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This study aimed to analyze the outcomes of stress intensity factor (KI) and new bond strength tests of oil well cement (class H) with a water-to-cement ratio (w/c) of 0.38. Mechanical properties of the cement paste, such as the compressive and flexural strengths, were tested and qualified at 1, 7, and 28 days of curing. The relationship between the elastic modulus and axial strain using the differential of the Vipulanandan p-q model for the cement paste was obtained. The stress intensity factor of the cement paste was between 0.3 and 0.6 MPa.m, and the crack tip opening displacement (CTOD) was between 2.798 and 6.254 µm at three different ratios between the initial notch height (a) and the thickness of the beam (d) (a/d = 0.3, 0.4, and 0.5). The nonlinear Vipulanandan p-q model was used to model the compressive and flexural stress–strain behavior of the cement at three curing times. The bonding strength between the cement and steel tube representing the casing in the borehole was 0.75, 1.89, and 2.59 MPa at 1, 7, and 28 days respectively.

The currently in use fluid loss model (American Petroleum Institute (API)) was developed using the Darcy relationship and assuming that there is no changes in the permeability, solid content in the filter cake and filter cake thickness during the 30 min of fluid loss. Hence, in the current API model, the fluid loss is directly propositional to the square-root of time. In this study, a new proposed hyperbolic fluid loss model has been developed based on a time dependent variation in the filter cake properties. Also, the new proposed model has the power to quantify the short-term and long-term fluid losses (more than 30 min). Moreover, the new model has a limit on the total fluid loss compared to the current API model that shows an infinite fluid loss with time. The new model parameters are related to the applied pressure and temperature using nonlinear power models. The new model predictions are verified with the fluid loss results reported in the literature (225 °C and 300 psi) and tests performed in the laboratory at high pressure and high temperature on bentonite drilling muds during this study. The laboratory tests are both limited to 2% and 8% (by weight) bentonite drilling muds at 100 °C and 100 psi (689.5 kPa) up to 420 min (7 hrs) till the end of the fluid loss. The new model predicts the experimental results on maximum fluid loss and changes in the filter cake porosity, permeability, solid content, and thickness with time, pressure and temperature very well.

According to experimental data results, both inherent anisotropy and loading direction significantly impact geomaterial failures. Clay soils are commonly encountered in many types of on the ground ...

With the growth in construction along the coastal regions, ports and offshore deepwater sea beds, ultra soft clay soils are encountered and are affecting the performance of the pipelines and other anchor systems placed in it. In this study, untreated and treated ultra-soft clay soils shear strengths were quantified using the modified vane shear device and correlated the shear strength to the CIGMAT miniature penetrometer penetration and electrical resisitivity. The ultra-soft clay soils were prepared by varying the bentonite content from 2 to 10%. The soil with 10% bentonite was treated with 2–10% lime and with 1–10% polymer separately to enhance the shear strength. The shear strength, pH, CIGMAT miniature penetrometer and electrical resistivity were used to characterize the untreated and treated ultra-soft clay soils. Untreated soft soil strength varied from 0.01 to 0.17 kPa when the bentonite content in the ultra-soft clay soil was increased from 2 to 10%. With 2% lime treatment the shear strength of 10% bentonite soil was increased to 0.27 kPa. Adding 10% lime to the 10% bentonite ultra-soft soil reduced the shear strength to 0.15 kPa. With 10% polymer treatment, the shear strength was increased by 45 times to 6.8 kPa for the 10% bentonite ultra-soft soil. The CIGMAT miniature penetrometer penetration varied linearly with the shear strength of the untreated ultra-soft clay soils and treated ultra-soft clay soils with 10% bentonite. pH was almost constant for untreated ultra-soft clay soils while it increased by 22% and 35% for the 10% lime and 10% polymer treated ultra-soft clay soilss respectively. Relative electrical resistivity decreased by 246% when the bentonite content was increased from 2 to 10% in the ultra-soft clay soils. Addition of 10% of lime to the ultra-soft clay soil with 10% of bentonite content decreased the relative electrical resistivity by 171%. Addition of 10% of polymer to the ultra-soft clay soil with 10% of bentonite content reduced the relative electrical resistivity by 545%. Power law, linear and Vipulanandan correlation models were used to predict the shear strength-resistivity relationship for the untreated, lime-treated and polymer-treated ultra-soft clay soils respectively. In addition, linear model was used to predict the water content relationship with electrical resistivity for the untreated and treated ultra-soft clay soils. The CIGMAT miniature penetrometer was modeled using 3-D axisymmetric finite element method, which predicted the penetration of CIGMAT penetrometer that agreed well with the experimental results of the untreated and treated ultra-soft clay soils. The CIGMAT miniature penetrometer penetration and the electrical resisitivity monitoring are two non-destructive methods that can be easily adopted in the field and the property correlations can be used to determine the shear strength of the ultra-soft caly soils in the field.

