Published on March 11, 2014
CRUDE OIL PRODUCTION SYSTEM by OMITOLA Oluwatobiloba. P INTERN January 2014
The Right to Win 2011 2 ne Outline • Introduction – What is Crude oil ? – How is crude Oil formed in place? • Exploration & Drilling • Surface Production Operations – Wellhead and Manifold – Separation Types of Separator Effect of Separator Pressure on separation – Gas Processing – Oil Treatment – Produced Water Treatment – Waste Utilization & Disposal Produced Water Gas Others • Conclusion
The Right to Win 2011 3 Introduction • What is Crude oil? • Crude oil also known as petroleum is a naturally occurring fossil fuel which contains mixture of HCs and inorganic compounds such as oxygen, sulphur, nitrogen, etc. and found in geologic formations beneath the earth surface. • It is formed when large quantities of dead organisms are buried underneath rocks and undergo intense heat and pressure. • The major classes of hydrocarbons in crude oils include: – Paraffins (Alkane family) – Aromatics (Benzene family) – Napthenes or Cycloalkanes – Other hydrocarbons types are the Alkenes • How is crude Oil formed in place? • Petroleum is a fossil fuel derived from ancient fossilized organic materials, such as zooplankton and algae. • Vast quantities of such remains settle on land, sea, lake bottoms, mixing with sediments thereby getting buried under anoxic conditions. • As further layers settle to the sea or lake bed, intense heat and pressure build up in the lower regions. • This process causes the organic matter to change, first into a waxy material known as kerogen and then with more heat into liquid and gaseous hydrocarbons via a process known as catagenesis. • Tectonic movements further push the crude oil until they are trapped.
The Right to Win 2011 4 ne Introduction • Crude oil-gas mixture once produced from oil wells drilled moves through two main distinctive processing operations in order to obtain useful petroleum products. • Surface Operations; where gases are separated from oil with further treatment of the separated fluids. • Refining Operations; where crude oil is fractionated into cuts with physical and further chemical conversion processes to produce different HC components of crude oil. Fig 1-0. A schematic Illustration of the three different production operations of the oil industry
The Right to Win 2011 5 Exploration & Drilling • Exploration involves the search for rock formations associated with oil or natural gas deposits. It includes geophysical prospecting and exploratory drilling. Before exploration can be done in an area of possible or probable reserves, an Oil Prospecting License (OPL) has to be given by the authorized body. • After prospecting and a region has been tagged a proven reserve, then an Oil Mining License (OML) is needed to begin drilling operations, be it exploratory, appraisal wells or developmental wells. • Drilling is the act of boring holes into the earth crust. • Once a promising geological structure has been identified; Exploratory wells also known as “wildcat” are drilled to confirm the presence or absence of HCs and also to determine the internal pressure of the reservoir Appraisal wells also known as “outstep” are drilled to determine the size, extent and quantify the hydrocarbon reserves. Development or Production wells exploit and transport oil and gas from the reservoir through formation pressure, artificial lift, and possibly advanced recovery techniques, until economically feasible reserves are depleted.
The Right to Win 2011 6 ne Surface Production Operations (SPO) • SPO covers the processing of all three streams from the well head as indicated in Fig. 3-0 while Fig 3-1 illustrates a typical process flow diagram of SPO • The need for field processing of crude oil-gas mixture is justified for four main reasons: These mixtures are very difficult to handle, meter, or transport. It is unsafe and uneconomical to ship or transport such two-phase mixtures overseas to refineries and gas plants. Oil producers have to abide with the specifications set for shipping and refining Environmental constraints established for safe handling of HCs and the disposal of produced salt water Fig. 3-0 An illustration of the Surface field operations
The Right to Win 2011 7 SPO Fig 3-1. A typical flow sheet of SPO
The Right to Win 2011 8 ne SPO Wellhead and Manifold • The production system begins at the wellhead installed on the cased hole to seal the annular space between casing and tubing, control wellhead pressure, adjust well flow rate and transport oil downstream. • The size of the opening in its choke (valve) determines the flow rate. • For high-pressure wells, it is desirable to have a positive choke in series with an adjustable choke. • Due to the high-risk situations, an automatic shutdown valve should be installed on the wellhead. • The flow-lines from several wells are gathered in a manifold and routed into a separator Fig 3-2 A wellhead
The Right to Win 2011 9 ne SPO Separation • Well effluents flowing from producing wells are usually identified as turbulent, high velocity mixtures of gases, oil and salt water. • As these streams reach the surface , they undergo continuous reduction in temperature and pressure forming a two phase fluid-flow: gas and liquid. • The physical separation of these phases is one of the basic operations in the production, processing, and treatment of oil and gas and it’s achieved by a Separator.
