Initial Electrical Resistivity Research Articles

Resistivity and Piezoelectrical Behavior of the Smart Oil Well Cement Incorporated with Aluminum Oxide and Iron Oxide Nanoparticles—Experimental and Analytical Study

Abstract The effects of individually adding 1 % nano aluminum oxide (NA) and 1 % nano iron oxide (NF) on the curing, compressive piezoelectric, and stress-strain characteristics of cement (Class H) were studied and quantified. X-ray diffraction and thermogravimetric analysis were used to evaluate the cement (class H) with and without the 1 % NF and 1 % NA modification. The cement’s initial electrical resistivity (ER) incorporated with 0.1 % conductive filler was improved by 16 and 31 %, respectively, with 1 % NF and 1 % NA. Including 1 % NF and 1 % NA enhanced the stress at the failure of the cement paste by 26 and 39 % and 17 and 42 %, respectively, after curing times of 1 and 28 d. The nonlinear Vipulanandan p-q curing model was employed to anticipate ER change with curing age. Depending on the curing period and type of nanomaterial, the piezoelectrical (piezoresistivity) of “smart” cement containing NF and NA was more significant than normal cement by 500 times. The nonlinear curing model has been applied to model variations in ER with the curing period. The gauge factor model relating strain to resistivity changes under compressive stress was also developed using a relation model.

Polymer/carbon nanotube nanocomposites as temperature sensing materials

Multi-walled carbon nanotubes and high-density polyethylene (MWCNTs/HDPE) nanocomposite sheets with (1.0, 0.5, and 0.1) wt.% MWCNT were successfully prepared by coating the MWCNTs on the surface of the matrix particles (HDPE). The sample resistivities of the nanocomposites were investigated in relation to the temperature influence. Several findings could be drawn from these experiments: For instance, among all of the prepared MWCNT/HDPE nanocomposite sheets with (0.1, 0.5, and 1.0) wt. % MWCNT, the electrical resistivity of the 1.0 wt. % MWCNT/HDPE nanocomposite was 33.18 kΩ.m, demonstrating the best electrical conductivity. The resistivities of 0.1 wt. % and 0.5 wt. % samples were found to be 2594 and 372.23 kΩ.m respectively. Also, the measurements of temperature versus electrical conductivity revealed that the rise in temperature causes the electrical resistivity for the MWCNT/HDPE nanocomposites to increase due to the expansion of the distances between the conductive nanofillers (CNT), i.e., the sample resistivity increased under heating due to the thermal expansion of the polymer matrix. For example, the initial electrical resistivity for the 1.0 wt. % MWCNT/HDPE nanocomposite sheet decreased from 36.25 kΩ.m to 33.18 kΩ.m after the heat treatment. Besides, heat treatment could effectively improve the reproducibility of the MWCNT/HDPE nanocomposites. The reproducibility of the 1.0 wt. % MWCNT/HDPE nanocomposite was better than that of the 0.5 wt. % MWCNT/HDPE nanocomposite.

Investigation of durability properties of grouted concrete pavement as alternative pavement for low traffic roads

This Study presents an experimental investigation on the durability properties mainly Initial surface absorption test (ISAT) and Electrical resistivity (ER) of construction of grouted concrete rigid pavement as a low cost and labour-intensive concrete pavement to be used in interior parts of the country catering to low traffic volume. Initially a optimum grout mix is designed based on its cost, flowability, compressive strength and flexural strength. Then 6 different grade proportion of coarse aggregate are taken for further investigation, ensuring minimum of 20% void ratio to a maximum of 35% void ratio after hand compaction, for allowing the proper flow of the grout mix. Then the resulted grouted concrete mix were tested for ISAT and ER after curing period of 28 days and 28–56 days respectively. Based on the test results it can be concluded that mix 4 show most favourable durability properties to be used as a pavement to be used in low traffic volume areas.

Effect of plastic deformation on the phase composition and electromagnetic characteristics of the 321N austenitic steel (08Kh18N10T)

The changes in the phase composition and electromagnetic properties of the 321N chromium-nickel austenitic steel under plastic deformation by uniaxial tension are studied. As strain increases from 0 to 0.37, the content of ferromagnetic α′-martensite in the steel increases monotonically to 60%. The electrical resistivity and the initial magnetic permeability increase monotonically by factors of 1,25 and 18, respectively. To monitor the strain state and the content of α'-martensite in products made of the 321N steel, it is preferable to use initial magnetic permeability rather than electrical resistance. The skin layer thickness of the deformed 321N steel for frequencies from 5 to 1000 kHz is calculated from the experimental values of initial magnetic permeability and electrical resistivity. Eddy current diagnostics of the state of the surface of products made of this steel, hardened by surface plastic deformation, is proposed to be performed at frequencies ranging between 100 and 200 kHz.

