石油储运英语教程(第二部分).doc

Unit FiveTypes of PipelinesMost oil and gas pipelines fall into one of three groups, gathering, trunk/transmission, or distribution. Other pipelines are needed in producing fields to inject gas, water, or other fluids into the formation to improve oil and gas recovery and to dispose of salt water often produced with oil.Small-diameter pipelines within an oil or gas fields called flow lines, are usually owned by the producer. They connect individual oil or gas wells to central treating, storage, or processing facilities within the field. Another gathering system made up of large-diameter lines, normally owned by a pipeline company rather than the oil or gas producer, connects these field facilities to. the large-diameter, long-distance trunk or transmission line. In some cases, individual wells are tied directly to the pipeline companys gathering system.Crude trunk lines move oil from producing areas to refineries for processing. Gas transmission lines carry natural gas from producing areas to city utility companies and other customers. Through distribution networks of small pipelines and metering facilities, utilities distribute natural gas to commercial, residential, and industrial users.Flow lines, the first link in the transportation chain from producing well to consumer, are used to move produced oil from individual wells to a central point in the field for treating and storage. Flow lines are generally small-diameter pipelines operating at relatively low pressure. Typical flow-line diameters in the United States are 2 in , 3 in , and 4 in. The size required varies according to the capacity of the well being served, the length of the line, and the pressure available at the producing well to force the oil through the line. Flow lines typically operate at pressures below 100 psi. In many fields around the world, high-capacity wells require larger-diameter pipelines.Individual oil flow lines are relatively short, typically ranging from less than a mile to a few miles. However, an oil field containing many wells, each of which is connected to central facilities by a flow line, can contain several hundred miles of pipeline in a relatively small geographical area.The throughput of oil flow lines ranges from a few bbl/day upward , depending on the capacity of the well being served. Many wells produce several hundred bbl/day, for instance, and some wells may produce as much as several thousand bbl/day.Offshore, relatively few flow lines are installed. For economic and operating reasons, most offshore development wells are directionally drilled from central platform, permitting the wellheads to all be placed in a small area on the platform. Individual wells therefore do not normally need to be connected by undersea pipelines to processing equipment. However, a few hundred offshore wells have been drilled remote from central abovewater platforms and are connected by flow lines laid on the ocean floor; Also, in some cases a platform containing a number of wells will be connected by an undersea line to a separate platform where the oil is processed and/or stored.Because oil flow lines are short, the energy (pressure) required to move the oil through the pipeline to central facilities within the field is relatively low. There are two types of oil wells those that flow unaided because of the natural energy of the reservoir and those that must be pumped. The pressure that forces oil in a flowing well to flow to the surface is usually sufficient to move the oil on to the central field facility. In wells in which a bottom hole pump must be used to lift the oil to the surface, the pumps energy also moves the fluid through the flow line. Additional pumps at points along the flow line are not normally needed.The destination of most oil flow lines is a tank battery. One or more tank batteries may be installed in a single field, each serving a number of individual wells. A typical tank battery contains a separator to separate oil, gas, and water; a fired heater to break water-oil emulsions to promote complete removal of water from the oil; and tanks for storing the oil until it can be shipped from the lease by truck or pipeline. Metering equipment is also included to measure the volume of oil leaving the lease. An additional separator, separate meters 9 and other equipment may also be installed for periodic testing of individual wells.The oil in each flow line coming to the tank battery from an individual well is measured before being mixed with the flow from other wells for treating and separation. This information is important for evaluating the performance of the well and the reservoir.Other equipment may be required at these field facilities under special conditions. Desalting facilities are needed if the produced crude contains large amount of salt, and heated storage may be required if the oil is too viscous at low temperatures to be pumped from lease storage.Flow lines are normally made of steel, though various types of plastic pipe have been used in a limited number of applications. Sections, or joints, of steel pipe for flow lines can be connected by welding or by the use of threaded couplings. Other specially joints and joining methods aimed at reducing construction time and cost have also been developed for both steel and other flow-line materials.Pipe used for oil flow lines is relatively lightweight because operating pressures are low. Wall thickness for a 3-in. diameter flow line, for example, might typically be 6. 216 in. , corresponding to a weight of 7. 58 Ib/ft . Heavier pipe in the 3-in. size is available in wall thickness to 0. 437 in. and in weights up to 14. 