The Right to Win 2011 10 SPO Types of Separator Separators are designed in either horizontal, vertical, or spherical configurations Fig. 3-4 Vertical separator Fig. 3-3.Horizontal separator Fig. 3-5 Spherical separator
The Right to Win 2011 11 SPO Horizontal Separator Vs. Vertical Separator • In the gravity settling section of a horizontal vessel, the liquid droplets fall perpendicular to the gas flow and thus are more easily settled out of the gas continuous phase. • Horizontal separators offer greater liquid capacity and are best suited for liquid-liquid separation and foaming crudes. • Horizontal vessels require more plan area to perform the same separation as vertical vessels but its large cross-sectional area allows more settling. • The relief valve and some of the controls of the vertical separator may be difficult to service without special ladders and platforms. • Smaller, horizontal vessels can have less liquid surge capacity than vertical vessels sized for the same steady-state flow rate. • Since the interface area is larger in a horizontal separator than a vertical separator, it is easier for the gas bubbles, which come out of solution as the liquid approaches equilibrium, to reach the vapour space.
The Right to Win 2011 12 ne SPO • Separators are classified as "two-phase" if they separate gas from the total liquid stream and "three-phase" if they also separate the liquid stream into its crude oil and water components. Fig. 3-6 Two-phase horizontal separator Fig. 3-7 Three-phase horizontal separator
The Right to Win 2011 13 SPO Advantages of the three-phase over the two-phase separator are: • It separates free water from oil-water mixture. • The three phase also has a larger liquid section allowing more retention time for the oil and water to separate. • Unlike two-phase units, three-phase separators have two liquid-level controllers that are often combined with internal baffles & weirs to regulate the oil-gas and oil-water levels. • At the oil/water interface there is a pneumatic displacement type level control which actuates the water dump valve.
The Right to Win 2011 14 SPO Effects of Separator pressure on separation • If the pressure for initial separation is too high, too many light components will stay in the liquid phase at the separator and be lost to the gas phase at the tank. • If the pressure is too low, not as many of these light components will be stabilized into the liquid at the separator and they will be lost to the gas phase. • The changes in separation pressure give rise Stage separation. Fig. 3-8 Stage separation
The Right to Win 2011 15 ne SPO Gas Processing The actual practice of processing natural gas to pipeline dry gas quality levels can be quite complex, but usually involves four main processes to remove the various impurities: Crude-oil carry over Removal • A scrubber which is a two-phase separator designed to recover liquids carried over from the gas outlets of production separators or to catch liquids condensed due to cooling or pressure drop is used at the first stage of gas processing. NGL Recovery • There are two techniques for removing NGLs from the natural gas stream: the absorption method and the cryogenic expander process • Absorption process involves the passage of the crude oil through an absorption tower in which a ‘lean’ absorption oil makes contact with the oil thereby absorbing the NGLs present in the oil.
The Right to Win 2011 16 ne SPO • The ‘rich’ absorption oil exits the tower through the bottom of the tower and is fed into lean oil stills, where it is heated to a temperature above the boiling point of the NGLs, but below that of the oil; • Cryogenic processes are required for high and economical recovery rates. Essentially, cryogenic processes consist of dropping the temperature of the gas stream to around - 120 degrees Fahrenheit. • In the turbo expander process, external refrigerants are used to cool the natural gas stream. Then, an expansion turbine is used to rapidly expand the chilled gases, which causes the temperature to drop significantly. This rapid temperature drop condenses ethane and other hydrocarbons in the gas stream, while maintaining methane in gaseous form.
The Right to Win 2011 17 ne SPO Dehydration There are two main processes of water removal in gas processing: Glycol(absorption) and Solid desiccant(adsorption) dehydration. • Glycol absorption method of dehydration is very similar to using absorption for NGL extraction but the main difference is the use of a glycol instead of an absorption oil. • It also entails the oil making contact with the glycol (e.g. TEG) , an hygroscopic substance in a glycol tower, the rich glycol re-boiled and stripped of its water component in form of steam, flashed of its dissolved gas in a flash tank and fed again into the tower. • Solid desiccants like activated alumina, silica gel are filled into adsorption towers • As the wet gas passes through the tower, water molecules are retained on the surface of these desiccant beds leaving the dry gas to exit the bottom of the tower. • To regenerate the desiccant, a high temperature gas is passed through the saturated desiccant bed and vaporizes the water in the desiccant tower, leaving it dry for further use.
The Right to Win 2011 18 ne SPO Fig. 3-9 Simple Gas processing flow-sheet Sweetening and Acid Gas Removal • One of the most important operations of gas processing is the removal of sulphur and acid gases such as carbon dioxide. • The removal of sulphur which exists in the form of H2S in ‘sour’ gas streams is achieved by a Sweetening process • The sour gas is run through a tower, which contains the amine solution. This solution has an affinity for sulfur, and absorbs it much like glycol absorbing water. • Like the process for NGL extraction and glycol dehydration, the amine solution used can be regenerated (that is, the absorbed sulfur is recovered), allowing it to be reused to treat more sour gases • It is also possible to use solid desiccants like iron sponges to remove the sulfide and carbon dioxide.
