Oil and gas are the most important raw materials in the world. A special place in the oil and gas industry is associated petroleum gas. This resource has not been used before. But now the attitude towards this valuable natural resource has changed.
What is associated petroleum gas
This is hydrocarbon gas that is released from wells and from reservoir oil during its separation. It is a mixture of vaporous hydrocarbon and non-hydrocarbon constituents of natural origin.
Its amount in oil can be different: from one cubic meter to several thousand in one ton.
By the specifics of producing associated petroleum gas is considered a by-product of oil production. This is where its name comes from. Due to the lack of the necessary infrastructure for gas collection, transportation and processing, a large amount of this natural resource is lost. For this reason, most of the associated gas is simply flared.
Gas composition
Associated petroleum gas consists of methane and heavier hydrocarbons - ethane, butane, propane, etc. The gas composition in different oil fields may vary slightly. Associated gas in some regions may contain non-hydrocarbon constituents - nitrogen, sulfur, and oxygen compounds.
Associated gas, which gushes after opening the oil reservoirs, is characterized by a smaller amount of heavy hydrocarbon gases. The heavier part of the gas is in the oil itself. Therefore, at the initial stages of oil field development, as a rule, a lot of associated gas is produced with a high methane content. During the operation of the deposits, these indicators gradually decrease, and most of the gas is made up of heavy components.
Natural and associated petroleum gas: what is the difference
Associated gas in comparison with natural gas contains less methane, but has a large number of its homologs, including pentane and hexane. Another important difference is the combination of structural components in different fields in which associated petroleum gas is produced. The composition of APG can even change at different periods in the same field. For comparison: the quantitative combination of natural gas components is always constant. Therefore, APG can be used for different purposes, and natural gas is used only as energy raw materials.
Getting APG
Associated gas is obtained by oil separation. To do this, use multi-stage separators with different pressures. So, at the first stage of separation, a pressure of 16 to 30 bar is created. At all subsequent stages, the pressure is gradually reduced. At the last stage of production, the parameter is reduced to 1.5–4 bar. APG temperature and pressure are determined by separation technology.
The gas obtained in the first stage is immediately sent to the gas processing plant. Great difficulties arise when using gas with a pressure below 5 bar. Previously, such APG was always flared, but recently the policy of gas utilization has changed. The government began to develop incentive measures to reduce environmental pollution. So, at the state level in 2009, the APG burning indicator was set, which should not exceed 5% of the total associated gas production.
APG application in industry
Previously, APG was not used in any way and was burned immediately after production. Now scientists have discerned the value of this natural resource and are looking for ways to use it effectively.
Associated petroleum gas, which is a mixture of propanes, butanes and heavier hydrocarbons, is a valuable raw material for the energy and chemical industries. APG has a calorific value. So, during combustion, it emits from 9 to 15 thousand kcal / cubic meter. In its original form, it is not used. Necessarily requires cleaning.
In the chemical industry, plastic and rubber are made from the methane and ethane contained in the associated gas. Heavier hydrocarbon components are used as raw materials for the production of high-octane fuel additives, aromatic hydrocarbons and liquefied hydrocarbon gases.
In Russia, more than 80% of the volume of associated gas is produced by five oil and gas producing companies: OJSC NK Rosneft, OJSC Gazprom Neft, OJSC Oil Company LUKOIL, OJSC TNK-BP Holding, OJSC Surgutneftegas " According to official figures, the country annually produces more than 50 billion cubic meters of associated gas, of which 26% is used for processing, 47% is used for industrial purposes, and the remaining 27% is flared.
There are situations in which it is not always cost-effective to use associated petroleum gas. The use of this resource often depends on the size of the field. So, gas produced in small fields, it is advisable to use to provide electricity to local consumers. In medium-sized fields, it is most economical to extract liquefied petroleum gas at a gas processing plant and sell it to chemical enterprises. The best option for large deposits is the production of electricity at a large power plant with subsequent sale.
Harm from burning APG
Associated gas burning pollutes the environment. Thermal destruction acts around the torch, which affects the soil within a radius of 10–25 meters and vegetation within 50–150 meters. In the process of combustion, nitrogen and carbon oxides, sulfur dioxide, and unburned hydrocarbons enter the atmosphere. Scientists estimate that as a result of APG combustion, about 0.5 million tons of soot is emitted per year.
Also, gas combustion products are very dangerous for human health. According to statistics, in the main oil refining region of Russia - the Tyumen region - the incidence of the population for many types of diseases is higher than the average for the whole country. Especially often, residents of the region suffer from pathologies of the respiratory organs. There is a tendency to increase the number of neoplasms, diseases of the sensory organs and nervous system.
In addition, APG combustion products cause pathologies that appear only after some time. These include the following:
- infertility;
- miscarriage;
- hereditary diseases;
- weakened immunity;
- oncological diseases.
APG utilization technologies
The main problem of oil gas utilization is the high concentration of heavy hydrocarbons. The modern oil and gas industry uses several effective technologies that make it possible to improve gas quality by removing heavy hydrocarbons:
- Gas fraction separation.
- Adsorption technology.
- Low temperature separation.
- Membrane technology.
Associated gas recovery methods
There are many methods, but in practice only a few are applied. The main method is the utilization of APG by separation into components. This processing process allows to obtain dry stripped gas, which, in fact, is the same natural gas, and a wide fraction of light hydrocarbons (BFLH). This mixture can be used as a raw material for petrochemicals.
Separation of petroleum gas occurs in low temperature absorption and condensation units. After the process is completed, dry gas is transported through gas pipelines, and NGL is sent to oil refineries for further processing.
The second effective way of processing APG is the cycling process. This method involves injecting gas back into the reservoir to increase pressure. This solution allows to increase the volume of oil recovery from the reservoir.
In addition, associated petroleum gas can be used to generate electricity. This will allow oil companies to significantly save money, since there will be no need to purchase electricity from outside.