The artificial ground freezing is an important technique for soft soil reinforcement and underground water sealing carried out by continuously refrigerating ground. It is of great significance to monitor the soil strength development in artificial ground freezing projects not only for better evaluation of the soil freeze–thaw status but also for predicting and controlling the concurrent adverse effects which may cause serious engineering accidents. In this study, the electromechanical impedance method was explored in monitoring the soil strength development in the freeze–thaw process. The lead zirconate titanate transducer was embedded inside the soil specimen, and changes in the conductance signatures were monitored throughout the soil freeze–thaw process. The experimental results indicate that the resonant frequency of the embedded lead zirconate titanate transducer can serve as a reliable index for assessment of the soil’s dynamic elastic modulus in the freeze–thaw process. More importantly, an analytical model was developed based on the piezo-elasticity theory to characterize the correlation between the electromechanical impedance of the lead zirconate titanate transducer and the soil’s mechanical properties, and its validity was further confirmed by the experimental research. Based on the proposed model, the development of the soil’s strength can be well predicted from the measured conductance signatures. As a nondestructive testing method, the proposed soil testing technique will help save considerable time and resources by avoiding the conventional sampling, specimen preparation, and testing of soil. The theoretical and experimental research will contribute to the future application of the electromechanical impedance method in real-life artificial ground freezing engineering projects.

In this study, the effects of a water soluble acrylamide polymer solution (PS) treatment on the index properties, compacted properties, free swelling, stress–strain relationship and compressive strength of an expansive CH soil obtained from the field in Houston, Texas was investigated. In order to characterize the clay before and after polymer treatment X-ray diffraction analyses and Thermogravimetric analyses were used respectively. In addition to characterizing the behavior of expansive CH soil (free swelling of 15%), the effect of treating the soil with a acrylamide PS was investigated and the performance was compared to 6% lime treated soil cured for 7 days at 25 °C and 100% relative humidity before testing. In treating the soil, PS content was varied up to 20% (by dry soil weight) using three different mixes (polymer content) and the soil samples were cured for 1 day at 25 °C and 100% relative humidity before testing. When the CH soil was treated with 10% PS, the liquid limit (LL) and plasticity index (PI) (index properties) of the expansive soil decreased by 33% and 57% respectively. The free swelling of the expansive soil decreased by 60% and the compacted (ASTM 698 standard method) compressive strength increased from 126 to 496 kPa. Polymer treatment also increased the compacted maximum dry density and reduced the optimum moisture content of the treated CH soil. The behavior of the LL, PI and swelling of the expansive soil treated with different percentages of the PSs have been quantified using the Vipulanandan property correlation model. Compressive stress–strain relationships of the expansive soil treated separately with lime and PS have been modelled using the nonlinear Vipulanandan p–q stress–strain model. The stress–strain model parameters were sensitive to the polymer content and the type of treatment.

The impacts of up to 3% salt contamination and temperature in the range of 25°C to 75°C on the bentonite drilling muds were investigated. The rheological and resistivity properties of 2% an...

Data analytics are becoming important to better characterize the material behavior. In this study, over 3000 data from the laboratory studies and literature for the field soils were analyzed to quantify the relationship between the density, natural moisture content, shear strength, deviatoric shear stress at failure (3-dimension stress) with the liquid limit (LL). With the increase in the construction of wells, tunnels, piles, and storage facilities, there is interest in determining the safety of soils under multiaxial loading. The range of liquid limit (LL) for the soil investigated varied from 20 to 60%. The ranges of the dry density (γd) and the natural moisture content (MC) for the soils varied from 1.2 to 2.6 g/cm3 and 13 to 56% respectively. The statistical distribution of the data collected varied from normal distribution to Weibull distribution. Vipulanandan correlation model correlated some of the physical properties of the soils. Vipulanandan failure model was used to the failure stresses for the soil and compared to the Mohr-Coulomb failure model and other failure models. Based on the coefficient of determination and root mean square error, the Vipulanandan failure model predicted the results more reliable than the other models. Vipulanandan failure model also predicted the maximum shear strength limit and maximum second deviatoric stress invariant for the soil, whereas none of the other models predicted the maximum shear tolerance for the soil investigated. With the Vipulanandan failure model, the maximum shear strength predicted for the soil was 57 kPa. The maximum second deviatoric stress invariant for the soil in the LL range of 20 and 60% varied from 44 to 30 kPa.

