Quality of cement is an integral part of well integrity. To ensure and improve cement quality, innovative polymers, based upon a family of polymers known as polyamides, are synthesized to improve the mechanical properties of Portland cement. This results in cement systems that have high resistance to impact breakage in set cement. With the addition of polyamides into cement, mechanical properties such as unconfined compression strength (UCS), confined compression strength (CCS), Young's modulus, and the effect of temperature on cement performance are used to show significant improvements to set cement elasticity and compression strength. Under dynamic force loading conditions, up to 30 MPa (4,350 psi) and at temperatures ranging from 20 to 180°C (68-356°F), a tri-axial load cell offers a more comprehensive method of measuring mechanical properties, of designing competent cement systems, and predicting cement integrity. These measurements are further compared to analyses from more traditional methods, such as confined acoustic and unconfined load cells, for information such as compressive strength. The polymer additive is a solid comprising of a polyamide that enhances the mechanical properties of set cement by rendering it high-strength and more elastic to reduce plastic deformation. Findings show that the new polyamide-cements exhibit unconfined compressive strength improvements greater than 25% when compared to latex-treated cement. Furthermore, tri-axial load cell measurements are able to quantitatively analyze the reliability of cement by measuring cumulative fatigue damage which predicts cement failure (Reddy, 2007). Strain-controlled cyclic tests to measure mechanical properties at 20°C show that polyamide cements resist deformation better because of higher durability than latex cements. Polyamide cements had only an 11% permanent strain when compared to latex cement, which had a 27% permanent strain. It is important to assess the mechanical performance of oil well cement, which is subject to cyclic loading due to dramatic changes in pressure and temperature during production (Ravi, 2004). Lastly, the effects of temperature on cement performance is well-documented to cause phase changes at different scales and a decrease in cement strength (Reddy, 2016). With polyamide-cements, the rate of cement strength retrogression is less at temperatures up to 180°C allowing the cement to have increased strength in comparison to latex cements, as well as to cement with no additives. Collectively, the data on elasticity and high compressive strength shows the value of this new polymer additive for cement systems on long-term zonal isolation in gas and oil wells. These polyamides maintained all favorable characteristics, proving to be the best performing additive that imparts the desired mechanical properties essential to extending the endurance of wellbore cement sheaths.
The oil well cement placed in the annulus between casings and the formations experience high stresses under downhole conditions. These frequent stresses deteriorate the mechanical properties of cement and lead to the formation of micro-cracks and fractures, which affect production and increases the cost of operation. Although several polymeric materials have been employed to improve tensile properties of the cement, these additives have also adversely affected the compressive strength of the cement. A highly stable polymeric additive, triazine-based polymers, is designed, synthesized, and compounded with the cement to improve the tensile properties of the well-cement. Triazine polymer was characterized by fourier transform infrared spectroscopy and thermogravimetric analysis. The triazine polymer was mixed with cement and the cement slurries were cured at 180 °F under 3000 psi for 3 days. The set-cement samples were subjected to mechanical testing under high temperature and high pressure to study the elastic properties of the cement. The introduction of this polymer into the cement has improved the elastic properties of the cement with minimum reduction in compressive strength. The thickening time, dynamic compressive strength development, rheology, fluid loss properties, and brazilian tensile strength of the control and cement with triazine polymers were studied to understand the effect of this newly developed polymeric additive. The molecular interaction of the triazine polymer with cement particles has shown formation of covalent linkage between the polymer and cement particle. We have observed a 15 % decrease in Young's modulus for cement compounded with 2%wt. of triazine polymer, indicating the introduction of elastic properties in wellbore cement.
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