Systems and methods for restarting downhole pump

A system for pumping downhole fluid in a wellbore after operation of the downhole pump in a forward rotation has ceased, the system comprising:

• a downhole pump locatable downhole in the wellbore;
• a pump motor connected to drive the downhole pump;
• and
• a variable speed drive connected to the pump motor to operate the pump motor and comprising a control system operable to conduct a restart process comprising:
• determining a pump reverse rotational frequency of the downhole pump caused by downhole fluid flowing in a downhole direction to cause the downhole pump to rotate in a reverse rotational direction using a phase locked loop;
• driving the pump motor at a motor reverse rotational frequency matching the pump reverse rotational frequency;
• driving the pump motor to accelerate the pump reverse rotational frequency in the reverse rotation direction and thereby pump the downhole fluid in an uphole direction;
• driving the pump motor to decrease the pump reverse rotational frequency while continuing to pump the downhole fluid in the uphole direction;
• and
• driving the pump motor to change the rotation of the downhole pump to a forward rotation at a pump forward rotational frequency to pump the downhole fluid in the uphole direction.

A device for pumping downhole fluid in a wellbore using a downhole pump locatable in the wellbore, comprising a variable speed drive connected to drive the downhole pump that comprises a control system operable to conduct a restart process after operation of the downhole pump in a forward rotation has ceased, the process comprising:

• determining a pump reverse rotational frequency of the downhole pump caused by downhole fluid flowing in a downhole direction to cause the downhole pump to rotate in a reverse rotational direction using a phase locked loop;
• driving a pump motor at a motor reverse rotational frequency matching the pump reverse rotational frequency;
• driving the pump motor to accelerate the pump reverse rotational frequency in the reverse rotational direction and thereby pump the downhole fluid in an uphole direction;
• driving the pump motor to decrease the pump reverse rotational frequency while continuing to pump the downhole fluid in the uphole direction;
• and
• driving the pump motor to change the rotation of the downhole pump to a forward rotation at a pump forward rotational frequency to pump the downhole fluid in the uphole direction.