In this study, the effect of acrylamide polymer modified bentonite on the fluid loss and yield stress of water-based drilling mud at different temperatures up 85 °C were studied. Bentonite content in the drilling mud was varied from 2 to 8% by the weight of water. The polymer content was varied between 0 and 0.24% by the weight of bentonite. The bentonite and polymer were characterized using X-ray analysis and thermal gravimetric analysis (TGA). Based on the X-ray diffraction analyses the major constituents of the bentonite were montmorillonite (MMT), (Na, Ca)0.33(Al, Mg)2(Si4O10)(OH)2·nH2O), feldspar (Albite) (NaAlSi3O8), kaolinite (Al2Si2O5(OH4)), Beidellite (Na, Ca0.5)0.3Al((Si, Al)4O10)(OH)2·nH2O and quartz (SiO2), also it was shown the major constituents of acrylamide polymer were ammonium hydroxide carbonate amine ((NH4)·CH3CONH2) and ammonia hydrate (2NH3H2O). The results showed that the polymer-modified bentonite decreased the fluid loss of the drilling mud by 28–52% based on the bentonite content and temperature in drilling mud. TGA analyses showed a notable reduction in the weight of bentonite between 600 and 800 °C. Modifying the bentonite using 0.24% of polymer reduced the total weight loss at 800 °C from 6.42 to 1.26%. an 80% reduction. The polymer modification decreased the yield stress (τo) of drilling mud by 30–60% based on the bentonite content and temperature. The results showed that fluid loss decreased with an increasing amount of polymer. The electrical resistivity of the drilling mud decreased from 8.5 to 3.9 Ω-m, a 53% reduction when the bentonite content increased from 2 to 8% at room temperature. The electrical resistivity of the filter cake formation of the bentonite drilling mud modified with 0.24% polymer decreased by 33–57% based on the bentonite content and temperature. The polymer is an excellent potential additive for reducing the fluid loss and yield stress of drilling muds. The effects of bentonite and polymer content on the model parameters have been quantified using a nonlinear model (NLM). The NLM quantified the effect of polymer treatment on all the model parameters.

In this study, the highly sensing chemo-thermo-piezoresistive smart cement behavior as a function of temperature and pressure with a water-to-cement ratio of 0.38 was investigated. Series of quality control, curing, compression and high-pressure high-temperature (HPHT) lab experiments were performed to evaluate the smart cement behavior with pressure and temperature variations. Vipulanandan p-q curing model was used to predict the changes in resistivity with curing time. The piezoresistivity strain of smart cement after 1 day of curing under 140 °F was 207% which is much higher than the regular cement failure strain of 0.2%. The Vipulanandan p-q piezoresistivity model also predicted the experimental results successfully. Observed fluid loss and gas leak after 30 minutes of testing was recorded. The measured fluid loss was predicted using the Vipulanandan fluid loss model and compared to the API static fluid loss model. Smart cement detected and sensed gas leak throughout the fluid loss test. During the gas leak through the piezoresistive smart cement slurry, the resistivity change was positive which could be used as an indicator for immediate gas migration. During the gas leak in the smart cement slurry, the resistivity increase was about 36% at pressure gradient of 1,800 psi/ft for 70 °F curing. Vipulanandan fluid flow model, generalized Darcy's Law, predicted the non-linear responses of gas leak velocity (discharge per unit area) to the applied pressure gradient. Additionally, the electrical resistivity changes predicted the gas leak velocity in the smart cement at different curing temperatures.

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.

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.

In this study, producing biosurfactant from used vegetable oil in the anode chamber of a microbial electrosynthesizing fuel cell (MEFC) with electrical energy production was investigated. Up to 10 mL/L used vegetable oil was used with an acclimated bacterial culture—Serratia sp. in the anode chamber. The biosurfactant production and bacterial growth in the anode chamber was compared to a continuously stirred batch reactor of comparable size. Up to 3.05 g/L of biosurfactant was produced in the anode solution and a reduction of surface tension to 25.2 mN/m was reached after 7 days of the MEFC operation. At the same time, a maximum power density of 1.13 mW/m2 was produced. The MEFC was further characterized using the electrochemical impedance spectroscopy. Mathematical expression was established to model the total impedance of the MEFC. The production of the biosurfactant from the used vegetable oil waste in the anode chamber and also producing electric power makes the MEFC multifunctional.

