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CIGMAT Report 2013
In this study, oil well cement was modified to have better sensing properties, or smart cement, so that the behavior can be monitored at various stages of construction and as well as during the entire service life of the oil wells. A series of experiments were performed to evaluate the behavior of oil well cements both with and without modifications to identify the most reliable sensing properties that can also be relatively easily monitored. For the cement, tests were performed from the time of mixing to hardened state behavior. During the initial setting of the cement, the electrical resistivity changed with time based on the type and amount of additives used in the cement. During the curing of the cement, initial resistivity reduced by about 10% to reach a minimum resistance and maximum change in resistance within the first 24 hours of curing varied from 50% to 300% based on the type of additive. Based on the current study, a new quantification concept has been developed to characterize the curing of the cement based on the changes in the electrical resistivity in the first 24 hours of curing. When the cement was modified with less than 0.1% of conductive additives, the piezoresistive behavior of the hardened smart cement was substantially improved without affecting the rheological properties and setting properties of the cement. For the modified smart cement, the resistivity change at peak stress was about 400 times higher than the change in the strain (Fig. 1).
Drilling mud is used for cuttings removal, suspension of cuttings, release of cuttings at seafloor, minimizing formation damage, reducing filtration rate, cooling and the lubrication of the drill bit and drill string, buoyancy support of the drill string and corrosion prevention. Drilling mud consists of two phases – a liquid phase (water or oil) which is the base and the solid phase which is the clay and other additives. Based on the composition, drilling muds are characterized as water-based mud (WBM), oil-based muds (OBM) and synthetic-based muds. Researchers at CIGMAT are working with all three types of muds to improve performance and enhance the sensing properties. The additives include organic and inorganic admixtures, nanoparticles and surfactants. The xanthan gum (C35H49O29) was very effective in reducing total fluid loss.