Distributed Temperature Sensing Measurements Research Articles

Characterization of artesian flow and heat transition in an ATES research wellbore using DTS monitoring and numerical modelling

Abstract. In the practice of Aquifer Thermal Energy Storage (ATES), the hydraulic connection to the wellbore of any other aquifers besides the planned thermal storage should be identified and prohibited in order to operate the ATES system in a sustainable way. The present study was aimed at locating an artesian aquifer other than the planned thermal storage in an ATES research wellbore (Berlin, Germany). Therefore, we analysed the wellbore temperature as monitored with a single fiber optic cable using the Distributed Temperature Sensing (DTS) technique in a series of artesian flow tests. The change in the wellbore temperature, the depth-dependent thermal gradients and the isotherms as derived from the DTS-monitored data helped positioning the artesian aquifer in the depth interval from 220 to 230 m. In addition, the transition from cooling to heating in the wellbore sections above the depth of 40 m was applied calculating the velocity of the artesian flow. A numerical model accounting for such artesian flow was built via matching the simulated volumetric flow rate to the wellhead measurements. The consistency of the simulated wellbore temperature with the DTS measurements validated this numerical model as well as the positioning of the artesian aquifer. These simulates extensively visualized the effect of the artesian flow on the near-wellbore temperature field.

Evaluation of Fluid Distribution and Perforation Erosion in Multistage Fracture Treatment

Summary Fracture monitoring and diagnosis by fiber-optic sensing technology provides invaluable information about stimulation efficiency. This technology becomes more critical for multistage fracturing over long horizontal wells. The combined analysis of distributed temperature sensing (DTS) and distributed acoustic sensing (DAS) measurements has been used to map the fluid distribution during hydraulic fracturing, and fracture volume at the cluster level and at the stage level can be estimated from the analysis. In this paper, based on the interpretation of models for DTS and DAS, we extend the application to fluid containment and stage isolation evaluation. In plug and perforation hydraulic fracturing, when a stage is finished pumping, the stage is isolated by a plug, and the next stage is perforated and then fractured. If the plug is not functioning correctly, fracture fluid enters the previous stage, causing an uneven fluid distribution, and possibly more severe perforation erosion. Both DAS and DTS monitoring can record this phenomenon when it happens. Interpretation models are built to quantify the fluid distribution with the effect of plug leakage included. From DTS measurements, cooling below the stage being completed is counted as the fluid from the current stage. Given this information, the reservoir thermal model can estimate the volume of leakage. From the DAS measurement, we interpret the volume distribution based on frequency band energy to compare with the DTS interpretation. Perforation erosion measurements from a downhole camera are used to confirm the estimation. With this approach, we assess the fluid distribution, plug performance, and the importance of stage isolation on perforation erosion during a multistage fracture treatment. The information can then be used to analyze and optimize completion and fracture treatment design. Field examples are presented in the paper to support the discussion, findings, and conclusions. Based on the results of the fluid distribution estimated, we observed that higher injection rate and larger fluid volumes may create more uniformly distributed fluid between clusters in a stage. When considering communication between stages, the DTS and downhole camera show that there is a correlation between fluid distribution and perforation eroded area. An inconsistency of eroded area and fluid received is observed at toe-side clusters from DTS, DAS, and downhole images. This could be caused by a short erosion time at the toe-side clusters. In the completion design, only a few parameters show a strong impact on fluid distribution and perforation erosion.

