Geophysical Monitoring Methods Research Articles

Preface

The 10th International Conference on Environmental and Engineering Geophysics (ICEEG) is hosted by China University of Geosciences, Beijing, China, from June 07-12, 2023. Held biennially since 2004, the ICEEG Conference is one of the most important events for geophysical research and applications in environmental and engineering. Drawing together scientists, engineers, industrial delegates and end-users, the conference is a place to see all of the advanced developments, ranging from fundamental achievement in geophysical methods to the most interesting case studies. Traditionally, the proceedings “Engineering Environmental Geophysics and Intelligent Detection Technology” of the 10th International Conference on Environment and Engineering geophysics is published for the readers from the near-surface geophysics communityShallow surface geophysics refers to the exploration theory and application research on the surface of the earth using physical principles and methods. The shallow surface supports the needs of human survival and development. On the one hand, human beings obtain water and minerals from it, and build the necessary underground space to contain water, electricity, gas, communication, transportation and other pipe network systems in modern cities. On the other hand, various kinds of waste generated by human activities is discharged and buried in it, forming a unique geological layer of the Anthropocene. Whether from the technical level (physics) or non-technical level (politics, society, law), shallow surface geophysics is becoming more and more important. Artificial intelligence technology has been widely used in various fields in recent years, and the construction of smart cities cannot be separated from the support of shallow surface geophysical exploration and monitoring methods and technologies. Due to the integration of urbanization and the development of geophysical technology in China, geophysicists have more opportunities for scientific research. In order to promote exchanges, improve the level of environmental and engineering geophysical exploration, and provide a first-class platform for extensive exchanges among workers engaged in scientific research, technology development and production applications in this field, the 10th International Conference on Environment and Engineering Geophysics will be held in China University of Geosciences (Beijing), a famous university of geosciences. We warmly welcome experts and scholars to contribute and participate in the conferenceIn the proceedings of 10th ICEEG, 160 peer-reviewed research expended abstracts are published according to the following topics: geophysical exploration of urban underground space, high frequency surface wave theory and application, ground penetrating radar technology and application, advances in shallow surface geophysics, engineering geophysics, hydrology and environmental geophysics, disaster geophysical survey, archaeological geophysics, unmanned aerial vehicle detection, smart city geophysics, intelligent detection technology, geophysical monitoring technique, geophysical instruments and software, shallow active source and passive source seismic detection, and young scientists forum.We are deeply grateful to the members of the scientific committee and institutional scientific partners of ICEEG: Chinese Geophysical Society, China University of Geosciences (Beijing), Shallow Surface Geophysical Committee of Chinese Geophysical Society, Professional Committee of Environmental Geophysics, Chinese Geophysical Society, Department of Earth Sciences, National Natural Science Foundation of China, China University of Geosciences (Wuhan), Central South University, Chengdu University of Technology, Chang’ An University, Institute of Geology and Geophysics, Chinese Academy of Sciences, China University of Mining and Technology (Beijing), Zhejiang University and Jilin UniversityWe would like to thank all reviewers for their great efforts to achieve the high quality of published articles.We would also like to extend our gratitude to all participants of 10th ICEEG for their interests and great contributions. Our special thanks go to the invited speakers for their significant contributions to the conference and the proceedings.We would also like to thank all the sponsors. It is your years’ support that makes the ICEEG conference a success.We would also extend our thanks to all committee members and student volunteers for their great efforts in organizing this wonderful event.We hope the proceedings show the challenges and the latest developments in the application of Engineering Environmental Geophysics and Intelligent Detection Technology.

