Downhole Pumps

Unless the well is artesian, downhole pumps are needed, especially in large-scale, direct utilization systems. Downhole pumps may be installed not only to lift fluid to the surface but also to prevent the release of gas and the resultant scale formation. The two most common types are lineshaft pump systems and submersible pump systems.

The lineshaft pump system (Fig. 10) consists of a multistage downhole centrifugal pump, a surface – mounted motor, and a long driveshaft assembly extending from the motor to the pump. Most are enclosed, with the shaft rotating within a lubrication column, which is centered in the production tubing. This assembly allow the bearings to be lubricated by oil since hot water may not provide adequate lubrication. A variable-speed drive set just below the motor on the surface can be used to regulate flow instead of simply turning the pump on and off.

The electric submersible pump system (Fig. 11) consists of a multistage downhole centrifugal pump, a downhole motor, a seal section (also called a protector) between the pump and motor, and electric cable extending from the motor to the surface electricity supply.

Both types of downhole pumps have been used for many years for cold water pumping and, recently, in geothermal wells (lineshafts have been used on the Oregon Institute of Technology campus in 89°C water for 45 years). If a lineshaft pump is used, special allowances must be made for the thermal expansion of various components and for oil lubri­cation of the bearings. Lineshaft pumps are preferred over the submersible pumps in conventional geother­mal applications because lineshaft pumps cost less and they have a proven track record. However, for setting depths exceeding approximately 250 m, a submersible pump is required.

Updated: March 14, 2016 — 4:17 am