Daily Question -- 03, 18: Answers have been released

The last edit to this post was made by 18 on 2010-3-24 at 12:04. The first approach is to transport the oil and gas mixture extracted from various individual wells to a centralized processing station (combined station), where it is collected; this is generally referred to as the oil collection process or gathering process. Secondly, at the centralized treatment station, the collected oil and gas mixture is separated into oil and gas, the crude oil is dehydrated, and various treatments are carried out to ensure that the oil and gas products meet the standards required for export; this process is generally referred to as the oil and gas treatment process. Third, at the centralized processing stations, the qualified oil and gas products are transported to oil and gas storage facilities, or to the initial transmission stations for further delivery; this is generally referred to as the transportation process. In many oil fields, the centralized treatment station or combined station is built together with the primary long-distance transmission station.

This post was last edited by 18 on 2010-3-24 at 12:04. For oil and gas transportation processes in oil fields that are located far from the shore and have a high gas content, a semi-offshore and semi-onshore transportation system is used; transporting oil and gas over long distances to the shore presents certain technical challenges. Therefore, a process of separating oil and gas before transport is adopted, with initial separation taking place on the offshore platform, and subsequent comprehensive processing of oil and gas once they reach the shore； If a fully offshore gathering and transportation system is adopted, with all oil and gas processing as well as storage and transportation equipment located at sea, then its specific process flow and equipment models will obviously differ from those of the former approach. Each oil field is designed and installed on modules based on its designed production process, main equipment, selection of engineering structures, and scale; it is generally designed according to the nature of production, and can be roughly classified into the following types. (1) Wellhead module: It is equipped with a wellhead production tree, testing separator, manifold, heat exchanger, etc. (2) Oil and gas treatment module: Generally, it includes production separator units, electric dehydrators, crude oil stabilization equipment, along with the associated pipelines, instruments, tanks, heat exchangers, etc. (3) Natural gas processing module: Generally equipped with separators, washers, compressors, light oil recovery units, etc. (4) Sewage treatment module: It includes oil separation and flotation, sedimentation and separation, filters, as well as pressure pumps and their auxiliary equipment. In addition, there are power generation and distribution modules, living modules, water injection modules, compression modules, and so on. The design requirements for these modules are such that they function as independent systems, while also taking into account compatibility with other systems. Some of the equipment in the production modules can be installed on land for testing; once they are lifted into place on the platform and the water, electricity, and piping systems are connected, full-scale testing can be carried out, thereby reducing the workload at sea and facilitating production management. When determining the scale of the module, factors such as the platform area, lifting capacity for construction, and production safety requirements also need to be taken into account.

This post was last edited by 18 on 2010-3-24 at 12:04. Oil and gas transportation and processing includes oil, gas, and water separation, crude oil treatment, natural gas treatment, wastewater treatment, etc

This post was last edited by 18 on 2010-3-24 at 12:05. Oil and gas gathering and transportation projects need to be designed and constructed based on oil field development plans, the physical properties of oil and gas, product specifications, and natural conditions. The oil and gas gathering and transportation process requires that: ① the pressure from the oil wells be utilized effectively, in order to minimize the number of times pressure boosting is necessary and thus reduce energy consumption ； ②By taking into account the thermal conditions in each process step, reducing the number of repeated heating cycles, and achieving thermal balance, fuel consumption can be lowered ； ③The process is sealed to minimize oil and gas losses ； ④Fully collect and utilize oil and gas resources to produce qualified products, purify crude oil, refine field gas and liquefied gas as well as natural gasoline, and treat wastewater to meet the requirements for reinjection into oil reservoirs or discharge ； ⑤Advanced technology, reasonable cost, safe and practical.

This post was last edited by 18 on 2010-3-24 at 12:05, including storage tanks, separation units, and long-distance transmission

This post was last edited by 18 on 2010-3-24 at 12:05: Crude oil dehydration processes, crude oil stabilization processes, crude oil transportation processes.

