Subsurface Monitoring Research Articles

The Hejiapingzi landslide in Weining County, Guizhou Province, Southwest China: a recent slow-moving landslide triggered by reservoir drawdown

The Hejiapingzi landslide is a slow-moving landslide along the shore of the reservoir created by the Xiangbiling hydropower dam in Weining County, Guizhou Province, Southwest China. Movement caused cracks in the land surface and residential buildings of Heping village on 20 August 2017 and was triggered after an 8-day continuous drawdown of the reservoir water by 2.2 m. Field investigations and borehole and landslide surface monitoring were carried out to determine the landslide features and deformation characteristics. Based on analysis of the monitoring data, the behavior of the landslide was neither spatially nor temporally uniform. In general, it could not move quickly due to the gentle sliding surface. The possible reasons for landslide occurrence were the drawdown of the reservoir water, the increase in seepage force, and the loss of strength in a soft mudstone layer to form the landslide slip surface. Although mitigation measures, including engineering control or resident relocation to a safe place, have not yet been finally determined, some interim measures including covering landslide cracks, subsurface monitoring, decreasing the reservoir drawdown velocity, and setting velocity thresholds of landslide displacement for warnings are advised to reduce the landslide risk caused by planned reservoir drawdown in 2019.

Monitoring subsurface ground movement using fibre optic inclinometer sensor

The monitoring of subsurface ground movement is important for the prevention and control of geological disaster including land subsidence, ground fissure, surface collapse, and landslides. Inclinometer and extensometer are examples of the conventional geotechnical instruments for monitoring the subsurface ground movement. However, most conventional geotechnical instruments for subsurface monitoring are limited to discrete sensing, high cost, and susceptible to various reading errors. This paper presents the advancement of technology mechanism to monitor horizontal ground movements as well as the data processing technique involved. Distributed optical fibre inclinometer is developed through laboratory pipe bending tests whereas the data is corroborated with conventional instruments. This system was installed on site, measuring the performance of the sensors as well as to monitor the associated ground movements. A simple cost comparative study between fibre optic inclinometer and conventional geotechnical instrumentation indicates the new technology is cost-effective for applications in ground monitoring particularly when monitoring a large number of borehole points and measurement arrays.

Tropical Cyclone Heat Potential and the Rapid Intensification of Hurricane Harvey in the Texas Bight

AbstractHarvey entered the Gulf of Mexico as a tropical depression on 23 August 2017; two days later it had strengthened to a category 1 hurricane. Over the following 30 hr Harvey rapidly intensified, reaching the Texas Bight as a category 3 storm. This intensification continued while Harvey crossed the shelf, making landfall as a category 4 storm 60 km east of Corpus Christi, TX on 26 August. A hydrographic survey two weeks prior to landfall shows that the tropical cyclone heat potential across the Texas Bight was approximately 35 kJ/cm2, which is 55 kJ/cm2 less than the amount of upper ocean heat normally associated with intensification. Combined with buoy, float, and satellite data, we use hydrographic surveys to study the conditions of the Texas Bight that contributed to Harvey's rapid intensification. We find that, at the time of landfall, the Texas Bight was well mixed with very warm water extending from the surface to bottom. As a consequence, mixing induced by Harvey had a small impact on surface temperatures which remained high and supported continued intensification. The results show that tropical cyclone heat potential is not an effective metric for hurricane intensity prediction in shallow water, and illustrate the need for continuous subsurface monitoring in order to improve hurricane forecasts.

Monitoring of remedial works performance on landslide-affected areas through ground- and satellite-based techniques

