These Applications were in heavy sandy petroleum wells. Since that time the PCP pumps are implemented in lighter, higher water cut wells up to 35 API and 100% water and volumes as large as 650 m3 or day. All drive heads are equipped with a backspin retarder or brake that controls the spring torque stored in the rod string. After the device is shut down or looses power, the pole torque will unwind and, since the liquid level equalizes, the down whole twist pump becomes a motor, turning the rod string from the bottom. The PCP pump may greatly improve the economics of a field in two ways
- decrease capital Price
- lower operating Price
Another advantage of the screw Pump system is that it uses the identical tube and sticks as standard beam pumps and the rotor landing procedures are very similar to that of spacing out the plunger on a conventional rod pump. This leads to minimum training for support rig personnel. The principle of this PCP pump is to create pressure and raise the fluid. This is achieved by creating equal and different cavities all around the pump span as the rotor rotates from the stator. Some pumps are going to have as many as 50 or additional cavities, based on the elevator requirement. The differential pressure needed to lift the fluid is then divided evenly among all of the cavities. Accordingly, on a pump with 50 cavities, the differential pressure across each cavity is one or fiftieth of the complete requirement. The actual creation of the pump will change and will be somewhat less that the theoretical production, because of pump slide. As you raise the differential pressure across the pump that the slide volume increases.
This is a result of the fact that, progressive cavity pumps, the rotor is an external single helical gear and the stator is a double inner helical gear. Theoretically, the faster the rotation of the rotor, the greater the output of PCP pumps. To offset the slide and to keep a continuous quantity, you can increase the rate. Therefore, it is extremely important to have a check valve on the flow as near the well head as you can, to stop the fluid from flowing out of the flow back down the well. Anchoring of the tube is important on the bigger PCP pumps in which the pump torque is greater compared to tube makeup torque and, if the service rig is not equipped with power tongs to torque the tube connections to the optimum price. Since the reactive torque of the stator is left hander, the tube will back off and part, if it is not torque properly or anchored. A fluid level over the PCP pump should always be preserved, because this pump requires net positive suction pressure so as to operate, or the pump will not suck.