Lease Pumper's Handbook Published
by the Commission on Marginally Producing
Oil and Gas Wells of Oklahoma, First
Edition 2003 Written by Leslie V. Langston
Table of Contents Introductions A. Cover
Sheet Book Title B. Publishing Information
First Edition, 2003
The Lease Pumper's Handbook
Published by the Commission on Marginally Producing Oil and Gas Wells of Oklahoma, First Edition 2003 Written by Leslie V. Langston Table of Contents Introductions A. Cover Sheet Book Title B. Publishing Information First Edition, 2003
Written by Leslie V. Langston
Publishing Information. First Edition, 2003. C. Foreword. Rick Chapman, Executive Director (1996-2000) Commission on Marginally Producing Oil and Gas Wells, State of Oklahoma. D. Dedication. John A. Taylor, Chairman (1992-1998) Commission on Marginally Producing Oil And Gas Wells, State of Oklahoma. E. Author’s Introduction. Leslie V. Langston, Author, First Edition F. Commission Introduction. Liz Fajen, Executive Director, Commission on Marginally Producing Oil and Gas Wells, State of Oklahoma.
The Lease Pumper’s Handbook
The Tank Battery
CIRCULATING ANDWATER DISPOSAL SYSTEMS
Figure 1. Diagram of the circulating and water disposal systems. Water lines are marked with a W.
F-1. Produced Water at the Tank Battery.
Many reservoirs are water driven, so producing water along with the oil and gas is a common situation. As the amount of water produced to the tank battery increases or is difficult to remove, special vessels, lines, and systems are installed and operated to assist in the removal and disposal of the additional water. (Figure 1) Water is removed by the heater/treater and the gun barrel by separating the incoming emulsion into natural gas, crude oil, and water. There 10F-2 are several other vessels that automatically separate out water, but these specialized vessels are beyond the scope of this study. By raising or lowering the water leg a few inches, the lease pumper can change the oil/water interface level dramatically inside the vessel, reducing or increasing the amount of oil held in the vessel. This also changes the treating ability. Occasionally the heater/treater or gun barrel water leg must be adjusted to obtain the best results.
F-2. Water Separation from the Heater/Treater and the Gun Barrel.
The heater/treater and the gun barrel utilize natural forces to separate the oil and water by line height. With the heater/treater pictured in Figure 2, the crude oil inlet line is the upper line on the right side. After the emulsion enters the vessel, most of the gas flash separates, and the oil and water flows downward through a tube. The water continues down and out through the water leg, and the emulsified oil passes by the firebox on its way back up to the upper oil level at the top. The gas goes out the center of the top, then down through the outer right line. The cleaned oil comes out the lower right or inside line. The water comes out the lower left line, travels up through the inner tube, spills over the top, and falls down through the outer tube. The upper connection on this line contains only gas and equalizes the pressure between the vessel and the top of the water leg. This connection also stabilizes the line and holds it upright. To compute the height of the water leg line, refer to Appendix F, Mathematics. The height of the liquid inside the oil and the water outlet lines remains constant at about 4 feet above the automatic diaphragm control valve. This valve is located within a few feet of the ground and is controlled by a weight on an arm. Additional weight can be added but is seldom needed. The level of oil and water inside the vessel is controlled by line height, not by the dump valves. Additional weight is occasionally added to the liquid dump valve when problems have been experienced. Figure 2. A vertical heater/treater with the water leg and other lines shown. The gun barrel. As shown in Figure 3, the emulsion enters the gun barrel through the line on the left side of the flume. The gas breaks out in the large boot at the top and enters the gas system in the top of the vessel. The liquid emulsion falls down through the large tube below the boot to the bottom. It then enters the vessel through a spreader across the bottom, where the oil works its way upward through the water inside. Figure 3. A gun barrel installed as part of an automated circulating system. The produced oil flows out through the line on the upper left side close to the top and flows to the stock tank. The water comes out the lower line in the front, moves upward through the water leg, spills over to the right, and flows to the water tank to the right. Since the lines are not made of steel, a stiff arm stands out from the center of the side of the tank. Vertical pipe saddle/clamps support the weight of the line and liquid to prevent leaks. The two lines on the left center of the vessel are special purpose, such as for steaming, hot oiling, pulling oil off to use in treating the wells, injecting water into the system to be cleaned before disposal, and other special procedures.
F-3. The Circulating System.
The circulating system (Figure 4) moves oil from the stock tanks back through the heater/treater or gun barrel to remove excessive BS&W from the oil. Figure 4. The stock tank drains are in the foreground while the heater/treater and circulating pump are in the background. The circulating system is usually operated manually for low-volume stripper production. In high-production wells with difficult-to-treat oil, the system equipment, lines, and vessels are upgraded. The pump will come on automatically and circulate the tank bottom back through the heater/treater for a short period of time. The frequency and duration of circulation must be based on production needs. This procedure is continued day and night until the tank of oil is full and has been isolated for sale. Because of the risk of high-volume fluid loss, the system must be kept in top condition. Spills can be expensive to clean up. The benefits, however, are enormous in saved treating time and chemical consumption. Frequent circulation alone can often reduce chemical costs dramatically.
F-4. TheWater Disposal Tank.