Geophysical and Geochemical Pilot Study to Characterize the Dam Foundation Rock and Source of Seepage in Part of Pensacola Dam in Oklahoma

Pensacola Dam, operated by the Grand River Dam Authority (GRDA), is a multiple-arch buttress dam constructed in 1940. The dam has little or no existing geophysical reports on the integrity of the dam foundation rock and even less knowledge at depth. Visual inspection indicated evidence of seepage at some arches of the dam. As a pilot study, we conducted a suite of geophysical surveys inside two arches (Arch-16 and Arch-17) and a part of the downstream berm to characterize the dam foundation rock, delineate seepage zones, and identify the most appropriate geophysical methods for temporal monitoring of the dam’s conditions. The geophysical methods included electrical resistivity tomography (ERT), self-potential (SP), multichannel analysis of surface waves (MASW), compressional (P)-wave refraction, and shear (S)-wave reflection. Water samples were collected for geochemical analysis to investigate the source of the seepage flow inside Arch-16. The geophysical results characterized the dam foundation rock into an unsaturated limestone and chert overlying a water-saturated limestone and chert. The ERT profiles indicated that groundwater is rising inside the arches and significantly dropping under the downstream berm, which can be due to the uplift pressure beneath the dam base. Zones of high seepage potential were detected near the buttress walls of the two surveyed arches, which may be related to previous blasting, excavation of the dam foundation, concrete placement, or improper grouting. The geochemical analysis of water samples taken from the artesian wells inside Arch-16 and the Grand Lake revealed different chemical compositions, suggesting that the source of water could be a mixture of groundwater and lake water or lake water interacting with rock and reaching the surface through fractures; however, more sampling and further analysis are required to ascertain the source of the seeps. This study showed that the ERT, SP, and S-wave reflection methods have effectively characterized the dam foundation rock and seepage zones beneath the arches. The study provided a better understanding of the conditions of the dam foundation rock, evaluated the utilized geophysical methods, and determined the optimum geophysical methods that can be used for the characterization and monitoring of the subsurface conditions along the entire length of the dam. In this study, we have demonstrated that the integration of effective geophysical surveys and geochemical analysis yielded optimum results in solving a complex dam safety problem. This strategy promotes the best practice for dam safety investigation.

Electromagnetic Monitoring of Modern Geodynamic Processes: An Approach for Micro-Inhomogeneous Rock through Effective Parameters

This study focuses on microscale anisotropy in rock structure and texture, exploring its influence on the macro anisotropic electromagnetic parameters of the geological media, specifically electric conductivity (σ), relative permittivity (ε), and magnetic permeability (μ). The novelty of this research lies in the advancement of geophysical monitoring methods for calculating cross properties through the estimation of effective parameters—a kind of integral macroscopic characteristic of media mostly used for composite materials with inclusions. To achieve this, we approximate real geological media with layered bianisotropic media, employing the effective media approximation (EMA) averaging technique to simplify the retrieval of the effective electromagnetic parameters (e.g., apparent resistivity–inversely proportional to electrical conductivity). Additionally, we investigate the correlation between effective electromagnetic parameters and geodynamic processes, which is supported by the experimental data obtained during monitoring studies in the Tien Shan region. The observed decrease and increase in apparent electrical resistivity values of ρk over time in orthogonal azimuths leads to further ρk deviations of up to 80%. We demonstrate that transitioning to another coordinate system is equivalent to considering gradient anisotropic media. Building upon the developed method, we derive the effective electric conductivity tensor for gradient anisotropic media by modeling the process of fracturing in a rock mass. Research findings validate the concept that continuous electromagnetic monitoring can aid in identifying natural geodynamic disasters based on variations in integral macroscopic parameters such as electrical conductivity. The geodynamic processes are closely related to seismicity and stress regimes with provided constraints. Therefore, disasters such as earthquakes are damaging and seismically hazardous.

Vertical Barriers for Land Contamination Containment: A Review.

Soil pollution is one of the major threats to the environment and jeopardizes the provision of key soil ecosystem services. Vertical barriers, including slurry trench walls and walls constructed with soil mix technology, have been employed for decades to control groundwater flow and subsurface contaminant transport. This paper comprehensively reviewed and assessed the typical materials and mechanical and permeability properties of soil–bentonite, cement–bentonite and soil mix barriers, with the values of mix design and engineering properties summarized and compared. In addition, the damage and durability of barrier materials under mechanical, chemical, and environmental stresses were discussed. A number of landmark remediation projects were documented to demonstrate the effectiveness of the use of barrier systems. Recent research about crack-resistant and self-healing barrier materials incorporating polymers and minerals at Cambridge University and performance monitoring techniques were analyzed. Future work should focus on two main areas: the use of geophysical methods for non-destructive monitoring and the optimization of resilient barrier materials.

