Measurement Techniques, Vol. 55, No. 3, June, 2012

PHYSICOCHEMICAL MEASUREMENTS IMPORTANCE AND MAIN AREAS OF METROLOGICAL PROVISION FOR ASSOCIATED GAS RECOVERY AND UTILIZATION

M. V. Okrepilov

UDC 543.27:621.64:658.562

The role of metrology is considered in carrying out the important task of utilizing associated petroleum gas in accordance with the Law on Technical Regulation. A requirement is demonstrated for creating a state system for providing and selecting an optimum method for selecting a state system of monitoring gas composition and associated measurement facilities connected with the different chemical composition of associated petroleum gas from natural gas. Keywords: associated petroleum gas, natural gas, monitoring associated petroleum gas composition.

Oil recovery is inseparably connected with associated petroleum gases (APG) forming during its recovery. It is well known that in our country according to different estimates from 35 to 50 billion m3 of APG is recovered each year, but only 10–12 billion m3 is processed, and the rest of the gas is burnt in oil field flares, worsening the ecological situation within these regions (for comparison we note that in Norway burning APG is entirely prohibited, and in the USA the level of gas recovery reaches 97%). On burning APG in flares there is not only contamination of the environment (thermal, contamination with dust, soot, and toxic compounds), but also a very valuable hydrocarbon raw material is lost. Therefore, it is no chance that particular attention has been devoted recently to the problem of utilizing APG within Russia, as within the whole world. New production processes are being developed for utilizing APG, stiffening specifications for resource users and calling upon them to be concerned with the development of a processing base, and creation of systems taking account of mineral usage and the ecological penalties. Nonetheless, there have not so far been movements in resolving this problem. In the Annual Message of President of the Russian Federation D. A. Medvedev (November 2009) the task of utilizing associated petroleum gas was set as a priority task for our country. An important role in carrying out this priority task in accordance with the Law on Technical Regulation [1] is played by metrology, which in our country is successfully resolving many complex tasks connected with provision of measurement unification in recovery, processing, and shipment of hydrocarbon raw material, in particular, natural gas (NG) [2, 3]. However, the question of metrological provisions for APG recovery and utilization processes has not until recently received sufficient attention, indicated by a lack of a single terminology for APG. For example, within the regulation for composition of production planning documents in the development of gas and oil deposits [4] the term “associated petroleum gas” is generally absent. An exception is only quantitative accounting for APG, since the standard [5] normalizes the permissible limit of main relative measurement errors for measuring its volume to a value of ±5.0%. At the same time, for successful development and implementation of contemporary technology for utilizing APG it is important to know chemical composition. Even in cases

Mendeleev All-Russia Research Institute of Metrology (VNIIM), St. Petersburg, Russia; e-mail: [email protected]. Translated from Metrologiya, No. 1., pp. 35–39, January, 2012. Original article submitted December 22, 2011. 0543-1972/12/5503-0357 ©2012 Springer Science+Business Media, Inc.

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TABLE 1. Gas Quality Indices in Accordance with Standard Specifications STO Gazprom 089–2010 and GOST 5542–87 Standard Index denomination

Hydrocarbon weight concentration, g/m3, not more than 3

Mercaptan sulfur concentration, g/m , not more than Lowest heat of combustion MJ/m3, at 20°C and 101.325 kPa, not less than Oxygen fraction, %, not more than

STO Gazprom 089–2010 [7]

GOST 5542–87 [6]

0.007 (0.02)

0.02

0.016 (0.036)

0.036

31.8

31.8

molar 0.020

volumetric 1.0

Dew point temperature for water (DPTw) with absolute pressure 3.92 MPa (40.0 kgf/cm3), °C, not above

–10.0 (temperate region) –(14–20.0) (cold region)

Dew point temperature for hydrocarbons (DPThc) with absolute pressure from 2.5 to 7.5 MPa, °C

–2.0 (temperate region) –(5.0–10.0) (cold region)

Range of Wobbe number values (highest), MJ/m3

Dew point below gas temperature. Presence of liquid phase not tolerated

–

41.2–54.5

TABLE 2. Gas Quality Indices for Hydrocarbon Liquefied Fuel Grade PBA Index denomination

