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
Testing, Treating, and Selling Crude Oil
TREATING WITH CHEMICALS
C-1. Purposes of Treating Chemicals.
Many substances are produced along with oil and gas. Water, salt, paraffin, asphalt, iron, sulfur, and sand create many emulsions and compounds that become difficult to treat. These must be reduced to acceptable levels in order to sell oil and gas. It can be confusing to the new lease pumper to dive right into terms such as demulsifiers, emulsion breakers, wetting agents, and other terminology. Instead, the explanations in this chapter will begin by describing the end objective of treating oil, the basic problem that needs to be solved, and how these goals can be reached. The use of detergents to remove water. The primary agent used to reduce surface tension of oil and water droplets is a soaplike compound called a surfactant. The surfactant can be both water- and oilsoluble. It is used to reduce the surface tension and viscosity of heavy crudes and can assist in removing iron sulfide. Detergents are often used in chemical treatments of oil to remove water. Also, they reduce the surface tension in emulsions to allow small droplets to form into larger ones that can then be separated by gravity. Use of solvents for paraffin. Paraffin solvents are used to thin paraffin and lower viscosity. These can be used downhole to prevent paraffin from clinging to the inside of the tubing, and in the tank battery to thin paraffin and reduce surface tension. It has a high penetrating capability similar to casing head gasoline or drip that condenses in gas transmission pipelines. Casing head gasoline can be very volatile or explosive. It can be used everywhere oil is treated and is usually not as expensive as surfactant-based chemicals. Bottom breakers for tank bottom emulsions. Bottom breakers are chemicals that are used to reduce the viscosity of the emulsions that accumulate on the bottoms of tanks. They are the most expensive of the common oil treating chemicals. A fivegallon container will usually cost more than $100 and may need to be specially blended for unique site problems. Other treating chemicals and mixtures are available but are also usually directed toward solving these three problems.
C-2. Introduction to Chemical Injectors, Styles, and Operation.
Several styles of chemical injectors or chemical pumps are pictured in this chapter. Appendix E gives an overview of mechanical, electrical, and pneumatic chemical pumps and special treating equipment. It is desirable to begin treatment as early as possible. As a rule, it is too expensive to begin the treatment in the formation. Treating for sand and scale production may possibly begin in the formation, but treating for BS&W in crude oil usually begins at the perforations where it enters the well, the Christmas tree or pumping wellhead, or the tank battery. Accurate injection records should be kept by the lease pumper, and when chemicals are added, consumption should be calculated regularly. Treating oil at the tubing perforations or downhole. Figure 1 illustrates a typical installation where the objective is to treat oil before it reaches the surface. Oil is injected into the casing on the side of the wellhead opposite the casing valve that allows formation gas to be produced into the flow line. Figure 1. Chemical injection to treat oil at the perforations at the bottom of the well. A small stainless steel bypass line from the bleeder opening of the pumping tee allows a small stream of circulating fluid to be injected with the chemicals. This increases the total volume of fluid and reduces the time required for the chemicals to reach bottom. A check valve is installed near the pumping tee to prevent the chemical from being diverted directly into the flow line. With a valve at each end, it is simple to isolate the line for repair purposes. By connecting another chemical line that contains a valve to bypass the circulating line, the injection of chemical can be diverted directly onto the flow line without going downhole. The mechanical pump shown in Figure 2 can be installed on the base of the pumping unit and connected with a small rope or cable, eliminating the need for electricity. One pump can inject paraffin solvent downhole to prevent paraffin buildup on the sucker rod string. The second container can inject oil treating chemicals either downhole or directly into the flow line. Figure 2. Mechanical chemical pump with a sash cord connection to the walking beam. It has a weight to move it down and is the safest method for operation. Note that the wellhead also has provisions whereby the well can be batch treated down the casing. The wellhead contains a pressure control that shuts in the well if the flow line pressure builds up above the setting level. A small blowout preventer allows pressure to be shut in while the upper polished rod packing and pressure packing are replaced. The advantage of injecting the chemical at the well is that the oil is treated while being pushed toward the tank battery and the chemicals are blended into the mixture. The disadvantage of injecting at the well is that when the well is down, even during a normal cycle, the tank battery is not receiving the chemicals needed for blending with other wells. It is too expensive to install and maintain chemical pumps at every well. There have been many injuries to arms and legs during the downstroke of mechanical pumps when construction reinforcement rods were used to operate the arm. The use of rope or small cable eliminates this hazard. Figure 3. Injecting chemicals at the tank battery. Injecting chemicals at the tank battery. The typical placement of chemical injector pumps at the tank battery is after the header where all wells come together but before the first vessel (Figure 3). This is just ahead of the separator or before the first vessel, whether it is pressure or atmospheric. Producing sellable crude oil. Tank bottoms should be kept clean. This is a cardinal rule to follow when pumping a lease. Most tank batteries have a minimum of two tanks. As soon as one tank of oil is sold, the remaining oil from that tank should be pumped through the treating facilities and into the second tank. There will always be almost a foot of oil. Also, this oil is pumped through the treating facility. Occasionally there will only be one stock tank. If so, simply hook up the portable pump (Figure 4) and pump it from the bottom back into the same tank. This will assist in keeping the oil clean and sellable.
