Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor

Dr. Moncef Nehdi

Abstract

The rheology of OWC slurries is generally more complicated than that of conventional cement paste. In order to contend with bottom hole conditions (wide range of pressure and temperature), a number of additives are usually used in the OWC slurries and the slurry shows different characteristics depending on the combination of admixture used. The objective of this research is to develop a fundamental understanding on the important mechanisms that affects the rheology of cement slurry incorporating various chemical and mineral admixtures. The thesis aimed at developing cement slurries by partial replacement of oil well cement using different mineral admixtures, offering both environmental and economic benefit.

The mechanisms underlying the effect of chemical admixtures on the rheology of oil well cement slurry were investigated at different temperatures using an advanced shear-stress/shear-strain controlled rheometer. The compatibility and interactions between the binder and chemical admixtures were explored. It was found that the rheological properties of oil well cement slurries are highly dependent on temperature, water/cement ratio and the type of admixture used. Coupled effects of temperature and chemical admixtures had a substantial effect on the flow properties of the slurries. The results indicated that current technical data for chemical admixtures need to be validated for oil well cementing; admixtures proven effective in normal cementing job at moderate temperature may become ineffective for oil well cementing at high temperature.

The coupled effects of temperature and supplementary cementing materials on the rheology of oil well cement slurry were also investigated. Because of differences in their chemical compositions and the mechanisms by which they act, cement slurries prepared with the addition of supplementary cementitious materials exhibit different rheological behaviour than those prepared with pure oil well cement. It was found that not all minerals/supplementary cementitious materials (SCMs) act in the same way when used as replacement of cement. For example, Fly ash, owing to its spherical particle shape, reduces the water demand when used as a partial replacement of cement. On the other hand, silica fume increase the water demand by adsorbing water because of their higher surface area. However results suggested that new generation polycarboxylate-based high-range water reducing admixture (PCH) improved the rheological properties of all slurries at all temperature tested. However, lower dosage of PCH was found to be less efficient in reducing the yield stress or plastic viscosity of OWC slurries when metakaolin (MK) or rice husk ash (RHA) was used as replacement of cement. PCH was found to enhance the shear thickening behaviour of oil well cement slurries and the intensity of this behaviour varied with the type and amount of SCM such as the phenomenon was amplified with metakaolin, reduced by SF, unchanged with FA and showed irregular behaviour with RHA.

Furthermore, new equations were proposed using multiple regression analysis (MRA) and design of experiments (DOE) to predict the Bingham parameters (yield stress and plastic viscosity) of cement slurries prepared in combination with or without supplementary cementitious materials considering various parameters including the ambient temperature, chemical admixture type and dosage, and superplasticizer type and dosage. An artificial neural network (ANN) model was developed to predict the rheological properties of oil well cement slurries. The results indicated that the predicted rheological parameters for cement slurries were in good agreement with corresponding experimental results. However, the ANN-based model performed better than the MRA-based model or DOE-based model in predicting the rheological properties of OWC slurries.

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