Standard according to [8] for grade PBA

Component weight fraction, %: total methane, ethane propane total butanes total unsaturated hydrocarbons, not more than

Not standardized 50 ± 10 Not standardized 6

Liquid residue content at plus 20°C, %, not more than

1.6

Saturated vapor pressure, excess, MPa, at +45°C, not more than

1.6

Mass fraction of hydrogen sulfide and mercaptan sulfur

0.01

including hydrogen sulfide, %, not more than Content of free water and alkali

0.003 Absent

of the supply of APG to a main gas pipeline for subsequent use it should be prepared in an appropriate way, i.e., it should correspond to specifications [5], and in the case of use for industrial and general communal-domestic service [6] (Table 1). In the case of using APG as a combustible hydrocarbon gas fuel (after preliminary liquefaction), its indices should correspond to the standard specifications [8], standard weight fraction of propane, total saturated hydrocarbons, liquid residue content at +20°C, saturated vapor pressure at +45°C, weight fraction of total hydrogen sulfide and mercaptan sulfur, including hydrogen sulfide, content of free water, and alkali, etc. (Table 2). It follows from this that for APG it is necessary to choose an optimum scheme for its purification from harmful admixtures, for which reliable monitoring of its chemical composition is required. These optimum technologies for PG utilization will make it possible not only to utilize it entirely within fields, but also to obtain additional electrical energy, heat, and hydrocarbon gas engine fuel, primarily liquefied hydrocarbon gas. It should be noted that APG differs markedly in chemical composition from natural gas, recovered from gas deposits, and correspondingly it should become an object the most tenacious attention of metrology (APG composition depends on the 358

nature of oil, within which it is included, and also on the scheme adopted for gas separation from oil during recovery from a borehole). In contrast to NG, containing on average (vol.%): CH4 96.0; C2H6 2.7; C3H8 0.3; nC4H10 0.01; N2 0.8; CO2 0.14, as a rule, APG composition varies within the following limits (vol.%): CH4 30–40; C2H6, C3H8, nC4H10 8–20; higher hydrocarbons 10; other gases (N2, CO2, H2S) 9–12. This means that in order to monitor the composition of associated petroleum gas the standard NG composition specimens are unsuitable, and for them it is necessary to create their own system of state standard specimens. It is also necessary to select the optimum method for monitoring APG composition and appropriate measurement facilities. In contrast to a chromatographic method [9], generally accepted for monitoring natural gas composition, for APG mass spectrometric or chromato-mass spectrometric analysis methods may be the optimum [10]. Currently at the Mendeleev All-Russia Research Institute of Metrology comprehensive work has been started in the field of creating an optimum system for metrological and instrument provisions of physicochemical measurements during APG recovery and shipment. They include creation of a Concept of metrological and instrument provisions for physicochemical measurements in order to modernize APG recovery and shipment within Russia in the first half of the twenty first century, development of a state standard Physicochemical Measurements during Recovery and Shipment of APG. Main conditions, and a verification scheme for composition, development, and creation of standard APG composition specimens, etc.

REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Federal Law of December 27, 2002, No. 184-FZ, Technical Regulation. Federal Law of June 26, 2008, No. 102-FZ, Provision of Measurement Unification. M. V. Okrepilov, Hydrocarbon Accounting and Quality [in Russian], Izd. Politekh. Inst, St. Petersburg (2009). RD 153-39-007–96, Regulation of the Composition of Planning Technological Documents in Development of Gas and Oil Deposits. GOST R 8 615–2005, GSI. Measurement of the Amount of Oil and Petroleum Gas Extracted from Oil and Petroleum Gas Mineral Resources. General Metrological and Technical Specifications. GOST 5542–87, Combustible Natural Gases for Industrial and General Communal-Domestic Purposes. STO Gazprom 089–2010, Fuel Gas, Supplied and Shipped by Main Gas Pipeline. Technical Conditions. GOST R 52087–2003, Combustible Fuel Hydrocarbon Gases. Technical Conditions. GOST 23781–87, Natural Fuel Gases. Chromatographic Method for Determining Component Composition. A. T. Lebedev, Mass Spectrometry in Organic Chemistry [in Russian], Binom, Moscow (2003).

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