Differential Interferometric Synthetic Aperture Radar (DInSAR) techniques have repeatedly proved to be an effective tool for built environments monitoring in areas affected by geological hazards. This paper describes how the Coherent Pixel Technique (CPT) approach has been successfully applied to assess the response of an unstable slope to the different phases of remedial works following a landslide event. The CPT technique was performed on 59 COSMO-SkyMed images obtained between May 2011 and August 2016 and centred on the Quercianella settlement (a small hamlet of Livorno municipality, Tuscany, Italy), where the reactivation of a dormant shallow slide had occurred in March 2011 and, hereafter, a geotechnical intervention, designed with the aim of mitigating the risks, has been conducted from August 2013, lasting thirteen months. The time series of CPT results show a deformation pattern with sudden accelerations (up to 21 mm in few months) corresponding to the beginning of the interventions, during which the area has been excavated to install a drainage well, followed by mild decelerations resulting from the stabilization of the area after the conclusion of the works. In particular, the integration of ground-based subsurface monitoring (inclinometers and piezometers) and DInSAR superficial data has provided consistent results for landslide characterization and helped defining the state of activity and the areal distribution of the sliding surface. Moreover, the performance of remedial works in the landslide-affected area has been observed, showing stabilization in the upper part of the hamlet and the ongoing movement in the lower part. The combined monitoring system also led the geotechnical company in charge of remedial works to design further stabilization works in order to preserve buildings and roads in the moving area. Therefore, the integration of remote sensing techniques and in situ instruments represents a timely and cost-efficient solution for intervention works monitoring, opening new perspectives on designing engineering solutions for the stabilization of unstable slopes.

A field experiment of inside CT walk-away DAS-VSP at a deep and highly deviated well for time-lapse subsurface monitoring

A field experiment of inside CT walk-away DAS-VSP at a deep and highly deviated well for time-lapse subsurface monitoring

Imaging and monitoring of the shallow subsurface using spatially windowed surface-wave analysis with a single permanent seismic source

Development of shallow subsurface monitoring systems is important for monitoring the ground stability of shallow formation, and also for conventional deep seismic monitoring because with current techniques, temporal changes in shallow seismic velocities can influence monitoring results for the deep subsurface. We have developed an effective shallow seismic imaging and monitoring system with high spatiotemporal resolution and accuracy using a continuous and controlled source system, the accurately controlled routinely operated signal system (ACROSS). The method applies surface-wave analysis to characterize and monitor the shallow subsurface from the spatiotemporal variation of phase velocities. Because the number of available ACROSS units is usually limited, estimating a shallow subsurface with high spatial resolution is a challenging issue in ACROSS-based monitoring. To overcome this problem, we introduced a 2D spatial window into multichannel analysis of surface waves. We analyzed continuous ACROSS data acquired during seven different data periods from 2014 to 2016 at the Aquistore [Formula: see text] storage site in Canada. As a result, we clearly estimated spatial variations of phase velocities using only a single ACROSS unit. The numerical experiments of our method suggested that the spatial variations could be associated with shallow geologic boundaries in the study area. We identified clear seasonal variations of phase velocities in winter, possibly related to ground freezing in shallow sediments, and we showed the high temporal stability of our monitoring approach in warmer seasons. These results indicated that our approach would have the potential to identify spatiotemporal change in shallow subsurface associated with natural phenomena or fluid leakage.

Lessons learned and best practices derived from environmental monitoring at a large-scale CO2 injection project

Near-surface soil gas and groundwater measurements can be helpful tools in assuaging concerns of potential out-of-zone migration of CO2 from a geologic storage unit into the overlying near-surface environment. These data, therefore, help to build confidence with local stakeholders and regulators that stored CO2 is not impacting surface/near-surface environments. Routine monitoring of soil gas concentrations in the vadose zone can be used to show a lack of change or effect. However, both air temperature modeling and the Romanak et al. (2012) process-based approach should be applied when soil gas data are evaluated, as increased CO2 concentrations can occur naturally from changes in the soil environment. Laboratory testing of groundwater and formation rock (drill cuttings) samples, exposed to varying concentrations of CO2 under in situ temperature and pressure conditions, yield valuable information with respect to water chemistry changes that could occur from a potential out-of-zone migration. Key field-measured groundwater monitoring parameters that change significantly in response to low levels of CO2 are pH (rapid decrease), alkalinity (increase), and conductivity (increase). Empirical models that predict soil gas concentrations using routinely measured climatic data such as air temperature, as well as models that predict the magnitude and duration of potential CO2 exposure in groundwater, should be employed as components of a broad surface and subsurface monitoring program.