The last edit to this post was made by 18 on 2010-3-24 at 12:06: 1. Oil and gas separation and oil and gas metering; 2. Crude oil purification; 3. Crude oil stabilization. Crude oil stabilization

Actually, it’s clearly stated in the textbooks. Simply put, it includes the following components: 1. Single-well oil gathering and metering, 2. Oil and gas transportation, 3. Oil and gas separation, 4. Crude oil purification (mainly dehydration) ； 5. Crude oil stability ； 6. Crude oil storage and transportation ； 7. Natural gas purification and light hydrocarbon recovery ； 8. Produced water treatment and reinjection, etc

This post was last edited by 18 on 2010-3-24 at 12:06. I. Oil and gas measurement and oil and gas production processing processes. Oil is a mixture of hydrocarbons; in geological formations, oil, gas, and water coexist. Moreover, due to the varying conditions under which oil and gas are formed, the composition of the crude oil extracted from different oil fields varies as well. In addition, the oil also contains small amounts of impurities such as oxygen, phosphorus, sulfur, and sand particles. The task of oil and gas production processing is to separate and purify the well fluid so as to provide users with qualified commercial oil and gas. Schematic diagram of the crude oil processing process. Due to the differences in the components and physical properties of oil and gas produced from various oil fields, the production and processing procedures also vary. For example, the crude oil produced offshore in China generally contains no sulfur or salts, so there is no need for desalination steps. In some oil fields, the crude oil produced is free of water, so there is no need for a dehydration step. Offshore crude oil processing includes oil and gas metering, oil and gas separation, crude oil dehydration, and crude oil stabilization. Since water injection is commonly used as a method to supplement energy in offshore oil fields, crude oil dehydration is one of the key steps in crude oil processing. (1) Oil and gas separation and measurement 1. Principles and processes of oil and gas separation Crude oil and natural gas are both hydrocarbons. Natural gas is primarily composed of methane and alkanes with fewer than 5 carbon atoms. They are gaseous at room temperature and pressure. Crude oil is composed of alkanes with relatively high molecular weights and is in a liquid state at room temperature. In the oil layer, due to high temperature and pressure, natural gas dissolves in crude oil. During the production and processing of crude oil, as the pressure continues to decrease, natural gas is separated from the crude oil; it is based on this physical principle that oil and gas are separated from one another. Two or more equilibrium flashings are carried out to achieve maximum recovery of oil and gas resources. Generally speaking, the higher the pressure, the smaller the inter-stage pressure drop, and thus the higher the final liquid yield ； The higher the fraction, the lower the pressure, and thus the higher the gas yield. Therefore, determining the pressure and number of stages in the separation process is a key factor in achieving the highest yields of gas and liquid. From an economic perspective, it is generally considered that the number of separation stages should be 3 to 4; at most 5 stages are acceptable, as exceeding 5 stages results in no economic benefit. The fluid produced by each oil well is collected at the manifold, where control mechanisms are used to measure the oil and gas production volumes of each well. The measured oil and gas then mix together and flow into the oil and gas production separator, where separation of oil, gas, and water takes place (as shown in the diagram, this separation occurs in two stages). After separation, the oil and gas are processed separately. 2. Oil-gas separator: The oil-gas separator is a mechanical device used for separating oil and gas from well fluid. It is required that the oil separated from the oil-gas separator be free of gas, and the gas be free of oil. Separators are generally divided into two-phase separation and three-phase separation categories. A two-phase separator is used to separate a mixture into gas and liquid ； A three-phase separator separates an oil-gas mixture containing free water into oil, gas, and water phases. Based on their shape, separators can be divided into vertical and horizontal types. The separation of oil and gas in a separator relies primarily on gravity-driven sedimentation. The oil-gas mixture enters from the upper part of the separator tangentially at the inlet and rotates along the cylinder. Under the action of gravity, oil and gas are separated, with the gas moving upward and the oil moving downward. Due to centrifugal force, the oil flows downward along the walls of the container, while the gas gathers at the center and moves upward. An oil droplet trap baffle is installed at the upper part of the separator; as the gas passes through this baffle, the mist-like oil droplets entrained in it are removed. The separated gas flows into the gas pipeline through the upper outlet, while the separated crude oil flows into the oil pipeline through the lower oil outlet valve. The performance indicators of a separator are mainly reflected in the degree of separation between oil and gas. If very thorough separation of oil and gas is required, multi-stage separation at different pressures can be used. Its working principle is the same as that of the vertical type. The following compares the two. ①The liquid level in vertical separators is easy to control ； Impurities such as sand are easy to remove, allowing it to handle oil and gas containing sand ； The likelihood of the liquid re-atomizing is low ； It occupies a small area. The disadvantages are high production costs, as well as difficulties in maintenance and assembly. ②When processing equal amounts of crude oil, horizontal separators require a smaller diameter, use less steel, and offer the advantages