Rinaldo A. de M. Vieira (Doctor of Philosophy in Petroleum Engineering)
Flow Dynamics in Oil Wells
Directed by Dr. Mauricio Prado
305 pp., Chapter 6: Contributions, Conclusions and Recommendations
(270 words)
Oil and gas wells frequently face production stability issues that lead to operational problems for surface and sub-surface equipements and/or productions losses. To determine whether or not an equilibrium solution is stable, two methodologies are used: local linearization analysis and transient simulation.
The first approach is based on local linearization around the equilibrium solution
in order to develop simple analytical criteria. Although represented by easy inequalities that depend on steady-state parameters, these criteria provide only limited information about the problem. In addition, due to simplifying assumptions, the criteria usually misrepresent reality and are also incapable of determining the existence of different attractors such as limit cycles and strange attractors.
The second approach, transient simulation, seems to be the method that leads to
results that are closer to reality. This work presents a review regarding instability of dynamic systems and its application to some liquid single phase flow system. The validity of such criteria is discussed and comparisons with incompressible and compressible transient simulations are made. The vast majority of existing transient simulation work for oil wells focused on semi-closed gas-lift systems. This type of instability is quite well understood by the petroleum industry. No transient simulation work has been conducted with bottom-hole gas segregation and storage effects, especially considering the use of Electrical Submersible Pumps and down hole separators.
A two-phase flow code based on the drift flux approach was developed in this
work, in order to simulate well configurations without packer. For wells equipped with ESPs, the two-phase flow pump performance as well as separation models where used. Several examples of casing heading and ESP oscillatory behavior are shown.
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