Evolvement of interpretation capacities of seismic measurements in mining of water-soluble minerals

The current development level of geophysical methods for mining monitoring of water-soluble mineral deposits provides opportunities to control the growing variety of potentially hazardous geological and mining conditions, to identify the critical states of rock mass and to monitor the emergency facilities. Seismic surveys for solving the specified problems have proven to be a highly informative method for studying the structural features and properties of productive and waterprotective overburden strata, which has a high information richness of the recorded data. The main set of parameters for the interpretation stage of seismic exploration has been formed based on the experience in shallow seismic surveys within a potash deposit; it incl udes the target reflection times, effective and interval velocities, amplitudes, frequencies and a number of derivatives from these parameters. Improvement and adaptation of world interpretation practices in relation to the indicated seismic studies conditions provides means for increasing reliability of anomalies identification and expanding the set of typical wave ‘images’ for various kinds of inhomogeneities in a wide range of wave field realizations and its attributes. The analysis of irregular wave field component in the results of scattered waves processing, spectral decomposition and RGB-mixing is considered as an additional techniques of qualitative interpretation. An approach is proposed to determining possible fracturing in rock mass based on the variability of interval velocities. In combination with the AVO-analysis, this approach makes it possible to assess the trend of rock disintegration within the emergency facilities. The interpretation results of the areal (quasi-3D) and spatial (3D) detailed surveys of a shallow potash deposit are presented.

Acoustic Monitoring of Anomaly Stressed Zones, Determination Their Positions, Surfaces, Evaluation of Catastrophic Risk

Problem statement. Self-organization is not a universal property of matter, it exists under certain internal and external conditions and this is not associated with a special class of substances. The study of the morphology and dynamics of migration of anomalous zones associated with increased stresses is of particular importance in the development of deep deposits, complicated by dynamic phenomena in the form of rock impacts. Applied method and design: An important tool for this study is geophysical exploration. To describe the geological environment in the form of an array of rocks with its natural and technogenic heterogeneity, one should use its more adequate description, which is a discrete model of the medium in the form of a piecewise heterogeneous block medium with embedded heterogeneities of a lower rank than the block size. This nesting can be traced several times, i.e. changing the scale of the study; we see that heterogeneities of a lower rank now appear in the form of blocks for heterogeneities of the next rank. A simple averaging of the measured geophysical parameters can lead to distorted ideas about the structure of the medium and its evolution. Typical results: We have analyzed the morphology of the structural features of disintegration zones before a strong dynamic phenomenon. The introduction of the proposed integrated passive and active geophysical monitoring into the mining system, aimed at studying the transient processes of the redistribution of stress-strain and phase states, can help prevent catastrophic dynamic manifestations during the development of deep-located deposits. Concluding note (Practical value/implications): Active geophysical monitoring methods should be tuned to a model of a hierarchical heterogeneous environment. Iterative algorithms for 2-D modeling and interpretation for sound diffraction and a linearly polarized transverse elastic wave on the inclusion with a hierarchical elastic structure located in the J-th layer of the N-layer elastic medium are constructed.

Assessment of geophysical monitoring methods for detection of brine and CO2 leakage in drinking water aquifers

