Lifting by rod pumps
They consist of long, thin cylinders with mobile and fixed elements inside. The pump is designed to be inserted into the extraction tube of the well and its main function is to accumulate fluids from below and lift them to the surface. Its main components are: the Production pipe, valves and piston (travel and fixing). They have another 18 or 30 components, which are called complementary or adjustment.
Each part of the pump is important for the correct functioning of the system. The most common parts are described below.
• - Motor: It is responsible for supplying the necessary energy to the pumping unit to lift the well fluids. These engines can be internal combustion or electric.
• - Gear box: Used to convert rotational moment energy, subjected to high speeds of the primary motor, to high rotational moment energy at low speed. The driving machine is connected to the speed reducer (gear box) by belt. The speed reducer can be: Single, double or triple. The double reducer is the most used.
• - Crank: It is responsible for transmitting the movement of the gear box or transmission to the rocker arm connecting rod, which is joined to them by pins attached to the low speed shaft of the gear box and each of them has an equal number of holes, which represent a certain stroke of the rocker arm, in which the connecting rods holding pins are placed. Changing pins from one hole to another is called a throw change.
• - Weights or counterweight: Used to balance the unequal forces that originate on the engine during the upward and downward strokes of the rocker arm in order to reduce the maximum effective power and the rotation moment. These weights are generally placed on the crank and in some units on the main beam, at the opposite end the head.
• - Stuffing press: It consists of a cylindrical chamber that contains the packaging elements that fit the polished bar, allowing the space between the polished bar and the production pipe to be sealed, to prevent the spillage of crude oil produced.
• - Pumping unit: Its main function is to provide the appropriate reciprocating movement, in order to drive the rod string and these, the subsoil pump. Through the action of belts and gears, rotation speeds are reduced.
The subsoil equipment is what constitutes the fundamental part of the entire pumping system. The API has certified the rods, production pipes and subsoil pump.
• - Production Pipeline: The purpose of the production pipe is to conduct the fluid that is being pumped from the bottom of the well to the surface. In terms of resistance, production tubing is generally less critical because wellbore pressures have been greatly reduced by the time the well is conditioned for pumping.
• - Rods or Suction Rods: The rod string is the link between the pumping unit installed on the surface and the subsurface pump. Their main functions in the mechanical pumping system are: transferring energy, supporting loads and driving the subsoil pump.
• - Pipe Anchors: This type is designed to be used in wells with the purpose of eliminating the stretching and compression of the production pipe, which rubs against the string of rods and causes wear of both. Normally used in deep wells. It is installed in the production pipeline, which absorbs the load of the pipeline. The rod guides are attached to the rods at different depths, depending on the curvature and previous occurrences of high pipe wear.
• - Subsoil Pump: It is a positive displacement (reciprocating) device, which is driven by the string of rods from the surface. The basic components of the subsurface pump are simple, but built with great precision to ensure pressure and volume exchange through its valves. The main components are: the barrel or sleeve, piston or plunger, 2 or 3 valves with their seats and cages or valve retainers.
• - Piston: Its function in the system is to pump indefinitely. It is basically composed of special seal rings and a special lubricant. The operating range is 10K lpc and a temperature no higher than 500 °F.
It is the first element that must be considered when designing a mechanical pumping installation for a well, since the rest of the components depend on the type, size and location of the pump. It is a positive displacement pump.
They are pumps that are resistant in construction and simple in design. The barrel connects directly to the pipe and the rod string connects directly to the piston. At the bottom of the barrel there is a seat nipple, which will house the fixed valve. One of the possibilities is to lower the fixed valve with a fisherman attached to the bottom of the piston, until it is fixed to the nipple. The piston is then released from the fixed valve by rotating it counterclockwise. The TH pump provides the maximum fluid displacement for a given production pipe, the diameter of the piston is slightly smaller than the internal diameter of the pipe. Sturdy in structure, the thick-walled barrel is directly connected to the pipe by a nipple. The rods connect directly to the upper piston cage, eliminating the need for a piston rod. The advantages of this pump make it one of the most used by producers in wells that do not require frequent interventions.
As limiting factors it can be noted that: To change the barrel you have to remove all the tubing. It is not the most advisable for gas wells, since it has a large harmful space due to the fixed valve fisherman, which in this case reduces the efficiency of the pump. The large volumes displaced mean that the loads on the rods and pumping equipment are very significant. These loads also cause large stretching of tubing and rods with consequences on the effective stroke of the pump.
Their main characteristic is that they are fixed to the pipe using an anchoring system, so to remove them from the well it is not necessary to remove the tubing, saving more than 50% of time in this operation. For installation, a fixing element called a seat nipple must be placed on the pipe. Subsequently, the pump is lowered using the string of rods, until the pump anchor is fixed to the seat, leaving it ready to operate. The widespread use of these pumps has led to the design of a wide variety of insertable pump options, among others:
The peculiarity of this pump is that the moving element is the barrel with its valve, instead of the piston. In this case, the piston is anchored to the seat by a hollow tube called the draft tube. The fixed and movable valves are located on the top of the piston and barrel respectively. The movement of the barrel, in its upward and downward stroke, maintains the turbulence of the fluid up to the seat nipple, making it impossible for sand to settle around the pump, imprisoning it against the pipe. By having the mobile valve in the upper cage of the barrel, if the well stops for any reason, the valve will close, preventing the settling of sand inside the pump, which is of utmost importance since only a small amount of sand deposited on the piston is enough for it to become trapped in the barrel when the pump is started again.