Borehole Measurements Research Articles

Positive Correlation between DYFI Intensity Data and Microzonation Site Classes for Ottawa, Quebec City, and the Metropolitan Area of Montreal

Abstract At the local scale, seismic risk is often poorly estimated when considering equal hazard values across any given community. Indeed, past damaging earthquakes have shown that site conditions, which may amplify or deamplify ground shaking, have an influence on the spatial distribution of damage in urban areas. In eastern Canada, Leda clay deposits from the old Champlain Sea are of particular concern for strong site effects in many parts of Quebec and Ontario. To capture the variability in seismic site response, microzonation maps characterizing average shear wave velocity for the upper 30 m of soil, and predominant resonance frequency have been developed for Montreal, Ottawa, and Quebec City. The maps derived from seismic and borehole measurements have been used to develop shake map scenarios but have not been validated, because there have not been any significantly large, close earthquakes in recent years, and because the seismograph network coverage is not adequate to provide a detailed picture of variations in shaking across a city. Nevertheless, all the three cities are in or near active seismic zones, and felt reports, although less accurate than instrumental data, are numerous and provide a dense dataset showing relative shaking levels across a region. Using intensity data for several moderate earthquakes collected largely via the Canadian internet “Did You Feel It?” page, we systematically compare reported shaking levels to soil conditions indicated by the microzonation maps. This study shows a clear correlation between high-reported intensities and soft soils for Montreal where the number of observations is the largest. The results suggest that intensity data collected via the internet and social media could provide a viable method for validating microzonation maps and shaking scenarios.

City-wide monitoring and contributing factors to shallow subsurface temperature variability in Nanjing, China

Shallow temperatures down to a depth of 100 m were measured over one year in 19 closed boreholes located in Nanjing, China, to reveal the conditions and factors influencing the subsurface thermal regime. A monitoring concept with distributed temperature sensing, fiber Bragg grating-based sensor, and a type of Resistance Temperature Detectors, is implemented, providing spatial distribution characteristics of subsurface temperatures. The results show that temperatures near the surface are most dynamic, influenced by the air temperature. The temperature remains stable at the depth of 10–20 m. The mean transition temperature is 18.1 °C. Borehole measurements are interpolated by using satellite images and surface temperature records to obtain large-scale surface temperature distributions and temporal variations of subsurface temperature. Geological and hydrological conditions are primary factors by affecting subsurface upward heat flux and heat loss. Urban land cover change and enhanced heat release from urbanization contribute to a subsurface urban heat island with intensities of 1.0–4.4 °C. The altered subsurface thermal regime is of primary concern for the management of shallow geothermal energy use. The monitoring concept in this study can provide spatially-temporally continuous profiles of subsurface temperature and become a reference for city-wide geothermal monitoring in other urban areas.

Probabilistic Contaminant Source Assessment-Getting the Most Out of Field Measurements.

This paper describes a methodology for undertaking probabilistic investigations into the locations at which contaminants have leaked into a groundwater system. The methodology is built with highly parameterized, stochastic history-matching in mind. It is able to reduce uncertainties associated with estimates of subsurface hydraulic properties at the same time as it reduces uncertainties associated with inferences of contaminant sources. Particles are used to simulate contaminant movement. This reduces simulator execution time while increasing simulator stability. Borehole measurements of groundwater chemistry are endowed with a binary classification that indicates the presence, or otherwise, of a contaminant plume. This classification is transferred to passing particles as a detect or nondetect status awarded to their trajectories. Because this status is continuous with respect to model parameters, the latter can be adjusted in order to ensure that the same trajectory cannot possess both a detect status and a nondetect status. Particle trajectory statuses can be assigned to model cells from which they are released. By calculating cell statistics using a large number of history-match-constrained, stochastic parameter fields, probability maps can be drawn. We illustrate two of these. The first maps the probability that a contaminant sourced at a particular location will go undetected by the current observation network. The second maps the probability that a contaminant source cannot exist at a particular location. The method is extended to examine the worth of supplementing an existing observation network with new wells.

