The issue of associated petroleum gas recovery has become more relevant in recent times. Billions of m3 of gas have been flared annually emitting tones of carbon dioxide, soot, nitrogen oxides, hydrogen sulphide and other harmful admixtures in the Russian Federation. In accordance with Resolution No. 7 of RF Government of 8.01.09 APG recovery on an oil field shall reach 95 % till 2012.
M. Y. Kutsak, I. G. Manilkin
Liquefaction and Processing of Associated Petroleum Gas (APG) on an Oil Field.
The issue of associated petroleum gas recovery has become more relevant in recent times. Billions of m3 of gas have been flared annually emitting tones of carbon dioxide, soot, nitrogen oxides, hydrogen sulphide and other harmful admixtures in the Russian Federation. In accordance with Resolution No. 7 of RF Government of 8.01.09 APG recovery on a field shall reach 95 % till 2012.
In order to understand at which stages APG is flared Fig. 1 shows standard flow chart of oil and gas production on a field without a gas processing plant (GPP).
Fig. 1 Flow chart of oil and APG production on a field without GPP.
W – well; FL – flare; GMS – Group Metering Station; FSS – First Stage Separator; PS – Pumping Station; CGS – Central Gathering Station; GPP – Gas Processing Plant.
Crude oil from a pattern of wells is fed to Group Metering Station (GMS) via separate oil pipelines. GMS meters crude oil fed from each well.
From GMS crude oil is fed to First Stage Separator (FSS). Partial separation of produced water and associated petroleum gas takes place in FSS.
Knock-out oil from all patterns of wells is pumped to Central Gathering Station (CGS) either by its own pressure or by a Pumping Station (PS). CGS is equipped with oil and produced water treatment plants. Oil is dehydrated, desalinated and degassed. The treated oil is pumped to a temporary storage from where it is supplied to the Oil Trunk Pipeline by the Pumping Station.
Fig. 2 Flow chart of oil and APG production on a field with GPP.
W – well; FL – flare; GMS – Group Metering Station; FSS – First Stage Separator; PS – Pumping Station; CGS – Central Gathering Station; GPP – Gas Processing Plant; CP – Chemical Plants.
First Stage Separators and Crude Oil Degassing Unit located at Central Gathering Station
(Fig. 1) are the main sources of associated petroleum gas in this chain. At the best case (Fig. 2) there is a GPP not far from CGS. Gas produced during crude oil degassing is fed to processing by a gas pipeline. However APG is still burnt out at First Stage Separators as it is very expensive to lay gas pipelines to each separator. As a result: flaring of valuable product, pollution of environment, fines and billions of Rubles of shortfall in profits.
A lot of various options of APG recovery has been proposed recently. APG processing at the production site is the most worth noticing. In this case expensive laying of gas pipelines and construction of gas compressor stations is not required.
Electric power generation at Gas Engine Power Plants (GEPP) is the most common method of APG recovery today. However application of this method is limited due to absence of high demands in electric power on an oil field.
Plants for APG conversion and production of methanol, gasoline fraction, aromatic hydrocarbons and olefinic condensate have been offered. These options are very promising but they require complicated equipment, expensive catalysers with limited useful life, high pressures and temperatures.
APG processing on Block-Modular Gas Treatment Units (APG BMTU) is the most promising direction. The same thermodynamic cycle as in large gas processing plants is used in APG BMTU. However several new technical solutions allowed designing all equipment in block-modular version. APG BMTU produces dry stripped gas (DSG), stable natural gasoline (SNG), wide light hydrocarbon fraction (WLHF) or commercial propane-butane (CPB).
The product is transported by a tank truck to the nearest GPP, a railway bulk station or directly to a consumer (Fig. 3).
Fig. 3 Flow chart of APG recovery at presence of powerful energy consumers or DSG pipeline.
W – wells; FL – flare; GMS – Group Metering Station; FSS – First Stage Separator; PS – Pumping Station; CGS – Central Gathering Station; APG BMTU – APG Block-Modular Treatment Unit; SSG – stable stripped gas; CP – Chemical Plants; GEPP – Gas Engine Power Plant.
APG BMTU-50 rated for treatment of 50 mln. m3 of gas per year produces about 5600 nm3 DSG per hour (depending on APG content). This amount of gas will be enough for generation of electric energy of almost 16 MW power. Therefore this unit can be used at oil central gathering stations only where dry stripped gas (DSG) pipeline is laid or large electric consumers are available.
However the use of APG BMTU does not solve the problem of gas recovery from First Stage Separators as there are no powerful electric consumers.
