Gas density under given conditions. Density of natural gas under normal conditions

Density of gases– is the mass of a substance per unit volume – g/cm3. For practical purposes, the relative density of gas relative to air is used, i.e. ratio of gas density to air density. In other words, this is an indicator of how much lighter or heavier a gas is than air:

where ρ in standard conditions is equal to 1.293 kg/m 3 ;

The relative density of methane is 0.554, ethane – 1.05, propane – 1.55. That is why household gas (propane) in the event of a leak accumulates in the basements of houses, forming an explosive mixture there.

Explosions can develop significant shock waves that typically destroy the site where they occur. Also, in the event of a gas leak in the open air, it may happen that the gas is mixed with air in a proportion within the flammability limit. If this happens, the spark may cause a localized fire. This is what is called deflagration. Unlike an explosion, the blast wave is small and has almost no destructive effects unless a major fire appears later if flammable substances are found nearby.

Deflagration usually occurs outdoors, on sidewalks, streets, etc. and can be caused by ruptures in distribution network pipes. The wind can move the gas cloud somewhere further away or deep into a neighboring home, where any spark can start a fire.

Heat of combustion or calorific value - the amount of heat that is released during the complete combustion of 1 m 3 of gas. On average it is 35160 kJ/m3 (kilojoules per 1 m3).

Gas solubility in oil depends on the pressure, temperature and composition of oil and gas. As the pressure increases, the solubility of the gas also increases. As temperature increases, gas solubility decreases. Low molecular weight gases are more difficult to dissolve in oils than fatter ones.

However, deflagration does not always occur where there is gas loss in the pipe. It may also happen that the accumulated gas quickly dissipates into the atmosphere and does not ignite. During the Industrial Revolution of the late eighteenth century, coal was the main primary source of energy. They continued to play a major role in the energy scene for the next 150 years. It was only in the twentieth century that petroleum products and natural gas gradually displaced coal from various industries. Today, the area of ​​natural gas is constantly expanding, despite dire predictions of its global depletion.

With increasing oil density, i.e. As the content of high-molecular compounds in it increases, the solubility of the gas in it decreases.

An indicator of the solubility of gas in oil is the gas factor - G, which shows the amount of gas in 1 m 3 (or 1 ton) of degassed oil. It is measured in m 3 /m 3 or m 3 /t.

According to this indicator, deposits are divided into:

The main reason for imposing natural gas as an energy source is its environmental friendliness. At a time when the general trend of global industrial development is focused on investment in environmentally friendly production technologies, natural gas is becoming the preferred source of primary energy. Of course, when we talk about the global gas market, we cannot forget about another trend, which is not only a short-term, but also a long-term aspect, which is the constant increase in its price.

The widespread use of natural gas is the reason for the development of an entire industry, covering not only technologies for the production, storage and transportation of natural gas, but also for measuring the parameters and quantity of the energy resource. Research in Germany, for example, suggests that if natural gas measurement accuracy improved by just 1%, the macroeconomic benefits to the industry would be in the order of millions of euros.

1) oil - G

2) oil with a gas cap - G- 650 - 900 m 3 / m 3;

3) gas condensate - G>900 m 3 /m 3.

Solubility of water in compressed gas.

Water dissolves in compressed gas at high pressure. This pressure makes it possible to move water in the depths not only in the liquid, but also in the gas phase, which ensures its greater mobility and permeability through rocks. As water mineralization increases, its solubility in gas decreases.

This article aims to provide you with a systematic overview of the main methods used to determine the calorific value and density of natural gas. The reason for this is the fact that in recent years natural gas has been increasingly used in both industrial and domestic applications.

Requirements for the calorific value of the fuel. Natural gas is known to burn in an environmentally friendly manner to produce carbon dioxide and water. By definition, the term calorific value includes all the energy that is discharged during the combustion process. Typically, automatic calorimeters and process gas chromatographs are used to calculate the natural heating value. This type of measuring instrument is subject to type approval by the State Agency for Metrology and Technical Supervision.

Solubility of liquid hydrocarbons in compressed gases.

Liquid hydrocarbons dissolve well in compressed gases, creating gas-condensate mixtures. This creates the possibility of transfer (migration) of liquid hydrocarbons in the gas phase, providing an easier and faster process of its movement through the rock mass.

With increasing pressure and temperature, the solubility of liquid hydrocarbons in gas increases.

In principle, the maximum permissible error when determining the calorific value of natural gas is 8%. To ensure the accuracy of measurements, it is necessary to provide specially defined conditions for the measurement process. There are also requirements for the installation and periodic testing of calibration gas meters. The normal volume of natural gas is determined to compare the results obtained.

Consequently, all parameters of natural gas when calculating their volume are made on the basis of the so-called normal volume, i.e. volume of gas at certain values ​​of temperature and pressure. Regardless of their design differences, all calorimeters operate on the same physical principle. A schematic diagram of the calorimeter design is shown in Fig. Generally speaking, a strictly defined amount of natural gas is burned in the combustion chamber of the calorimeter. The heat released during the combustion of natural gas is transferred through a heat exchanger to a certain amount of coolant, most often air or gas.