Quantitative Stability Analysis of Ground Penetrating Radar Systems

The hardware instability of a ground penetrating radar (GPR) system has a severe impact on the quantitative analysis of GPR data, which is aimed for material characterization and subsurface monitoring. In this letter, an instability index is proposed to quantify the stability performance of a GPR system and the influences of the GPR system type, warm-up time, environmental noise, and the antenna vibration on it are evaluated through a series of laboratory experiments on a sandbox model. It is found that the GPR signal recorded by a stepped-frequency GPR system based on a vector network analyzer is much more stable than that by a commercial impulse GPR system at a cost of more sweep time. A warm-up time of several minutes is enough for an impulse GPR system. Environmental noise has a negligible influence on the stability performance of a GPR system. Mechanical vibrations of GPR antennas have a severe impact on the stability performance of the GPR system, and the instability index and timing jitter can be increased by more than one order of magnitude in a vibrating condition over those in a static condition. The instability index of the direct signal has a negligible difference with that of the reflection signal from a metal plate; thus, a simple measurement of direct signal on the ground surface is suggested for the evaluation of the instability of a GPR system in field in the future.

Technical and economic assessment of subsurface rock mass deformation and pore pressure monitoring using a network of wireless devices

Technical and economic assessment of subsurface rock mass deformation and pore pressure monitoring using a network of wireless devices

A large coaxial reflection cell for broadband dielectric characterization of coarse-grained materials

Knowledge of the frequency-dependent electromagnetic properties of coarse-grained materials is imperative for the successful application of high frequency electromagnetic measurement techniques for near and subsurface monitoring. This paper reports the design, calibration and application of a novel one-port large coaxial cell for broadband complex permittivity measurements of civil engineering materials. It was designed to allow the characterization of heterogeneous material with large aggregate dimensions (up to 28 mm) over a frequency range from 1 MHz–860 MHz. In the first step, the system parameters were calibrated using the measured scattering function in a perfectly known dielectric material in an optimization scheme. In the second step, the method was validated with measurements made on standard liquids. Then the performance of the cell was evaluated on a compacted coarse-grained soil. The dielectric spectra were obtained by means of fitting the measured scattering function using a transverse electromagnetic mode propagation model considering the frequency-dependent complex permittivity. Two scenarios were systematically analyzed and compared. The first scenario consisted of a broadband generalized dielectric relaxation model with two Cole–Cole type relaxation processes related to the interaction of the aqueous phase and the solid phase, a constant high frequency contribution as well as an apparent direct current conductivity term. The second scenario relied on a three-phase theoretical mixture equation which was used in a forward approach in order to calibrate the model. Both scenarios provide almost identical results for the broadband effective complex relative permittivity. The combination of both scenarios suggests the simultaneous estimation of water content, density, bulk and pore water conductivity for road base materials for in situ applications.

Modified APEX model for Simulating Macropore Phosphorus Contributions to Tile Drains.

The contribution of macropore flow to phosphorus (P) loadings in tile-drained agricultural landscapes remains poorly understood at the field scale, despite the recognized deleterious impacts of contaminant transport via macropore pathways. A new subroutine that couples existing matrix-excess and matrix-desiccation macropore flow theory and a modified P routine is implemented in the Agricultural Policy Environmental eXtender (APEX) model. The original and modified formulation were applied and evaluated for a case study in a poorly drained field in Western Ohio with 31 months of surface and subsurface monitoring data. Results highlighted that a macropore subroutine in APEX improved edge-of-field discharge calibration and validation for both tile and total discharge from satisfactory and good, respectively, to very good and improved dissolved reactive P load calibration and validation statistics for tile P loads from unsatisfactory to very good. Output from the calibrated macropore simulations suggested median annual matrix-desiccation macropore flow contributions of 48% and P load contributions of 43%, with the majority of loading occurring in winter and spring. While somewhat counterintuitive, the prominence of matrix-desiccation macropore flow during seasons with less cracking reflects the importance of coupled development of macropore pathways and adequate supply of the macropore flow source. The innovative features of the model allow for assessments of annual macropore P contributions to tile drainage and has the potential to inform P site assessment tools.

