The positive displacement pump used in reservoirs commonly works in Sucker Rod Pumping mechanism.
Sucker rod pump equipment:
The rotary motion of the crank is translated to a reciprocating motion of the polished rod by the Pitman and the walking beam; the sucker rods transmit the reciprocating motion from the polished rod to the downhole pump. The
pump consists of a barrel with a ball-and-seat check valve at its bottom (the standing valve) and a plunger containing another ball-and-seat check valve (the travelling valve.) When the plunger moves up, the standing valve opens, the travelling valve closes, and the barrel fills with fluid. On a downstroke, the travelling valve opens, the standing valve closes, and the fluid in the barrel is displaced into the tubing.
Volumetric displacement with sucker rod pumps:
Positive-displacement pump performance is evaluated based on the volume of fluid displaced, not the pressure
increase generated by the pump, since the compression of the wellbore fluid in the pump will create enough pressure to displace the fluid in the tubing.
The volumetric efficiency is less than I because of leakage of the fluid around the plunger. The volumetric efficiency is usually 0.7 to 0.8 for a properly working rod pump.
Hydraulic Piston Pumping:
The use of sucker rod pumps is not feasible in deep or highly deviated wells because of the weight or large amount of friction of the rods. A positive-displacement pump that can be used in these applications is the hydraulic piston pump.
A hydraulic piston pump consists of an engine with a reciprocating piston driven by a power fluid connected by a short shaft to a piston in the pump end. The pump acts much like a rod pump, except that hydraulic pumps are usually double acting, meaning that fluid is being displaced from the pump on both the up and the down strokes. The high-pressure power fluid is injected down a tubing string from the surface and is either returned to the surface through another string of tubing or is commingled with the produced fluid in the production string. Either water or oil may be used as the power fluid.