With the ever-increasing trend of oil production from lower pressure wells, application of artificial lift techniques is becoming inevitable. Beam pumps and electrical submersible pumps are two of the most common artificial lift methods for low and high oil production rates. But these techniques are susceptible to high gas-oil ratios, particularly at lower wellbore pressures causing gas break-out and possible gas lock. Various types of downhole separators have been recently designed upstream of the pump to resolve this issue and improve the pump efficiency. The objective of this study is to construct a state-of-art experimental facility and simulate the flow in an oil well with varying gas-oil ratios. The facility is then used to evaluate the performance of a centrifugal downhole separator.
The experimental multiphase flow setup is designed, fabricated, and constructed in an efficient and automated way to simulate a typical horizontal wellbore. The well trajectory includes a 31-ft horizontal section, inclinable to ±10o, followed by a 27-ft vertical section. The casing ID is 6-in., and a 2-in. ID tubing is placed with end-of-tubing at the bottom of vertical section. The casing and tubing streams are each led to a return column, where gas and liquid flows are metered. Automated and modulated control valves are used to monitor the pressure and production from casing and tubing streams. Five Coriolis flow meters quantify density and flow rate of different fluid streams. All of the equipment is connected to a control computer via DAQ cards.
The experiments are performed with air, supplied by a screw-type compressor, and water, supplied by a moyno pump. The experiments are conducted with different gas (Qg = 30-230 Mscfd) and liquid (QL = 17-700 bpd) flowrates to simulate the cases with both rod pump and ESP operations. The air-water ratio is increased for fixed water rates to identify the ranges of separator effectiveness. The tested downhole separator is an innovative design, applying gravity and centrifugal effects to perform the separation. The results indicate that average gas separation efficiency of the separator is 93% and average liquid separation efficiency is 96% over a wide range of operating conditions, as measured by return line flow meters for casing and tubing streams. The characteristics of multiphase flow in horizontal and vertical sections of the setup are observed and evaluated using surveillance cameras. The separator can be used widely in oil fields to improve gas-liquid separation and artificial lift performance.
The application of pumping artificial lift methods in high GOR wells can help significantly improve the production from a wide range of volatile oil and condensate wells. This illustrates the value of utilizing innovative downhole separation strategies. This paper presents one such centrifugal downhole separator and studies its performance in enhancing the production.