Injectable Contrast Agents for Enhanced Subsurface Mapping and Monitoring

Injection of fluids into geologic formations for long term disposition (CO2) or to improve energy extraction operations can benefit from subsurface monitoring programs capable of providing three dimensional spatial imaging of fluid distributions in the host reservoirs. More importantly, advancements in horizontal drilling and fluid fracking technologies are attracting a broader portfolio of non-traditional engineered subsurface reservoirs that possess complex fluid flow typically through engineered fracture networks. For example, producing fossil fuels from tight sands or shale formations, geothermal based heat extraction operations in low-permeability rock formations, and storing injected fluids (i.e. CO2, acid gases, waste waters, etc.) in the subsurface all require rigorous tracking techniques capable of identifying fluid migration. Current methodologies for four dimensional (3D spatial changes over time) subsurface monitoring of injected fluids are typically geophysical, using surface stations and borehole devices which employ seismic, electromagnetic, and gravitational techniques. However current methods often lack sufficient measurement sensitivity to adequately track fluid migration, and often incur a large economic cost. In this paper, we describe an entirely new class of acoustically responsive contrast agents to enable high-sensitivity, high-resolution tracking of injected fluids via conventional seismic imaging that have the potential of improving subsurface fracture network mapping and plume monitoring in CO2 storage operations.

Validating Subsurface Monitoring as an Alternative Option to Surface M&V - The CO2CRC's Otway Stage 3 Injection

Future CO2 storage projects will require Monitoring and Verification (M&V) operations at the CO2 storage site to understand the behavior of the CO2 plume, including the assurance that leakage of the CO2 has not occurred. Current surface based monitoring technologies may be unable to yield sufficient resolution or accuracy. CO2CRC, in conjunction with its Australian partners, is developing the Otway Stage 3 Project to identify and validate sub-surface monitoring techniques and configurations as a key element of a risk-based M&V program in large scale CCS projects. Subsurface monitoring approaches will be tested on a plume of CO2 from an array of monitoring wells. Primary monitoring methods will be pressure tomography and downhole seismic, although other modalities (gravity, electromagnetic) are also being considered.

Measured short-term ground surface response to EPBM tunnelling in London Clay

Earth-pressure-balance machines (EPBMs) were used for the construction of Crossrail tunnels in London, providing opportunities for field investigation of consequent ground response. Analysed results from an instrumented research site in Hyde Park with extensive surface and subsurface monitoring arrays are presented and discussed. The Crossrail tunnels at the site are 34·5 m below ground, deeper than those in most case histories of tunnelling in stiff clay in the UK. This paper characterises the tunnelling-induced ground response, both ‘greenfield’ and in the proximity of the existing Central Line tunnels, dealing with measurements at the ground surface. A companion paper covers the subsurface ground response. Vertical and horizontal ground surface displacements were obtained from manual precise levelling and micrometer stick measurements. Several key findings will benefit future tunnelling projects involving EPBMs. Volume loss values measured at the instrumented site were low, being less than 0·8% and 1·4% for the first and second tunnel drives respectively, higher values being associated with ground softening from the first tunnel construction. Smaller volume losses were recorded in the vicinity of the existing Central Line tunnels, compared with the greenfield location, suggesting that their presence inhibited the development of ground movements. Asymmetric settlement troughs developed due to either the nearby pre-existing tunnels or the construction of the first tunnel. Marginally smaller values of trough width parameter, Ky, were determined for these deeper tunnels compared with previous greenfield ground case histories. Resultant vectors of ground surface displacement were directed to well-defined point-sinks above the tunnel axis level.

Estimation of fracture height growth in layered tight/shale gas reservoirs using flowback gas rates and compositions–Part II: Field application in a liquid-rich tight reservoir