Light weight cement slurries with foam additions are being used in multiple applications including onshore and offshore deep wells installed in varying geological formations with low strength rocks. Also, the foam cement has reduced thermal conductivity making it a better insulator. It is also important to model the behavior of the foam cement for real time monitoring with the artificial neural network (ANN) models for adaptation in machine learning for various applications. The investigation was on the performance of highly sensing foam added smart cement and verified with various behavior models. Added foam was characterized based on stability, half-life, electrical resistivity, oxidation-reduction potential (ORP), and pH. Highly sensing smart oil well cement with water to cement (w/c) ratio of 0.38 was modified by adding 5% and 20% foam by weight and was first characterized using the impedance–frequency response to identify the critical electrical property for monitoring. Based on the Vipulanandan Impedance Model, electrical resistivity was the monitoring property. Also rheological properties, fluid loss and piezoresistivity (slurry) were investigated. With the addition of 20% foam the density reduced by 45 the thermal conductivity reduced by 65%.With the addition of 20% foam the initial resistivity increased by 94% indicating a potential quality control parameter for monitoring in the field. The thermal conductivity and the initial resistivity were related to the density using the Vipulanandan Correlation Model. The slurries investigated were piezoresistive, when pressure was applied the electrical resistivity changed. The rheological behavior of the smart foam cement slurries have been quantified using the new Vipulanandan rheological model and compared with Artificial Neural Network (ANN) Model. The total fluid loss with the addition of 20% foam, reduced by about 90% and the Vipulanandan fluid loss model and the ANN model were used to predict the behavior. The slurry piezoresistivity model was used to predict the piezoresistive behavior and compared it to an ANN model. The accuracy of the all the model predictions were compared using the statistical parameters.

In this study, metallic nanoparticles (Fe, Ni, and Fe/Ni) were used as cathode catalysts to enhance power production and to improve the anode performance of a two-chambered microbial fuel cell (MFC). The metallic nanoparticles were rod-shaped and produced by the precipitation/co-precipitation method. A biosurfactant was produced in the anode chamber of the MFC from used vegetable oil by the bacteria Serratia sp. Overall cell voltage, power density, bacterial growth, and biosurfactant production were studied by applying different types of metallic nanoparticles to the cathode electrode. The influence of various types of nanoparticles on the impedance of the MFC was also investigated by electrochemical impedance spectroscopy (EIS), including analyses of anode impedance, cathode impedance, anode solution resistance, cathode solution resistance, and membrane resistance. The nanoparticles improved MFC performance in the following order: Fe > Ni > Fe/Ni. The addition of 1.5 mg/cm 2 Fe nanoparticles to the cathode surface enhanced power production by over 500% to 66.4 mW/m 3 , promoted bacterial growth and biosurfactant production in the anode solution by 132.5% and 32.0%, respectively, and reduced anode impedance, cathode impedance, and membrane resistance by 26.8%, 81.6%, and 33.8% to 159.00 Ω, 7.69 Ω, and 261.09 Ω, respectively. For the first time, biosurfacant production in the anode chamber of the MFC was promoted by using the metallic nanoparticles as cathode catalysts. By improving the cathode properties, this study showed a new way to manipulated the performance of the anode chamber of the MFC.

The characterization of ultra-soft clayey soil exhibits extreme challenges due to low shear strength of such material. Hence, inspecting the non-destructive electrical impedance behavior of untreated and treated ultra-soft clayey soils gains more attention. Both shear strength and electrical impedance were measured experimentally for both untreated and treated ultra-soft clayey soils. The shear strength of untreated ultra-soft clayey soil reached 0.17 kPa for 10% bentonite content, while the shear strengths increased to 0.27 kPa and 6.7 kPa for 10% bentonite content treated with 2% lime and 10% polymer, respectively. The electrical impedance of the ultra-soft clayey soil has shown a significant decrease from 1.6 kΩ to 0.607 kΩ when the bentonite content increased from 2% to 10% at a frequency of 300 kHz. The 10% lime and 10% polymer treatments have decreased the electrical impedances of ultra-soft clayey soil with 10% bentonite from 0.607 kΩ to 0.12 kΩ and 0.176 kΩ, respectively, at a frequency of 300 kHz. A new mathematical model has been accordingly proposed to model the non-destructive electrical impedance-frequency relationship for both untreated and treated ultra-soft clayey soils. The new model has shown a good agreement with experimental data with coefficient of determination (R2) up to 0.99 and root mean square error (RMSE) of 0.007 kΩ.

