Cementing is a well-established practice in the oil and gas industry. Its main purpose is to protect the wellbore from the surrounding downhole environment which includes prevention of unwanted communication of formation fluids with the wellbore or other permeable horizons. During a cement job the existing mud in the wellbore will be displaced by the spacer, to clean the pipe and borehole wall, followed by cement and a displacement fluid which usually is a mud. The intermixing between these fluids (spacer, cement, and mud) could arise during the placement phase which tends to affect the specified cement properties and hence jeopardize the quality of a cement job. Thus, a better understanding of intermixing during the fluid displacement phase is required to improve the fluid compatibility in mitigating this problem. The main goal of this thesis is to generate ultrasonic data for several commonly used materials in the oil and gas industry to prepare muds, spacers, and cements. A baseline study is conducted to measure the variation in sonic velocity of individual materials dispersed in water. The generated baseline database will serve as a reference point to predict the sonic velocity in the mixed fluid. A feasibility study is conducted to determine the practicality of ultrasonic sensors to determine the sonic velocity of different fluids. The result of this study poses new questions which have been answered in the static single additive experiments. A total of thirteen (13) commonly used drilling and cementing additives are analyzed using a custom-made ultrasonic setup. Therefore, fluids of different concentration of each additive are mixed and the average sonic velocity determined. The results of this study give an intrinsic insight into the effect of each additive on the sonic velocity. Finally, a proof-of-concept experiment is presented to display how the acquired knowledge can be applied in the field. Therefore, two (2) muds of different density are mixed and displaced on a benchtop setup. Fluid discrimination, density evaluation, degree of intermixing calculation and required volume for full displacement prediction is successfully conducted and presented. Most of the objectives of this thesis are successfully achieved and are presented in detail.