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 Chapter 18 Gas Wells Section D GAS COMPRESSION AND SALES D-1. Natural Gas Compression. In some systems, natural gas has to be compressed to a high pressure to be transported by pipeline across the country. If pressure at the location needs to be more than 500 pounds, compression is required. As this pressure falls due to line resistance and the line volume increases as other wells are added to the gathering system, other compressors are installed. The gas compressor will have a series of automatic controls that shut it in in the event of problems such as a loss of pressure indicating a line break, a high buildup of pressure indicating a plugged or frozen line, or a low supply pressure. If an engine is utilized in compressing the gas, a series of engine safety switches will also be installed. Figure 1. At this site, the gas measurement meter is protected against weather in a building. D-2. Natural Gas Measurement. A gas meter is installed on the location a short distance after the compressor to measure the amount of gas sold (Figure 1). The production company owns the gas as it comes out of the well and through the threephase hydrocarbon separation unit. As the gas leaves the production unit, it is usually owned by the gas company. This means the gas purchasing company also owns the dehydration unit and the compressor. In this event, the gas company will also own the small vessel that stores condensate that has been separated from the dehydration unit and is responsible for emptying the knee tub as needed. The gas reservoir must be large enough and have sufficient pressure to make it a commercially profitable investment. The factor that governs who owns what is how much gas does the well produce. For low producers, the production company may not only own everything, but the company may be required to lay the line at their expense to connect to the natural gas gathering system. The gas from the wells is sold by contract, and the conditions of that contract are agreed upon by both parties. A gas meter is installed a short distance from the compressor to measure the amount of natural gas sold. This may be a simple chart meter or a more complex one with a 18D-2 solar panel and radio communication with the gas company (Figure 2). Figure 2. A gas meter powered by a solar panel. Readings are sent to the gas company via radio. D-3. Testing Gas Wells. Several methods are used in testing gas wells. One of the simplest tests is to shut the well in for a specified length of time and record the shut-in pressure. After this has been done, the well is returned to service. The purpose is to determine reservoir pressures remaining to project remaining reservoir volumes as well as projecting when a gas compressor may be required. A second method of testing is to begin from a shut-in condition and flow the gas well where a specific backpressure curve is maintained to determine correct choke settings and to determine condensate (or distillate) and/or water production at various flow rates. Some tests are performed to meet regulation requirements and to set allowables. In preparing to test the well, the pumper may need to flow the well vigorously enough to clean up the well bore prior to shutting it in. Wells that stabilize bottom hole pressure slowly may need to be shut in up to four days prior to the test. The equipment used to measure the volume is basically the same as with oil production wells but in some situations will handle a larger volume of gas. Abbreviations commonly used in measuring gas flow are: BCPMM Barrels of condensate per million cubic feet of gas BHP Bottom hole pressure CF Cubic feet CFM Cubic feet per minute MCF 1,000 cubic feet MMCF 1,000,000 cubic feet MMCFD Million cubic feet per day MSCF 1,000 standard cubic feet D-4. Pipelines and Pipeline Problems. As the gas goes down the pipeline, the amount of water and condensate remaining in the gas is of great concern to the pipeline company. As the fluid condenses back into a liquid state, it has to be pushed along with the gas or it will accumulate in low spots and result in back pressure while the gas is trying to push it over the next rise. The water will also freeze in winter time, and between the water, distillates, and other contaminants, a jelly-like substance called hydrates forms in the line and results in line restrictions. When a mist of water accompanies the distillate and condenses back to a liquid, it contains little or no salt so it freezes easily, at around 32° Fahrenheit or 0° centigrade. This causes the lines to freeze on the inside and chokes off production. Appropriate production techniques must be adapted to overcome this problem. The well will begin to freeze and flow in cycles, and in the winter it may just stay frozen. 18D-3 In Figure 3, the chemical tank near the gas compressor injects methanol, an antifreeze, into the line. This antifreeze, trickling into the line, assists in keeping the water from freezing and blocking the line. Figure 3. A gas compressor with a methanol injection tank. The removal of liquids from pipelines. The problem of liquid, popularly called drip, being pushed down the line still exists. This liquid must be removed. Liquid collection tanks (Figure 4) are installed in low areas where this drip accumulates. In the past, these containers were often referred to as drip pots. This condensate is very volatile, unpredictable, and good safety practices must be used to handle it. With oxygen and a spark, it is very explosive and requires training to be able to handle it safely. Figure 4. Gas lines in a collection system with drain lines to condensate tanks or drip pots. D-5. Treating and Drying Natural Gas. Before natural gas can be transported long distances across the country for consumption in other areas, all liquids must be removed. In addition to the petroleum condensates, which can be compared to gasoline, the butane and propane must also be removed. Special natural gas processing plants (Figure 5) are constructed in many locations in a large gas field to be able to process the gas. Figure 5. A plant for drying gas and processing natural gas. D-6. Transporting Natural Gas Long Distances. Before natural gas can be transported, it must be dried and all liquids removed. Natural gas is a very clean burning fuel and can be marketed in many ways. It supplies steam power for operating electrical generating plants, manufacturing plants, and the petro-chemical industry. It can be compressed and marketed for short-distance travel as CNG, compressed natural gas. Marketing natural gas in this form is becoming more popular across the country. Some city bus companies and service companies are converting to this system. It can be reduced even further into LNG, or 18D-4 liquefied natural gas. New Zealand has been using LNG for long distance travel automobiles for some time. It is gaining in popularity. China used ANG, atmospheric pressure natural gas, for city buses many years ago. The large gas bladders attached to the top were as large as the buses. Cross-country gas lines. Cross-country gas lines are large and transport gas all across the country. Compressor stations along the line boost pressure for continuous flow. When problems occur in the line, the line is large enough to act as a surge chamber, or reserve supply, so that minor interruptions do not affect the end-user. The pipeline companies do a good job in supplying gas with little or no interruptions.