For Electrical Submersible Pump (ESP) systems in high-GLR wells, presence of gas inside ESP results in the degradation of hydraulic head. As a remedial tool to improve the ability of handling gas-liquid mixtures, Downhole Gas Separator (DGS) is of crucial importance. However, conventional DGS has limited capability in separating free gas and a maximum separating efficiency of 45%. It can't meet the field applications to a wider range of flow conditions and different pump models. Therefore, the paper proposed a solution to improve gas handling ability of DGS to expand its application.

Combining centrifugal separation method and gravity separation method, three-annular design was proposed to address the problem of two-stage separator with fairly long length. In the new design, a device is used to accelerate the fluid for higher velocity flowing into the annular between the spiral outer pipe and the central pipe. Then, the helical blades in the annular separate the gas-liquid mixture, leading gas attaching on the out wall of the central pipe and subsequently discharge into casing through the vent holes. The liquid attached on the inner wall of the spiral outer pipe flows reversal because of gravity. Afterwards, liquid is forced into the central pipe through the drainage holes and then flow into the ESP. In order to improve separating efficiency, the structure of helical blades, including distance and number of thread for centrifugal separator was then optimized by numerical simulation. In addition, an experimental study was conducted in different GLR and deviation. The experimental results show separating efficiency ranges between 88% and 96% while the conventional is under 60%. Furthermore, the separation efficiency decreases with the increasing of deviation, and maximum deviation of the new separator can be applied is 50°[1 ].

The novel DGS provide an economic solution for ESP application in gassy reservoir with low cost and power; since the new design greatly shorten the length of traditional two-stage separator.

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