In this study, carbon steel corrosion was evaluated in salt water solutions using the newly developed non-destructive electrical method which can be easily adopted in the field for real-time monitoring and the results were compared to some standard test methods such as weight loss, corrosion rate and potential difference. The average weight loss in 10% salt solution (accelerated corrosion and also representing the hydraulic fracking fluids) in one year was 1.05% and corrosion rate was 1.54 mm/year, using the ASTM G1 method. Vipulanandan correlation model was used to represent the weight loss versus time relationship. The potential difference between the corroding steel and standard calomel electrode in 1M salt solution reduced from -0.680 V to -0.791 V in two years, a 15% total change. The use of the new nondestructive electrical method was to detect and quantify the surface and bulk corrosion in the field. Tests were performed to first verify the best electrical property that will be highly sensitive and represent the steel corrosion. The findings from this study indicated changes in the newly developed electrical corrosion index for the surface (2D representation) and the resistivity (second order tensor, 3D representation) for the bulk material using the Vipulanandan Impedance Corrosion Model. Corrosion development in 30 inches long steel specimens were studied in the 3.5% salt solution (simulating sea water) for 500 days. The changes in the specimens were monitored at regular intervals using the new two probe method and measuring the impedance-frequency relationship using alternative current up to a frequency of 300 kHz. The surface corrosion was quantified using the new electrical corrosion index parameter, which changed from point to point on the surface of the corroding steel and the change was over 200%. The change in the bulk resistivity along the length of the steel specimen was over 40,000 times (4,000,000%) in 3.5% salt solution compared to the weight loss and reduction in the potential difference. Hence the electrical resistivity for the bulk material and the new corrosion index for the surface corrosion are highly sensing parameters for detecting and quantify the corrosion in the steel.

In this study, commercially available styrene butadiene rubber (SBR) polymer up to 3% was added to the highly sensing chemo-thermo-piezoresistive smart cement with a water-to-cement ratio of 0.38 to investigate the effects on the sensing properties. Series of quality control, curing and high pressure high temperature (HPHT) experiments were performed to evaluate the smart cement behavior with and without the SBR polymer. Addition of 1% and 3% SBR polymer increased the initial resistivity by 4% and 12% respectively and hence this parameter can be used for quality control in the field. Vipulanandan p-q curing model was used to predict the changes in resistivity with curing time. Addition of 1% and 3% SBR polymer also increased the compressive strength of the smart cement by 18% and 32% after 1 day of curing respectively, The piezoresistivity of smart cement with the addition of SBR polymer after 1 day of curing was over 500 times (50,000%) higher than the regular cement failure strain of 0.2%. The Vipulanandan p-q piezoresistivity model also predicted the experimental results very well. Addition of SBR polymer reduced the fluid losses 30 minutes and 24 hours after curing. The fluid loss was predicted using the Vipulanandan fluid loss model and compared it to the API model. The smart cement with and without SBR polymer detected the gas leak during initial slurry condition and after solidification. Addition of SBR polymer reduced the gas leak. During the gas leak in the piezoresisitive smart cement slurry the resistivity change was positive and for the solid smart cement the resistivity change was negative. During gas leak in the smart cement slurry the resistivity increase was about 45% and it reduced to 30% with the addition of 3% SBR polymer at pressure gradient of 2000 psi/ft. During gas leak in the solidified smart cement the resistivity reduced, opposite to the piezoresistive response to compressive stress, by about 30% and it reduced to 12% with the addition of 3% SBR polymer at a pressure gradient of 2000 psi/ft. Vipulanandan fluid flow model, generalized Dary's Law, predicted the non-linear responses of gas leak velocity (discharge per unit area) to the applied pressure gradient. Also electrical resistivity changes can be used to predict the gas leak velocity in the smart cement with and without SBR polymer.

In-situ monitoring of soft soil strength development is of great significance in artificial ground freezing (AGF) projects. It can not only help engineers estimate the soil freeze-thaw status, but also provide useful data for predicting and controlling the concurrent adverse effects which may cause serious engineering accidents. As a useful nondestructive testing method, the electromechanical impedance (EMI) method has already been extensively employed in a wide range of monitoring applications. In this research, the applicability of the EMI method was extended to monitoring the soil freeze-thaw process and the strength development for the first time. Through the experimental research, a lead zirconate titanate transducer was adopted to measure the changes in the conductance signature during the freeze-thaw process. Furthermore, the lateral and vertical shifts of the resonance peak in the electromechanical spectra and three statistic indices were employed as indicators for the quantitative evaluation of the unconfined compressive strength of the soil specimen. The experimental results verified the effectiveness and reliability of the proposed method in monitoring the soil compressive strength development. This method will have broad prospects in in-situ monitoring of the soil strength development in AGF projects.