Associated Petroleum Gas Block-Modular Liquefaction Unit (APG BMLU) can become an alternative to the above mentioned options.
Such units allow liquefying associated petroleum gas directly on First Stage Separators and on CGS.
APG recovery can be arranged under the scheme shown in Fig. 4 in case of presence of a gas processing plant with sufficient production capacity and absence of a gas pipeline from CGS to GPP on an oil field.
Fig. 4 Flow chart of APG recovery at presence of GPP and absence of gas pipeline
W – wells; GMS – Group Metering Station; FSS – First Stage Separator; PS – Pumping Station; CGS – Central Gathering Station; GPP – Gas Processing Plant; APG BMLU – Associated Petroleum Gas Block-Modular Liquefaction Unit; LAPG – liquefied associated petroleum gas; SSG – stable stripped gas; CP – Chemical Plants; GEPP – Gas Engine Power Plant.
Liquefied APG (LAPG) from all First Stage Separators and from CGS is transported in tank trucks to GPP. LAPG is regasified at GPP by cooling for further processing.
Such option is possible in case of development of a new oil field before laying of gas pipeline to GPP.
APG recovery can be arranged under the scheme shown in Fig. 5 in case of presence of a remote gas processing plant with sufficient production capacity and a gas pipeline from CGS to GPP.
Fig. 5 Flow chart of APG recovery at presence of remote GPP and gas pipeline
W – wells; GMS – Group Metering Station; FSS – First Stage Separator; PS – Pumping Station; CGS – Central Gathering Station; GPP – Gas Processing Plant; APG BMLU – Associated Petroleum Gas Block-Modular Liquefaction Unit; APG BMRU – Associated Petroleum Gas Block-Modular Regasification Unit; LAPG – liquefied associated petroleum gas; SSG – stable stripped gas; LNG – liquefied natural gas; S – settlements; CP – Chemical Plants; GEPP – Gas Engine Power Plant.
LAPG from all First Stage Separators is transported in tank trucks to Block-Modular Regasification Unit (APG BMRU) located on CGS. APG is evaporated in the Regasification Unit and then it is pumped via gas pipeline to GPP together with gas from the Oil Degassing Unit.
However this option is feasible in case of GPP isolated location and absence of roads as cold lost at regasification can be used for processing.An option shown in Fig. 6 is more reasonable. LAPG from all First Stage Separators is transported in tank trucks to Block-Modular Treatment Unit (APG BMTU) located on CGS. LAPG intake to storage and subsequent processing in modular fractionating columns will be organized at CGS. LAPG fractionating allows producing any product, if required, including: WLHF, SNG, CPB, CP, CB, ethane concentrate, liquefied natural gas (LNG). Liquefied APG supply to fractioning will allow saving money for treatment and dehydration unit, expensive compressor and turbine expander/compressor unit. The cold generated at LAPG regasification can be used for processing of APG produced at oil degassing on CGS.
Fig. 6 Flow chart of APG recovery at presence of GPP and gas pipeline.
W – wells; GMS – Group Metering Station; FSS – First Stage Separator; PS – Pumping Station; CGS – Central Gathering Station; GPP – Gas Processing Plant; APG BMLU – Associated Petroleum Gas Block-Modular Liquefaction Unit; APG BMTU – Associated Petroleum Gas Block-Modular Treatment Unit; LAPG – liquefied associated petroleum gas; SSG – stable stripped gas; LNG – liquefied natural gas; S – settlements; CP – Chemical Plants; GEPP – Gas Engine Power Plant.
Commercial products produced on CGS will be transported by trucks to the nearest GPP for further shipment or directly to consumers.
In addition vehicles can be fueled with compressed natural gas that meets the requirements of GOST 27577 or by liquefied natural gas under TS 51-03-03-85 at APG BMLU. Thus all trucks transporting LAPG can be conversed to eco-friendly cheap fuel.
Possibility to produce some liquefied natural gas (LNG) at APG processing will allow providing all neighboring ungasified settlements with natural gas.
A compact plant with high liquefaction factor, minimum number of units and low capital costs can be created on the basis of high pressure cycle and expander/compressor unit. The block-modular design will allow reducing the period of construction and erection works and time of putting the project into operation to the maximum. In case of field depletion the plant can be demounted and removed to a new site easily.
Using of APG BMLU allows not only to recover associated petroleum gas but also to solve some other issues: provide Gas Processing Plants and Chemical Plants with raw materials; provide oil fields with required energy resources completely; gasify the nearest settlements and create more jobs.