Design of an electronically-actuated gas lift safety valve

Abstract

Gas lift valves are widely used in oil production fields to pump recycled gas and nitrogen into the production tubing, to sustain production by aerating the oil and lifting it to the ground or sea surface. Today's industry standard, a pressure-actuated valve, is susceptible to various modes of failure, including corrosion and jamming. Safety mechanisms are needed to seal the valve in case of a backflow event, in which oil flows backward through the production tubing. Since human monitoring is difficult to implement at deep level underground, these safety mechanisms have to be highly sensitive and autonomous. This thesis documents the design of an electronically-actuated gas lift safety system that builds on a prior invention based on shape-memory alloy, but, among other features, can handle the slowly changing temperature conditions downhole. The newly-designed control circuit is integrated into the original shape memory alloy (SMA) scheme. The selection criteria and features of various sensors in this circuit are reviewed in relation to oil's physical and chemical characteristics. System functionality is proved through model-scale prototype testing within a controlled environment. At the same time, the system is modeled with heat transfer and structural analysis to predict its behavior in different environments with air or water, or their mixture with oil. Overall, our concept satisfies many of the key operational needs in artificial gas lift.