With the addition of conductive fibers cement can be modified to become a piezoresistive material so that it is highly sensitive to the type of additive, curing and the changes in the stress and can be monitored via changes in the electrical resistivity. In this study, the effect of two conventional admixtures, a superplasticizer (acetone-formaldehyde-sulfite (AFS)) and a retarder (sodium lignosulfonate (Na-LS)), on the piezoresistive properties of the cement were investigated. It was found that both polymers which present conductive polyelectrolytes decreased the resistivity of the cement, but captured all the critical parameters during curing and also the cement was piezoresistive and the strength was enhanced with 0.3% AFS and 0.4% Na-LS addition after 2 and 28 days of curing. The non-destructive method can be used for real-time sensing of cement and concrete properties in the field.

Monitoring the early-age hydration and setting process of cement paste is of great significance to help engineers determine the cement solidification status and evaluate the development of the strength and stiffness of cements. As a promising non-destructive testing (NDT) method, the electromechanical impedance (EMI) method has been extensively applied in many fields of structure health monitoring (SHM) using piezoelectric transducers. In this research, the feasibility of this method in monitoring the early-age hydration and setting process of Portland cement paste was explored. Experiments and observations on the conductance signatures obtained from the embedded piezoelectric transducers inside the cement pastes with two different water-to-cement (w/c) ratios have been conducted within 72 h of hydration. Moreover, the trends of EMI spectra in response to two different excitation frequency ranges, 100 Hz–1000 kHz and 100 Hz–3000 kHz, were captured. It is revealed that the variation of the conductance signatures in the higher frequency range well corresponds to each stage of the cement setting process determined by the Vicat needle testing. Both the resonance peak shift and the statistic index-based approaches perform effectively in monitoring the transformation of cement pastes from liquid to solid state controlled by the cement hydration. In addition, the hydration mechanism has also been interpreted through the hydration exothermic test, XRD and SEM measurements on cement specimens at different ages.

To improve the performance, sensibility, rheological properties, fluid loss of the bentonite water-based drilling mud (WBM), and minimizing the fluid loss of the WBM. The impact of bentonite modified with nanoclay (NC) on the sensibility, rheological properties, and fluid loss of the WBM was investigated. Depend on the information collected from different research studies, the percentage of bentonite in the WBM was ranged from 2%-8% as a percentage of the weight of water. The percentage of NC was ranged between 0 and 1% by mass of drilling mud. The tests were performed under various temperature conditions ranged between 25 °C and 85 °C. From the lab studies and numerical examinations, the electrical resistivity (ER) was identified as a sensing property of the WBM so that the rheological properties can be estimated during the construction. The additional 1% NC reduced the ER of the WBM by 15% to 36% depending on the composition of the drilling fluid and the temperature of testing. The nanoclay modification increased the yield stress (yield point) and shear stress limit tolerance of the WBMs measured using Vipulanandan rheological model by 32% to 60%, and the outcome of the model prediction was related with Vocadlo model. The laboratory HPHT fluid loss tests were conducted on the drilling fluids based bentonite modified with NC using an American Petroleum Institute (API) standard test up to 420 min until the end of the fluid loss. Zero fluid loss was obtained when 8% of bentonite drilling mud modified with 1% of NC at 25 °C. The Vipulanandan fluid loss model predicted the short and long-term fluid loss and the upper limit of fluid losses very well.

Real-time health monitoring of cementitious materials under external loadings is of great significance to help engineers evaluate structural safety state and ensure timely maintenance. As a promising nondestructive testing method, the electromechanical impedance (EMI) method has been widely applied in the field of structure health monitoring (SHM) in civil engineering. In this study, this method was explored in monitoring the stiffness degradation of hardened cement paste subjected to compression loadings. Based on the theoretical modelling, a simplified one-dimensional analytical model was established based upon the piezo-elasticity theory to interpret the correlation between the PZT transducer and the cement specimen in the presence of uniaxial compression loading. Moreover, by embedding the PZT transducer inside cement specimens, the conductance signatures in two different frequency ranges throughout the entire loading process were captured and analyzed. It is revealed that the trend of the EMI spectra is compatible with the cement deterioration. More importantly, the resonance frequency and the statistic metric correlation coefficient (CC) can serve as good indicators to quantitatively assess the stiffness degradation of cement paste under uniaxial compression loadings. This research well validates the effectiveness and applicability of the EMI method in real-time monitoring of cement stiffness degradation under compression loadings.