A distributed-temperature-sensing-based soil temperature profiler

Abstract. Storage change in heat in the soil is one of the main components of the energy balance and is essential in studying the land–atmosphere heat exchange. However, its measurement proves to be difficult due to (vertical) soil heterogeneity and sensors easily disturbing the soil. Improvements in the precision and resolution of distributed temperature sensing (DTS) equipment has resulted in its widespread use in geoscientific studies. Multiple studies have shown the added value of spatially distributed measurements of soil temperature and soil heat flux. However, due to the spatial resolution of DTS measurements (∼30 cm), soil temperature measurements with DTS have generally been restricted to (horizontal) spatially distributed measurements. This paper presents a device which allows high-resolution measurements of (vertical) soil temperature profiles by making use of a 3D-printed screw-like structure. A 50 cm tall probe is created from segments manufactured with fused-filament 3D printing and has a helical groove to guide and protect a fiber-optic (FO) cable. This configuration increases the effective DTS measurement resolution and will inhibit preferential flow along the probe. The probe was tested in the field, where the results were in agreement with the reference sensors. The high vertical resolution of the DTS-measured soil temperature allowed determination of the thermal diffusivity of the soil at a resolution of 2.5 cm, many times better than what is feasible using discrete probes. A future improvement in the design could be the use of integrated reference temperature probes, which would remove the need for DTS calibration baths. This could, in turn, support making the probes “plug and play” into the shelf instruments without the need to splice cables or experience in DTS setup design. The design can also support the integration of an electrical conductor into the probe and allow heat tracer experiments to derive both the heat capacity and the thermal conductivity over depth at high resolution.

The Modeling of Two-way Coupled Transient Multiphase Flow and Heat Transfer during Gas Influx Management using Fiber Optic Distributed Temperature Sensing Measurements

Effective management of gas influxes during drilling for either oil-gas or geothermal wells is crucial for ensuring operational safety and minimizing non-productive times, especially for high-pressure, high-temperature (HPHT) situations. In recent years, there has been a growing demand for comprehensive modeling techniques that can accurately predict gas influx behaviors during Managed Pressure Drilling (MPD). However, many existing approaches have neglected the heat transfer processes between wellbore fluids and the surrounding formation during gas influx management, which can significantly impact the estimation accuracy.To address this issue, this paper presents an advanced transient multiphase flow and heat transfer modeling framework that integrates the solution of the energy conservation equation with the multiphase mass and momentum equations using a two-way coupled approach. A set of full-scale experimental data, including fiber-optic-based Distributed Temperature Sensing (DTS) measurements, were used to perform thorough validation and verifications of the developed modeling framework. Multiple existing heat convection correlations were benchmarked against the DTS measurements to determine the best match. The data from multi-depth downhole temperature sensors and Distributed Acoustic Sensing (DAS) were also compared to the results from numerical simulations.The estimation results of the wellbore fluids temperature profiles showed good agreement with the DTS data for both transient single-phase flow cases and gas influx management scenarios. A comparative analysis revealed that the selection of convective heat transfer correlations could significantly affect the simulation accuracy of fluid temperature distributions and gas influx behaviors. The benchmarking and optimized selection of convection correlations help to improve the performance of transient heat-transfer modeling. In addition, the two-way coupled approach shows improved accuracy compared to the decoupled methods, particularly for HPHT situations and more transient processes.

Degradation Analysis of Single-Mode and Multimode Fibers in a Full-Scale Wellbore and Its Impact on DAS and DTS Measurements

Distributed fiber optic sensors (DFOS) are viewed as a promising technology for efficient, cost-effective, and non-intrusive real-time monitoring for a variety of applications. The chemical passivity, non-magnetic interference behavior, and ability to acquire continuous measurements at high-spatial resolution have made DFOS very attractive for in-situ measurement of temperature, strain, vibration, etc. The accuracy of the measured parameter by the DFOS is highly dependent on the strength and quality of the optical signal returning from the point of interest. The signal degradation in DFOS results from optical losses due to attenuation, absorption, scattering, bending, dispersion, and coupling. This study analyzes the degradation observed in both the single-mode and multimode fibers installed in a 1574 mdeep wellbore for acquiring distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) data, respectively. The degradation was unexpected as it was observed within three years of DFOS installation in an experimental, non-producing well that contains non-corrosive fluids and operates in a low-temperature (<54.4 °C) and low-pressure (<3500 psi or 24131 kPa) environment. A root-cause analysis was performed to investigate the cause of this degradation using time-lapse optical loss measurements acquired at different wavelengths using an optical time-domain reflectometer. Degradation of the multimode fiber was also examined by the time-lapse analysis of the Raman backscatter that is used for DTS measurement. Based on the investigation, microbending was found to be the main cause of the observed degradation. Its impact on the quality of the DAS and DTS measurements was also analyzed both qualitatively and quantitively. Recommendations for minimizing degradation are presented.