MulT_predict - An optimised comprehensive multicomponent geothermometer

In this study, we introduce MulT_predict as a fully integrated solute multicomponent geothermometer, combining numerical optimisation processes for sensitive parameters to back-calculate to chemical reservoir conditions. This results in a state of the art geothermometer, providing an accurate reservoir temperature estimation validated by geothermal borehole measurements on a worldwide scale. In addition, a universally valid mineral assemblage for an unknown reservoir composition is developed, focusing on worldwide applicability. Using the evolved methodology, the limits of the optimisation processes are determined by using a synthetic brine (150 °C, pH 6, aluminium concentration 0.003 mmol/l) and successively perturbing its geochemical equilibrium state. Individual back-calculation of reservoir conditions lead to valid temperature estimations of 145 °C, 3.4% lower than the initial temperature while a simultaneous and interdependent optimisation reconstructs the sensitive parameters even more precisely with a deviation of 0.056 for the initial pH value, and 0.164 µmol/l for the aluminium concentration.

Errors in positioning of borehole measurements and how they influence seismic inversion

Inversion of seismic data using information from horizontal wells is often hampered by cumulative well-location errors. These errors can have a significant influence on the final subsurface model derived from the data. To achieve a proper data integration and arrive at correct uncertainty estimates, we formulate the problem in a fully probabilistic framework and present a numerical approach for improving subsurface imaging using uncertain well-log data and their uncertain locations as well as uncertain seismic data. The result is improved model error quantification in the seismic inversion process.

A Device to Register Temperature in Boreholes in Northwest Spain for Geothermal Research.

This paper presents a device used to measure and register temperature for long-term subsoil measurements in boreholes. The borehole of this study is located in Gijón (Asturias, Spain). The measurements were made through two fixed sets of sensors coupled to the geothermal pipe, constituting two independent installations: (a) a commercial device called “Hobo”, which uses TMCx-HD-specific sensors based on resistors with variable resistance; and (b) a device built by this research group, which uses DS12B20 Maxim sensors, a bus 1-wire, and a recording device based on a conventional Arduino board. Temperature was registered every 5 min across several years. These measurements were used to thermally characterize the subsoil, determining the apparent thermal diffusivity, and to study the thermo-hydrogeology of the Lower Jurassic Gijón’s formation made of Liassic limestones and dolomites. This work is part of the Q-Thermie group’s research called “Shallow Thermal Energy”.

Experimental measurements of monopole inner/outer collar waves and estimation of P wave velocity in acoustic LWD

Acoustic logging while drilling (LWD) technology is extensively applied for petroleum prospecting. It utilizes the acoustic characteristics of stratum to deduce the formation properties such as porosity, permeability, and oil saturation, etc., which can help to detect the location of oil reservoirs. In acoustic logging process, the formation longitudinal (P) and transverse (S) wave velocity is the primary factor of interest. Nevertheless, an accurate identification of P/S wave velocity in different formations is hard to be performed due to the influence of the collar waves, which has become an urgent problem in LWD measurements. To study this issue more practically, a small-sized measurement system based on the propagation mechanism of collar waves is established in our laboratory. With this system, we design and perform multiple sets of monopole acoustic LWD experiments with different models. After recording the experimental data, the attenuations of inner and outer collar waves received along the axial direction are compared and analyzed. The result shows that the collar waves have an exponential decay in amplitude by the expansion of source-receiver distance, but the outer collar wave decreases more rapidly. We also conduct experiments at different source frequencies (20–400 kHz) to quantitatively describe the relationship between the amplitude and frequency. The result suggests that the inner/outer collar waves and P/S waves have a similar frequency response, and it's difficult to remove collar waves from the full waveforms of LWD signals by only changing source frequency. Therefore, we present a new data processing method for extracting the formation wave velocities according to the energy distribution of the componential waves, and then apply it in the analysis of two borehole measurements. The inner and outer collar waves are almost removed from the processed time domain waveforms, which leads to a successful verification of formation P/S wave velocities. These experimental results prove the feasibility and repeatability of our method, and propose an alternative method for the LWD data explanations.