We evaluated and compared the effectiveness of four surface-based geophysical monitoring methods to downhole pressure and chemical methods to detect brine and CO2 leakage in underground sources of drinking water overlying a CO2 storage reservoir. This assessment uses synthetic monitoring data generated from 400 simulated aquifer impact data sets. The six monitoring techniques can detect impacted groundwater once 20,000 tonnes of CO2 have leaked into the drinking water resource. Geophysical methods are most effective at detecting shallow plumes. Although downhole monitoring methods outperform geophysical methods in detecting deep plumes, geophysical methods may help reduce the false negative during the post injection site care because they detect impacted groundwater where downhole sensors may be absent.This analysis informs future monitoring plans by defining the size of leaks that can be detected for a range of techniques and the need for using complementary methods that measure CO2 gas and changes in groundwater chemistry spatially in addition to discrete point source measurements. A comprehensive monitoring plan consists of (1) site specific reservoir, wellbore leakage and geochemical models to predict likely aquifer impact; (2) downhole TDS sampling to provide an early indication of brine and CO2 leakage; (3) downhole pressure monitoring to track migration of the CO2 plume; and (4) surface-based geophysical methods to track the shallow leakage plumes. It is important to combine downhole measurements with geophysical methods that are sensitive to CO2 gas and TDS to improve leak detection and add confidence that “no detection” means no leak.

Integration of Wellbore Pressure Measurement and Groundwater Quality Monitoring to Enhance Detectability of Brine and CO2 Leakage

Abstract Leakage detectability is a key consideration in evaluating the effectiveness of a measurement, monitoring and verification (MMV) plan for a geologic carbon storage (GCS) project. While studies have shown that surface-based, geophysical monitoring methods may be sensitive enough to detect CO2 leakage, these methods are an indirect indicator of leakage. A drawback to relying on direct geochemical monitoring is that by the time a significant leak is confirmed, it may be too late to mitigate or remediate the environmental impacts. In this study, we combine information from geophysical and geochemical monitoring methods to provide an integrated diagnosis of leakage events. The detectability for various monitoring parameters (pH, TDS, alkalinity, Ca, Cl, Na, and pressure) collected from monitoring wells are evaluated by leakage detection probability, using simulated wellbore-leakage/plume-migration events and monitoring scenarios for a hypothetical GCS operation at the Kimberlina site in California, USA. The NUFT code is used to model these events, by coupling wellbore-leakage simulations to 3-dimensional reactive, multi-phase, flow and transport simulations of brine and CO2 leakage-plume migration in aquifers overlying the GCS reservoir. Wellbore leakage in legacy wells located 1.4, 3.4 and 6.8 km from the CO2 injector is evaluated for a range of (1) wellbore bottom-hole pressure and CO2 saturation determined by GCS simulations, (2) regional groundwater gradient in the aquifers, and (3) wellbore permeability. Simulated leakage-induced changes in seven monitoring parameters at different depths are used to calculate the corresponding detection probabilities, based on the background distribution data and selected monitoring-technology detection thresholds. The responses for these monitoring parameters are tested and combined to enhance the overall detectability. The results indicate the leakage signals are more easily detected at shallower depths where buoyant CO2 has migrated and flashed from supercritical to gas phase, causing a large increase in CO2 volume. While the results suggest pH monitoring is more responsive to the simulated leakage events than TDS monitoring at shallower depths, TDS changes may be more readily observed at greater depths. The addition of carbonate alkalinity can confirm CO2 leakage detection and help distinguish CO2 leakage from other contamination sources. Direct pressure change measurements are very sensitive to leakage, but the rapid and broad propagation of the pressure response hinders using such measurements to easily locate the origin of leakage. Combining measurements could greatly improve the confidence of leakage diagnosis. High bottom-hole CO2 saturation, such as that for a leaky well close to the injector (˜1.4 km), high regional groundwater gradient, and high wellbore permeabilities all increase the leakage plume size, and thus the leakage detectability. Our analysis suggests pressure monitoring is a valuable indicator of leakage events at early stages, while pH, TDS and carbonate alkalinity monitoring can directly diagnose leakage impacts by providing more detailed information in the groundwater receptor. Finally, an example Bayesian belief network model is presented for evaluating the effect of risk reduction options in terms of joint monitoring detection probability using the associated simulation scenarios. This framework is demonstrated to inform how pressure and groundwater quality information can be integrated into site MMV and risk management plans.

