Gas lifting mechanisms are used to produce oil from wells where flow does not occur naturally. A primary application for this technology is in the prevention of oil backflow during gas lift assisted oil extraction.
With current methods, there is a danger of oil passing from the tubing into the annulus (backflowing) when the reverse-flow check valve opens or has leaks. This occurs when, simultaneously, the reverse-flow check valve has a lead and the tubing pressure exceeds the gas pressure. The combination of high tubing pressure and low gas pressure allows the bellows valve to open, thus allowing for backflow. If this were to happen, the passage of product through the annulus can cause an undesirably high accumulation of hydrocarbons at the well and surface to occur, thus increasing the risk of injury to personnel and/or damage to equipment. This invention prevents product from entering the annulus by placing a thermally-actuated safety valve at the gas lift where gas is supposed to pass during well production.
This invention proposes the design of a thermally-actuated gas lift safety valve that prevents oil backflow. In a backflow event, oil passes through the gas lift valve into the annulus because the oil is warmer than the injection gas. Before unloading begins, the thermally-actuated gas lift valve is at oil temperature and thus the safety valve is in the closed position. With the invention, the modified unloading process follows the normal unloading process, but with the subsurface safety flapper valve in the tubing initially closed. This allows for the normal unloading process to be unaffected by the thermal gas lift valve at this point because the safety valve is closed and it cannot pass gas. The new design uses shape memory alloys to close the valve in this event. If the check valve ever leaks and allows oil to pass through the thermal gas lift valve, the shape memory alloy wires will heat up and the ball valve located in the venturi orfice of the gas lift valve will close to prevent backflow.
- Prevents oil from entering the annulus
- Tunable transition temperatures of the shape memory alloys to match well conditions
- Invention and operational procedures work well with a safe level of hysteresis