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Multiple fluids are likely to exist in fractures and flow paths associated with leaky wellbores, including liquids (e.g., crude oil) and gases (e.g., gas exsolved from liquid). These fluids occupy and move through different portions of the pore spaces within the fractures depending on many factors, including fluid properties, fracture size, and the amount of the different fluids. Upward leakage of any phase, through the fracture, can contaminate water-bearing formations, create hazardous surface conditions, and compromise the functionality of the wellbore. Early signs of wellbore leaks may be expressed by anomalous pressure behavior at surface monitoring points on cavern storage wells. These pressure anomalies are difficult to interpret, necessitating knowledge of the factors that affect the multiphase flow in fractures and porous media. These parameters are critical to modeling multiphase flow in fractures. This insight can guide further diagnosis and maximize leak remediation. Our study focuses on the relationship of the liquid–gas relative permeabilities for representative variable-aperture wellbore cement fracture. To obtain the relative permeability of each phase, two-phase flow tests were conducted where both fluids were flowing simultaneously through a fractured wellbore cement specimen under a range of factors, namely (1) aperture size, (2) capillary numbers, and (3) viscosity ratio. The flow experiments were conducted under a range of confining stresses and flow velocities, using nitrogen gas and silicone oils (of different viscosities) in a specially designed pressure vessel. The sum of gas and oil relative permeabilities were found to be less than one under all conditions, which indicates that the presence of one phase affects the permeability of the other phase, and vice versa. Since the gas phase flow conditions include a significant inertial flow component in addition to viscous flow, the inertial flow coefficients at different saturation states are presented. The factors affecting the relationship between the relative permeabilities are discussed in detail. A new mathematical model for estimating the relative permeability of wellbore cement fracture is presented and experimentally validated.

Self-compacting concrete (SCC) was developed in the 1980s in Japan and has since received wide attention and use in the construction industry worldwide. Numerous investigations have been conducted on SCC to establish comprehensive knowledge of its mixture requirements and performance. The use of high powder content, mostly cement, is one of the SCC mixture’s requirements, although it is not desirable, as it will increase the cost and has other negative environmental effects. The use of industrial solid waste materials such as slag, fly ash, and limestone powder as fillers in SCC has proven to be a successful way of solid waste recycling without impairing SCC properties. Ceramic waste powder (CWP) produced during the manufacture of ceramic tiles is dumped in landfills and will cause soil, air, and groundwater pollution which pose a serious problem on the society. The use of CWP as a partial replacement of portland cement in SCC can convert the landfilled waste material to a valuable ingredient and will also contribute to the reduction in the overall energy consumption and CO2emission accompanying the production of portland cement. In this study, the utilization of CWP, in large quantities, as a partial cement replacement in making SCC will be evaluated. Its effect on hardened concrete properties, durability characteristics, and microstructure development is studied. It is found that CWP can be used successfully to partially replace cement in large quantities to produce eco-friendly SCC.

The bond of polymer concrete (PC) to a steel surface is a critical aspect in many infrastructure applications. Bond strength can be evaluated through several means including pull-off, flexural, twist-off, and slant shear tests. While pull-off strength tests are the most common method for evaluating bond for PC overlays in bridge and parking structures, slant shear tests are more suitable when vertical rather than horizontal bond lines are used. In this paper, we discuss the use of slant shear tests to examine bond of polymer concrete repair material to steel pipes used to ensure wellbore integrity of abandoned oil wells used for CO2 sequestration.Bond strength of Novolac PC incorporating nanoalumina particles to a steel surface was measured using slant shear tests. Different amounts of nanoalumina were used in the PC to improve bond strength without significantly reducing PC flowability. Slant shear testing confirmed the ability of nanoalumina to improve the steel-PC bond strength. A finite element (FE) model using the ABAQUS simulation environment was developed to compare the apparent versus the true bond strength. A cohesive contact element surface was used to simulate bond along the interface line. The FE model showed that the stiffness mismatch between the PC and steel controls the maximum shear stress developed at the interface surface. The true bond strength extracted from the FE model appears to be about twice that of the apparent bond strength.

Polymer concrete (PC) overlays are typically used in infrastructure applications, specifically bridges and parking structures, to provide durable protection to the structural system. However, PC suffers from cracking and crack propagation during its service life mostly due to fatigue. Fatigue cracking of PC results in limiting the service life of PC considerably. Monitoring of fatigue damage in PC can help extend PC service life.In this paper, we demonstrate the possible use of carbon nanotubes to monitor damage initiation and propagation in PC under fatigue loading. PC prisms were produced using epoxy polymer concrete with varying contents of multi-walled carbon nanotubes (MWCNTs). The percolation level of MWCNTs necessary to produce conductive PC was first determined. Fatigue testing using an AASHTO modified test set-up was conducted. Electrical conductivity of PC overlay was continuously measured during fatigue testing. Damage initiation and propagation in PC incorporating MWCNTs overlays can be detected and monitored.

Composite homogenization is a numerical simulation method that allows determination of the effect of microstructure constituents on the mechanical properties of composite materials. This homogenization technique allows cement paste to be modeled as a composite material in which microparticles are randomly dispersed in the cement paste matrix. By using microstructural homogenization, a representative volume element (RVE) can be developed and used to simulate the constitutive model of the composite cement paste by considering its constituent phases. A four-phase cement paste model is considered to describe cement paste incorporating nanosilica. Cement paste microstructures are divided into Phase I, hydrated cement paste; Phase II, unhydrated cement paste; Phase III, nonreacted nanosilica; and Phase IV, capillary porosity. Cement hydration models are used to predict the volume fraction of the four phases on the basis of the mixture proportion of the cement paste mix. Constitutive models for Phases I, III, and IV are assumed on the basis the literature. A constitutive model for Phase II is identified with the RVE model by matching the stress–strain curves of the cement paste extracted from nanoindentation experiments. The validated RVE model is then used to examine the effect of changing the nanosilica content in the cement paste on the stress–strain curve of the composite cement paste. It is evident computationally that increasing the nanosilica content will increase the strength and stiffness of the cement paste and therefore will increase the ability of the cement paste to absorb energy represented by the area under the stress–strain curve.