Calibration of Hydrodynamic Models of Groundwater Flow in Aquifers Polluted by Liquid Radioactive Waste

Pollution of aquifers by liquid radioactive waste is especially hazardous due to high permeability of aquifer rocks. Pollution can take place as a result of deep injection disposal of liquid waste or due to its leakage from a surface reservoir. The ecological hazard depends on distribution of aquifer permeability, which can be highly heterogeneous. The only source of data for determination of such distribution is measurements in exploratory boreholes at the polluted site. A technique is proposed for determination of spatial distribution of aquifer transmissibility on the basis of hydrological measurements in a limited number of boreholes. The problem is reduced to a minimization problem which was solved numerically.

New development of sensitivity improvement for compensated neutron porosity tool in gas-filled boreholes

Porosity is one of the most important indicators used for hydrocarbon reservoir evaluation and extraction. However, obtain accurate formation porosity measurements in gas-filled boreholes can be challenging, this is because gas cannot slow down neutrons as effectively as water due to its lower hydrogen index, which results in measurement sensitivity reduction and consequently impacts the obtained porosity. One way to address this issue is loading water into the borehole which is commonly referred to as water loading. However, this process significantly increases operational time and cost, as well as shielding perforated gas zones. Therefore, a new strategy is proposed to improve the sensitivity of porosity measurement in gas or air-filled boreholes without the need for water loading. The key to this strategy is to incorporate a sleeve design outside the tool to enhance its performance in gas-filled intervals. The sleeve is composed of a downhole applicable material whose neutron slowing down ability is close to water. The optimized deployment orientation of the sleeve could then be determined through simulation. In this work, three potential sleeve materials are identified and compared based on an existing neutron porosity tool. The impacts of different tool-sleeve-borehole orientations are analyzed to determine the most effective design strategy. A series of test pit experiments is conducted to validate the feasibility of the design.

Coupled full-waveform inversion of horizontal borehole ground penetrating radar data to estimate soil hydraulic parameters: A synthetic study

Coupled inversion is a promising technique for determining soil hydraulic properties from time-lapse geophysical measurements. In this inversion approach, a hydrological model is coupled with ground penetrating radar (GPR) forward modelling to avoid interpretation errors from data processing. In this study, a workflow for coupled GPR full-waveform inversion (CFWI) is proposed that combines the benefits of coupled inversion and full-waveform inversion (FWI) to estimate soil hydraulic properties from time-lapse horizontal borehole GPR measurements. In particular, a synthetic modelling study is presented that compares the performance of coupled inversion of full waveforms and first arrival time data from zero-offset profile (ZOP) borehole measurements obtained during an infiltration event for estimating hydraulic parameters and the thickness of the first layer for a 2-layer soil profile. It was found that the thickness of the first layer could be more accurately estimated by CFWI because of the additional information contained in reflected and refracted waves from the air–soil layer boundary. Furthermore, the hydraulic parameters estimated by the coupled inversion of GPR travel times slightly deviated from true values and showed a relatively large uncertainty, whereas the results of CFWI precisely matched the known water retention and hydraulic conductivity functions. Despite these promising results, several challenges should be solved before CFWI can be applied to experimental GPR data. First, conducting CFWI needs accurate conceptual setups for the hydro(geo-)logical model. Furthermore, a robust approach should be developed to accurately estimate an effective source wavelet from the experimental ZOP data, and a more sophisticated hydrological modelling approach has to be considered to better estimate the distribution of soil electrical conductivity during the infiltration event. Finally, the accuracy and efficiency of current GPR modelling methods may need to be improved.