3 Ib/ft . Pipeline pipe is usually referred to by its nominal size, 3-in. in this case . The outside diameter of nominal 3-in. diameter pipe is actually 3,500 in.Some flow lines are coated internally to protect against corrosion. Whether or not internally coated pipe is used depends on the corrosion potential of the oil, the expected producing life of the well being served, and other factors. Where flow lines are buried, they are usually 73页also coated externally to minimize corrosion.When water and gas have been removed from the oil, it is in lease tanks for shipment. Oil may be trucked from the lease if a pipeline is not available, but this method is used primarily when small volumes of oil are produced on the lease and a pipeline is not justified, or when a new well is completed and the pipeline has not yet been laid to the lease.Oil leaving the lease must be measured, either manually or automatically. Manual measurement involves gauging the lease tanks before and after oil is removed. The volume shipped is then calculated. Oil can be shipped from the lease by manually operating a valve in the storage tank that lets oil flow into a truck or into the pipeline companys gathering line.Today, lease automatic custody transfer (LACT) units are used where significant oil volumes are involved. In this method, a pump is automatically started when the level in the storage tank reaches a prescribed height, and oil is pumped into the gathering line. The pump remains on until the level in the tank is lowered to a designated point; then the pump is automatically shut off. The volume of oil flowing through the LACT system is automatically measured. A sampler also measures the water and sediment in the stream so a correction can be made to the volume measurement when calculating the payment to the lease owner. In fields producing large volumes of oil, shipment may be virtually continuous from the lease storage tanks. The next link in the oil pipeline chain is gathering lines that transport oil from field-processing and storage facilities to a large storage tank or tank farm where it is accumulated for pumping into the long-distance crude trunk line. These gathering system are normally owned by the pipeline company that operates the main trunk line. In the United States, these systems typically consist of lines ranging from 4 in. to 8 in. in diameter. Size, of course, depends on the volume of crude to be moved, pipeline length, and other factors. Operating pressure is higher than that of flow lines.Gathering system throughput obviously varies widely, depending on the number of field storage tanks served and the producing capacity of wells in each field. These gathering systems are quite flexible their capacity can be increased through various methods to accommodate new producing fields in an area or other volume changes.The mileage contained in both crude and products-gathering systems in the United States is reported by the FERC to be about 38,500 miles. Though an accurate count of gathering-system mileage outside the United States is not available, the same concept is used in gathering oil production.From large central storage facilities, oil is moved through large-diameter, long-distance trunk lines to refineries or to other storage terminals. In the United States, much of this traffic is from the oil-producing areas of the West, Southwest, and Gulf Coast to refining centers in the central and upper Midwest and the U. S. Gulf Coast.This network of crude trunk lines comprises a wide variety of pipe sizes and capacities. Pumps are required at the beginning of the trunk line, and pumping station must also be spaced along the pipeline to maintain pipeline pressure at the level required to overcome friction,74页changes in elevation, and other losses. The different sections of the system are sized to handle expected volumes? if new fields must be tied in by a new branch line the capacity can often be increased by installing additional pump station.Crude trunk lines operate at higher pressures than field-gathering systems and are also made of steel. Individual sections are jointed by welding. These lines are, in the United States at least, almost always buried below ground surface and are coated on the exterior to protect the steel pipe from corrosion.Crude oil trunk lines serving the United States can be several hundred miles long. Control of such a system is a complex operation. Sophisticated monitoring and control systems have been developed to permit the pipeline operator to fulfill delivery commitments and avoid a malfunction of the system.The complexity of these systems varies so widely that it is difficult to select a typical system. The fact that they traverse long distances complicates their construction and operation. Flow lines are usually confined to a single field, and the parties involved in the decision making and permitting are few. But when a line must cross land owned by many different owners, most of whom receive no benefit from the pipeline, just the job of obtaining right of way, for example, becomes significant.Environmental laws also require that many permits be obtained to cross roads and streams, pass through wildlife areas, and for other purposes. For example, about 1,400 permits had to be obtained from various state and federal agencies to begin construction of a crude pipeline from the West Coast to Minnesota.The trans-Alaska crude pipeline, completed in 1977, is one of the most widely publicized examples of special requirements involved in building a long-distance pipeline. Not only was the permitting process a complex and lengthy onean act of Congress was required to speed environmental review in the courtsbut new techniques and equipment had to be specially developed to ensure the line did not damage the sensitive Alaskan environment. The possibility of a significant oil spill also had to be minimized.It is difficult to pinpoint a typical throughput for an individual crude trunk line. The trans-Alaska pipeline, a 48 in. diameter line, is designed to carry up to 2 million b/d, but that volume is by no means typical of all systems. However, data are available on an individual company basis for common carrier oil pipelines. Total deliveries of crude by those pipelines was reported by the FERC as about 6. 