Quantification of fluid losses and filter cake formations during the drilling operations using water-based muds (WBM) are some of the critical issues related to successful operations. In this study, short term (30 min) and long term (420 min) fluid loss tests on the drilling mud with various amounts of bentonite contents were performed using the API fluid loss device with filter paper and compared it to the field clay soil (porous media) at a pressure of 100 psi (0.69 MPa). The permeability of the saturated clay soil was 0.026 mD, representing a porous formation. Bentonite content in the drilling mud was varied from 2% to 8% (by the weight of water). The field soil and bentonite were characterized using the particle size distribution and X-ray diffraction (XRD) analyses. Bentonite particle size distribution was finer than the field clay soil. Vipulanandan correlation model predicted the changes in the permeability with time in the clay soil with the filter cake formation very well. With the API fluid loss study, the long-term (420 min) fluid losses were about 2.5–4 times greater than the standard fluid loss study of 30 min (short-term). The filter cake thickness was high with the soil formation compared to the API method. Also, the fluid loss per unit area with the API method was higher than the clay soil formation agreeing with the observed differences in the filter cake thicknesses. The Vipulanandan fluid loss model predictions were compared to the API model and it predicted both short term and long term fluid losses very well based on the root mean square error (RMSE) values. Also, the Vipulanandan fluid loss model predicted the maximum fluid losses under various testing conditions.

In this investigation, highly sensing smart cement grouts were developed using 0.8 water-to-cement (w/c) ratio and adding up to 3% sodium silicate. The sensing grout was also used to repair...

During the installation of oil and gas production wells, it is critical to have a successful cementing operation. The quality of the cementing job strongly depends on the cleaning efficiency of the spacer fluid in removing not only the drilling fluid with the cuttings but also the filter cakes during the drilling operation. Based on the depth applications, different types of spacer fluids are used in the oil gas industry. In this experimental study modifying the smart spacer fluid properties in-situ was investigated. Optimization of spacer formulation was carried by having material properties such as density, rheology and cleaning efficiency as the variables. In this study, using the maximum shear stress tolerance of the spacer fluid determined using the Vipulanandan rheological model was investigated to quantify the cleaning efficiency of the spacer fluid. In this study, the effects of pressure, temperature and magnetic field strength on the electrical resistivity and rheological properties of a sensing smart spacer fluid modified with iron oxide nanoparticles (nanoFe2O3) were investigated. The temperature was varied from 25°C to 75°C. The magnetic field strength was varied from 0 T to 0.6 T. The nanoFe2O3 contents (particle size of 30 nm and surface area of 38 m2/gm) in the spacer fluid were varied up to 1% by the weight of spacer fluid to enhance the sensing and rheological properties of the spacer fluid. The initial resistivity of the spacer fluid without any nanoFe2O3 at 25°C was 0.2 Ωm. Addition of 1% nanoFe2O3 increased the electrical resistivity by 3.5%. Adding nanoFe2O3 enhanced the piezoresistive behavior of the smart spacer fluid. The electrical resistivity changed by 0.7, 5 and 12% for the spacer fluids with 0,0.5% and 1% nanoFe2O3 respectively for a maximum pressure of 500 psi. Increase in the magnetic field strength improved the rheological properties while increasing the temperature decreased the rheological properties of the spacer. The rheological properties of the spacer fluids were characterized by high strain rate to determine the nonlinear behavior of the shear thinning spacer fluid. The spacer fluid rheology was modelled using Bingham-plastic model, Herchel Bulkley model and Vipulanandan model. The electrical resistivity was used as sensing parameter to monitor the percentage of oil cleaning efficiency of the spacer fluid. Based on the new Vipulanandan rheological model, the yield stress (τo) of the modified spacer fluid increased by 6% to 100% depending on the oil content, nanoFe2O3 content, temperature and magnetic field strength. The maximum shear stress tolerance (τmax) for the spacer fluid increased from 49.4 Pa to 65.5 Pa, 33% increase at the temperature of 25°C with 1% addition of nanoFe2O3. The cleaning efficiency of the spacer fluid in removing oil based drilling fluid contamination was 79.8% without the addition of nanoFe2O3. With the addition of nanoFe2O3 the cleaning efficiency increased from 79.8% to 99.4%, 20% increase in the efficiency. The maximum shear stress tolerance (τmax) correlated well with the cleaning efficiency. Also the change in the electrical resistivity of the spacer fluid after cleaning correlated well with the cleaning efficiency and hence can be used for in-situ monitoring of the cleaning operation.

