Modeling of wax precipitation

Thesis (M.S.) University of Alaska Fairbanks, 2007Due to increasing oil demand, oil companies are moving into deep water and arctic environments for oil production. In these regions, due to lower temperature, wax starts depositing when the temperature in wellbore falls below Wax Appearance Temperature (WAT). This leads to reduced production rates and larger pressure drops. Wax problems in production wells are very costly due to production down time and removal of wax. Therefore, it is necessary to develop the solution to overcome wax deposition. Wax precipitation is one of the most important phenomena in wax deposition, and hence, it needs to be modeled. There are various models present in literature. The purpose of this study is to compare two major classes of wax precipitation models. Won's model which considers the wax phase as a non-ideal solution and Pedersen's model which considers the wax phase as an ideal-solution were compared. Comparison indicated that Pedersen's model gives better results but the assumption of wax phase as an ideal solution is not realistic. Hence, Won's model was modified to consider different precipitation characteristics of the different constituents in the hydrocarbon fraction. The results obtained from the modified Won's model were compared with existing models and it was found that predictions from the modified model are encouraging

Effect of twist and rotation on vibration of functionally graded conical shells

This paper presents the effect of twist and rotational speeds on free vibration characteristics of functionally graded conical shells employing finite element method. The objective is to study the natural frequencies, the influence of constituent volume fractions and the effects of configuration of constituent materials on the frequencies. The equation of dynamic equilibrium is derived from Lagrange’s equation neglecting the Coriolis effect for moderate rotational speeds. The properties of the conical shell materials are presumed to vary continuously through their thickness with power-law distribution of the volume fractions of their constituents. The QR iteration algorithm is used for solution of standard eigenvalue problem. Computer codes developed are employed to obtain the numerical results concerning the combined effects of twist angle and rotational speed on the natural frequencies of functionally graded conical shells. The mode shapes for typical shells are also depicted. Numerical results obtained are the first known non-dimensional frequencies for the type of analyses carried out here