While hydraulic fracturing is the key to unlocking the potential of unconventional low-permeability hydrocarbon resources, challenges remain in the monitoring of subsurface propagation of fractures and the determination of which geologic intervals have been contacted. This is particularly challenging for wells that are completed in multiple hydraulic fracture stages (multi-fractured horizontal wells or MFHWs) where fracture spacing may be very close and fracture geometry complex. Understanding the fracture extent is important not only for assisting with hydraulic fracture design, but also for mitigating unwanted fracture growth into non-target geologic intervals that do not contain hydrocarbons (e.g. zones with high water saturation). Popular current technologies used for hydraulic fracture surveillance include microseismic (surface and subsurface monitoring) and tiltmeter surveys. While these methods have proven useful for characterizing the extent of created hydraulic fractures, they do not necessarily lead to an understanding of what portions of the geologic section (bounding and target intervals for MFHWs, for example) are in direct hydraulic communication with the well.A solution for establishing the extent of hydraulic fracture growth from target to bounding zones is to first obtain a fluid composition fingerprint of those intervals while drilling through them, and then compare these data with fluid compositions obtained from flowback after hydraulic fracturing. In the current work, a MFHW completed in a liquid-rich tight reservoir is used to test this novel concept. Gas samples extracted from the headspace of isojars® containing cuttings samples, obtained during drilling of the MFHW well, were used to geochemically fingerprint geologic intervals through which the well was drilled. The cuttings samples were collected at high frequency in the vertical, bend and lateral sections of the well over a measured depth range of 4725 ft (1440 m). A compositional marker was identified in the bend of the horizontal well above which the average methane to ethane (C1/C2) ratio was 15.7, versus 2.6 below it. The flowback gas compositions were observed to be intermediate (average C1/C2 = 7.4) between the reservoir above and below the marker, suggesting fracture height grew above the compositional marker.In order to estimate fracture height growth from the geologic interval and flowback compositions, a compositional numerical simulation study was performed. An innovative approach was used to estimate recombined in-situ fluid compositions, on a layer-by-layer basis, by combining the cuttings gas compositional data with separator oil compositions. The resulting numerical simulation model, initialized through use of the layered fluid model and a detailed geological model developed for the subject well and offset drilling locations, was used to history match flowback rates, pressures and gas compositions. The gas compositions of the fingerprinted geologic intervals were therefore employed as a constraint on fracture height growth, estimated in the model to be 175 ft (53 m, propped height). However, because of the uncertainty in model input parameters, a stochastic approach was required to derive a range in hydraulic fracture properties.The current study demonstrates for the first time that it is possible to constrain fracture height growth estimates from flowback data, combined with gas compositional data obtained from cuttings data, provided that the geochemical fingerprints are distinct.

Automated Electrical Resistivity Tomography Testing for Early Warning in Unstable Permafrost Rock Walls Around Alpine Infrastructure

Subsurface monitoring of permafrost conditions at depths up to 20–30 m is crucial to assess the safety and reliability of mountain infrastructure, because permafrost degradation critically affects rock slope stability in high mountains. Electrical resistivity tomography (ERT) provides a straightforward tool for monitoring near-surface bedrock permafrost at monthly or longer intervals. But as rockfalls are often prepared over periods of hours or days, ERT for early warning purposes should also detect short-term triggering events such as pressurised water flow. Here, we present the first approach to monitor steep permafrost rock walls quasi-continuously with ERT. We measured ERT every 4 h at the up to 67° steep rock wall below the Kitzsteinhorn cable car, Austria. Wenner datasets (n = 996) were analysed from February 2013 to February 2014 in terms of data stability, raw data characteristics and measurement errors coinciding with potential disturbing factors. Strong resistivity changes coincided with rapid freezing or water inundating rock fractures. Automatically detected periods with large resistivity changes produce ERT time series with low resistivities extending from the bottom upwards during times of snowmelt. We infer that flow of pressurised water in fractures warms the surrounding rock in an upward direction, based on fracture inventories, visual observations of cleftwater and near-surface temperature measurements. We develop a strategy for ERT monitoring suitable for potential early warning systems, where high apparent resistivity changes in 4 h intervals may precede critical hydrostatic events confined by permafrost rocks. Copyright © 2016 John Wiley & Sons, Ltd.

Urban subsurface drainage as an alternative water source in a drying climate

The Swan Coastal Plain in Western Australia has been undergoing rapid urban growth and with it comes two primary water related concerns. The first is the spread of development into areas with shallow water tables which requires costly water management to control groundwater level rise; the second is the limited groundwater allocation available in areas earmarked for development. In regard to the second, a potential water source for developments on low-lying land is subsurface drainage that has been installed to control groundwater levels. This research project is being undertaken at two urban developments on low-lying land and includes subsurface drain flow and quality monitoring. The field data will inform numerical hydrogeological and hydrogeochemical models. The objective is to quantify the subsurface drainage volume available as a water resource, and the environmental and operational risk of utilising the resource. The results to date show potential for diverting subsurface flow for direct irrigation in the drier months without the requirement for wet season storage and dry season reuse. Annual subsurface drainage flows provide multiple times the annual irrigation demand if wet season flows are stored and reused by aquifer storage and recovery, and provides opportunity for beneficial use of excess water.