1 billion bbl in 1981. Those companies operated almost 58 , 000 miles of crude trunklines.75页Reading Material 1Types of OperationStation operation varies not only with the size and type of equipment, but also in themethod of moving the oil or products through the line. The most common types of operation can be classified as in the following paragraphs.A- Put and Take OperationWith put and take operation, each station draws from tankage and pumps into tankage at the next station; thus, each station works with tank head on the suction side and pumps independently of the stations either upstream or downstream. Advantages of this method are$(1)A slow-moving or heavy oil does not slow actual delivery until it enters the last section of the line, provided that sufficient oil is available in tankage at stations downstream from the initial station.(2) It is not necessary to keep all stations in exact step.(3) There is less chance of moderate to high pressure on the line on the suction side of the station. No pressure control is necessary on the suction side of the station.B. Float Tank OperationSome systems pump directly from one station into the suction manifold of the next . A small tank, called a float tank, is open to the suction line at each station. This is very similar to the put and take operation: The real difference is that the capacity of the float tank is usually small. Unless oil is available in other tanks, each station floating on the line must maintain a pumping rate approximately the same as the station immediately upstream.C Tight Line OperationWhen one station pumps directly into the suction side of the pumps at the next station and no tankage is open to the suction manifold at the intermediate station, it is called tight line operation. The advantages of this method are: 1. Highly volatile crudes or products are conserved because they are pumped with a positive pressure at all times. 2. Increased flow rate of heavy crudes may be obtained by blending with light ends to reduce viscosity with less loss of the lighter materials.3. Evaporation losses which occur when pumping into or out of tankage are eliminated.4. Investment in tanks at intermediate stations is eliminated.5. Commingling between tenders or batches is reduced to a minimum by holding the fluid in the line and under pressure until it is delivered at its destination.D. Operating ProceduresThe initial station on a trunk line receives crude oil or products from adjacent tanks. It produces pressure required to move the oil to the next station. A positive suction pressure on the main pumps usually is needed and is frequently supplied by booster pumps close to the tanks. Where the booster is close to the tanks, in-line or horizontal pumps are most frequently used. A deep well pump or pump in a can serves well when one booster draws from several tanks and must be some distance from each.In recent installations the booster is started by a switch or pushbutton in the station;however, a manual lockout pushbutton usually is installed at the unit as a precaution against pumping from the wrong tank,Before starting a main station the operator must be certain that all equipment is in proper operating condition. Checks which he should make before starting the unit include:1. All fans or blowers should be operating properly to insure adequate pressure and ventilation throughout the station.2. All protective devices should be in service. For example, valves in the line to the pressure switches should be fully opened.3. Flow of water should be started in the cooling systembearing jackets, stuffing box jackets and water quench lines.4. The lubricating oil for all bearings should be checked for level and cleanliness.5. All valves between tanks and the unit to be operated should be checked to assure an unobstructed flow. Pressure gauges mounted on the suction line or in the control room indicate the pressure on the suction side of the pump. Caution must be exercised when opening or closing any valve on the line; a valve in an improper position can result in serious damage to the equipment or line or contamination of crudes or products being pumped.6. Air pressure should be checked to insure that the air supply for the pneumatic control instruments is in order . All dripwells and air filters should be blown to remove moisture or foreign particles from the air lines. .7. Indices on the pressure control instruments should be set to control the pressure as the dispatcher has instructed.8. All couplings on the units should be checked for lubrication and to see that drain or filling plugs are in place.9. Where a speed increaser or reduction gearing is used, its oil system should be checked for level and cleanliness.These checks apply to station and units in general. In an electrically-operated station the following must also be checked:1. Ducts furnishing air to motors should be checked for moisture if the motor has been shut down for some time and periodically during operation-every two or three weeks in any event.2. The main station circuit breaker must be closed to bring current into the starting equipment. When this is accomplished the voltage should be checked to see that it is of proper value and that it does not vary too much.3. Where switchgear employs dc control circuits, the voltage must be checked. Insufficient voltage will prevent operation because the coil holding the breakers in closed position is energized through this circuit.4. Where the unit breakers are removable, each section should be checked to see that the breaker is in proper position and that the circuit to the pushbutton control is closed.5. Where the motor starting equipment includes d