3D Shear Wave Velocity Model of Salt Lake Valley via Rayleigh Wave Ellipticity across a Temporary Geophone Array

Abstract We construct a 3D shear velocity model of the Salt Lake Valley using Rayleigh waves excited by the 31 March 2020 Mw 6.5 central Idaho earthquake recorded on a 168-station temporary nodal geophone network and the 49-station permanent regional network. The temporary array—deployed in response to the March 18 Mw 5.7 Magna earthquake—serendipitously recorded clear surface waves between 10 and 20 s period from the Idaho event at ∼500 km epicentral distance, from which we measure both Rayleigh wave phase velocity and ellipticity (H/V ratio). In addition, we employ multicomponent earthquake coda cross correlation to extend the measurements down to 5 s period. Because Rayleigh wave ellipticity features outstanding shallow sensitivity, we invert for a 3D upper crust VS model of the Salt Lake Valley. Our model shows basin structure in general agreement with and complements the current Community Velocity Model, which is mostly constrained by borehole and gravity measurements. Our model thus provides critical information for future earthquake hazard assessment studies, which require detailed shallow velocity structure.

Network of Multidisciplinary Borehole Measurements at the Petropavlovsk-Kamchatsky Geodynamic Testing Area

Network of Multidisciplinary Borehole Measurements at the Petropavlovsk-Kamchatsky Geodynamic Testing Area

DNAPL flow and complex electrical resistivity evolution in saturated porous media: A coupled numerical simulation

Induced Polarization (IP) is a non-intrusive geophysical method to monitor Dense Non-Aqueous Phase Liquid (DNAPL) contamination and remediation processes underground. In this study, an advanced numerical code simulating DNAPL flow and complex electrical resistivity is presented. The model was validated against existing IP results and image measurements that were carried out previously in a series of 2D tank experiment. Multiphase flow modeling in porous media is coupled with electrical current modeling to simulate the process of DNAPL migration and the associated IP response. This brings a broader view of the contamination in space and time compared to surface and borehole measurements, especially when the results are supported by field measurements or laboratory experiments. The simulations are developed in 3D and are performed in COMSOL Multiphysics®. The simulations using petrophysical relationships for in-phase and quadrature resistivity and the results of the experiments are in complete accordance with each other in the parts of the tank where the saturation of DNAPL is relatively low (i.e. especially in the cone of depression in the pumping scenario). However, the parts associated with high saturation of DNAPL show high errors between the in-phase resistivity simulations and the results from experiments. The present work can be regarded as a preliminary study toward further applications of coupled IP-multiphase flow for more accurate detection and monitoring of DNAPLs. It is suggested that the choice of tool/approach in this study be extended to larger-scale studies for further investigation.

A General Anisotropic Effective Medium Model for Laminated Sequence

SummaryEffective medium rock physics model is the basis for the quantitative petrophysical interpretation of seismic and borehole acoustic measurements, because it links the formation petrophysical parameters with elastic properties, and the latter can be directly inferred from relevant measurements. Many existing works are based on conventional effective medium theories assuming isotropic underground formations, which may lead to erroneous estimates of formation properties. In this work, we extend the existing theories and develop a novel general anisotropic effective medium model to obtain the elastic constants of underground rocks. Three anisotropic effective medium theories are studied: self-consistent approximation (SCA), differential effective medium (DEM), and their combination. A newly extended Kuster-Toksöz (KT) model is also presented for the isotropic effective model. All these effective theories for elastic moduli are verified and validated with independent numerical results and experimental data. Then three workflows are implemented to obtain general stiffness coefficients for different formation models including the shaly sand model, the cracked sand model, and the shaly sand model with cracks. Furthermore, we also study the sensitivity of elastic moduli with respect to variations in pore aspect ratios.

