Improving local class A to Oil Well Cement using PET plastic waste

Mkhize, Msizi
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Addition of polyethylene terephthalate (PET) waste plastic in cement mixtures mostly negatively affect cement matrix properties. Mainly, decreasing the compressive strength, while also affecting slurry properties of the cement mixtures. However, recent findings for concrete cement mixtures show that through prior pretreatment of the plastic waste material, via irradiation technique or through oxidizing solutions, the strength of cement mixtures is regained. Promoting sustainable practices, this work considered the utilization of local class A cement, improved into oil well cement, and then further investigates the prospect of using PET plastic waste in cementing oil and gas wells. Local class A was formulated into standard oil well cement utilizing chemical additives, whereby their compatibility and interactions were explored. A temperature of 38 ℃ and atmospheric pressure were utilized as bottom hole circulating conditions. Three unique PET derivatives as additives, counting pure PET fibres, irradiated PET fibres, and powder Bis(2-hydroxyethyl) Terephthalate (BHET) synthesized through PET glycolysis, were each then added in 0.2%, 1.0%, and 1.8% BWOC dosages. Varyingly, their addition increased the oil well cement compressive strengths, each optimally, by 22.05%, 19.34%, and 81.82%, respectively. Overall, plastic viscosities increased with increasing incorporation dosages, with slip effect resulting due to PET fibres incorporation. Addition of a superplasticizer among the additives is crucial in controlling rheological behavior and most importantly in improving compressive strength of PET plastic incorporated oil well cements. PET fibres have a potential to be used as reinforcements while BHET can be readily used as an oil well cement additive.
A research report submitted in partial fulfilment of the requirements for the degree of Master of Science in Engineering to the Faculty of Engineering and Built Environment, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, 2022