| dc.description.abstract | Abstract
Primary cementing operations in the oil and gas industry are considered critical and complicated. For cementing operations to be successful, the fluid displacement in the annular volume has to be close to perfect. The overall aim is to completely displace the drilling fluid without contaminating the injected cement slurry, as well as leaving residual drilling fluid behind. The quality of a cement job is crucial for the estimated lifetime of a well, since the placed and hardened cement provides zonal isolation and provides the casing with structural integrity. In the industry, there frequently emerge new techniques for improving cementing operations, a newer technique, with little research surrounding it, is vibrational assisted cementing. The idea is that with added vibrations to the inner pipe the placed cement slurry contains less contamination and provides an overall increased quality and strength. The method is already often used in other industries, for instance in the foundation of buildings where vibrational tools are used to get a stable placement of concrete.
In this thesis, the vibration-assisted cementing concept is investigated using the opensource software OpenFOAM for conventional cementing in a vertical, eccentric well scenario. Three aspects of the method were studied: the impact on displacement, the impact on fluid velocity and the pressure variations. The corresponding results suggested increased volume fraction in the vibration-applied cases when compared to the static cases, and indications that amplitude played the larger role. The increased volume fraction appeared to be a consequence of the displacing inner-pipe which created transversal velocity components, or flow currents, providing more circulation in the annular volume which in turn reduced mixing of fluids. In the pressure studies, fourteen cases of an eccentric annuli of different frequencies and amplitudes were performed and compared, 0.5 & 1-milliemetre amplitudes with a frequency of 1 hertz and afterwards, comparing pressure gradients of frequencies varying from 1 to 9 hertz with a 0.5 and 1-millimetre amplitude. The results showed oscillating pressure gradients and an increased pressure loss in an eccentric annulus. For a given amplitude, the pressure amplitudes and the pressure loss increased with increasing values of frequency. | |