Graphene nanoplatelet, multiwall carbon nanotube, and hybrid multiwall carbon nanotube–graphene nanoplatelet epoxy nanocomposites as strain sensing coatings

Strain monitoring is of great interest in order to check components structural life, to prevent catastrophic failures, and, possibly, to predict residual life in case of unexpected events. In this study, strain sensing epoxy-based coatings containing carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs), and a mix of the two (MWCNT+GNP) have been produced, with the same initial electrical resistivity, and applied on glass fiber reinforced composites. Morphological, mechanical, and electrical tests have been then performed evaluating the resistance variation and the strain sensing performance of the sensors. A theoretical model to relate the resulting gauge factors to the different types of nanofillers has been applied. The results showed that all systems present a strain sensing performance with different gauge factors (and hence sensitivity) at low strain: GNP samples showed the highest gauge factor (10.3), MWCNT samples the lowest (1.5), and the mixed system lies in the middle (4.3). From analytical analysis, the value of initial distance among conductive particles was found to be 0.3 nm in the case of MWCNT and 1.2 nm for GNP, explaining why the gauge factors of the produced sensors are different.

Magnetic Field Strength and Temperature Effects on the Behavior of Oil Well Cement Slurry Modified with Iron Oxide Nanoparticles and Quantified with Vipulanandan Models

Abstract The focus of this study was to investigate the methods that could potentially be easy to adopt in field to modify cement slurry rheological properties in situ during the installation of oil and gas wells. In this study, we investigated the effects of magnetic field strengths and temperatures on the rheological properties of an oil well cement (Class H) modified with iron oxide nanoparticles (NanoFe2O3). Also, the sensitivity of using electrical resistivity in monitoring changes in the cement slurry was also investigated. The water-to-cement ratio used in this study was 0.38, since it is a popular ratio used in oil well cementing. The NanoFe2O3 contents (average particle size of 30 nm) in the cement slurry were varied up to 1 % by the weight of cement. The temperature was varied from 25°C to 85°C. The magnetic field strength was varied up to 0.6 T. The initial electrical resistivity of the cement slurry modified with NanoFe2O3 decreased by 6 % to 52 % based on the NanoFe2O3 content, temperature, and magnetic field strength. The shear thinning behavior of the cement slurry with and without NanoFe2O3 has been quantified using the Vipulanandan rheological model and compared to the Herschel-Bulkley model. The results show that the Vipulanandan rheological model predicted the shear thinning relationship between the shear stress and shear strain rate of the NanoFe2O3-modified cement slurry very well with the maximum shear stress tolerance. The rheological properties of the cement slurry modified with NanoFe2O3 under different magnetic field strengths have been correlated to the electrical resistivity of the cement slurry using a nonlinear resistivity and Vipulanandan property correlation models. Thus, the performance of the cement slurry with and without NanoFe2O3 can be characterized based on the electrical resistivity, which can be used as a real-time monitoring tool in the field.

A molecular dynamics study of the mechanical and electrical properties of Polydimethylsiloxane-Ni conductive nanocomposites

Molecular dynamics was applied to develop a novel PDMS and PDMS-Ni nanocomposite model. First, the PDMS model was validated in terms of the elastic and compressive moduli using available experimental data. The model was then used as a benchmark to add Ni nanoparticles and create a PDMS-Ni conductive nanocomposite model. This model was studied under uniaxial tensile and compressive loading conditions for different Ni filler ratios and mean particle diameters. The electrical resistivity of the model was then obtained as a function of pressure and the compressive stresses. The PDMS-Ni MD model was validated via the literature and shown to successfully predict electrical resistivity variations versus compressive stresses. The results show that as the Ni filler ratio increased from 3:1 to 6:1, the drop in initial electrical resistivity of the composites occurred much faster and at lower stresses. Furthermore, as the mean Ni particle diameter size was increased from 1 nm to 5 nm, the electrical conductivity of the PDMS-Ni improved at different filler ratios. The developed PDMS-Ni MD model can be used to study the electrical and mechanical behaviors of such materials in biosensor applications. It can further be used to study the effects of adding other fillers to PDMS matrix.

