Abstract
The seat and the ball are the only two components of a Gas Lift Valve (GLV) that can be switched out to meet changing gas throughput requirements. For this reason, individual pairings of balls and seats must be designed to meet the particular requirements of specific situations. While conventional GLV seats have sharp edges, a modified seat design with partially beveled edges has been shown to improve gas throughput. This design was then tested using benchmark valve and was optimized by beveling the entire port of the seat. These experiments were conducted using a ball diameter that was 0.0016 m larger than the diameter of the port top, although the effects of even larger ball sizes have also been studied using benchmark valves with conventional seats. Researchers have yet to explore the effects of ball diameters smaller than the Port Top Diameter (PTD) and larger than the Port Bottom Diameter (PBD) for modified and optimized seat designs. In this paper, the effects of smaller ball size on the GLV gas throughput have been analyzed using both modified and optimized seat designs and actual GLV. The ball was 0.0016 m smaller than the PTD of the seats. Geometric models have been deduced to calculate the generated upstream area (frustum area) open to flow. This frustum area is a function of stem travel, and the dimensions of the seat and ball. Theoretical calculations have been compared with results obtained through robust experimental methods. The entire experimental program was divided into four individual experiments. The static testing was used to fix the dome pressure and the opening pressure. The hysteresis effect associated with the bellows assembly was minimized using the aging procedure. Probe tester was used to measure the stem travel. Finally, the gas throughput of the GLV was measured using dynamic testing. The smaller ball sizes were found to significantly improve the gas throughput of actual GLV. This improvement was as high as 179% for large PBD seats. However, the frustum area practically decreased for these cases. This result suggests that the flow coefficient has more effect on GLV gas throughput compared to frustum area.
Highlights
Artificial lift covers approximately 96% of the US oil well market of which roughly 10% uses gas lift for production (Salinas and Xu, 2014)
When the ball is seated below the port top, both the major and the minor frustum areas change with the ball’s upward movement (Fig. 5)
The minor frustum area changes as the stem moves upward and is dependent on Port Top Diameter (PTD), stem travel, and ball diameter: 1.3.2.1 First subcase: When the perpendicular drawn from the center of the ball to the edge of the seat is inside the seat (Fig. 7)
Summary
Artificial lift covers approximately 96% of the US oil well market of which roughly 10% uses gas lift for production (Salinas and Xu, 2014). The injection pressure, operating on the effective bellows area minus the port area, produces the first opening force. The second opening force is produced by the production pressure acting on the valve port area. The difference between the opening and closing forces, and the bellows assembly load rate dictates the stem travel in the actual GLV system. One of the most important parameters in each GLV is the upstream flowing area This area is generated by the stem movement away from the seat. In an actual GLV, the bellows assembly performs the most important function by allowing the valve stem tip to move on and off the seat while maintaining the domecharged pressure (Takacs, 2005). The ball can no longer move upward, and the frustum area ceases to increase
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