The stability of clay dispersions when mixed with dissolved electrolytes is important to assess, especially for use in wellbores and in the subsurface where electrolytes can be present naturally or introduced during operations (e.g., mix water). It is well known that the type and concentration of dissolved electrolytes impact stability; however, most studies are devoted to dispersions with relatively low clay concentrations that do not assess the impact of the clay concentration on overall stability. This study examined the effects of two electrolyte salts on the stability of high concentration sodium bentonite dispersions (prepared with solid content of 4%, 6%, 8%, and 10% by mass) of commercially available brands. At these high concentrations, classical theories and more standard approaches (e.g., optical) to determine dispersion stability become non-applicable. Each clay concentration was mixed with CaCl2 (in concentrations from 0.75-12 g CaCl2/L H2O) or NaCl (in concentrations from 8-90 g NaCl/L H2O) and the degree of dispersion was recorded over time as agglomeration and eventually sedimentation occurred in the samples. A quantitative method was developed to determine the minimum amount of electrolyte to cause colloid sedimentation, the critical coagulation concentration (CCC). For the high bentonite concentrations tested, CCC is almost a linear function of solids concentration for both mono- and divalent electrolytes. Relatively low levels of CaCl2, for example at levels commonly found in public water sources, were identified as the CCC where sedimentation is initiated; however, bentonite concentration, composition, and type can be optimized to control dispersion stability.

Carbon-based nanomaterials, such as carbon nanoplatelets, graphene oxide, and carbon quantum dots, have many possible end-use applications due to their ability to impart unique mechanical, electrical, thermal, and optical properties to cement composites. Despite this potential, these materials are rarely used in the construction industry due to high material costs and limited data on performance and durability. In this study, domestic coal is used to fabricate low-cost carbon nanomaterials that can be used economically in cement formulations. A range of chemical and physical processing approaches are employed to control the size, morphology, and chemical functionalization of the carbon nanomaterial, which improves its miscibility with cement formulations and its impact on mechanical properties and durability. At loadings of 0.01 to 0.07 wt.% of coal-derived carbon nanomaterial, the compressive and flexural strength of cement samples are enhanced by 24% and 23%, respectively, in comparison to neat cement. At loadings of 0.02 to 0.06 wt.%, the compressive and flexural strength of concrete composites increases by 28% and 21%, respectively, in comparison to neat samples. Additionally, the carbon nanomaterial additives studied in this work reduce cement porosity by 36%, permeability by 86%, and chloride penetration depth by 60%. These results illustrate that low-loadings of coal-derived carbon nanomaterial additives can improve the mechanical properties, durability, and corrosion resistance of cement composites.

This study compares the rheological properties of several cement slurries of Class H, Class G, and two pozzolan-amended cement recipes. Viscosity measurements were taken on both preconditioned and unconditioned cement slurries. Tests were performed using a dual cylinder viscometer following the recommendations of the American Petroleum Institute (API). It was observed that the effect of conditioning on viscosity increased with the increase of particle size in the comparison of Class G to Class H cement. The addition of fly ash significantly changed how cement would react to conditioning. The unconditioned pozzolan-amended cement slurry’s viscosity decreased with the addition of fly ash, whereas the conditioned pozzolan-amended cement slurry increased with the addition of fly ash.

An approach is introduced using the multi-component lattice Boltzmann method (LBM) to numerically simulate multi-layered wellbore plug placement and investigate the effects of the rheological and physical properties of cement slurry and bentonite clay gel as plugging materials. As a proof of concept, this approach is applied to simulate the placement of a layer of cement slurry within a layer of bentonite clay gel to form three distinct alternating material layers in a wellbore. Prior to investigating this system, the LBM approach is validated through physical lab-scale plug placement tests. Then, a computational field-scale case study is examined to evaluate how variations in plug material properties and placement processes affect the resulting multi-layered wellbore plug. The analyses show that cement slurry density is the property that most affects the wellbore plugging process. At lower concentrations of bentonite clay gel, more cement slurry is needed to create the three-layer system, since the cement slurry penetrates further into the bentonite clay gel. Alternatively, for high concentrations of bentonite clay gel, higher density cement slurry can be placed as a distinct layer without having a significant increase in the amount of cement slurry needing to be pumped. For the cases considered, variations in yield stress and viscosity of the cement slurry have negligible effects on the plugging process. Lastly, although the pumping velocity controls the rate of cement slurry layer placement, it has a relatively small effect on the placement process. Overall, the LBM approach is shown to be an effective method to evaluate wellbore multi-layered plugging processes.

The integrity of wellbore cement is vital for the long-term success of applications such as enhanced oil recovery and carbon storage. Intact cemented well casings are crucial to preventing leakage and fluid migration, as well as maintaining safety of operations. To investigate the changes to fractures in foamed wellbore cement in a carbon storage scenario, four cores were fractured lengthwise and injected with deionized water at equilibrium with CO2. The experiment duration was five days for the first core and was increased for each successive test, with the final test lasting 20 days. The fractured cores were periodically imaged with a NorthStar M5000 Industrial Computed Tomography (CT) scanner, documenting the changes to the fracture during dissolution, as well as the reaction zone in the surrounding cement matrix. For two cores with the most robust reactions, the fracture and two reaction zones (proximal and distal to the fracture) were segmented from the raw CT data. They were quantified volumetrically and in the form of fracture aperture maps. A Local Cubic Law (LCL) modeling suite was used to map out localization of flow within the open portions of the fractures.