Interpretation of Fracture Initiation Points by In-Well Low-Frequency Distributed Acoustic Sensing in Horizontal Wells

Summary Low-frequency distributed acoustic sensing (LF-DAS) exploits the optical phase shift of Rayleigh backscatter in fiber-optic cables to obtain distributed measurements of changes in strain and temperature. Fiber-optic cables are often installed for multistage hydraulic fracture diagnostics in horizontal wells. LF-DAS in an untreated well provides far-field strain measurements, while offset wells are hydraulically fractured. Such a configuration is called crosswell LF-DAS sensing. Crosswell LF-DAS measurements have proved useful in diagnosing fracture hits, fracture azimuth, planarity, cluster efficiency, fracture propagation rates, and the dynamic distance to the fracture front. In contrast, in-well LF-DAS is conducted on the actively fractured well. Due to cool fracture fluid being injected at high injection rates, the strain component of the LF-DAS response is largely obscured by temperature changes. In permanent fiber-optic cable installations, distributed temperature sensing (DTS) is often conducted simultaneously with LF-DAS. An opportunity exists to decouple the temperature and strain components of LF-DAS sensors to observe strain changes on in-well LF-DAS. The LF-DAS response is modeled as linearly dependent on strain and temperature changes. Theoretical LF-DAS temperature and strain sensitivity coefficients are derived based on the changes to the index of refraction and length of the fiber. Using the DTS measurements, temperature changes are computed, smoothed, filtered, and compared to the LF-DAS response. Crossplots of the in-well LF-DAS measurements and temperature changes from DTS measurements far from the actively fractured region are used to validate the theoretical sensitivity coefficients. Uncertainty in the temperature component of the LF-DAS response is quantified. The difficulty in corresponding the different spatial and temporal resolutions of the DTS and LF-DAS measurements is overcome by comparing the responses over a moving temporal and spatial window. If the LF-DAS response at the center of the window agrees with the DTS response within uncertainty, the measurement is filtered out. After filtering, the remaining nonzero in-well LF-DAS measurements are due to changes in strain. The data are then visualized in waterfall plots. The results indicate that the theoretical and observed strain and temperature coefficients agree within 10%. After the temperature component of the in-well LF-DAS response is extracted, the remaining nonzero measurements are located primarily within the actively treated region. Locations with peaks in the strain response are interpreted to indicate fracture initiation points. These fracture initiation points are compared with in-well DTS and high-frequency DAS noise measurements across multiple stages to better understand fracture initiation along the horizontal well.