Nano aluminum oxide (NanoAl2O3) up to 1% was added to the smart cement with a water-to-cement ratio of 0.38 to investigate the effects on the sensing properties and compressive strength. Series of physical, curing and compressive loading experiments evaluated the smart cement behavior with and without NanoAl2O3 up to 28 days of curing. The addition of 0.5% and 1% NanoAl2O3 increased the initial sensing property (electrical resistivity) of the smart cement by 10% and 30% respectively. In a one day of curing, the maximum change in the electrical resistivity (RI24hr) for the smart cement without NanoAl2O3 was 375%. The RI24hr for the smart cement with NanoAl2O3 increased with the amount of NanoAl2O3. Addition of 1% NanoAl2O3 increased the compressive strength of the smart cement by 14% and 42% after 1 day 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 the addition of NanoAl2O3 was over 500 times (50,000%) higher than the regular cement depending on the curing time and NanoAl2O3 content. Also a gage factor correlation model was used to relate the strain to the resistivity changes under compressive loading. The Vipulanandan p-q stress-strain and the piezoresistivity models also predicted the experimental results very well. A linear correlation was obtained between the RI24hr and the compressive strength of the modified smart cement based on the curing time.

In this study, synthetic based drilling fluids (SBF) were developed for high temperature applications and modified using nanoclay to improve the sensing properties for monitoring. The major constituents of drilling fluids were fatty acid methyl esters, surfactant and water. The ratios of synthetic based fluid to water (S/W) ratios of the SBF were 50/50 and 70/30. The temperature was varied from 25°C to 85°C. The nanoclay concentration was varied up to 1% by the weight of the SBF to modify the rheological properties and the sensing electrical resistivity of the SBF. The effect nanoclay on the rheological properties and electrical resistivity of the SBF was investigated. PV of SBF (50/50) was increased 100% and 286% at 25°C and 85°C respectively and additional of NC reduced the effect of temperature on the PV of SBF. Hyperbolic model has been suggested for modeling the rheological behavior of the SBF to predict the ultimate shear stress. Adding 1% of NC affected the rheological properties by increasing yield point and ultimate shear stress of the SBF with S/W ratios of 50/50 and 70/30. The electrical resistivity of the drilling fluid with and without nanoclay decreased with the increase in the temperature. The results also showed that even 1% nanoclay decreased the electrical resistivity of the drilling fluid 30.2%. This clear indication of the sensitivity of electrical resistivity to the nanoclay contents and the electrical resistivity is a good tool for quality control for the SBF.

In order to enhance the performance and sensing properties of the water based bentonite drilling mud hydrophilic bentonite based nanoclay was used. The bentonite content in the drilling muds were varied from 2% to 8% by the weight of water and temperature was varied from 25°C to 85°C. The nanoclay (particle size in range of 12 nm to 20 nm) content was varied up to 1% by the weight of the drilling mud to modify the rheological properties, enhance the sensing electrical resistivity and reducing the fluid loss of the drilling mud. The fluid loss experiments were performed on bentonite drilling muds modified with nanoclay at 100 psi up to about 420 minutes till the end of the fluid loss. Based on the experimental and analytical study the electrical resistivity was identified as the sensing property of the smart drilling mud so that the changes in the properties can be monitored in real-time during construction. Addition of 1% nanoclay to 8% bentonite drilling mud reduced a fluid loss to zero at 25°C. The results also showed that 1% nanoclay decreased the electrical resistivity of the drilling mud from 15% to 36% based on the bentonite content in the drilling mud and temperature. Compared to the Vocadlo model, Vipulanandan rheological model better predicted the shear stress- shear strain rate relationships all the drilling muds investigated in this study. In all cases, except for the 8% bentonite drilling mud at 25°C, adding 1% nanoclay more than doubled the yield stresses and the maximum shear stress tolerances. The rheological properties of the drilling muds have been correlated to the electrical resistivity of the drilling mud using the Vipulanandan correlation model. The API fluid loss model was compared to the new kinetic Vipulanandan fluid loss model in predicting the experimental results for fluid loss. Compared to the API fluid loss model, Vipulanandan fluid loss model was effective, based on the lower value of root mean square error value, in predicting the short-term and longterm fluid loss with time, nanoclay content and temperature. The new model predicted the short-term and long-term fluid losses very well. This model also has a limit on the total fluid loss but the API model doesn't have a limit.