the scientific ocean drilling of shallow boreholes (up to 100 m) during a short-term expedition. The proposal flow is a simplified version of that of the International Ocean Discovery Program (IODP). Although there are several limitations for a SCORE project, the opportunity to retrieve 100 m of continuous core samples will be of great interest for the scientific ocean drilling community in multiple disciplines. The first expedition of the SCORE program was implemented off Cape Erimo, Hokkaido, northern Japan. The target of the drilling was to investigate the impact of submarine mass transport on the subseafloor sedimentary biosphere. In the preliminary observation of the core samples, including X-ray computed tomography (CT) scan image analysis, chaotic and inclined beds were found and interpreted as mass transport deposit (MTD) units.

Surface traces and related deformation structures of the southern Sanyi Fault, Taiwan, as deduced from field mapping, electrical-resistivity tomography, and shallow drilling

The southern Sanyi Fault extends across a highly urbanized area in central-west Taiwan. It is within 1–2 km from and generally parallels the northern Chelungpu Fault, which last ruptured in 1999 (Mw = 7.6 Chi-Chi Earthquake) and caused about 2400 fatalities. Several questions thus arise: is the Sanyi Fault likewise active? what is its geometry and extent? and should it be zoned or otherwise designated to mitigate risk through restrictions on development or engineering design? We address these questions by mapping river-exposed outcrops, by interpreting nine, near-surface geophysical surveys (electrical resistivity tomography [ERT]), and by compiling and assessing existing shallow borehole data. Outcrops in the Dajia River show that the Sanyi Fault is mainly a low-angle thrust that juxtaposes poorly lithified sandstone over alluvial gravels. Fault branches are common both in the hanging wall and footwall. To the south, the fault is not marked by a break in topography and its trace has not been clearly mapped within the alluvial plain, in part motivating the current effort. Here the ERT surveys identify the hanging-wall sandstone by a relatively low resistivity of <100 Ωm, whereas the footwall conglomerates and alluvial gravels generally exceed ~300 Ωm and ~ 100 Ωm, respectively. Borehole data likewise constrain the extent and character of the Sanyi Fault, which we identify as extending across the eastern part of Fengyuan, a city with a population now exceeding 160,000. The fault system is clearly imaged in two of five surveyed sites, and we integrate these data with drilling data to map the Sanyi fault surface trace as a ~ 400 m wide zone in the city of Fengyuan. Compiling previously documented paleoseismic data at one site, the Sanyi Fault system likely slipped in the thousand-year range throughout the Holocene. The Sanyi Fault is therefore ‘active’ and warrants zoning or other forms of mitigation to minimize potential, seismically induced loss of life and property.

Characteristics of a fracture network surrounding a hydrothermally altered shear zone from geophysical borehole logs

Abstract. Hydrothermally active and altered fault/shear zones in crystalline rocks are of practical importance because of their potential similarities with petrothermal reservoirs and exploitable natural hydrothermal systems. The petrophysical and hydraulic characterization of such structures is therefore of significant interest. Here, we report the results of corresponding investigations on a prominent shear zone of this type located in the crystalline Aar massif of the central Swiss Alps. A shallow borehole was drilled, which acutely intersects the core of the shear zone and is entirely situated in its surrounding damage zone. The focus of this study is a detailed characterization of this damage zone based on geophysical borehole measurements. For this purpose, a comprehensive suite of borehole logs, comprising passive and active nuclear, full-waveform sonic, resistivity, self-potential, optical televiewer, and borehole radar data, was collected. The migrated images of the borehole radar reflection data together with the optical televiewer data reveal a complicated network of intersecting fractures in the damage zone. Consequently, the associated petrophysical properties, notably the sonic velocities and porosities, are distinctly different from intact granitic formations. Cluster analyses of the borehole logs in combination with the structural interpretations of the optical televiewer data illustrate that the variations in the petrophysical properties are predominantly governed by the intense brittle deformation. The imaged fracture network and the high-porosity zones associated with brittle deformation represent the main flow pathways. This interpretation is consistent with the available geophysical measurements as well as the analyses of the retrieved core material. Furthermore, the interpretation of the self-potential and fluid resistivity log data suggests a compartmentalized hydraulic behavior, as evidenced by inflows of water into the borehole from different sources, which is likely to be governed by the steeply dipping structures.

Using the borehole permeameter to estimate saturated hydraulic conductivity for glacially over-consolidated soils

The borehole permeameter (BP) method was developed in the 1950s by the United States Bureau of Reclamation to estimate saturated soil hydraulic conductivity (KS) in shallow boreholes completed above the water table. The approach has been improved over the years, and now accounts for flow due to pressure, gravity and soil capillarity. However, the BP method is calibrated only for normally consolidated soils and ponding depth (H) versus borehole radius (r) ratios (H/r) ≤ 22. The primary objective of this study was to recalibrate the BP method for use in glacially over-consolidated soils with H/r ranging from 0.05 to 200. Recalibration consisted of using numerically simulated steady BP flow for five representative glacially over-consolidated soils to update the BP shape function fitting parameters (Z1, Z2, Z3) for nine specified KS values and 15 test pit and borehole configurations. Four sets of fitting parameters were determined, which apply for H/r ≤ 20, H/r ≥ 20, soil with <12% silt content, and soil with >12% silt content. Relative to specified KS, the updated shape function parameters yielded BP estimates of KS with a maximum error of 13% and an average error of 3%, whereas the original shape function parameters (developed for normally consolidated soils and H/r ≤ 22) produced a maximum KS error of 94% and an average error of 23%. The numerical simulations were also used to develop criteria for estimating time required to achieve steady BP flow, and for correcting BP estimates of KS where steady flow was not achieved.