Permanent Fiber-Optic DTS Evaluates Production Enhancement

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 31654, “Production Enhancement Evaluation Through Permanent Fiber-Optic Distributed-Temperature-Sensing Interpretation for a Gas-Lifted Producer in Field B, Offshore Malaysia,” by Chang Siong Ting, Nur’ain Minggu, and Dahlila Kamat, Petronas, et al. The paper has not been peer reviewed. Copyright 2022 Offshore Technology Conference. Reproduced by permission. _ In the complete paper, the authors evaluate the effectiveness of production-enhancement activities for Well B Long-String (i.e., Well BL) using distributed-temperature-sensing (DTS) technology. Installation of permanent fiber-optic cable across the reservoir sections has enabled gas-lift monitoring, identification of well-integrity issues, and zonal inflow profiling from perforation contribution. The effectiveness of executed remedial jobs is described along with findings and interpretations of DTS results. Field and Well BL Background Field B is a mature brownfield 45 km offshore east Malaysia in a water depth of approximately 230 ft. The field’s structure has a gentle rollover anticline with a collapsed crest caused by growth faulting. The reservoirs were deposited in a coastal shallow marine environment with channels. The production wells completed in these reservoirs were completed with internal gravel packs. The typical completion types for wells in Field B are dual strings with sliding sleeve doors (SSD), intended for commingled production from the multilayered reservoirs. Most of the wells in Field B were installed with permanent downhole gauges (PDGs), and five wells were equipped with permanent DTS across the reservoir section. The well was completed in 2015 as a gas-lifted dual-string producer with a 3½-in. completion string for short string (BS) and 3½×2⅞-in. tubing crossover for long string (BL). The long string of Well B also produces from two zones, Zones 2 and 3, while the short string of Well B produces from only one zone, Zone 1. Each zone consists of sublayers. In addition, DTS fiber-optic cable was installed along the long string across the reservoir sections in Well BL, and the system enabled the operator to monitor continuously the wellbore temperature across all producing intervals. Each zone also was equipped with a zonal PDG (temperature and pressure) and SSDs. DTS System The double-ended DTS system was installed permanently across the multilayered reservoir in Well BL to measure the dynamic change of temperature in the near-wellbore region over time. Double-ended temperature measurement was used to correct for differential light losses (light-loss correction) that appear gradually over the lifetime of the fiber as its quality is degraded because of hydrogen darkening or exposure to high temperatures. This measure improves the quality and accuracy of the measurement signal backscattered to the surface receiver for processing. With double-ended DTS, small thermal changes over time in the well can be tracked. Temperature measurements are detected in 1.6-ft intervals along the length of the cable. This generates a profile of temperature effects along the production string by analyzing backscattered Raman wavelength light from a pulsed laser source. This DTS measurement allows continuous monitoring of production events as they happen.

Study on the Influence Law of Temperature Profile of Vertical Wells in Gas Reservoirs

Due to the lack of a robust temperature model and poor knowledge about the influence law of temperature profile, it is still highly challenging to interpret the production profile of vertical wells in layered gas reservoirs from distributed temperature sensing (DTS) quantitatively. In this paper, a coupled temperature prediction model for vertical wells in the layered gas reservoir is developed, considering several microthermal effects and non-isothermal seepage. Based on the theoretical simulation, several single factors' influence on the vertical well's temperature profile in a layered gas reservoir has been analyzed. The sensitivity of temperature profiles on different affecting factors has been evaluated through orthogonal test analysis. It has been found that the influence degree of each factor on the temperature profile of the vertical well in the layered gas reservoir is as follows: formation permeability &gt; production rate &gt;water saturation &gt; wellbore inclination angle &gt; relative density of natural gas &gt; formation thermal conductivity &gt; wellbore diameter (k &gt;Qg &gt; SW &gt; θ &gt; dg &gt; Kt &gt; D). The dominant factors affecting the temperature profile of vertical wells in layered gas reservoirs are formation permeability, production rate, and water saturation. The proposed temperature prediction model can serve as the forward model when developing the inversion system to interpret DTS measurement. The findings of this paper provide solid theoretical support for the quantitative interpretation of the flow rate profile for vertical wells in layered gas reservoirs.

The borehole thermal energy storage at Emmaboda, Sweden: First distributed temperature measurements

Xylem in Emmaboda, Sweden, has one of the first borehole thermal energy storage (BTES) sites storing excess heat and has been previously thoroughly studied and monitored. Here, the results from distributed temperature sensing (DTS) measurements in observation boreholes, UB1, 10 m outside the BTES, and UB46, inside the BTES, are presented. The measurements were performed in February and March to September 2019. DTS combined with geological and hydrogeological knowledge give qualitative insights into Emmaboda’s heat transfer in operation. To analyze the DTS measurements, knowledge about the borehole deviations and relative physical locations among boreholes is necessary. The measured temperature profile in UB1 is parallel to the geothermal gradient, follows BTES temperature, and does not seem disturbed by groundwater flow and production boreholes. The flat terrain and several rivers and dams in the area, together with results from the thermal response test following the mineralogical composition of the bedrock, verify no regional groundwater flow. Emmaboda’s heat loss is conductive only. In UB46, the temperature irregularities are interpreted as contact points or vicinity to production boreholes. Larger temperature responses in heat charging than in extraction mode are probably due to higher temperatures. Three-dimensional to four-dimensional design, documentation and visualization should further examine the influence of borehole deviation.

