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Abstract Oil-well cementing is considered as one of the most critical operations in petroleum and gas industry. Therefore, it becomes one of the most interesting areas of research for the last decades. Oil well cementing is less tolerant of errors than conventional cementing works. If the cement does not provide a good seal, gas or liquid fluids can migrate to the surface and lead to work accidents or environmental problems. So, the full understanding of interfacial phenomena behind oil well cement procedures has scientific, economic and environmental importance. Chemical admixtures have become one of the essential components of cement in cementing technology in recent years. Various chemical admixtures different in composition have been offered to the users today in response to the needs of the construction market. The major type of admixtures which used in oil well cementing is superplasticizers (high range water reducers). This investigation is divided into three sections: Part I Part I aims to preparation of the superplasticizers particularly sulfanilic acidcyclohexanone formaldehyde (CFS), sulfanilic acid-acetone formaldehyde (AFS), sulfanilic acid-cyclohexanone glyoxylic (CGS), sulfanilic acid-acetone glyoxylic (AGS) and sulfanilic acid-melamine glyoxylic (MGS), confirm their structures using FTIR spectra. Part II Study the effect of the prepared superplasticizers on the water of consistency and setting time. On the basis of the results obtained in this investigation, the conclusions could be derived:1. Sulfanilic acid-cyclohexanone glyoxylic (CGS) shows the most water reducing agent at all ratios in comparison with the other cement admixtures 2. Also, increasing the admixture dosages decreases the water of consistency for all admixtures. 3. The least amount of admixture and the most effective dose is 1% of the provided CFS which reduces the mixing water from 28% to 21%. This means that it reduces the water of consistency by 7% or the total reduction in relative to the original mixing water is 25/0. 4. The initial and final setting times of the cement pastes prepared by using different dosages such as 0.0, 0.25, 0.50, 0.75 and 1.00/0 as well as the previously cement admixtures. 5. CFS and AFS acts as somewhat water reducing agent at all dosages. It shows change in the initial setting time at all dosages in respective to the reduction of mixing water and the admixed cement paste with the mixing water accelerated the initial setting. 6. The initial and final setting times of the hardened cement pastes using 0.25. 0.50. 0.75 and l.0% of CGS or AGS or MGS. The results show that the initial and final setting times are retarded by the addition of these admixtures. As the dose of admixture increases the initial setting time increases. It can be concluded that the CGS or AGS or MGS acts as water reducer and retarder. Part III Part III study the effect of these admixtures on the physico-chemical and mechanical characteristics of hardened pastes made of OWC. The pastes were prepared using the values of standard water of consistency (W/C ratio) with various dosages of each type of superplasticizers then molded into one inch cubic molds. The resulting hardened cement pastes containing 0.10%, 0.25%, 0.50% and 1.00% of prepared superplasticizer by weight of OWC, respectively. The applied hydration time intervals are 2, 6 hours, 1, 3, 7, 28 and 90days. At each time of hydration the hydrated pastes were tested for compressive strength, while the other physico-chemical properties were investigated using the ground dried samples. On the basis of the results obtained in this investigation, the conclusions could be derived: 1. The values of the chemically combined water content of the different cement pastes admixed with different dosages of each prepared superplasticizers are lower than that of the control sample which is related to the initial W/C ratio. 2. For the all admixtures, as the dosage increases the compressive strength increases. Evidently, there are some inter-related parameters; namely, W/C ratio, admixture dosage and degree of hydration that affect the main characteristics of the fresh and hardened cement pastes. Part VI Part VI studies the phase composition and microstructure of the formed hydrates of the admixed hardened OWC pastes. The phase composition and microstructure of the formed hydrates for some selected admixed hardened OWC pastes were identified using X-ray diffraction (XRD) analysis, differential scanning calorimetry (DSC) and scanning electron microscope (SEM). 1. DSC thermograms and XRD difractograms obtained for the tested pastes indicate the formation of nearly amorphous calcium silicate hydrates (mainly as CSH-I and CSH-II), calcium sulphoaluminate hydrates (ettringite and monosulphate hydrates), CH and CaCO3. 2. A relatively high porosity pastes which are almost similar to that of the neat OWC paste made without any admixture; which have high water / cement ratio; the hydration products formed within the available pore system of the cement paste possess a relatively high crystalline character; these hydrates are initially formed as nearly amorphous and microcrystalline (CSH and calcium hydroxide) after 1 day of hydration and with a higher degree of crystallinity after 28 days of hydration with a more denser structure after 90 days of hydration. Part V Part V studies the rheological properties of OWC slurries with different dosages of each prepared superplasticizers at different temperatures. The rheological properties of OWC slurries are affected by numerous factors including the w/c, size and shape of cement grains, chemical composition of the cement and relative distribution of its components at the surface of grains, presence and type of additives, compatibility between cement and chemical admixtures, mixing and testing procedures, etc. Moreover, slip at the slurry-shearing surface interface, particle-particle interactions, chemical reactions, non-homogeneous flow fields, and human errors can make the rheological experiments difficult to reproduce. However, during the present tests, every effort was made to minimize experimental error by strictly following a consistent mixing and testing procedure. The effect of the w/c and temperature on the rheological properties of OWC slurries incorporating various chemical admixtures was studied using an advanced rheometer. The coupled effects of the temperature and dosage of admixture on yield stress, plastic viscosity and apparent viscosity were studied. Based on the experimental results, the following conclusions can be drawn: 1. The rheological properties of OWC slurries are highly dependent on temperature; they generally increased nonlinearly with temperature increase. This is mainly due to the dependence of the formation of hydration products on temperature. 2. As expected, the viscosity of OWC slurries decreased significantly with the increase of the w/c. 3. The rheological properties of OWC slurries depended on the type of admixture used. AGS and MGS improved fluidity at all test temperatures and for all dosages used, while slurries incorporating CFS and AFS required more energy to initiate slurry flow since the yield stress increased at all dosages tested. 4. The admixture dosage had a significant effect on the slurry rheology. At lower dosages CGS acted as accelerators. |