Effect of total dissolved solids-contaminated water on the properties of concrete

Total dissolved solids (TDS) is one of the main impurities in the mixing water that can influence the properties of concrete, and therefore, the codes of practice limit the concentration of TDS in water used for producing concrete. The present study investigates the effect of TDS present in the mixing water on the properties of concrete in fresh and hardened states. Concrete mixtures were prepared using water with different selected concentrations of TDS (500, 1000, 5000, and 15000 ppm) keeping the proportions of the main ingredients invariant. Experimental tests including workability, initial setting time, air content, compressive strength, water absorption, water permeability, chloride permeability, and electrical resistivity were conducted. The results showed that the workability and initial setting time were reduced with increase in the TDS concentration, however, these properties remained within the acceptable limits as specified by ASTM C191-18a. At higher concentrations of the TDS, air content and water absorption of concrete deceased by about 31% and 6%, respectively, and compressive strength increased by about 20%, indicating positive effect of the higher concentration of TDS on the quality of concrete. However, the compressive strength was found to be slightly lower at the TDS content of 15000 ppm. Resistance against water penetration and electrical resistivity of concrete decreased slightly at higher TDS concentrations, however, water permeability class and the likelihood of reinforcement corrosion remained unaffected. The chloride permeability increased from moderate to high level when TDS concentration exceeded 1000 ppm. Based on the finding of this study, it may be concluded that the waters having TDS up to 1000 ppm can be recycled for concrete production that would benefit in cost reduction and conservation of water resources.

A Comparative Study between Knocked-Down Aligned Carbon Nanotubes and Buckypaper-Based Strain Sensors.

Carbon nanotubes (CNTs) are one of the most promising materials in sensing applications due to their electrical and mechanical properties. This paper presents a comparative study between CNT Buckypaper (BP) and aligned CNT-based strain sensors. The Buckypapers were produced by vacuum filtration of commercial CNTs dispersed in two different solvents, N,N-Dimethylformamide (DMF) and ethanol, forming freestanding sheets, which were cut in 10 × 10 mm squares and transferred to polyimide (PI) films. The morphology of the BP was characterized by scanning electron microscopy (SEM). The initial electrical resistivity of the samples was measured, and then relative electrical resistance versus strain measurements were obtained. The results were compared with the knocked-down vertically aligned CNT/PI based sensors previously reported. Although both types of sensors were sensitive to strain, the aligned CNT/PI samples had better mechanical performance and the advantage of inferring strain direction due to their electrical resistivity anisotropic behavior.

Smart Cement Compressive Piezoresistive, Stress-Strain, and Strength Behavior with Nanosilica Modification

Abstract In this study, smart cement with a water-to-cement ratio of 0.38 was modified with up to 1 % silica nanoparticles (NanoSiO2) to evaluate the effect not only on the sensing properties but also on the compressive stress-strain relationship and strength. The oil well cement (class H) and cement modified with NanoSiO2 were characterized using X-ray diffraction analysis and thermal gravimetric analysis. The smart cement was prepared by adding 0.1 % of the conductive filler based on the percolation theory concept to make the cement piezoresistive yet remain a nonconductive material. Testing evaluated the smart cement behavior with and without NanoSiO2 to verify the sensitivity of electrical resistivity changes with time and compressive loading. The addition of 0.5 and 1 % NanoSiO2 increased the initial electrical resistivity of the smart cement by 17 and 35 %, respectively. In one day, the maximum change in the electrical resistivity (RI24hr) for the smart cement without NanoSiO2 was 364 %. The RI24hr for the smart cement with NanoSiO2 decreased with the amount of NanoSiO2. The addition of 1 % NanoSiO2 increased the compressive strength of the smart cement by 14 and 42 % after 1 and 28 days of curing, respectively. The nonlinear Vipulanandan p-q curing model was used to predict the changes in electrical resistivity with curing time. The piezoresistivity of smart cement with NanoSiO2 was over 500 times higher than the regular cement, depending on the curing time and NanoSiO2 content. The Vipulanandan p-q stress strain and stress change in resistivity models also predicted the experimental results very well. For smart cement modified with NanoSiO2, the resistivity change at peak stress was over 1,250 times higher than the change in the compressive strain. A linear correlation was obtained between the RI24hr and the compressive strength of the modified smart cement based on the curing time.

