PCP Artificial Lift System

Overview

A progressing cavity pump artificial lift system raises crude oil from a well by rotating a steel helix inside an elastomer cavity. The Downhole PCP Pump sits at the bottom of the Production Tubing String and is turned by a Sucker Rod String that runs to a Surface Drive Head at surface. The Prime Mover & Transmission drives the head, the Wellhead & Flow Tee contains pressure and routes fluid to the flow line, and the Control System sets speed and protects the equipment. The system handles heavy and sandy crude that defeats other lift methods because the pump is a low-shear, sealed-cavity device with no valves to clog.

The downhole rotor and stator pump

The pump element is a single-lobe set: a single-helix PCP Rotor (single helix) turning inside a double-helix PCP Stator. The stator has one more lobe than the rotor, so the two surfaces meet along a continuous sealing line that forms a chain of cavities. As the rotor turns, each cavity moves steadily up the pump axis, carrying a fixed volume of fluid from intake to discharge. Flow is nearly pulse-free and proportional to speed, which is why a Variable Frequency Drive can meter production directly.

The Stator Elastomer Lining is molded and bonded inside the Stator Tube, and its interference fit against the rotor sets the seal between cavities. Too much interference overheats and tears the elastomer; too little raises slip and drops volumetric efficiency. The rotor is installed to a defined depth by spacing it off the Tag Bar / Rotor Stop and Stop Bushing at the stator base, and it connects to the rod string through the Rotor Pin Coupling.

The rod string

The Sucker Rod String transmits rotation and torque from surface to the rotor. It is built from Sucker Rod joints about 25 feet long, threaded together with Rod Coupling connections. Unlike beam-pump rod strings that see axial cycling, a PCP string carries continuous torque plus the axial load of the rod weight and pump down-thrust, so rod grade and coupling makeup are selected for combined loading. Rod Centralizer units along the rod body hold the string off the tubing wall to limit rod-on-tubing wear, which is the main rod-string failure mode in deviated wells. At surface the string ends in a Polished Rod that passes through the seal, carried by a Polished Rod Clamp that lands its weight on the drive-head thrust bearing.

The surface drive head

The Surface Drive Head supports the rod string, seals the well, and turns the rod. The rod weight and hydraulic down-thrust land on the Thrust Bearing Assembly, while Ball Bearing units carry radial load on the Hollow Drive Shaft. The polished rod passes through the hollow shaft and through the Stuffing Box, whose Polished Rod Packing Set seals against the rotating rod and is adjusted at the Packing Gland to balance leakage against rod heat and wear. When the drive stops, the torque stored in the twisted rod string releases as reverse rotation; the Backspin Brake dissipates that energy through a Brake Disc and Brake Shoe set so the head and polished rod are not damaged. Shaft bores are sealed by Oil Seal elements and the cover is closed with a Fastener Set.

Prime mover and speed control

The Prime Mover & Transmission is a Electric Motor (TEFC) turning the head through either a Sheave & Belt Drive or a Gear Reducer. The belt drive uses a Motor Sheave, a Drive Head Sheave, and a Drive Belt set, and the ratio is changed by swapping sheaves. The geared option uses a Gearbox Housing and Helical Gear Pair sets for a fixed reduction. The Variable Frequency Drive varies frequency to set rotor speed, ramp starting torque, and control backspin, drawing power through its Power Supply and running its logic on an Microcontroller. The Motor Control Panel adds protection and pump-off control, reading a Pressure Sensor on tubing and casing and a Rod Torque Sensor on the rod string to detect sanding, gas interference, or stator wear.

Elastomers and materials

The Stator Elastomer Lining governs service life. NBR resists oil and abrasion at moderate temperature; HNBR extends temperature and chemical resistance for hotter or more aromatic crude. Elastomer swell from aromatics and gas, and hardening from heat, both shift the rotor interference fit, so the compound is matched to the fluid. The PCP Rotor (single helix) is chrome plated to resist the abrasion of sand-laden flow, and a worn rotor is re-chromed or replaced rather than re-machined.

Applications

The system is the standard lift for heavy oil. In cold heavy oil production with sand (CHOPS), the well deliberately produces sand with the oil, and the sealed cavities of the Downhole PCP Pump pass that slurry where valved pumps would jam. A Downhole Gas Separator below the pump lets free gas break out so the cavities stay liquid-filled, and a Tubing Torque Anchor holds the Production Tubing String against reaction torque. The same low-shear action suits high-viscosity and emulsion-prone crude, since the pump does not whip the fluid the way a high-speed centrifugal stage does.