Alhanati, Francisco Jose Soares (Doctor of Philosophy in Petroleum Engineering)
Bottomhole Gas Separation Efficiency in Electrical Submersible Pump Installations
(140 pp. – Chapter VIII)
Directed by Dr. Zelimir Schmidt and Dr. Dale R. Doty
(344 words)
Bottomhole gas separation efficiency is required information to allow an adequate design of Electrical Submersible Pump Installations for gassy wells. However, the bottomhole separation process has not been well understood, and no reliable procedure to quantify the bottomhole separation efficiency has been available. As a result, for design purposes, the bottomhole separation efficiency has been, most of the time, simply guessed.
The objective of this research was to reduce the past uncertainty in predicting bottomhole separation efficiency, thus allowing a better design of Electrical Submersible Pump Installations for gassy wells.
A full scale experimental apparatus was constructed and new experimental data were collected. The apparatus consisted of a 7″ casing section, about 50′ tall, in which a commercial 400 series rotary separator was installed. The experiments were conducted with water and air for liquid flow rates up to 900 bpd, gas-liquid ratios up to 200 scf/stb and pressures up to 200 psig.
For the first time, a prediction method based on fundamental physical principles was developed. The method involves the modeling of a two-phase, two-dimensional flow in the annulus region around a bottomhole gas separator and inside the separator centrifugal chamber. The drift flux approach was used to formulate the model equations. Single-phase flow numerical procedures were extended to solve for the two-phase flow variables.
According to the model, when rotary gas separators are used, two possible operating regions can be identified on a map of separation efficiency versus liquid flow rate and pressure : one in which the separator is quite effective and one in which the separator is not effective at all. The transition between these two regions is sharp. Its location on the map depends on the produced fluid properties, formation gas-liquid ratio, bottomhole geometry, separator characteristics and rotational speed.The experimental data confirm the predictions of the model regarding both the existence of these two operating regions and the sharpness of the transition between them. Measured efficiencies are also in good agreement with the efficiencies predicted by the model, in both the high efficiency region and the low efficiency region.
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