Figure 4. A portable chemical pump. (courtesy of Arrow Specialty Co.)
The employer must be willing to cooperate with the pumper by providing a few suitable tools necessary to treat the oil. When treating equipment is acquired, it must be designed to perform the task. The pumper should sit down with the employer as needed to secure workable equipment to do a good job. Since the pumper works alone, if a portable circulating pump is used, it must be light enough to transport conveniently. The portable circulating pump is small. If it is not trailer-mounted, the centrifugal pump is bolted directly to the motor and not skidmounted. Otherwise, it is too heavy for one person to handle. Batch treatment while circulating. When circulating oil for treatment, chemicals may need to be added while the tank is still circulating. One easy solution to adding chemicals slowly is to use a container such as an empty gallon plastic container that has a small drip hole punched in the bottom. This should be set in the thief hatch opening and chemical poured into it while the oil is being circulated. It will take fifteen minutes or so for the chemical to drip in for a good treating blend. Some operators use a bottle of butane and a 50-foot air hose to roll the tank. The air line to the bottle is connected with it sitting on the ground. The end of the hose is weighted and carried up the ladder. The end is then lowered into the tank until it reaches bottom. The drip container is placed in the hatch and the bottle turned on to a low setting. Other problems on the lease can be tended to while the tank is being rolled and treated by the butane mixing the chemical with the tank bottom. Some lease operators use dry ice instead of butane for this procedure.
C-3. Special Treating Processes. Cleaning tank bottoms.
Tanks occasionally accumulate an emulsion that must be removed. When this occurs, the manway plate may have to be removed from the back of the tank and the tank cleaned. A small depression may be dug and lined and a vacuum truck called. The vacuum truck has a diaphragm-operated pump with flapper check valves and can pump almost anything from the tank The hot oiler. Occasionally, the tank of oil may develop so much paraffin and such a large volume of water that it does not react to normal treating procedures. Often this occurs during the colder winter months. In this case, a hot oiler truck (Figure 5) must be called. Figure 5. The hot oiler can heat oil as well as produce super hot steam for steam treating. The hot oiler will load 20 or more barrels of oil on the truck from the tank battery into its oil tank. The oil is heated and pumped back into the tank through a flexible highpressure metal hose to the battery. It is then pumped through a line that extends down through the thief hatch to the bottom of the tank. As the oil is heated and pumped back into the tank, it will raise the temperature of the tank high enough that the paraffin will melt and become fluid again. Water will then fall to the bottom. It normally will take a hot oiler several hours to complete this heating and rolling procedure. Upon completion, the free water is pumped off. As soon as the temperature of the oil falls to an acceptable level, the oil is sold. Figure 6. A slop tank used in treating very difficult-to-treat oil. The slop tank. When treating problems recur at a tank battery, some companies solve the problem by installing a slop tank (Figure 6). This is a potentially invaluable tank that has become popular in areas where the use of lined pits is limited, and where a tank habitually develops high bottoms. When the tank of oil has a high bottom that is difficult to treat, a few inches of the bottom is pumped off into the slop tank to make the tank sellable. As soon as the oil is sold, the bottom is pumped back through the treating facilities and into the tank of oil being filled. When the tank is filled, and the high bottom occurs again, the procedure is repeated. Other systems, such as the rolling system, may also be installed to combat treating problems.