Integration of wellbore pressure measurement and groundwater quality monitoring to enhance detectability of brine and CO2 leakage

Leakage detectability is a key consideration in evaluating the effectiveness of a measurement, monitoring and verification (MMV) plan for a geologic carbon storage (GCS) project. While studies have shown that surface-based, geophysical monitoring methods may be sensitive enough to detect CO2 leakage, these methods are an indirect indicator of leakage. A drawback to relying on direct geochemical monitoring is that by the time a significant leak is confirmed, it may be too late to mitigate or remediate the environmental impacts. In this study, we combine information from geophysical and geochemical monitoring methods to provide an integrated diagnosis of leakage events. The detectability for various monitoring parameters (pH, TDS, alkalinity, Ca, Cl, Na, and pressure) collected from monitoring wells are evaluated by leakage detection probability, using simulated wellbore-leakage/plume-migration events and monitoring scenarios for a hypothetical GCS operation at the Kimberlina site in California, USA. The NUFT code is used to model these events, by coupling wellbore-leakage simulations to 3-dimensional reactive, multi-phase, flow and transport simulations of brine and CO2 leakage-plume migration in aquifers overlying the GCS reservoir. Wellbore leakage in legacy wells located 1.4, 3.4 and 6.8 km from the CO2 injector is evaluated for a range of (1) wellbore bottom-hole pressure and CO2 saturation determined by GCS simulations, (2) regional groundwater gradient in the aquifers, and (3) wellbore permeability. Simulated leakage-induced changes in seven monitoring parameters at different depths are used to calculate the corresponding detection probabilities, based on the background distribution data and selected monitoring-technology detection thresholds. The responses for these monitoring parameters are tested and combined to enhance the overall detectability. The results indicate the leakage signals are more easily detected at shallower depths where buoyant CO2 has migrated and flashed from supercritical to gas phase, causing a large increase in CO2 volume. While the results suggest pH monitoring is more responsive to the simulated leakage events than TDS monitoring at shallower depths, TDS changes may be more readily observed at greater depths. The addition of carbonate alkalinity can confirm CO2 leakage detection and help distinguish CO2 leakage from other contamination sources. Direct pressure change measurements are very sensitive to leakage, but the rapid and broad propagation of the pressure response hinders using such measurements to easily locate the origin of leakage. Combining measurements could greatly improve the confidence of leakage diagnosis. High bottom-hole CO2 saturation, such as that for a leaky well close to the injector (˜1.4 km), high regional groundwater gradient, and high wellbore permeabilities all increase the leakage plume size, and thus the leakage detectability. Our analysis suggests pressure monitoring is a valuable indicator of leakage events at early stages, while pH, TDS and carbonate alkalinity monitoring can directly diagnose leakage impacts by providing more detailed information in the groundwater receptor. Finally, an example Bayesian belief network model is presented for evaluating the effect of risk reduction options in terms of joint monitoring detection probability using the associated simulation scenarios. This framework is demonstrated to inform how pressure and groundwater quality information can be integrated into site MMV and risk management plans.

Correlations between acoustic and electromagnetic emissions and stress drop induced by burst-prone coal and rock fracture

Rockburst is a global problem in underground mining industry, threatening mining safety. Acoustic emission (AE) and electromagnetic emission (EME) are nondestructive and real-time geophysical monitoring methods with great significance for the accurate monitoring and early warning of rockburst hazard. To further evaluate the correlations between AE, EME, and stress drop quantitatively and provide an experimental basis for the in-site monitoring of rockburst hazard, an AE, EME, and load synchronous test system was established and used to obtain the full-waveform data of AE, EME, and load in the failure process of burst-prone coal and rock samples under uniaxial compression. The correlations between AE, EME, and stress drop and the spectral characteristics of AE and EME were studied. The results show that the number of AE events is greater than that of EME events. EME is generally accompanied by the stress drop and high-intensity AE and has better correlation with stress drop than AE. Rock samples have greater correlations among AE, EME, and stress drop than coal samples. For rock samples, the correlation coefficients between AE and stress drop, EME and stress drop, and AE and EME are 0.782, 0.889, and 0.697, respectively, while for coal samples, they are 0.529, 0.889, and 0.538, respectively. The frequency spectra of AE and EME have a high correlation, and they have the same low-frequency components of 1–17 kHz, which can be used as the frequency band of local monitoring in working face scale.