Vipulanandan models to predict the electrical resistivity, rheological properties and compressive stress-strain behavior of oil well cement modified with silica nanoparticles

In this study, the effect of silica nanoparticles (NS) and temperature on the rheological properties with ultimate shear stress and weight loss of the oil well cement (class H) modified with NS were investigated. The NS content was varied up to 1% by the weight of the cement. The total weight loss at 800 °C for the oil well cement decreased from 6.10% to 1.05%, a 83% reduction when the cement was mixed with 1% of NS. The results also showed that 1% of NS increased the rheological properties of the cement slurry. The NS modification increased the yield stress (τo) and by 5% to 65% based on the NS content and the temperature of the cement slurry. The addition of 0.5% and 1% NanoSiO2 increased the initial electrical resistivity of the cement by 17% and 35% respectively. The shear thinning behavior of the cement slurry with and without NS has been quantified using the Vipulanandan rheological model and compared with the Herschel-Bulkley model. Based on the Vipulanandan rheological model the maximum shear stress produced by the cement slurry modified with 0% and 1% of NS at the temperature of 25 °C were 148 Pa and 179 Pa respectively hence an increase of 21% in the ultimate shear stress due to the addition of NS. The addition of 1% of NS increased the compressive strength of the cement by 14% and 42% after 1 day and 28 days of curing respectively. Effects of NS content and the temperature on the model parameters have been quantified using a nonlinear model (NLM). The NLM quantified the effect of NS treatment on all the model parameters.

Characterizing the pulse velocity and electrical resistivity changes in concrete with piezoresisitive smart cement binder using Vipulanandan models

In this study the behavior of concrete made using piezoresisitive smart cement as the binder was investigated to test and model the concrete as a bulk sensing material. The coarse aggregate content in the concrete was varied up to 75% (by volume). The concrete property changes during curing were tested using the ultrasonic pulse velocity and compared it to the electrical resistivity, since it can be easily adopted for real-time monitoring. The initial (immediately after mixing) compressive pulse velocity for the piezoresistive smart cement (binder only) was 1050 m/s and it increased to 1490 m/s with the addition of 75%, a 42% increase in the initial pulse velocity. After 28 days of curing, the pulse velocity of smart cement increased from 3520 m/s to 4750 m/s with the addition of 75% aggregate, a 35% increase in the pulse velocity. Also the addition of coarse aggregates increased the initial electrical resistivity of the smart cement composite as well as the long term electrical resistivity. The initial electrical resistivity of smart cement was 1.02 Ω·m which increased nonlinearly to 3.74 Ω·m. with the addition of 75% aggregate, a 267% increase in the initial electrical resistivity. After 28 days of curing, the electrical resistivity of smart cement was 14.14 Ω·m and with 75% aggregate it increased to 61.24 Ω·m, a 333% increase in the electrical resistivity. Applicability of the mixture theory to predict the resistivity of the concrete from the constituents was verified and a new composite resistivity model was developed. Also Vipulanandan p-q curing model was used to predict the resistivity changes in the concrete with the curing time. The piezoresistivity of the smart cement without and with 75% aggregate after 28 days of curing were 204% and 101% at the peak compressive stresses of 21.7 MPa and 12.4 MPa respectively. The reduction in the piezoresistivity at peak compressive stress was due to not only the reduction of smart cement content in the composite but also the strength. Compared to the compressive failure strain of 0.3%, the resistivity change for the concrete with 75% gravel after 28 days of curing was over 336 times (33,600%) higher making the concrete with the smart cement binder a highly sensing bulk material. The composite behaviors (with curing time and applied stress) were modeled using the Vipulanandan pulse velocity, concrete resistivity and piezoresistivity models and compared with the current models used in the literature. Based on the coefficient of determination (R2) and root mean square error (RMSE), Vipulanandan models predicted the experimental results very well.

Smart Portland cement curing and piezoresistive behavior with montmorillonite clay soil contamination

In this study, the effects of up to 5% montmorillonite clay soil contamination on the curing and piezoresistive behavior of the Smart Portland cement was investigated. Smart Portland cement was made by mixing the cement (Type I) with 0.1% conductive filler to enhance the sensing properties. Based on the type of construction, cement might get contaminated with varying amounts of clay soils. Hence, a series of experiments were performed to evaluate the cement behavior with and without up to 5% of montmorillonite clay contamination to determine the effects on the curing, piezoresistivity and strength up to 28 days under two different curing conditions. The test results showed that the montmorillonite clay contamination increased the initial electrical resistivity of the smart Portland cement slurries and also affected the electrical resistivity with curing and the piezoresistive properties of the hardened cement. Vipulanandan p-q models predicted the curing and piezoresistive responses very well.

