Associated petroleum gas: composition. Natural and associated petroleum gas

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Oil and gas are the world's most important raw materials. Associated petroleum gas occupies a special place in the oil and gas industry. This resource has never been used before. But now the attitude towards this valuable natural resource has changed.

What is associated petroleum gas

This is a 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.

According to the specifics of production, associated petroleum gas is considered a by-product of oil production. This is where its name comes from. Due to the lack of 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 composition of gas in differentoil fields may differ slightly. In some regions, associated gas may contain non-hydrocarbon components - compounds of nitrogen, sulfur, oxygen.

Associated gas that gushes out after the opening of 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 with a high content of methane is produced. During the operation of deposits, these indicators gradually decrease, and heavy components account for most of the gas.

Natural and associated petroleum gas: what is the difference

Associated gas contains less methane compared to natural gas, but has a large amount of its homologues, including pentane and hexane. Another important difference is the combination of structural components in different fields where associated petroleum gas is produced. The composition of APG can even change in different periods at the same field. For comparison: the quantitative combination of natural gas components is always constant. Therefore, APG can be used for various purposes, while natural gas is used only as an energy feedstock.

Getting APG

Associated gas is obtained by separation from oil. For this, multi-stage separators with different pressures are used. 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 miningthe parameter is reduced to 1.5–4 bar. Temperature and pressure values of APG are determined by separation technology.

Gas obtained at 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. Thus, in 2009, at the state level, the APG flaring rate was set, which should not exceed 5% of the total associated gas production.

Application of APG in industry

Previously, APG was not used in any way and immediately after extraction it was burned. Now scientists have seen 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 releases from 9 to 15 thousand kcal / cubic meter. It is not used in its original form. Definitely needs cleaning.

In the chemical industry, plastics and rubber are made from methane and ethane contained in 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 Russiamore than 80% of the volume of associated gas produced is accounted for by five oil and gas producing companies: OAO NK Rosneft, OAO Gazprom Neft, OAO Oil Company LUKOIL, OAO TNK-BP Holding, OAO Surgutneftegaz. According to official data, the country annually produces more than 50 billion cubic meters of APG, of which 26% is recycled, 47% is used for industrial purposes, and the remaining 27% is flared.

There are situations in which it is not always profitable to use associated petroleum gas. The use of this resource often depends on the size of the deposit. Thus, gas produced in small fields is expedient to use to provide electricity to local consumers. In medium-sized fields, it is most economical to recover LPG at a gas processing plant and sell it to the chemical industry. The best option for large deposits is to generate electricity at a large power plant with subsequent sale.

Harm from APG flaring

Combustion of associated gas pollutes the environment. There is thermal destruction around the torch, which affects the soil within a radius of 10-25 meters and vegetation within 50-150 meters. During combustion, oxides of nitrogen and carbon, sulfur dioxide, and unburned hydrocarbons enter the atmosphere. Scientists have calculated that as a result of APG burning, about 0.5 million tons of soot are emitted per year.

Also, gas combustion products are very hazardous to he althperson. 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 the inhabitants of the region suffer from pathologies of the respiratory organs. There is a trend towards an increase in the number of neoplasms, diseases of the sense organs and the nervous system.

In addition, APG combustion products cause pathologies that appear only after a while. These include the following:

• infertility;
• Miscarriage;
• hereditary diseases;
• immunity weakening;
• oncological diseases.

APG utilization technologies

The main problem of utilization of petroleum gas 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:

1. Gas fractional separation.
2. Adsorption technology.
3. Low temperature separation.
4. Membrane technology.

Ways to utilize associated gas

There are many methods, but only a few are used in practice. The main method is APG utilization by separation into components. This refining process produces dry bottom gas, which is essentially the same natural gas, and a broad fraction of lighthydrocarbons (NGL). This mixture can be used as a raw material for petrochemicals.

Petroleum gas separation takes place in low-temperature absorption and condensation units. Once the process is completed, the dry gas is transported through gas pipelines, and NGL is sent to refineries for further processing.

The second effective way of processing APG is the cycling process. This method involves injecting gas back into the formation 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.