Modelling Medium-Depth CO2 Injection at the Svelvik CO2 Field Laboratory in Norway

The CO2 field laboratory at the Svelvik ridge near Oslo, Norway, is presently being upgraded as part of the European research infrastructure initiative (the ECCSEL laboratories). The test site was established in 2010 by the SINTEF-coordinated CO2FieldLab project with the overall objective to study the performance of monitoring systems to detect and quantify CO2 migration and leakage. At the site there is a possibility of injecting CO2 in a sand-rich sedimentary interval at 60-m depth, under a clay-rich interval. The feasibility of using geophysical monitoring methods to detect and quantify such an injection was studied earlier for injection of nitrogen. Nitrogen, with a low solubility in brine, was used to get a clear saturation response. In this paper we revisit the modelling work and extend the scenarios by also modelling injection of CO2. The large difference between solubility of N2 and CO2 in reservoir brine gives markedly different behaviour of the injected gases. Results from these modelling studies will be useful in the mapping of options for future projects at the field laboratory.

Microseismic and electromagnetic coupling method for coal bump risk assessment based on dynamic static energy principles

Electromagnetic emission (EME) and micro-seismic (MS) monitoring are two most important and commonly used geophysical methods for coal bump monitoring in China coal mines. Research have proved during the preparation and development of coal bump the EME can represent energy accumulation in coal seam, while MS have a duality of stress concentration and energy release. And Field investigations have revealed that coal bump events occurred in longwall coal mines manly induced by static coupling dynamic loads. So it is much more valuable and useful for risk evaluate if these two methods synthesized together. Based on energy principles the precursory rules of coal bump are studied in this paper combining with the EME and MS monitoring, the coupling evaluation system was established based on the monitoring results of a specific coal bump colliery, the critical values of EME and MS are formulate based on laboratory test and a large number of site investigation that more than 100 mines in China. A typical precursory of coal bump is that the EME strength exceeds the critical value while total MS energy maintains a low lever at the same time the number of tremors appears an increase tendency. The risk will be gradually reduced when the MS events keep a steady energy release under the critical value even though the EME strength is higher. The research outcomes also provide a foundation for the control and effect inspect of coal bump.

Energy storage in the geological subsurface: dimensioning, risk analysis and spatial planning: the ANGUS+ project

New techniques and methods for energy storage are required for the transition to a renewable power supply, termed “Energiewende” in Germany. Energy storage in the geological subsurface provides large potential capacities to bridge temporal gaps between periods of production of solar or wind power and consumer demand and may also help to relieve the power grids. Storage options include storage of synthetic methane, hydrogen or compressed air in salt caverns or porous formations as well as heat storage in porous formations. In the ANGUS+ project, heat and gas storage in porous media and salt caverns and aspects of their use on subsurface spatial planning concepts are investigated. The optimal dimensioning of storage sites, the achievable charging and discharging rates and the effective storage capacity as well as the induced thermal, hydraulic, mechanical, geochemical and microbial effects are studied. The geological structures, the surface energy infrastructure and the governing processes are parameterized, using either literature data or own experimental studies. Numerical modeling tools are developed for the simulation of realistically defined synthetic storage scenarios. The feasible dimensioning of storage applications is assessed in site-specific numerical scenario analyses, and the related spatial extents and time scales of induced effects connected with the respective storage application are quantified. Additionally, geophysical monitoring methods, which allow for a better spatial resolution of the storage operation, induced effects or leakages, are evaluated based on these scenario simulations. Methods for the assessment of such subsurface geological storage sites are thus developed, which account for the spatial extension of the subsurface operation itself as well as its induced effects and the spatial requirements of adequate monitoring methods.

