1 SECTION 3 ARTIFICIAL LIFT Sucker Rod Pumps Mechanically simple this is the most common of the pumping systems. The system basically consists of a downhole standing valve and a traveling valve that is moved by a string of sucker rods that connect it to the surface equipment. The pumping cycle starts with the lifting of the traveling valve (TV) at the bottom of the stroke, the TV is closed and the standing valve (SV) is opened. This lifts the fluid above the TV and allows fluid to enter the pump through the SV. At the top of the stroke when the TV starts down and is opened and the SV is closed. The fluid that is now in the pump is trapped there by the closing of the S V and TV moves under the fluid by being open. The TV and SV are ball and seat type valves that are in cages to restrict the movement of the ball.2 There are 4 major components in a sucker rod pumping system, I) Prime mover, the energy source of the system (motor or engine) 2) The surface pumping equipment, moves the rods (pump jack) 3) The sucker rods, connection of the surface to downhole 4) The downhole pump The system is a complex interconnection of all these parts and each has to be designed with the others in mind for a total desired result. The Pump There are two types of rod pumps, tubing pump and the rod or insert pump. 1) Tubing Pump, the barrel of this type of pump is part of the tubing string. The plunger (traveling valve) is run on the end on the rods, the standing valve is dropped before running the rods and plunger and can fished out without removing the barrel of the pump. This system allows for larger pump barrels and plunger thus the ability to move large volume of fluids, the downside is if the barrel needs to be repaired the entire tubing string has to be pulled from the well. 2) Rod or Insert Pump, the entire assembly of this system is run on the rods, and inserted into a seating nipple in the tubing. The advantage here is the ease of maintenance; it is easier to pull the rods to recover the pump for repair than the tubing string. Downside is the pumps are smaller, they have to fit inside the tubing, smaller volumes are be pumped. Rods The rods that connect the pump to the surface are basically steel but in some high corrosion environments fiberglass rods are used. The steel rods come in various grades depending on the strength and corrosion resistance needed. The rods are the weakest part of the system, and is the main focus of maintenance required for this pumping system. Design of the rod string is critical to the overall performance and economics of the well. Rod strings have single or tapered diameters depending on the depth of the well and the amount of fluid needed to be pumped. The rod consists of two components, the rod body and the box which connects the individual rods. The pins of the rod, the threaded ends, are also an area of weakness in the system.3 The care of the rods during shipping, storage and, running is very important as they are easily damaged. The amount of torque when making up the rods is also very important in the longevity of the rod string. At the top of the rod string is a polish rod, this is a smooth rod that goes through the stuffing box, the packoff on the tubing, and is clamped so it can be hung in the bridle of the pump jack. The Pump Jack (Surface Equipment) The major components of the pump jack to be considered in design of the pumping systems are, 1) the gear box, 2) Polish rod load, 3) length of stroke, and 4) the maximum allowed counterbalance. The API designation of pump jacks is a series of 3 numbers, inch pounds of torque on the gear box in thousands, polish rod load in hundreds of pounds, and the stroke in inches. So a jack with the model number of 456 -650 -144 API will have 456,000 inch pounds of torque, a maximum prl of 65,000 pounds, with a maximum stroke of 12 feet. Each manufacturer will also have some company designations in the model number for the design of the jack. The main function of the jack is to convert the rotary motion of the prime mover to an up and down motion so the rods can move the TV up and down in the well. There some different designs to do this without the shock in the4 change of direction and to help with the counterbalancing of the jack. The air-balance unit and Lufkins Mark series are examples of this. Once the Jack is sized properly it is important to have the counter balance weights set right, this will increase the life of the gear box and lower the required horsepower needed to pump the well. The Prime Mover Is the engine or electric motor that runs the system. Electric motors give a flexibility for the timing of pumping cycles. They also have a lower maintenance costs than gas engines. Not all wells are near a power grid and start costs of bring in a line can be high. Gas engines can be cheaper to operate since they can run on gas from the well. Design Considerations The pump, after deciding how much volume needs to be pumped, the length and the diameter of the plunger of the pump is calculated with the speed of the pump jack in strokes per minute. The length of the pump must be long enough to allow for the "overtravel" of the plunger, this is caused be the stretch of the rods as they change direction. The length of the stroke is limited by the pump jack, smaller jacks have smaller strokes. After the pump is sized the rod string is designed that can handle the stresses of the fluid and its own weight along with the weight of the fluid. This is restricted by the size of the tubing in the well as is the barrel size of the pump. A pump jack that meets all the design criteria is found and the horsepower required is calculated along with the counterweight that will be needed for an efficient pumping system. Other Down hole equipment Tubing Anchor The loading and unloading of the standing valve causes the tubing to stretch and contract in the well. This motion has to be accounted for in design the length of the pump stroke. This can be very large in deep wells and wells that are pumping a large volumes of fluid. A tubing anchor eliminates this problem by anchoring the tubing to the casing usually just above the pump. The tubing is set in tension to keep the rods from rubbing on the tubing if possible.5 Gas Anchor This is a tube with holes in the bottom portion that screws in the pump intake and helps