Investigating effects of the ball configuration on the gas throughput using partially curved and wholly curved seats
Gas lift is considered the most important artificial method in the oil and gas industry. Although, there are several components in the Gas Lift Valve (GLV), the ball and the seats are the only two adjustable components. The objective of this study is to maximize the gas throughput using the new design seats of partially curved design (PCD) and wholly curved design (WCD) to increase oil production. Five main seat designs were evaluated using Computational Fluid Dynamics (CFD) and lab experimental: The Sharp Edge (SE), modified design (MD), the optimized design (OD), Partially Curved Design and Wholly Curved Design. The Sharp Edge, modified design and the optimized design have been previously evaluated with lower gas pressure. However, PCD and WCD were invented and evaluated in this research. To maximize the gas throughput, twenty-eight seat sizes and five different ball sizes have been selected in this study (simulation and experimental). Each seat has Port Bottom Diameter (PBD) and Port Top Diameter (PTD). The criterion of the best case is to have the highest gas throughput. Blowdown test and probe test have been conducted using actual valve and nitrogen gas at 600 psi injection pressure. Developing on this study, these seat-deigns have now been tested using 600 psi injection pressure. The CFD results showed that PCD has higher gas throughput than the modified design at the ball size 6/16 inches, PBD 5/16 inches and PTD 7/16 inches. Also, WCD has higher gas throughput than the optimized design at the ball size 7/16 inches, PBD 6/16 inches and PTD 8/16 inches. The results also demonstrated that the best design seat is the Wholly Curved Design compared to the others when the PBD, PTD and the ball are 6/16 in, 8/16 in and 7/16 in, respectively resulting in the highest gas flow rate of 0.739 kg/s. Also, the results of the experimental work revealed that WCD promised the highest gas throughput comparing to the other seat designs. Each seat has a port top diameter (PTD) and a port bottom diameter (PBD). The results showed that PTD size almost has no effect on the gas throughput whereas the PBD size proportionally affects the gas throughput. When the PTD was increased from 6/16 in to 9/16 the gas throughput had an insignificant change. On the other hand, the gas throughput increased by 46% when the PBD increased from 4/16 in to 6/16 in. The results also demonstrated that the ball size has an inversely proportional relationship with the gas throughput. When the ball size was decreased from 9/16 in to 5/16 in, the gas throughput was increased by 19% (fixing the PTD and PBD). The results show that the optimal seat size is when PBD and PTD are 6/16 inch and 8/16 inch. Also, when the ball size is 7/16 inch (1/16 in smaller than PTD) giving a gas throughput of 2.2 MMSCF/D, which matches the simulation results with an error of 4%.