ASSOCIATED PETROLEUM GAS PROCESSING

One of the challenges of oil and gas industry may easily be noticed while flying over vast starches of Siberia: countless flares. Associated petroleum gas is being flared.

One of the challenges of oil and gas industry may easily be noticed while flying over vast starches of Siberia: countless flares. Associated petroleum gas is being flared.

Some sources state that there are few thousand large flaring systems active on the territory of Russian Federation. Utilization of the associated petroleum gas is a problem which all of the oil producing countries face. Sadly, Russia is a leader at being unable to cope with the requirements to utilize the gas, followed by Nigeria, Iran and Iraq.

Associated petroleum gas (APG for short) compositions vary from field to field but generally include methane, ethane, propane, butane and heavier hydrocarbon components. It may also contain nitrogen, argon, carbon dioxide, H2S, helium. As the name implies APG usually accompanies crude oil by being dissolved in the latter and is separated at initial stages of crude production. It may also reside at the top of crude oil forming the cap of natural crude reservoirs.

Utilization of APG typically refers to a specific usage of the gas produced alongside the crude oil that has some economically viable effect over burning it at the flare.

Types and methods of APG utilization 

There is a number of directions to follow when faced with a need to process associated petroleum gas in Russia:

- processing at small-scale gas processing plants or employing small field treating stations to reach PAO Gazprom requirements to be sold to its pipeline for dry stripped gas and simultaneous production of LPG and NGLs products 

Transportation of APG to the gas processing plant for further treatment can require minimal capex when a developed pipeline infrastructure is in place. The disadvantage of this method for low-accessible fields is a possible necessity to construct new gas compressor stations or even new pipelines.

A construction of a small-scale gas processing plant is an ideal solution for production fields with a steady large harvest of APG that happen to be close to a long-distance main pipeline or a network of transportation routes that are readily available. In this scenario, propane-butane fuel fractions (LPG) will be produced at the plant alongside treating the gas to meet PAO Gazprom conditions for entering the gas pipeline main. Light components may also be liquefied to produce LNG-like products. The downside of this method, of course, is its inadequacy for fields that are hard to reach. 

The scope of process equipment for such a scenario will include the following: vessels (separators, storage vessels), heat-exchanging equipment (heat-exchangers, rectification columns), compressors, pumps, vapor condensation chillers, gas liquefiers all in a modular form.

 

- electric power generation (gas turbines generators, generators powered by reciprocating gas engines)

High calorific value of APG allows for its use as a fuel. Various APG compositions make it an acceptable fuel source for gas compression or for electric power generation with either gas turbines or reciprocating gas engines. For fields with larger deposits and APG production a construction of a whole power station may be feasible with power transfer to regional power grids. 

The disadvantages of this method are stemmed from strict requirements of traditional gas turbine and reciprocating engines to the composition of their fuel gas (H2S content of less than 0,1%)/ This will require additional capital expenses for creating fuel gas treatment systems as well as additional operational expenses for running those systems. Again, for the fields that are situated away from populated areas, only a limited amount of electric power volumes may be consumed locally while a lack of distributive power grid connections renders excessive power generation ineffective.

The main advantage of this method is independence of the field production from outside power and heating grids/connections. Compact size of modern gas turbine generators is also a bonus. Specialized micro-turbines units effectively run on APG with an H2S content of 4-7%.

The scope of process equipment for this scenario: vessels (separators, storage tanks), modular Gas turbine generators or Generators powered by reciprocating gas engines.

 

- chemical processing (patented processes like «APG to BTX», «Cyclar»)

APG to BTX process was developed by PAO «NIPIgazpererabotka»/ The general idea is to catalytically process APG to produce a mixture of aromatic hydrocarbons (namely Benzol, Tolulene and Xylene), that is then mixed in with the crude in the main oil transportation pipeline and streamed to the oil refractory. The remaining light hydrocarbons are used as a fuel for heating or power generation at the site.

The «Cyclar» process was developed by UOP and British Petroleum and is about producing a product which is a mixture of aromatic hydrocarbons (similar to APG to BTX product) out of propane-butane fraction of APG. The disadvantage in comparison to the former process is a necessity for pre-processing treatment of the feed APG to produce LPG for further processing.

In any case a common drawback of this direction is a requirement for vast capital investments to construct the necessary infrastructure at the production site.

Process equipment set up for this method: vessels (separators, storage tanks), heat exchangers, catalytic reactors, rectification columns, compressors, pumps.

 

- gas-chemical process (Fischer-Tropsch)

APG processing by Fischer Tropsch method is a complex multi-stage process. Initially synthesis gas (a mix of CO and H2) is produced by thermal oxidation of feed APG. The synthesis gas is further processed into methanol or synthesis hydrocarbons used as an engine fuel. The downside of the process lies in the high capital and operational expenses.

Process equipment for this method includes: vessels (separators, storage tanks), heat exchangers, catalyst reactors, columns, compressors, pumps.

 

- utilization for production process needs (cycling-process, gas lift)

Reinjection of APG into the oil-field layers (cycling-process) is about streaming the compressed gas back into the top of the natural oil reservoir. This increases the bed pressure in the oil-producing layer and enhances the oil production. The advantage of this method is clear – low capital investment costs. The downside, however is a practical absence of utilization – permanent solution is exchanged for a delay of the problem.

The gas lift process is about enhancing the oil production through compression of APG into the crude. The advantages of this method are the ability to implement it for oil wells with a high gas factor, negligent effect of the particle impurities presence in the feed APG or it’s pressure and temperature on the process. Another bonus is the possibility for a flexible management of the oil wells operation, ease of servicing and maintenance of the oil wells. The downside is the necessity of infrastructure for treatment and regulation of the feed gas, which increases the capital costs of investment into site.

The process equipment required: vessels (separators, storage tanks), compressors, pumps.

 

The reasons for APG processing

Environmental problems are an obvious outcome of the APG utilization infrastructure absence and uncontrolled flaring of the gas. When APG is flared a lot of pollutants are released into atmosphere: carbon soot particles, CO2, Sulphur dioxide. High concentration of these pollutants leads to reproductive health diseases, congenital defects, cancer.

Failure to effectively promote best APG practices in Russia also leads to substantial losses from an economical standpoint. Rational employment of APG leads to added value in energy and chemical industries.

Officially, a yearly production of APG is around 55 billion scm. About 15-20 billion scm only are utilized in the chemical industry, a small portion is reinjected and the remaining 20-25 billion scm are flared. Such losses are comparable with the yearly consumption of domestic gas in all of Russia. 

There are of course some special factors that hamper the development and prolification of APG utilization:

- remote and isolated location of production fields from the process centers;

- absence or lack of developed infrastructure for APG collection and transportation;

- variations in APG capacities and flows;

- impurities within APG that make treatment harder;

- low prices on gas and extremely low interest in long-term financing that such projects require;

- environmental fines for APG incineration and flaring are much lower than the cost of it’s utilization.

Lately oil producing companies pay much closer attention to APG utilization. A big push was initiated by administrative regulation №7 adopted by the Government of the Russian Federation on the 8 January 2009 «On measures to stimulate reduction of atmosphere by pollutants from associated petroleum gas flaring». The regulation targets APG utilization to level up to 95% of the produces gas. As of 2012 fines for flaring more than 5% of the produced APG are set to be multiplied by a coefficient of 4,5. As of 2013 this coefficient was raised to 12, as of 2014 – up to 25, and where precise measuring devices were absent – up to 120. An additional stimulating measure adopted in 2013 is a process of reduction of fiscal fines for flaring for the amount spent on APG utilization.