Testing, modeling and optimizing a modified design of gas lift valve seat

Date

2017-08

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Abstract

Laboratory gas dynamic throughput testing indicates that each injection-operated Gas Lift Valve (GLV) often does not open fully in actual operations, mainly because of the bellows stacking phenomenon. The stacking occurs before the minimum required stem travel to generate equivalent port area is reached. As a result, the gas-lift valve stem acts as a restriction on the flow path. Therefore, actual flow through the gas lift valve is less than what is expected. A modified design for the GLV seat is built to help reduce the required stem travel to generate a flow area equal to the port area. The specifications for the modified GLV seat are controlled by changing the angle of the taper part. These angles are selected to create a certain port top diameters where the available ball sizes can be used at the same API recommended ratios (the ball is 1/16-in. larger in diameter than each port size). Thus, each port may be designed using several seats. An equation to calculate minimum stem travel for modified design is also derived. Theoretical calculations showed that the minimum stem travel for the modified design reduces by 58% compared to using a conventional sharp-edged seat. This improvement could have a rather high impact on the GLV performance. To verify the theoretical results, the modified seats for different ports sizes were built and tested using Benchmark valve test. The experimental results showed that for the same amount of stem travel, the modified design provides a larger flow rate than the sharp-edged seat. Using optimizing the modified design requires manufacturing and testing numerous seats, which is a very costly and time consuming process. Computational Fluid Dynamics (CFD) technique was used to simulate the process. CFD technique provides an excellent alternative solution. The CFD simulations are performed using ANSYS Fluent 15 commercial software to simulate the flow behavior through GLV and to develop an in depth understanding of pressure distribution and fluid flow pattern inside the valve. The model was first validated with experimental results for twelve different cases. Using CFD model, the effects of the various components of GLV on the overall performance of the valve were studied. The simulation results match well with the experimental results with maximum error of 6%. Using experimental results, the performance of the all three types of seats; optimum design which was obtained from the simulation model, modified design, and conventional sharp-edged were evaluated. The experimental results demonstrate significant improvement in the gas flow rate using the optimized design compared with the other two seats.
To verify the optimized cases, the seats and corresponding balls were manufactured and their performances was assessed. The experimental results of the optimized cases matched results of the numerical modeling well.

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Keywords

Production, Artificial Lift, Gas Lift Valve

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