Editorial: Thematic Issue for the International Conference: novel methods for subsurface characterization and monitoring: from theory to practice (NovCare 2015)

Editorial: Thematic Issue for the International Conference: novel methods for subsurface characterization and monitoring: from theory to practice (NovCare 2015)

Characterization of recharge and flow behaviour of different water sources in Gunung Kidul and its impact on water quality based on hydrochemical and physico-chemical monitoring

Karst aquifers are important water resources but highly vulnerable due to their heterogeneous and complex characteristics. Various hydrological aspects (recharge, flow behaviour) have to be known in detail to develop a sustainable concept for water collection, distribution and treatment. In the karst area of Gunung Sewu (Java, Indonesia) such a concept was to be implemented within a German–Indonesian joint IWRM project. The basic hydrogeological conditions and water quality aspects were characterized on a regional scale through hydrochemical monitoring of springs, wells, subsurface and surface rivers. More detailed information about the recharge, flow and storage behaviour was obtained from high resolution monitoring of T, EC and discharge in one large underground river system. The water quality is well below any guideline values with regard to inorganic pollutants during dry season. During rainy season, dissolved Al concentrations are frequently above the Indonesian guideline value. Slow matrix flow is the most important recharge component during dry season, thus assuring the year-round water availability in the subsurface karst. During rainy season, quick infiltration of the surface water is a dominant recharge component. Rapid response of discharge, T and EC to heavy rain suggests the presence of point recharge that feeds a highly karstfied conduit system with fast conduit flow and short transit time of water. The strong variations in discharge and hydrochemistry are particularly challenging for technical water usage and treatment facilities. Piston flow is indicated to be the third important flow component and is induced by heavy rainfall.

Technology Focus: Production Monitoring/Surveillance (March 2016)

Technology Focus Despite the market conditions during the last year, our industry continued to demonstrate further advances in the monitoring and surveillance field and to attest to the added value provided. General trends from past years are still being pursued to further our knowledge related to the issues seen as most important for production optimization and field management. Studies and methods were shared regarding unconventional development such as fracturing performance and analysis. New developments for multiphase-flow-metering evaluation and verification continue to be a leading topic. Additional studies were shared in understanding flow regimes in long horizontal wells using new methods and combined data gathering. Downhole solutions providing data in horizontal and difficult wellbore trajectories without intervention were further developed with tracers and other technology. New and novel methods for the use of fiber optics continue to come forth with advancements in strain and acoustic measurements that have been shown to add value. Challenges regarding the management of large data streams are still being discussed, although some interesting practical applications incorporating multiple data streams managed simultaneously in real-time scenarios were shared during the past year. Newer trends indicate further cooperation across the industry. Results from multiple collaboration efforts were released and discussed that involved partners from government agencies, operators, service providers, and various third parties working together to solve problems for the future. Case studies are now being presented for practical applications of advanced technology and optimization methodology that were considered only visions not that many years ago. It is very exciting for us to see the results from the efforts that have taken place over the past several years. Success cases for fieldwide implementation of real-time data gathering combined with work flows, modeling, and predictive analysis are becoming more prevalent. Subsurface monitoring applications relating to kick detection and managed-pressure drilling are gaining more attention as we also push the limits on the drilling side of the surveillance field. The technology initially developed for production monitoring may be forging the way for wide applications across oilfield operations. The following is a selection of articles to demonstrate the accomplishments shared by the exceptional peers who chose to publish their knowledge from the last year. Additional reading suggestions are also provided. JPT Recommended additional reading at OnePetro: www.onepetro.org. SPE 173452 Lessons Learned From Worldwide Deployments of Model-Based Real-Time Production-Optimization Solutions by Amol Bakshi, Chevron, et al. IPTC 17773 Real-Time Calculation of Fluid Level Using Dynamometer Card of Sucker-Rod-Pump Well by Yang Haitao, PetroChina, et al. SPE 172593 Combining Horizontal Production-Logging and Distributed- Temperature Interpretations To Diagnose Annular Flow in Slotted-Liner Completions by T. Ben Haoua, Schlumberger, et al.