Determination Of Flow Velocities Using Fiber-Optic Temperature Measurements

A novel flow measuring technique is introduced to measure under harsh circumstances in environments with dirt, high pressures and elevated temperatures as in boreholes within the earth's crust. A glass fiber embedded in a cable with heating wires measures the temperature within the heated cable with distributed temperature sensing (DTS). Similar to Hot Wire Anemometry, the velocity dependence of convective heat transfer is exploited to measure the velocity of the cable as a cylinder in crossflow. A borehole-mimicking test rig and a realistic prototype of a borehole probe were built and the flow along the borehole axis was investigated. The expected Nusselt Reynolds characteristic of a cylinder in crossflow has been measured which proves the concept of this novel measurement technique. Challenges arise with the insufficient spatial resolution of DTS measurements and in the heat transfer modeling because the temperature profile of the cables cross-section must be taken into account. More detailed investigations and developments are planned to elevate this measurement technique from the current proof-of-concept stage to a reliable flow measurement technique. As a first step, the DTS technique will be extended the application of fiber Bragg grating (FBG) temperature measurements at specific points along the glass fiber. Subsequently a straight segment of a new hybrid cable will be placed in a water channel perpendicular to the flow direction. The Flow will be precisely specified using Particle Image Velocimetry and multiple temperature sensors in the channel and on the cable's sheath will deliver the information for enhanced heat transfer modelling.

Extension of Duplexed Single-Ended Distributed Temperature Sensing Calibration Algorithms and Their Application in Geothermal Systems.

Fiber-optic distributed temperature sensing (DTS) has been widely used since the end of the 20th century, with various industrial, Earth sciences, and research applications. To obtain precise thermal measurements, it is important to extend the currently available DTS calibration methods, considering that environmental and deployment factors can strongly impact these measurements. In this work, a laboratory experiment was performed to assess a currently available duplexed single-ended DTS calibration algorithm and to extend it in case no temperature information is available at the end of the cables, which is extremely important in geothermal applications. The extended calibration algorithms were tested in different boreholes located in the Atacama Desert and in the Central Andes Mountains to estimate the geothermal gradient in these regions. The best algorithm found achieved a root mean square error of 0.31 ± 0.07 °C at the far end of a ~1.1-km cable, which is much smaller than that obtained using the manufacturer algorithm (2.17 ± 0.35 °C). Moreover, temperature differences between single- and double-ended measurements were less than 0.3 °C at the far end of the cable, which results in differences of ~0.5 °C km−1 when determining the geothermal gradient. This improvement in the geothermal gradient is relevant, as it can reduce the drilling depth by at least 700 m in the study area. Future work should investigate new extensions of the algorithms for other DTS configurations and determining the flow rate of the Central Andes Mountains artesian well using the geothermal profile provided by the DTS measurements and the available data of the borehole

Quantifying the coastal urban surface layer structure using distributed temperature sensing in Helsinki, Finland