Assessing geodynamic activity of rock by the borehole survey results

Research objective is to assess the modern geodynamic environment of the geological environment through borehole measurements of signals of geoacoustic emission and electromagnetic radiation. Research relevance is due to the need to identify geodynamically active zones and areas of increased rock fracturing in wells. Methods of research. Rock geodynamic activity was studied in a well of the North-Taratashsky area of a magnetite quartzite deposit in the Chelyabinsk region. MESh-42 hardware and software complex designed for synchronous registration of geoacoustic emission and electromagnetic radiation signals was used to solve this problem. Geoacoustic emission (GAE) and electromagnetic radiation (EMR) signals were recorded using the shuttle logging technique, which makes it possible to identify zones of rock geodynamic activity along well sections and track the dynamics of these sections in time. Results. The results of the method of geoacoustic emission and electromagnetic radiation signals shuttle logging in well no. 7 of the North-Taratashsky area are shown. Conclusions. In the course of geoacoustic emission and electromagnetic radiation signals studies in well no. 7 of the Severo-Taratashsky area according to the shuttle logging method, zones of increased stress in the geological environment and areas of increased fracture formation were identified, which, in turn, made it possible to subdivide the studied interval according to the geodynamic activity of rocks

High-fidelity subsurface resistivity imaging incorporating borehole measurements for monitoring underground construction

Subsurface imaging by electrical resistivity tomography (ERT) is increasingly used in geotechnical, geo-environmental, and hydrogeological investigation and monitoring. Cross-hole ERT (CHERT) is often used to avoid loss of resolution with increasing depth. However, symmetric artifacts may be induced because the measurement sensitivity around boreholes for some electrode configurations is fairly symmetric. This study aimed to investigate the best practice of ERT for monitoring underground construction or process through an actual scenario of ground improvement with jet grouting columns. The limitation of conventional surface ERT method was first vividly illustrated in an easy-to-understand context. Characteristics and performances of distinct types of CHERT configurations were then studied considering different borehole spacings. Further improvements were explored by evaluating various mixed arrays, model resolution-optimized array, and the comprehensive array. The results show the necessity of mixing two distinct types of electrode configuration. Among various combinations, a combination referred to as the nominal optimal (NOPT) is recommended when imaging resolution, the symmetric effect, and the measurement efficiency are all factored in. Unexpectedly, the resolution-based optimization does not lead to better results and could even induce negative effects. The results also show that the minimum aspect ratio of 2 may not be large enough for imaging complex underground conditions due to reduced sensitivity and increased 3D effect. The above findings are justified by the eigenvalue spectrum of the Hessian matrix, which is considered a better appraisal index than the model resolution for CHERT.

Greenland Ice Sheet Subsurface Temperature Estimation Using Ultrawideband Microwave Radiometry

Ice sheet subsurface temperature is important for understanding glacier dynamics, yet existing methods to obtain the temperature of the ice sheet column are limited to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> sources at present. The ultrawideband software-defined microwave radiometer (UWBRAD) has been developed to investigate the remote sensing of ice sheet internal temperatures. UWBRAD measures brightness temperature spectra from 0.5 to 2 GHz using 12 subchannels and employs a sophisticated algorithm for detection and mitigation of radio frequency interference (RFI). The instrument was deployed during a flight over northwestern Greenland in September 2017 and acquired the first wideband low-frequency brightness temperature spectra over the ice sheet and coastal regions. The results reveal strong spatial and spectral variations that correlate well with internal ice sheet temperature information. In this article, the section of the flight path ranging from the Camp Century to NEEM to NGRIP boreholes is used for subsurface temperature estimation. A “partially coherent” forward model is applied along with a Robin model for the temperature profile and a two-scale model of ice sheet density variations to describe measured brightness temperatures. Using this model, vertical temperature profiles are retrieved along the flight path using a sequential Bayesian estimator; borehole measurements at the three campsites are used to obtain Bayesian priors. The retrieved temperature profiles show reasonable behaviors and demonstrate the potential of ultrawideband microwave radiometry for remotely sensing internal ice sheet temperatures.