Stress–Strain–Electrical Evolution Properties and Damage-Evolution Equation of Lateritic Soil Under Uniaxial Compression

Abstract Finding an internal variable that characterizes the effects of change in the mesoscopic structure of soil and can be nondestructively measured simultaneously with stress and strain during the entire compressive process is an intriguing problem for geotechnical engineers and researchers. In this study, the geoelectrical resistivity technique, combined with a mechanical test, was applied to explore the stress–strain–electrical evolution properties of lateritic soil during the entire process of uniaxial compression. Complete testing data were obtained for the stress–strain and resistivity–strain curves. Results show that both curves for each specimen were identified by six distinct stages. The effects of initial water content and dry density were analyzed and indicated that soil failure patterns and initial electrical resistivity are significantly influenced by the initial water content. The initial electrical resistivity of lateritic soil decreases when the dry density increases. Electrical resistivity was regarded as an internal variable to characterize information on damage change. Damage-evolution equations were proposed; these equations include three variables, namely, stress, strain, and electrical resistance, as well as data-fitting parameters (c, d and β).

Moisture-dependent piezoresistive responses of CNT-embedded cementitious composites

This study experimentally investigated the effect of moisture content on the piezoresistive responses of carbon nanotube (CNT)-embedded cementitious composites. In an experiment, changes in electrical resistance were measured under repeated application of sinusoidal compressive forces to the CNT-embedded cementitious composite specimens with different moisture contents. Experimental results revealed that as the internal relative humidity (IRH) of the specimens decreased, the piezoresistive responses, such as initial electrical resistivity, amplitude of electrical resistivity change, and piezoresistive sensitivity, increased significantly. The rate of change in piezoresistive sensitivity resulting from IRH variation increased nonlinearly with IRH drop, and rapid increase was observed when IRH drop was more than 35%, which was related to evaporation of surface multilayer adsorbed water in the specimens. The results of this study can be used for improving quantitative evaluation of the piezoresistive responses of CNT-embedded cementitious composites with variable moisture content, in the long term.

Tuning the Network Structure in Poly(vinylidene fluoride)/Carbon Nanotube Nanocomposites Using Carbon Black: Toward Improvements of Conductivity and Piezoresistive Sensitivity

Piezoresistive poly(vinylidene fluoride) (PVDF) nanocomposites are very intriguing for strain sensor applications in structural health monitoring (SHM) systems. In general, high piezoresistive sensitivity combined with broad measurable strain ranges are greatly favored in those sensors. Here, a facile strategy, i.e. constructing strain susceptible conductive networks using hybrid filler systems consisting of carbon nanotubes (CNTs, 0.5-1 wt %) and carbon black (CB, 0.5-4 wt %), was introduced to tune both electrical conductivity and piezoresistive sensitivity of melt mixed PVDF nanocomposites. At the same filler content CNTs, due to their larger aspect ratio, contribute more to electrical conductivity improvements of nanocomposites than CB, while contacts between CB particles are more sensitive to tensile strain. With retained ductility of PVDF, tunable electrical conductivity and ΔR/R0-strain sensitivity can be achieved by combining the advantages of CNTs and CB by adjusting the conductive network structure. Conductivity improvement is more remarkable if the mass ratio of CNTs to CB (mCNTs/mCB), varied between 1:1 and 1:4, is higher in hybrid filler compositions. Lower mCNTs/mCB ratios result in higher ΔR/R0 values in PVDF nanocomposites whether they have the same content of total filler or similar/the same initial electrical resistivity. At 10% tensile strain, the highest ΔR/R0 of 0.65 was obtained for the nanocomposite filled with 0.5 wt % CNTs and 0.5 wt % CB, while that for the counterpart containing 1 wt % CNTs is 0.35 at the same strain. The concept of using hybrid fillers provides a low-cost and effective way to fabricate piezoresistive polymer nanocomposites toward SHM applications.

Scaling-up the acid-enhanced electrokinetic remediation of a real contaminated soil

Although there is a lot of experimental work published about the use of Electrokinetic Remediation for the removal of toxic metals from soils, very few have reported results for different scales. Scaling-up is a difficult task, since the behavior of each metal is different and is also site-specific. In this paper we present a convenient parameter for the comparison of the energy requirements at different scales. This parameter consists on the definition of a specific-energy for each metal, based on the amount mobilized and the maximum removal expected as determined from the BCR fractionation analysis. The tests, which were carried out with soil columns holding soil samples of 16g and with soil samples of 2000g, are giving similar values of this parameter. Our results indicate that this specific-energy depends on the target metal to be recovered, but for each metal is quite similar for the experimental conditions of the two scales essayed. These conditions included that the initial electrical resistivity times the column length were equal for the two scales. A simple mathematical model predicts these results, and that for equal resistivity the specific energy requirement will be proportional to the distance between electrodes.

