Technical Value

Liquid Loading Abatement

Abatement
Liquid loading in horizontal wells. Images source: Colorado School of Mines and the University of Tulsa.

The subsurface compressor can reverse the vicious cycle of liquid loading, which causes decreased gas production from gas wells prematurely into a virtuous cycle of increased gas production.

When the gas well is liquid loaded, the back pressure generated by the liquid blockage in the wellbore or pore space in the formation will reduce gas production. The reduced gas flow will reduce gas velocity, which in turn reduces liquid sweeping capability, and allows more liquid accumulation in the gas well or formation.

With the installation of the SCS, the gas velocity at both the intake and discharge of the subsurface compressor will increase. The increased gas velocity can carry more liquid out of the wellbore and reduce the back pressure on the formation caused by the liquid blockage. Once the liquids are removed and the liquid loading is abated, the gas production will increase. The increased gas production will further increase the gas velocity to carry more liquids, thus the virtuous cycle of increased gas production is enacted. Increased gas velocity will improve vertical and horizontal holdup profiles by altering flow behavior and fluid flow distribution, thus enhancing liquid lift efficiency in gas wells.

Virtuous Cycle

Besides the higher gas velocity, the temperature of the discharged gas from the SCS will increase due to the gas compression. The injected thermal energy into the gas stream will promote the evaporation of the liquids, increasing liquid lifting and eliminating condensation at the wellbore, which reduces liquid loading.

The increased gas velocity and increased temperature allows more gas and liquids to flow freely, which in turn further increases the ability of the gas to carry more liquids to the surface.

Abandonment Pressure Drop

The SCS will provide suction effects to lower intake pressure near producing zones and boosting effects to increase discharge pressure downstream of the SCS.

  • The suction effects with the lower intake pressure will lower the downhole flowing pressure and increase drawdown to flow more gas from the formation into the wellbore.
  • The boosting effects with the higher discharge pressure from the SCS will overcome the pressure losses along the pipe and increase the wellhead pressure to flow the gas into the surface gathering system.

With both the suction effects and the boosting effects of the SCS at work, the gas well can still produce gas from the formation under the lowest possible downhole pressure or even vacuum, while forcing the produced gas uphole.

  • Without the SCS, for the gas to flow from the formation to the wellhead, the formation pressure needs to be higher than the downhole pressure, which in turn needs to be higher than the wellhead pressure to push the gas upward.
  • With the SCS, the downhole pressure does not need to be higher than the wellhead pressure as long as the SCS discharge pressure is high enough to push gas upward.

In this case, the effective abandonment pressure when the gas cannot move from the formation to the wellhead is dropped significantly by the SCS. In addition, high velocity gas flowing in low pressure wells is very sensitive to viscous and kinetic pressure effects. A small drop in pressure can significantly decrease the velocity of the gas and the ability to lift liquids, therefore causing premature well abandonment.

Pressure Graph 1 Pressure Graph 2 Pressure Graph 3
Pressure Graph Key

Increased Reliability

The Upwing Subsurface Compressor Systems™ (SCS) are engineered with a “protector-less” and “no-physical-contact” architecture, which offers extremely high reliability in the downhole environment.

It is well known that the motor protector of an electric submersible pump (ESP) is one of the major failure modes of downhole artificial lift devices. To eliminate the protector from the SCS, the motor section is completely hermetically isolated from the downhole fluids by a sealing can with conventional non-rotating seals and welds.

To transmit the torque from the motor to the hydraulics section, a magnetic coupling, which can transmit torque via magnetic forces, is placed on the motor and hydraulics shaft and acts through the sealing can, replacing the solid shaft between the motor and the pump, in the case of an ESP. When there is no direct connection from the motor to the pump or compressor and the motor can be completely isolated from the environment, there is no need to have rotary seals and dielectric oil to isolate the motor from downhole fluids, thus there is no need for a protector. The thrust and radial loads from the pump or compressor are supported by magnetic bearings, which completely levitate the bearing rotors and prevent any physical contact between the rotating and stationary parts.