Numerical modelling of CO2 injection at small-scale field experimental site in Maguelone, France

To evaluate the performance of downhole and surface geophysical monitoring methods, a series of shallow gas injection-monitoring experiments has been performed in a coastal saline aquifer at Maguelone, France. The recorded data include pressure measurements with a Westbay multilevel completion and CO2 saturation at an observation well derived from electrical resistivity with a modified Waxman-Smits (MWS) model. In this work, the aim is to develop a simulation model capturing the gas transport behavior and consistent with field data. For this purpose, the simulation of the CO2 injection experiment is carried out with two conceptual models, a homogeneous model and a heterogeneous model treated with multiple realization Monte Carlo simulations. Numerical simulator TOUGH2 with the equation of state module EOS7C is used for the simulations. Comparison of the model results with field data suggests that the pressure responses are captured with relatively good accuracy. Similarly, the model also provides an overall reasonable agreement and correct order of magnitude for predicted gas saturation values. However, as the heterogeneity pattern in the field data remains largely unknown, the model predictions can only be used to capture the mean behavior as well as to provide insights into how heterogeneity can influence the system behavior, by means of sensitivity analyses of the influence of heterogeneities on individual realizations.

Application of geophysical methods for monitoring of surface and subsurface changes of origin archaeological terrains &ndahs; case studies of sites in the Czech Republic

Abstract. Geophysical methods could be used in wider scale for monitoring of changes of different archaeological terrains and types of archaeological situations. Agriculture, afforestation or other changes of land use play important role in real preservation of surface and subsurface and subsoil archaeological layers. Quality of many prehistoric, early medieval or medieval archaeological sites is rapidly changing during the time. Many of archaeological situations are today preserved only as subsurface remains of archaeological situations and various anthropogenic activities. A substantial part of these activities and their state of preservation can still be also traced by geophysical methods. Four examples from various types of archaeological sites in this paper document different possibilities of applied geophysical methods always dependent on state of archaeological site and conditions of measurements.

Bayesian inversion of gravimetric data and assessment of CO2 dissolution in the Utsira Formation

Offshore gravimetric monitoring has been introduced as a complement to seismic monitoring of fields with moving fluids. The Sleipner field in the North Sea is a fully operational carbon capture and storage facility, where [Formula: see text] is injected for storage. Gravimetric measurements are one of the geophysical monitoring methods applied, and the data have been used to estimate the in situ density and dissolution of the [Formula: see text]. We defined a Bayesian inversion of gravimetric data, and we used this to analyze gravimetric data at Sleipner field. In our approach, we included spatial uncertainty in the model and performed a Bayesian analysis of the in situ [Formula: see text] density and dissolution. We also analyzed the impact of mass changes due to gas production from the Ty Formation. Our estimates were comparable with published results.

Geochemical Monitoring of the Thermal Manifestations Located Near the Bouillante Geothermal Power Plant, in Guadeloupe (FWI)

The Bouillante high-temperature geothermal field, 250-260°C, is developed around the Bouillante Bay along the western coast of Basse-Terre Island, in Guadeloupe (French West Indies, FWI). Since 2005, the new geothermal power plant has an installed capacity of 15.5 MWe gross, which represents about 6-7% of the annual electricity needs in the Island.Among the research efforts carried out by the BRGM group and partially funded by ADEME (French Environment and Energy Management Agency), different geophysical and geochemical monitoring methods of the geothermal exploitation have been started, tested and developed1in order to optimize and secure electricity production and to control its impact on the immediate environment of the power plant. This is especially important because the power plant is located inside the Bouillante town. Among these methods, this paperpresents the main results and conclusions obtained for the geochemical monitoring of the terrestrial thermal manifestations located near the geothermal power plant. This study shows that, except for the “Tuyau” hot water,located inside the main production area and for which the steam contribution increases and salinity decreases when the power plant is in production (decreasing reservoir pressure), no significant geochemical change depending on the geothermal exploitation is observed in the fluids of the other terrestrial thermal manifestations. Consequently, the quality of the thermal waters of the Bouillante area can be considered as not damaged by the geothermal exploitation.