Embedded optical fiber sensors (OFS) are an emerging technology that can address real-time monitoring of wellbore integrity for carbon storage, oil/gas, and geothermal systems. Optical fiber sensors are capable of physical and chemical monitoring to observe the structural health of wellbores during operations. While embedded sensors add real-time monitoring capabilities, it is vital to understand how they interact with cement to impact the physical, mechanical, and flow properties of the cement in a well. Previous results showed that embedded OFS prototypes improved cement mechanical strengths and increased the axial permeability when OFS ran through the full length of the cement core. To simulate the most susceptible part of a cemented well, OFS prototypes were embedded within cement with a cement end cap at one end. The samples were then CT scanned for sample visualization and to determine the end cap thickness. Physical and mechanical properties (porosity, permeability, Young’s modulus, etc.) were measured on the sensor embedded cement samples. The cement cap demonstrated promising results in mitigating the undesired permeability increase for the OFS prototypes, while largely maintaining the mechanical enhancement.

In order to reduce greenhouse gas emissions while recovering hydrocarbons from unconventional shale formations, processes that make use of carbon dioxide to enhance oil recovery while storing carbon dioxide (CO2) should be considered. Here, we examine samples from three shale basins across the United States (Utica and Marcellus Shales in the Appalachian Basin, Barnett Shale in the Bend Arch-Ft. Worth Basin, and Eagle Ford in the Western Gulf Basin) to address the following questions: (1) do changes from reaction with CO2 and fluids at the micrometer and nanometer scale alter flow pathways and, in turn, impact hydrocarbon production, CO2 storage, and seal integrity and (2) can CO2 or fluid reactivity be predicted based on physical or chemical properties of shale formations? Experiments were conducted at 40 degrees C and 10.3 MPa to characterize the interaction between CO2 and shale using X-ray diffraction (XRD), carbon and sulfur analysis, in situ Fourier transform infrared spectroscopy (FT-IR), feature relocation scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), mercury (Hg) intrusion porosimetry, and Brunauer-Emmett-Teller (BET) surface area and pore size analysis coupled with density functional theory (DFT) methods. Changes in mechanical, physical, and flow properties of shale cores due to CO2 exposure were addressed using a New England Research Autolab 1500 and Xenon X-ray computed tomography (CT) scanning. Results showed that CO2 did not promote significant reactivity with the shale if water was not present; only shales with swelling clays or residual interstitial pore water reacted with dry CO2 to promote reactivity in shale. When water was added as a reactant, CO2 formed carbonic acid and reacted with the shale to dissolve carbonate pockets, etched and pitted the shale matrix surfaces, and increased the microporosity and decreased nanoporosity. Porosity and permeability increased appreciably in core shale samples after exposure to CO2 saturated fluid due to dissolution of carbonate. Shale mechanical properties were not altered. Trends were not observed that could tie CO2 or fluid reactivity to physical or chemical properties of the shale formations at the basin scale from the samples we examined. However, if the shale contained significant amounts of carbonate and water was available to react with the CO2, pore sizes were altered in the matrix and permeability and porosity increased.

This report discusses the results of baseline geochemical data from a carbon dioxide (CO2) enhanced oil recovery (EOR) field in the Permian Basin’s Central Basin Platform. This report focuses on understanding the variability in geochemistry during normal oil field practices, including the transition from water flooding to a water-alternating-gas (WAG) technique. The primary objectives of this study were to focus on 1) determining the best general geochemical parameters to identify produced water intrusion into overlying groundwaters, 2) observing if there was any intrusion during the sampling period, and 3) identifying changes in produced water following CO2 injection.

Geologic CO2 storage (GCS) is a method to mitigate the adverse impact of global climate change. Potential leakage of CO2 from fractured cement at the wellbore poses a risk to the feasibility of GCS. Foamed cement is widely applied in deepwater wells where fragile geologic formations cannot support the weight of conventional cement. Thus, it is critical to know whether fractures in foamed cement self-seal in a similar manner as conventional cement systems. This study is the first to investigate the changes in physical and chemical attributes of foamed cement under dynamic flow conditions using CO2-saturated water. Self-sealing of fractures in the cement was observed at a solution flow rate of 0.1 mL/min and a pressure of 6.9 MPa. The formation of CaCO3 precipitates in pore spaces and fractures led to a decrease in permeability by 1 order of magnitude. The extents of self-sealing in foamed cement samples, specifically the 20 and 30% air volume formulations, were similar to that of conventional cements. We attribute this to the greater alteration depth in the foamed cement, which compensated for the reduced availability of Portlandite and higher initial porosity. The results can be used to evaluate the risk of leakage associated with foamed cement.