of being able to handle foamy crude oil, being skid-mounted, easy to transport, and easy to maintain. The downside is that it takes up a lot of space and is difficult to clean of sand. 3. Metering separator: Since oil and gas are extracted together, an oil-gas separator is used to separate them before measuring each one separately. Oil fields in our country use metering separators for measurement. The working principle of the metering separator and the production separator is exactly the same; the former simply uses glass tubes to measure the amount of crude oil after separation. In addition to the aforementioned measurement methods, oil can also be measured using turbine flowmeters. The measurement of natural gas is generally carried out using an orifice plate flow meter or a diaphragm pressure gauge installed on the outlet pipe at the top of the metering separator. (II) Crude oil purification treatment Crude oil purification treatment refers to the dehydration, desanding, and desalination of crude oil. 1. Crude oil dehydration: Crude oil extracted from oil wells generally contains water. In addition to formation water, the water content in the crude oil increases as a result of water injection during the extraction process to replenish the energy in the formation; especially in the later stages of oil field development, the water content in the crude oil can sometimes exceed 90%. In addition to existing as large free droplets, water in oil can also be present as water-in-oil emulsions, in which water is suspended in the oil as tiny spherical particles. Emulsions are primarily formed during oil extraction, as oil and water are forced to pass through nozzles at high pressure and thus atomized, as well as during transportation due to the intense mixing caused by oil pumps and mechanical devices. The presence of water in crude oil is highly harmful; it not only increases fuel consumption during storage, transportation, and refining processes (as water absorbs heat as the oil temperature rises), thereby raising storage and transportation costs, but it also affects the safe operation of refineries and accelerates the corrosion of pipelines and equipment. Therefore, it is necessary to dehydrate the crude oil, with the requirement that its water content after dehydration be below 0.5%. (1) Principle of dehydration: For free water droplets, separation can be achieved through static settling due to the difference in gravity between oil and water; however, tiny water droplets in a water-in-oil emulsion are difficult to separate. For emulsified water, oil fields widely employ chemical dewatering methods, electrical dewatering methods, and combined electrochemical dewatering methods to address this issue. ①Principle of chemical dehydration: Oil and water are inherently incompatible, that is, they do not dissolve in each other. However, due to a layer of gum-like oil film surrounding the tiny mist-like particles, it prevents the water droplets from coming close to one another, allowing them to remain stable in an emulsified state within the oil. The role of chemical treatment agents is to demulsify, specifically by reducing the surface tension of the oil film on the surface of water particles, thereby allowing those water particles to be released from the oil film. In practical applications, it is referred to as chemical dosing for demulsification and dewatering. Using an appropriate demulsifier can achieve good dehydration results. This dehydration method has a simple process, does not require complex equipment, and is easy to manage; however, its efficiency is low. The settling time typically ranges from 8 to 12 hours, which is only about 1/4 of the efficiency achieved by electrical dehydration. It also requires two large tanks, occupying more space on the platform and increasing the cost of building such a platform. Moreover, it is difficult to control the quality of dehydration achieved with this method. ②Working principle of electrical dehydration: Electrical dehydration can be divided into high-voltage AC dehydration and high-voltage DC dehydration. Under the influence of an alternating electric field, the positive and negative poles change direction 50 times per second, causing the charges at the ends of the water particles to keep changing. This **weakens the strength of the oil film on the surface of the water particles, making it easier for them to come into contact with each other and form larger droplets that can separate from the oil. In a direct current electric field, with the positive and negative electrodes remaining fixed, the charged water particles in the oil attract one another and arrange themselves in an orderly manner to form water ripples. As they move, water particles of different sizes collide with each other due to their varying speeds, aggregating into larger water droplets that then settle out of the oil under the effect of gravity. Comparing the two electro-dehydration methods, DC electro-dehydration yields better results than AC electro-dehydration. Abroad, to enhance the effect of electrical dehydration, a new dual-electric-field dehydration process is now being adopted. Commonly used electrical dehydrators come in vertical and horizontal types, both of which belong to the category of volumetric dehydrators. Electric field treatment and oil-water sedimentation separation are carried out in the same container, enabling continuous operation and high production efficiency. The upper part of the container is the electric field space, while the lower part is the space for oil-water sedimentation and separation. The electric field space is composed of many layers of suspended electrodes. The electrode spacing decreases layer by layer from bottom to top, and the electric field strength increases layer by layer. The aqueous crude oil enters the dehydrator through the lower middle inlet and flows from bottom to top within the electric field, where the water droplets are successively removed under the influence of the