A combined seismic and geoelectrical monitoring approach for CO2 storage using a synthetic field site

This paper presents an approach to assess the methods of 2D elastic seismic full waveform inversion (FWI) and electrical resistivity tomography (ERT) for monitoring storage of CO2 in deep saline formations. As at a real site the subsurface is not fully known, this approach uses a synthetic field site. Densities and saturations are obtained from a numerical simulation of the injection process and are introduced into geophysical forward models which simulate the geophysical data acquisition from the surface (FWI) and boreholes (ERT). These synthetic geophysical data are then evaluated with respect to changes in CO2 saturation and are compared to the fully known CO2 saturation of the numerical process model to verify the geophysical monitoring methods. Results show that both methods are capable of detecting a thin CO2 phase body in about 2,200 m depth for a synthetic site in the North German Basin. Inverted CO2 saturations are in good agreement, however, both methods cannot resolve the CO2 phase edges of less than 4 m saturated thickness. The maximum error of estimated CO2 saturation is 10 % for the FWI method and 15 % for the ERT method, if accurate baseline models are available. The FWI method sensitivity on the baseline model is tested by a sensitivity analysis demonstrating high sensitivity on bulk density, but low sensitivity on fluid densities and porosity. ERT results are considerably improved using structural information from the FWI as constraint.

Reservoir monitoring of steam‐assisted gravity drainage using borehole measurements

ABSTRACTThis paper presents the results from a research project focusing on permanent cross‐well geophysical methods for reservoir monitoring during steam‐assisted gravity drainage. A feasibility study indicated detectable differences in seismic and electrical reservoir properties based on expected changes in temperature and fluid saturation during the production of extra heavy oil. As a result of this, a permanent cross‐well system was installed at the Leismer Demonstration Area, located in the Athabasca Oil Sands region in Alberta, Canada. Baseline data sets, including cross‐well seismic, three‐dimensional vertical seismic profiling and cross‐well electrical resistivity tomography, have been acquired. Comparisons between conventional surface seismic and downhole seismic data show an increase in resolution and frequency content as expected. Steam‐assisted gravity drainage‐induced time‐lapse effects are clearly visible in the 3D vertical seismic profiling and electrical resistivity tomography data sets, even after a few months of oil production. In general, the 3D vertical seismic profiling images show a higher resolution than the surface seismic data, in particular when dealing with vertical positioning of the time‐lapse events. The electrical resistivity tomography baseline shows clear separation between zones of high and low electrical resistivity, and during 23 months of electrical resistivity tomography measurements the maximum reduction of resistivity is 85%. Time‐lapse observations from acoustic and electrical borehole data correspond well, and are also supported by temperature measurements in the two observation wells. Emerging technologies, updated models, improved flexibility, and reduced costs will allow future reservoir monitoring with surface and borehole data in combination, or even with borehole data exclusively.

Geophysical Monitoring Methods Evaluation for the FutureGen 2.0 Project

A comprehensive monitoring program will be needed in order to assess the effectiveness of carbon sequestration at the FutureGen 2.0 carbon capture and storage (CCS) field-site. Geophysical monitoring methods are sensitive to subsurface changes that result from injection of CO2 and will be used for: (1) tracking the spatial extent of the free phase CO2 plume, (2) monitoring advancement of the pressure front, (3) identifying or mapping areas where induced seismicity occurs, and (4) identifying and mapping regions of increased risk for brine or CO2 leakage from the reservoir. Site-specific suitability and cost effectiveness were evaluated for a number of geophysical monitoring methods including: passive seismic monitoring, reflection seismic imaging, integrated surface deformation, time-lapse gravity, pulsed neutron capture logging, cross-borehole seismic, electrical resistivity tomography, magnetotellurics and controlled source electromagnetics. The results of this evaluation indicate that CO2 injection monitoring using reflection seismic methods would likely be difficult at the FutureGen 2.0 site. Electrical methods also exhibited low sensitivity to the expected CO2 saturation changes and would be affected by metallic infrastructure at the field site. Passive seismic, integrated surface deformation, time-lapse gravity, and pulsed neutron capture monitoring were selected for implementation as part of the FutureGen 2.0 storage site monitoringmore » program.« less