Study of electrical and magnetic properties of Ni–Zn–Mg ferrite system

Polycrystalline nickel–zinc ferrites of chemical formula Ni 0.65-x Mg x Zn 0.35 Fe 2 O 4 (x = 0.00 to 0.2 in steps of 0.04) have been prepared by conventional ceramic technique. Calcination and sintering of all samples have been carried out in air atmosphere at 950°C and 1250°C, respectively, followed by natural cooling to room temperature. All the samples were characterized by the X-ray diffraction (XRD) for structure determination. These samples were then investigated for their magnetic and electric properties, including saturation magnetization, Curie temperature, initial permeability measurements and DC electrical resistivity. Porosity was decreased drastically from 15% to 5% showed better quality of the sintered samples. There were increments in initial permeability and DC electrical resistivity throughout the series of samples. Variations in the observed properties as a function of magnesium concentration have been discussed in light of the existing understanding.

A free-standing, flexible lithium-ion anode formed from an air-dried slurry cast of high tap density SnO2, CMC polymer binder and Super-P Li

A free-standing electrode film composed of high tap density SnO2 particles and carboxymethyl cellulose binder with Super-P Li (SP-Li) conductive carbon was formed from an aqueous slurry cast by doctor-blading. Upon air-drying, the free-standing film spontaneously evolved via delamination from the substrate as the slurry solvent evaporated. The electrodes cut from the free-standing film were ∼5 μm thick with a SnO2 loading of ∼0.5 mg cm−2. The films were found to be easily handled, flexed and folded. For evaluation of the durability of the free-standing films, the tensile strength and elongation at break were measured: 13 MPa and 1.7%. The robustness of the electrically conductive network was measured with a four-point probe: the initial electrical resistivity of the film (0.6 Ω cm) was observed to increase by 6% after folding, applying pressure to the crease and unfolding. When tested in a coin cell, the electrode cycled stably with near 100% coulombic efficiency at up to 2 C and without capacity fade for 100 cycles at 1 C. To adjust the areal capacity of the cell, multiple free-standing films could be stacked. An electrode formed from several stacked films with an active material mass loading of greater than 4 mg cm−2 was found to cycle stably at 2.6 mA h cm−2 tested at 0.33 mA cm−2 current density. For evaluating cycling performance of the electrode while flexed, an electrode was placed in a once-folded pouch cell for testing at 1 C and cycled stably for 20 cycles before slight capacity fade was observed. For free-standing electrodes, 1D or 2D carbons such as carbon nanotubes (CNT) or graphene are commonly used to provide both mechanical strength and electrical conductivity. Here, CNTs were substituted for the SP-Li and similar free-standing films were made and compared. With CNT, the electrode strength at break as well as the electronic conductivity increased, but, despite this, the cycling performance of the electrodes made using the low-cost SP-Li carbon exceeds that of the electrodes made with orders-of-magnitude more expensive 1D carbon.

The CO2-Vadose project: Time-lapse geoelectrical monitoring during CO2 diffusion in the carbonate vadose zone

Experimental observations of electrical resistivity variations were carried out in a field site (CO2-Vadose project) in order to investigate the evolution of this geophysical property in response to possible leakages of geologically sequestered CO2. The dynamic evolution of electrical resistivity was measured using time-lapse electrical resistivity tomography during a sub-surface leakage of CO2 released under controlled conditions in a cavity of about 9m3 located in an abandoned limestone quarry. The experimental CO2 induced leakage was performed to study the gas migration in a carbonate vadose zone. Initial electrical resistivity tomographies were carried out before the gas release in order to have reference values and to characterise the heterogeneity of the limestone massif around the injection room. Significant relative variations of resistivity were found in correlation with the CO2 concentrations, which allowed not only to detect a leakage of CO2 on free surfaces of the massif but also to follow the propagation of the CO2 plume inside the limestone massif. The limestone resistivity decrease observed in this study is probably caused by CO2 dissolution in the pore-water. The feasibility of this explanation was confirmed by laboratory measurements. Relative variations of resistivity and CO2 concentrations were exponentially correlated.