Abstract
Trouble shoot analysis of wells on gas lift is a very complex task, which requires knowledge and experience on behalf of the production optimization personnel. The complexity of the diagnostic process stems from the fact that a considerable number of possibilities can take place in a normal operation of a well on gas lift and the ever-present uncertainties of the quality of the data needed for the calculations.
The goal of a trouble shoot analysis is to determine the cause of any malfunction of the gas lift equipment or any other component of the completion that is limiting the well's production capability. The result of the analysis will determine the type of action needed to be taken in the field, which will eventually translate into maintenance cost.
The gas lift trouble shoot analysis is based on the fact that any of the valves installed in the well can be the operating valve. For a given point of injection, a force balance determines which valves could be open. If a valve is open and the gas pressure at depth is greater than the tubing pressure, the gas flow rate through the valve is calculated depending on how open the gas lift valve is. For the same given point of injection, the flowing bottom hole pressure is calculated and compared with the one predicted by the inflow equation. Then, for each possible point of injection or scenario, using fuzzy logic the gas injection mass balance and deviations from what the inflow equation predicts are used to determine the most probable point of injection.
This paper describes the most important principles underlying a gas lift trouble shoot analysis and how it can be integrated using fuzzy logic analysis to handle the complexity of the lifting process and the uncertainties of the data.
