Transportation of oil and gas can be made by road and rail transport, tankers and pipelines. Among them pipelines have proved to be the most economical method for transportation of oil and distribution of natural gas.
Most oil and gas pipelines fall into one of three groups: gathering, trunk or distribution. Small diameter gathering pipelines within an oil or gas field are called flow lines. They connect individual oil or gas wells to central treating, storage or processing plants. Another gathering system made up of larger-diameter lines connects these field plants to the large-diameter, long-distance trunk line which moves oil from producing areas to large refineries for processing. Gas transmission lines carry natural gas from producing areas to city commercial, residential and industrial users.
Flow lines are generally small diameter pipelines operating at pressures below 100 psi. Typical flow-line diameters in the United States are from 2 in. to 4 in. The destination of most oil flow lines is a tank battery. A typical tank battery contains a separator to separate oil, gas and water; a fired heater, metering, desalting and some other equipment.
The next link in the oil pipeline chain is gathering lines that transport oil from oil processing plant and tank battery to a large storage tank farm where it is accumulated for pumping into the long-distance crude trunk line. These gathering lines typically consist of pipes ranging from 4 in. to 8 in. in diameter with operating pressure higher than that of flow lines. The size of the gathering line depends on the volume of crude to be moved, pipeline length and other factors.
From large central storage tank farm oil is moved through large-diameter long-distance trunk lines to large refineries or to other storage terminals. Powerful pumps are required at the beginning of the trunk line and pumping stations must also be placed along the pipeline to maintain high pressure. Crude trunk lines like field-gathering systems are made of steel with individual sections welded together. These lines are almost always buried below ground surface.
The purpose of gas gathering pipelines and transmission lines is similar to that of oil pipelines but operating conditions and equipment are quite different. Flow lines from individual wells carry gas to the field processing plant where the gas is treated to make it suitable for sale. Water and acid gases, hydrogen sulfide or carbon dioxide are removed from the gas stream because they can cause corrosion and other problems in long-distance pipelines. Hydrocarbon liquids are removed because of their value as individual products for petrochemical industry.
From field-processing plants, dry clean natural gas goes into the gas transmission pipeline system for movement to cities where it is distributed to individual businesses, factories and residences. In general, gas pipelines operate at higher pressures than oil lines and gas is moved by compressors rather than by pumps. Gas transmission pipelines are made of steel pipe and are buried below ground surface.
In addition to all these, pipelines help to transport different other petroleum products, such as gasoline, aviation gasoline, home heating oils and even several different products in the same pipeline.
Generally, oil and gas pipeline sizes vary from 2 in. to 60 in. in diameter. Typically, flow lines range from 2 in. to 6 in. in diameter; gathering systems consist of pipe from 4 in. to 12 in., and long-distance crude trunk lines and natural gas transmission lines can range up to 56 in. in diameter and even more.
18. ќтветьте на следующие вопросы:
1. What is the most economical method for transportation of oil and distribution of natural gas? 2. What are the three groups of oil and gas pipelines?
3. What is the function of flow lines? 4. What are the typical flow line diameters in the US? 5. What does the size of the gathering line depend on? 6. Powerful pumps are required at the beginning of the trunk line, arenТt they? 7. What are crude trunk lines made of? 8. Where does dry clean natural gas go into from field processing plants? 9. Do oil lines or gas pipelines operate at higher pressures? 10. What are the possible variations of oil and gas pipeline sizes?