The Right to Win 2011 19 ne SPO • Oil Treatment After free water removal, produced oil often contains excessive impurities which are required to be reduced to a value acceptable for transportation or sales: Dehydration/Desalting • It is usually the first process in crude oil processing. It involves removal of salt dissolved in the water in the crude oil. It is achieved by a process unit called desalter • There are also electrostatic dehydrators which enhance coalescing of small water droplets and assist in settling Emulsion Treatment • For an emulsion to exist there must be two mutually immiscible liquids, an emulsifying agent, and sufficient agitation to disperse the discontinuous phase into the continuous phase. • A common method for separating this emulsion is to heat the stream thereby deactivating the emulsifying agent, allowing the dispersed water droplets to collide. This is achieved by heater treaters
The Right to Win 2011 20 ne SPO • The process of coalescence is also required in emulsion treatment. Hence, electrostatic coalescers subject emulsions to a high voltage electric field thereby causing the small droplets dispersed in the oil phase to coalesce and settle. • Demulsifying agents: Chemicals sold under trade names such as Tretolite™, Visco™, and Breaxit™ are examples which act as surface acting agents to neutralize the effect of emulsifying agents Stabilization • It refers to lowering the vapour pressure to a value that will allow safe handling and transport. • It is achieved by stage separation, reboiled distillation and sometimes the combination of the two methods Fig. 3-10 Simple Oil processing flow-sheet
The Right to Win 2011 21 SPO • Water Treatment In producing operations it is often necessary to handle produced water properly before reuse or disposal. The water must be separated from the crude oil and disposed of in a manner that does not violate established environmental regulations. Oil Removal • Table 3-11 lists the various methods employed in produced-water treating systems and the type of equipment that employ each method Method Equipment Type Approximate minimum Drop size removal Capabilities(10-6 m) Gravity Separation Skimmer Tanks and Vessels 100-150 API Separators Disposal Piles Skim Piles Plate Coalescence Parallel Plate Interceptors 30-50Corrugated Plate Interceptors Cross Flow Separators Enhanced Coalescence Precipitators 10-15 Filter/Coalescers Gas Floatation Dissolved Gas 15-20 Dispersed Gas Enhanced Gravity separation Hydrocyclones 15-5 Centrifuges Filtration Multi-Media 1+ Table 3-11 Produced-Water Treating Equipment
The Right to Win 2011 22 SPO • Produced water will always have some form of primary treating prior to disposal. • This could be a skim tank, skim vessel or gun barrel. • Most of these devices employ gravity separation techniques. • Depending upon the severity of the treating problem, secondary treating, utilizing a CPI, crossflow separator, or a flotation unit may be required. • Liquid-liquid hydrocyclones are often used either in a single stage or with a downstream skim vessel or flotation unit. Fig. 3-12 Typical produced-water treating system.
The Right to Win 2011 23 SPO • Waste Utilization and Disposal SPO generate dangerous wastes just like the drilling operations further upstream and can be harmful to life and the environment especially in offshore situations. These wastes include: produced water, gas flares, oil spills, deck drains, chemicals which contain heavy metals and radioactive materials, etc. Some of these wastes can be reused after further treatment while some are subject to disposal Produced water • Onshore, produced water will normally be re-injected in the formation to serve as artificial lift for wells which cannot further achieve optimal production by its natural drive mechanism • It can also be pumped into a disposal well when not needed Gas flares • As shown in Fig. 3-13, compressed gas could also be re-injected into the formation through injection wells to lighten the column of fluid and allow the reservoir pressure to force the fluid to the surface. • At high pressure, the gas could also be used in Industrial power plants to generate electric power in large quantities that can be supplied to end users • At low pressure, it can be used in internal combustion engines to power locomotives. Other wastes like deck drains are collected in a gathering system, treated and disposed overboard or added to the treated produce water for reinjection. Waste lube oil and waste lube oil filters are usually sent to offsite reclamation plant
The Right to Win 2011 24 SPO Fig. 3-13 Gas lift System o Other forms of artificial lift include electric pumps which could be Positive Displacement in near-surface production or Submersible pumps where the well flowing pressure is very low.
The Right to Win 2011 25 CONCLUSION • The significance of a production facility is to separate the well stream into three components, typically called phases (oil, gas, and water), and process these phases into some marketable product(s) or dispose of them in an environmentally acceptable manner. • To achieve optimal production each process must be carried out efficiently.
The Right to Win 2011 26 THANK YOU
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