Abstract. The structure of the urban boundary layer, and particularly the surface layer, displays significant complexity, which can be exacerbated by coastal effects for cities located in such regions. Resolving the complexity of the coastal urban boundary layer remains an important question for many applications such as air quality and numerical weather prediction. One of the most promising new techniques for measuring the structure of the surface layer is fibre-optic distributed temperature sensing (DTS), which has the potential to provide new significant insights for boundary layer meteorology by making it possible to study thermal turbulence with high spatial and temporal resolution. We present 14 weeks of profile measurements with a DTS system at an urban site in Helsinki, Finland, during the winter and spring of 2020. We assess the benefits and drawbacks of using DTS measurements to supplement sonic anemometry for longer measurement periods in varying meteorological conditions, including those found difficult for the DTS method in prior studies. Furthermore, we demonstrate the capabilities of the DTS system using two case scenarios: a study of the erosion of a near-ground cold layer during the passage of a warm front, and a comparison of the near-ground thermal structure with and without the presence of a sea-breeze cell during springtime convective boundary layer development. This study demonstrates the utility of DTS measurements in revealing the internal surface layer structure, beyond the predictions of traditional surface layer theories. This knowledge is important for improving surface layer theories and parametrisations, including those used in numerical weather prediction. The study also highlights the drawbacks of DTS measurements, caused by low signal-to-noise ratios in near-neutral atmospheric conditions, especially when such a system would be used to supplement turbulence measurements over longer periods. Overall, this study presents important considerations for planning new studies or ongoing measurements utilising this exciting and relatively new instrumentation.

Diagnosing multiphase flow regime in multilayered reservoir by distributed temperature sensor measurements

The article discusses the possibility of diagnosing the multiphase flow regime in the multilayered reservoir by using DTS (distributed temperature sensing) data. The analysis of the theoretical and actual curves of temperature build up and drawdown, corresponding to the main modes of multiphase flow of formation fluids are given in this article. The possibility of diagnosis of the multiphase flow regime is found based on analysis and interpretation of the characteristics of temperature build-up and drawdown in different intervals of the reservoir at the start of the well or shut in, or by changing opening degree of the choke. The possibility of diagnosing water breakthrough (WBT) intervals, based on the analysis of the changes in temperature curves according to the DTS is shown. For a more detailed analysis and interpretation of temperature change curves in the wells more frequent DTS measurements are required. It is necessary to conduct a comparative analysis of the dynamics of the temperature and pressure redistribution in the productive zone of the well, with the results of geophysical logging, production logging, taking samples of reservoir fluids from different zones of productive layers in the multilayered reservoir, moisture metering, hydrometry and others. Keywords: well; monitoring; multilayer reservoir; temperature profile; distributed temperature sensor; multiphase flow regime.

Suitability of fibre-optic distributed temperature sensing for revealing mixing processes and higher-order moments at the forest–air interface

Abstract. The suitability of a fibre-optic distributed temperature sensing (DTS) technique for observing atmospheric mixing profiles within and above a forest was quantified, and these profiles were analysed. The spatially continuous observations were made at a 125 m tall mast in a boreal pine forest. Airflows near forest canopies diverge from typical boundary layer flows due to the influence of roughness elements (i.e. trees) on the flow. Ideally, these complex flows should be studied with spatially continuous measurements, yet such measurements are not feasible with conventional micrometeorological measurements with, for example, sonic anemometers. Hence, the suitability of DTS measurements for studying canopy flows was assessed. The DTS measurements were able to discern continuous profiles of turbulent fluctuations and mean values of air temperature along the mast, providing information about mixing processes (e.g. canopy eddies and evolution of inversion layers at night) and up to third-order turbulence statistics across the forest–atmosphere interface. Turbulence measurements with 3D sonic anemometers and Doppler lidar at the site were also utilised in this analysis. The continuous profiles for turbulence statistics were in line with prior studies made at wind tunnels and large eddy simulations for canopy flows. The DTS measurements contained a significant noise component which was, however, quantified, and its effect on turbulence statistics was accounted for. Underestimation of air temperature fluctuations at high frequencies caused 20 %–30 % underestimation of temperature variance at typical flow conditions. Despite these limitations, the DTS measurements should prove useful also in other studies concentrating on flows near roughness elements and/or non-stationary periods, since the measurements revealed spatio-temporal patterns of the flow which were not possible to be discerned from single point measurements fixed in space.