Features of Adjusting the Frozen Soil Properties Using Borehole Temperature Measurements

The paper examines the theoretical issues of using borehole temperature survey data to control a frozen wall formed around the sinking mine shafts of the Nezhinsk mining and processing plant potash mine. We consider adjusting the parameters of the mathematical model of the frozen soil based on temperature measurements in boreholes. Adjustment of the parameters of the mathematical model (thermophysical properties of the soil) is usually carried out by minimizing the discrepancy functional between the experimentally measured and model temperatures in the temperature control boreholes. An important question about the form of this functional and the existence of minima remained after the previous studies. The study aimed at this question included analysis of heat transfer in two horizontal layers (sand and chalk) for two shafts under construction using artificial ground freezing. It was shown that the discrepancy functional minimum under certain conditions moves over time or is nonunique. This phenomenon results in ambiguity in adjusting the mathematical model parameters in the frozen soil to fit the borehole temperature survey data. At the stage of the frozen wall growth, the effective thermal conductivity in the frozen zone can be determined ambiguously from the temperature measurements in the boreholes—its value can change over time. At the stage of maintaining the frozen wall, the solution turns out to be dependent on the ratio of effective thermal conductivities in the frozen and unfrozen zones.

Generation and fate of basal meltwater during winter, western Greenland Ice Sheet

Abstract. Basal sliding in the ablation zone of the Greenland Ice Sheet is closely associated with water from surface melt introduced to the bed in summer, yet melting of basal ice also generates subglacial water year-round. Assessments of basal melt rely on modeling with results strongly dependent upon assumptions with poor observational constraints. Here we use surface and borehole measurements to investigate the generation and fate of basal meltwater in the ablation zone of Isunnguata Sermia basin, western Greenland. The observational data are used to constrain estimates of the heat and water balances, providing insights into subglacial hydrology during the winter months when surface melt is minimal or nonexistent. Despite relatively slow ice flow speeds during winter, the basal meltwater generation from sliding friction remains manyfold greater than that due to geothermal heat flux. A steady acceleration of ice flow over the winter period at our borehole sites can cause the rate of basal water generation to increase by up to 20 %. Borehole measurements show high but steady basal water pressure rather than monotonically increasing pressure. Ice and groundwater sinks for water do not likely have sufficient capacity to accommodate the meltwater generated in winter. Analysis of basal cavity dynamics suggests that cavity opening associated with flow acceleration likely accommodates only a portion of the basal meltwater, implying that a residual is routed to the terminus through a poorly connected drainage system. A forcing from cavity expansion at high pressure may explain observations of winter acceleration in western Greenland.

Experience in VES investigation of resistivity structure of the Tuymaada Valley, middle Lena River

This paper discusses experience from the application of direct current vertical resistivity sounding in engineering surveys conducted in 1973–1995 in the Tuymaada Valley of the middle Lena River. Using 349 borehole measurements, the probabilistic variability of three main parameters of resistivity sections is examined for the northern and southern parts of the valley outside of Yakutsk. The first two parameters are electrical resistivities of the frozen Quaternary deposits and the underlying bedrock consisting of sedimentary rocks. The third parameter is bedrock depth. The resistivities of the Quaternary deposits and the bedrock depths show normal probability distributions. The sample estimate of the arithmetic mean resistivity values for the Quaternary deposits in the 95 % confidence interval is 3519 ohm-m, with individual values varying from 2052 to 5238 ohm-m. The probability distribution of the bedrock resistivities is not normal and consists of three groups with modes of 350, 780 and 2500 ohm-m. The multimodal distribution suggests that the bedrock is lithologically inhomogeneous containing a range of rock types with different strengths. The resistivities in each mode group are normally distributed. The overall sample estimate of the most probable mean modal resistivity of the rocks in the southern and northern parts of the valley is 779 ohm-m, while the measured values range from 30 to 3347 ohm-m. The higher mean resistivities compared to Yakutsk are due to the lower anthropogenic salinity of the Quaternary deposits and the higher density of the rocks. The bedrock depths determined by VES are generally consistent with drilling data, with errors mostly less than 20 %. In order of magnitude, the error of the VES method in the Tuymaada Valley is similar to that observed in other permafrost regions of northeastern Russia. The similar levels of error in the available local- and regional-scale VES measurements indicates that VES provides a reliable tool for accurately describing the resistivity structure of river valleys in permafrost regions of Yakutia and elsewhere in Eastern Siberia and the Far East.