There is a need for embedded sensor technologies to monitor wellbore integrity in real-time for carbon storage and geothermal applications. Emerging sensing technologies such as optical fiber sensors and wireless sensors have been studied for physical parameter monitoring (e.g. temperature, vibration, and strain) and chemical parameter monitoring (e.g. pH, CO2, corrosion) to monitor structural health of the wellbore. The desirable sensors need to be able to withstand the harsh environments relevant for carbon storage and geothermal wellbores, and they must not inadvertently cause potential sources of wellbore failures. Therefore, we investigated the cement properties with embedded sensors to compare with baseline cement properties, including porosity, permeability, mechanical properties (e.g. Young's modulus, Poisson's Ratio, etc), and 3D computed tomography (CT) scans. The sensor devices (optical fiber sensors [OFS] and wireless chip sensors) were embedded in cement cores under wellbore relevant conditions. Then, the cement samples were examined using AutoLab 1500, nitrogen permeability testing, helium porosity testing, and 3D CT scanners. Results show that the cement samples with embedded sensor devices had a slight increase in porosity of 1.5% to 3.6% compared to the blank cement samples. Permeability slightly increased by 0.001 mD with embedded chip sensors. The embedded chip sensors did not significantly change the cement mechanical properties; whereas, the embedded OFS prototypes improved the cement mechanical strengths, e.g. increasing the Young's modulus by as much as 10% and the bulk modulus by up to 25.5%. CT scans confirmed the proper embedding and good bonding between sensor devices and cement.

The purpose of this study is to quantify geochemical reactions of CO2 and brine with subsurface samples taken from the Mt. Simon sandstone and identify any potential alterations of the geomechanical rock properties that could lead to changes observable in seismic monitoring or result in changes of micro seismicity such as those observed at the Illinois Basin-Decatur Project (IBDP) site. Two Mt. Simon sandstone samples from 6919.3 feet (2109.0 m) and 6926.1 feet (2111.1 m) depth were exposed to supercritical CO2 (scCO2) dissolved in brine at in situ reservoir conditions for one month. Geochemical, spectral, scanning electron microscopy, and petrophysical methods were used to analyze the samples before and after the one-month exposure. Significant changes were observed. Multiple geomechanical properties were chosen to form the framework against which to interrogate the petrophysical data: Young's modulus (E), Poisson's ratio (nu), lambda center dot rho (lambda rho), and mu center dot rho (mu rho). In this study we conclude that framework composition, porosity, heterogeneities, effective pressure, and reactive geochemistry are first order controls on trends in the E-mu and lambda rho-mu rho cross plot spaces. Changes in porosity, permeability, dynamic moduli, and brittleness with exposure to these fluids were observed. No change in ultrasonic P-wave attenuation (QP) was observed. Geochemical alteration causes a distinct shift in lambda rho-mu rho in both samples as well as changes in E, nu , and P and S wave seismic velocity values. These observations could provide insight into subsurface monitoring using seismic methods including amplitude variation with offset (AVO) classification.

Abstract The objective of this paper is to evaluate the physical and dynamic mechanical properties of foamed cement generated at a field site and compare them to similar cements fabricated within the laboratory. Physical and mechanical properties such as porosity, permeability, Young's modulus, Poisson's ratio, bulk modulus, shear modulus, etc. will be discussed. Mechanical properties were obtained under cyclic confining pressures ranging from 12 – 52 MPa. This paper will document the final results of a long-term project that examined the differences between foamed cements generated with laboratory equipment and field foamed cementing equipment. The cement samples in this study were generated at pressure using field foamed cementing equipment as part of a joint effort between the API Sub-Committee 10 and the National Energy Technology Laboratory (NETL). The samples were characterized using helium porosimetry, ultrasonic velocity, and permeability measurements after they were depressurized. To test the variation in permeability and strength parameters of various foam cements, stepwise loading and unloading experiments were conducted. Effective pressures varied between ≈6.8 MPa to ≈46 MPa in ≈4 MPa increments. Permeability was measured at each effective pressure step to determine the change in flow pathways due to cyclic confining pressures. Dynamic moduli including Poisson's ratio and Young's modulus were calculated to determine the impact of effective pressures on the flexibility of the cement. The data shows that the cement's physical and mechanical behavior varied along the length of the sampling containers. During the initial loading of some of the samples, permeability decreased to a point lower than the initial permeability and stayed constant for the remainder of the pressure cycle, which was observed in previous experiments. However, some of the permeability values increased suggesting that the pressure cycles had permanently reconfigured the internal structure of the samples. Our approach to evaluating foamed cement is somewhat novel in that we have collaborated with the API, operators, and service companies, to obtain foamed cement generated at pressure using field equipment enabling a robust comparison to those generated in a laboratory per the API's RP 10-4B. Not only will the information provided by these comparisons help to facilitate the better design and implementation of foam cement generation processes but it will also help improve the understanding of the physical and mechanical behavior of foam cement.