electric field. The extracted crude oil escapes from the upper part of the dehydrator ； The separated water is settled at the bottom of the container and then sent to the wastewater treatment system. Electrodehydrators are generally designed based on the pressure and treatment volume requirements for dehydration, and their diameter can be determined as desired. Based on the practical experience of oil fields in our country, horizontal electric dehydrators are suitable for being built on a large scale; they require less manufacturing effort and save steel, which is why they are widely used. ③Electrochemical dehydration: In this method, an emulsifier is added to the water-containing crude oil before it enters the heater; thereafter, it goes into an electrodehydrator for dehydration, which improves the efficiency of dehydration. Its principle is a combination of the above two dehydration principles. (2) Dehydration process flow: The oilfield technical department usually selects the dehydration method and process flow based on the crude oil production volume and its water content. ①Chemical sedimentation dehydration process: This method of dehydration is not restricted by the level of water content, and it is currently primarily used for dehydrating crude oils with a water content of over 30%. This method involves adding a demulsifier to the aqueous crude oil, and using the demulsifying effect of the demulsifier to remove water from the crude oil. The separated water can be obtained by allowing it to stand for a while before lowering the machine. To enhance the dehydration effect, the crude oil must be heated to 60–70°C before dehydration, which is why it is also known as thermochemical sedimentation dehydration. ②The electrical dehydration process is used for crude oil with a water content of less than 30%. ③Electrochemical dehydration process: The electrochemical dehydration process is generally used to dehydrate crude oil with a water content of over 30%. In fact, it is a combination of the two aforementioned processes, which is why it is also known as the two-stage dehydration method. 2. Desalination: The salts contained in crude oil are generally water-soluble, and they are removed along with the water during dehydration. In crude oil with a high salt content, salt crystallization may occur under changes in temperature and pressure; in such cases, desalination (including desulfurization) can be achieved using hot fresh water and other chemical solutions for washing. 3. Sand removal: The sediment carried up with the crude oil from the well needs to be removed. At this point, it is necessary to heat the crude oil to reduce its viscosity, so that the sand can settle at the bottom of the tank. The treated crude oil is required to have a water content of <0.5% and a salt content of <50 mg/L in order to meet the standards for commercial crude oil. (III) Crude oil stabilization: Crude oil stabilization is aimed at reducing the evaporation losses of oil and gas during transportation, by removing as much of the volatile light hydrocarbons from the crude oil as possible, thereby lowering its vapor pressure at normal temperature and pressure. Crude oil is a mixture of hydrocarbons; at normal temperature and pressure, methane, ethane, propane, and butane are in gaseous form. As these light hydrocarbons evaporate from crude oil, they also carry away large amounts of heptane and hexane, resulting in a loss of the light components in the crude oil. During the collection and transportation of oil and gas, measures such as heating, pressure reduction, and storage taken to meet process requirements all result in losses of oil and gas. According to statistics from recent years, losses of oil and gas during transportation account for about 40% of the total losses. Moreover, the light hydrocarbons that are lost are high-quality fuels for domestic use as well as important raw materials for the petrochemical industry; therefore, stabilizing crude oil is one of the key measures for saving energy and making rational use of oil and gas resources. 1. Principle of crude oil stabilization The working principle of crude oil stabilization relies on the property that, under the same temperature and pressure, light components with high vapor pressures tend to evaporate easily, while heavy components with low vapor pressures are less likely to evaporate; this property is utilized to separate the C1–C4 components from the crude oil. 2. Methods for reducing vapor pressure: The commonly used ones are flash evaporation and distillation. (1) Flash separation method. The dehydrated crude oil is heated to around 120°C in a heater before entering the stabilizer, where the separation pressure is 0.3 MPa. The stable crude oil coming out of the bottom of the tower has a high temperature, and this heat can be used to heat the feed crude oil ； The vapor emerging from the top of the tower is cooled to 40°C in a cooler, and then enters a three-phase separator for gas-liquid separation, yielding non-condensable gas, crude light oil, and water. This separation method belongs to a single-stage equilibrium vaporization process; it features a low processing depth, a simple process flow, low investment costs, and a high processing capacity. It is widely used in onshore oil fields in China, and the BZ28—1 oil field in the Bohai Sea has adopted this method on its production storage tankers. (2) The fractional distillation stabilization method: In crude oil components, the light fractions have high vapor pressures, low boiling points, and are easy to vaporize, while the heavy fractions have low vapor pressures, high boiling points, and are difficult to vaporize. Taking advantage of this property, the C1–C4 components are separated out using fractional distillation. The fractional stabilization method requires many pieces of equipment and has a relatively complex process, but it offers high separation precision and results in good stability of crude oil quality. It is widely used abroad.