The water disposal tank for a small battery usually holds the equivalent of one transport load or about 250 barrels. It is usually made of fiberglass, stands 8 feet high, and has net material or a fiberglass dome across the top for bird safety. Large tank batteries and large water flood projects may have 20-foot tall water tanks that hold 2,000 barrels. A satisfactory set of steps for inspecting and gauging the tank is a necessity. Inspections are to check water levels and the accumulation of crude oil in the system. In some closed systems, an oil blanket is preserved over the water to prevent oxygen saturation, oxygen corrosion, and plugging problems downhole. This oil blanket assists in blocking oxygen/water contact. Figure 5. The basic water disposal system involves draining the water from the gun barrel and moving it through a line to the water disposal tank.
F-5. Solving Circulating and Disposal Problems.
Three processes occur in the water system and may be going on at the same time:
· The heater/treater and gun barrel are producing water into the water disposal tank or the pit.
· A stock tank is circulating the bottom of the tank being produced into.
· The water flood pump is injecting water back into the formation.
All of these operations occur automatically for planned intervals and durations. Yet the lease pumper must be able to override the systems, engage the pump to empty any vessel on location, refill and reactivate any vessel on the location, and possibly perform other functions according to the need of the moment. This requires careful consideration when designing the systems. Some systems are designed for single-purpose conditions and have no flexibility of action. Other systems are very complex to achieve the desired objectives. It is not usually possible to solve every problem easily, but some of the common problems that may be encountered are: Circulating oil while removing water from the system. A good installation allows circulation of a tank bottom without interfering with the normal water disposal operation. The discharge of water from the three-stage separation vessels (the heater/treater and the gun barrel) to the disposal tank should be able to continue without interruption while the circulating is in process. During this dual operation, the lease pumper must ensure that liquids do not build up in these vessels faster than the vessel can 10F-5 handle them. This results in excessive volumes of water flowing to the disposal tank. After the circulating is finished, too much oil and not enough water are contained in the vessels, throwing them out-of-balance and possibly causing oil to go down the disposal system line.
Out-of-balance conditions can occur due to several reasons, such as:
· Undersized or restricted oil lines.
· Undersized or restricted water lines.
· Circulating too long in one cycle.
· Not enough time between cycles to permit the vessels to re-balance.
· Water production is low so it takes a long time to re-balance
· Water leg is set at wrong level.
· Water flood has caused the weight of the water to change, and the water leg has not been re-set to compensate for this change. Automatic circulation from the LACT unit. When the BS&W level goes up beyond the set percentage in the LACT unit, the three-way diverter valve will automatically open and send the oil back through the heater/treater for re-cleaning or BS&W removal. When the BS&W level is reduced, the oil will automatically be diverted back through the barrel counter and sales line. The volume of oil diverted must be low enough for the heater/treater to function with this new volume, in addition to the regular volume produced, and still remain in balance. Emptying vessels for maintenance. Any vessel in the system may need to be emptied for repairs. This can be done by opening and closing the correct valves. When drain lines are installed to every vessel, this capability to empty any vessel in the system individually is built-in. This saves time and expense when repairs become necessary. Operating without such lines can cause much higher maintenance expenses and will lead to a system that is inefficient and frustrating to operate as it consumes too much of the lease pumper’s time every time a minor problem occurs. Cleaning tank bottoms. Cleaning tank bottoms without removing the manway plate usually involves extensive use of the circulating pump. This function requires different procedures from the routine circulating procedure. It might even require the use of a flexible hose and a pipe extension that will reach the bottom of the tank and extend out through the thief hatch. It may also require forcing the liquid alternately in both directions—into the tank through the line stirring up the bottom—and vacuuming the liquid out for cleaning. This may require a portable pump with hoses.
F-6. The Circulating Pump.
The circulating pump is an essential tool to maintain clean tank bottoms and for selling crude oil with an acceptable level of BS&W. Most of the time it is used for cleaning crude oil, but it can also pump all of the liquid out of any vessel when that vessel must be opened for cleaning or repair. It is also utilized to pump liquid back into some vessels as needed when placing them back into service after repairs. By use of the circulating pump, the operation of these vessels may be balanced within hours. It may also be used to pump all oil contained in several vessels as well as tank bottoms into one tank in order to sell as much oil as possible each month. With proper installation, for small batteries and limited operations, it may also be used to pump the produced water back into the 10F-6 reservoir for water flood or water disposal. Methods of connecting the pump to allow operation in either direction are reviewed in Chapter 17, in the surface pump section.
F-7. Hauling theWater by Truck.
Produced water is often hauled by truck to the nearest injection well, which may have tanks located nearby to receive water. The load of water will range from 160-200 barrels. The operator may pay someone else to dispose of the water or do this on the lease as a water disposal or a water flood project. Hauling liquids by truck transport is reviewed in Chapter 15, Enhancing Oil Recovery.
F-8. Water Injection.
For the small water injection project, the total project may be operated by a simple water-level control switch to turn the pump on and off. A typical disposal tank switch is illustrated in Figure 6. The pump moves the water to one or more injection wells. Some of the latest technology involves water injection into a currently producing well. Water injection is reviewed in Chapter 15, Enhancing Oil Recovery. Figure 6. A typical water injection control.