High‐Resolution Measurement of Soil Thermal Properties and Moisture Content Using a Novel Heated Fiber Optics Approach

AbstractHydrological parameters are scale dependent. Efficient monitoring techniques capable of measuring hydrological parameters, such as soil moisture content (θ), over a wide range of spatial scales are essential for understanding the complexity of water and energy movement across the landscape. Techniques to measure θ over spatial scales in the range from centimeters to thousands of meters, however, are sorely lacking. Recent improvements in the distributed temperature sensing (DTS) technology supported the development of novel techniques to fill that gap. However, improvements in the accuracy and applicability of DTS techniques are still needed. This study investigates the possibility of improving the accuracy of the fiber optics dual‐probe heat‐pulse (FO‐DPHP) DTS technique by using a new design to maintain the spacing between the FO‐DPHP probes and by introducing a novel data interpretation approach. The accuracy of the novel FO‐DPHP design was tested at different θ in a sand column experiment. The FO‐DPHP measurements obtained using traditional and novel data interpretation approaches were compared against independent measurements from several calibrated soil water content (EC5) sensors. Monte‐Carlo analyses were also performed to assess the impact of DTS measurement errors on the accuracy achieved using the data interpretation approaches. The novel design and data interpretation approach allowed for accurate measurements of soil thermal properties and θ without the need to perform a hard‐to‐achieve soil‐specific calibration. Measured θ had mean errors and standard deviations &lt;0.03 and &lt;0.01 m3 m−3, respectively, for moisture conditions ranging from dry to near saturation. The standard deviation in the measured heat capacity was &lt;0.01 MJ m−3 K−1.

Application of distributed temperature sensing for mountain permafrost mapping

AbstractPermafrost distribution in mountains is typically more heterogeneous relative to low‐relief environments due to greater variability in the factors controlling the ground thermal regime, such as topography, snow depth, and sediment grain size (e.g., coarse blocks). Measuring and understanding the geothermal variability in high mountains remains challenging due to logistical constraints. This study presents one of the first applications of distributed temperature sensing (DTS) in periglacial environments to measure ground surface temperatures in a mountain permafrost area at much higher spatial resolution than possible with conventional methods using discrete temperature sensors. DTS measures temperature along a fibre‐optic cable at high spatial resolution (i.e., ≤ 1 m). Its use can be limited by power supply and calibration requirements, although recent methodological developments have relaxed some of these restrictions. Spatially continuous DTS measurements at a studied rock glacier provided greater resolution of geothermal variability and facilitated the interpretation of bottom temperature of snowpack data to map patchy permafrost distribution. This research highlights the potential for DTS to be a useful tool for permafrost mapping, ground thermal regime interpretation, conceptual geothermal model development, and numerical model evaluation in areas of heterogeneous mountain permafrost.

Application of distributed temperature sensing for cracking control of mass concrete

This paper presents a framework of cracking control for a mass concrete structure in a reservoir project, by taking advantage of Distributed Temperature Sensing (DTS) system. The DTS system in this project, mainly consisting of an Optical Backscatter Reflectometer (OBR) interrogation unit and a single fibre-optic cable, was deployed to measure and monitor concrete temperatures of an intake tower in block placement. The temperature measurements in concrete blocks were utilized as the fundamental data to determine the thermal properties of the cast-in-situ concretes, through the inverse analysis method based on temperature simulation. Based on thermal stress simulation using the thermal properties, cracking risks of each concrete block were predicted and evaluated under the modes of temperature control associated with the time-varying construction and ambient conditions, for appropriate modes before and after the concrete placement. The framework of cracking control, developed by integrating the DTS measurement with the temperature forecast and the cracking prediction based on thermal stress simulation and cracking risk evaluation, improves the efficiency of temperature regulation and cracking control in mass concrete construction, and can be further integrated into the intelligent construction management of concrete projects.

