Saudi Arabian Oil Company (inventors: Hasmukh A. Patel, Peter Boul and Carl Thaemlitz) filed a patent application on cyclodextrin containing sliding-ring polymers to enhance the elastic properties in oil-well cement (patent application number US20220169909).
Well cementing is an important operation during drilling and completion of oil wells. The cement sheath must maintain well integrity behind the casing and provide long-term zonal isolation to ensure safety and prevent environmental problems. The cement placed in the annulus between the casing and the formation experiences frequent stresses, such as varying or extreme temperatures and pressures. These frequent stresses can deteriorate the mechanical properties of the cement over a period of time and lead to the formation and propagation of micro-cracks and fractures, thus affecting the production and increasing the cost of operation.
Since cement tends to fracture under downhole conditions due to the brittleness of the cement in its neat form, various polymeric or organic-inorganic hybrid material-based additives were tested cements. Traditional polymeric additives typically do not have strong interactions with the cement particles and instead form weak, interfacial interactions and lack the ability to distribute stress. Such interactions can be separated or ruptured under stresses frequently encountered in downhole conditions, resulting in uneven distribution of stresses in the cement matrix and disruption of the polymer chains. Once the polymer chains are broken, the fracture can propagate in the cement and can eventually result in a reduction or loss of the mechanical properties necessary to sustain the downhole conditions. Thus, while these additives can improve the tensile properties of the cement, such additives tend to impart a significantly negative attribute to the cement in the form of a reduction in compressive strength. Therefore, there is a need for additives and methods that improve the mechanical properties of cement, including the tensile and elastic properties, while having a minimum impact on the compressive strength, for adequate long-term zonal isolation in oil wells. |
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