Evaluation of Sensitivity of Downhole Temperature Estimates From Distributed Temperature Sensing Measurements

A range of Australian CCS research activities (CO2CRC Otway Stage 3, CO2CRC Otway shallow controlled release and CSIRO Insitu-lab) involving subsurface characterisation and/or CO2 injection are at the planning stage. Fibre-optic sensing is considered as part of the downhole reservoir characterisation and surveillance monitoring system for all of these projects. In this work, we investigate the sensitivity of DTS for the detection of thermal anomalies in view of the design of future geological storage activities in Australia. Ahead of Phase 2 of the CO2CRC Otway shallow CO2 controlled release experiment, a DTS system was installed in the CRC-3 well for equipment testing and baseline characterisation, at the same time as the acquisition of the CO2CRC Stage 2C M5 seismic survey. Temperature measurements were acquired from well-head to bottom-hole for 13 days at a rate of one-minute measurement every 4 minutes. The temperature profile did not change significantly over time. The integration and processing of more than 3400 temperature traces enabled estimation of a temperature profile with a resolution of 0.01 °C. The use of DTS during the CO2CRC M5 survey highlights the detectability of a VSP tool producing 11W and 4W at two distinct depths. The setup was capable of detecting a 0.7 °C anomaly very quickly. A smaller anomaly (0.1 °C) was detected with the benefit of data processing of the long term dataset. The high spatial resolution of DTS enables location of thermal anomalies to within 2 metres.

Using hydrogeophysical methods to assess the feasibility of lake bank filtration

Lake Tissø is the fourth largest lake in Denmark with sufficient, continuous surface water input making lake bank filtration an optimal surface water extraction method provided that there are suitable shallow aquifers with a good hydraulic connection to the lake. The shallow subsurface under the lake was mapped by five waterborne Electrical Resistivity Tomography (ERT) and eight Ground Penetrating Radar (GPR) surveys to locate potentially suitable aquifers. Distributed Temperature Sensing (DTS) was used for the general characterisation of the hydraulic connection between the lake and aquifer. The waterborne ERT surveys showed several zones of coarser material along the shore extending up to five meters depth below the lake surface, while on-land ERT surveys confirmed that these zones extend to the lakeshore with similar thickness. Both waterborne ERT and GPR profiles agreed that at a selected field site the highest possibility of coarse sediments is 60–140 m from the lakeshore. Lakebed temperatures measured in December 2016, May and June 2017 all indicated potential groundwater discharge to the lake at approximately 135 m from the shoreline supporting the results of geophysical surveys showing coarser sediments in that area. A 2D numerical flow model of the area with a geological setup based on geophysical information and slugtest data, also showed upward groundwater discharge peaks at 60 and 140 m from the shoreline confirming the findings of the field surveys. Thus, this study shows that the combination of waterborne ERT and GPR surveys with DTS measurements is a fast and efficient way to assess the feasibility of lake bank filtration in these settings. This approach of combined hydrogeophysical methods is robust and has a potential to site lake bank filtration areas not only next to large rivers where coarse sediments are found in abundance, but even in different sedimentary environments where suitable layers for lake bank filtration are more difficult to identify.

Using distributed temperature sensing to detect CO2 leakage along the injection well casing

The objective of this study is to evaluate the sensitivity of Distributed Temperature Sensing (DTS) data to detect CO2 leakage along an injection well casing. This paper describes the relationship between the CO2 leakage rate and temperature response at DTS locations, and the method and numerical model used for understanding such a relationship. The uncertainties in the parameters are propagated to the interpretation of DTS measurements, which may lead to false positive and false negative identifications of CO2 leakage. We propose to identify CO2 leakage by analyzing both temperature history plots at selected vertical locations as well as the vertical temperature profiles at different times. The analysis should be combined with numerical simulations for the estimation of leakage rates. In addition, leakage needs to be confirmed by data from a warm-up test (temperature recovery after injection of cold CO2 is stopped) to minimize the probability of false identifications.