Compressibility of reservoir gases- This is a very important property of natural gases. The volume of gas under reservoir conditions is 2 orders of magnitude (i.e., approximately 100 times) less than its volume under standard conditions on the earth's surface. This occurs because the gas has a high degree of compressibility at high pressures and temperatures.

The degree of compressibility is depicted through the volumetric coefficient of reservoir gas, which represents the ratio of the volume of gas in reservoir conditions to the volume of the same amount of gas under atmospheric conditions.

The calorific value of the fuel is determined by the change in coolant temperature. Or, more precisely, there is a direct relationship between the temperature of the coolant and the calorific value of the fuel. Although the principle of calorimetry has not changed since their inception, the functionality of modern instruments for measuring the calorific value of fuel has undergone significant development. Modern calorimetry is more accurate with increased processing, storage and analysis of measured values ​​and even greater communication capabilities.

This type of meter is used to determine the heating value of gas mixtures based on the heating value of the individual components of the mixture. Of course, a prerequisite for studying the calorific value of gas mixtures using a gas chromatograph is preliminary information about their composition. Gas chromatograph is a well-known gas analysis tool among metrologists. It has been used for decades in laboratory research. The main disadvantage of gas chromatographs is their manual operation, which limits their scope of application as a function of the calorific value of natural gas.

Condensation formation is closely related to the phenomena of gas compressibility and the solubility of liquid hydrocarbons in them. Under reservoir conditions, with increasing pressure, liquid components transform into a gaseous state, forming “gas-dissolved oil” or gas condensate. When the pressure drops, the process goes in the opposite direction, i.e. Partial condensation of gas (or vapor) occurs into a liquid state. Therefore, when gas is produced, condensate is also extracted to the surface.

With the development of technological chromatography over the years, accurate measurement of the calorific value of natural gas based on this principle has become a reality. It is known that the main design element of a gas chromatograph is a separation column filled with granular material. The individual components of gas mixtures travel over varying periods of time from the base to the top of the separation column. By measuring the time during which individual substances included in the gas mixture reach a sensor installed at the outlet of the separation column, the amount of substances participating in the composition of the gas mixture is measured.

Condensation factor– KF is the amount of raw condensate in cm3 per 1m3 of separated gas.

A distinction is made between wet and stable condensate. Raw condensate is a liquid phase in which gaseous components are dissolved.

Stable condensate is obtained from raw condensate by degassing it. It consists only of liquid hydrocarbons - pentane and higher ones.

Based on the calculated caloric content of the individual components, the calorific value of the gas mixture is calculated. Methods for determining the density of natural gas. There are many ways to determine the density of natural gas. Among the most widely used principles for determining the density of natural gas is the action of lifting force. These measuring instruments analyze the lifting force acting on a body of a strictly defined volume and density in a gaseous environment. It is known that the magnitude of the lift depends on the density of the gas.

Under standard conditions, gas condensates are colorless liquids with a density of 0.625 - 0.825 g/cm 3 with an initial boiling point from 24 0 C to 92 0 C. Most fractions have a boiling point of up to 250 0 C.

• ethane (C 2 H 6),
• propane (C 3 H 8),
• butane (C 4 H 10).

as well as other non-hydrocarbon substances:

An induction coil is commonly used to determine lift in industrial applications. The amount of electric current required to compensate for the driving force acting on a body in a gaseous environment is proportional to the density of the gas. Measuring instruments based on the described principle are not suitable for determining the density of gas flows. This method provides high accuracy in determining the density of a stationary amount of natural gas. It is mainly used to measure normal density.

Another principle for determining the density of natural gas is based on the excitation of a vibration process. This method is widely used to determine the density of gas flows. A special element is installed in the measuring chamber of the instruments, the operation of which is based on this principle. It vibrates at a certain, previously known frequency. As gas passes through the measuring chamber, the frequency at which the element flickers is disrupted. It was found that there is a non-linear relationship between the gas flow density and the frequency shift of the vibrating element.

Pure natural gas is colorless and odorless. To be able to detect a leak by smell, a small amount of substances that have a strong unpleasant odor (rotten cabbage, rotten hay) (so-called odorants) is added to the gas. Most often, ethyl mercaptan is used as an odorant (16 g per 1000 cubic meters of natural gas).

There is a technique for very accurately determining the gas flux density corresponding to each frequency offset. Two vibration sensors are used to calculate the normal gas density. The first sensor is installed in a control measuring chamber filled with a strictly defined amount of natural gas. The second measuring chamber, which houses another vibration sensor, is filled with sample gas. A necessary condition for the correctness of the measured results is that the gas temperature in the two chambers is the same.

The density of natural gas in the second chamber is estimated by the difference in frequencies at which the two sensors vibrate. The rationale for the widespread use of such a natural gas density measuring device is the high accuracy with which the oscillation frequency of the vibration sensor can be measured and further processed.

To facilitate transportation and storage of natural gas, it is liquefied by cooling at elevated pressure.

Physical properties

Approximate physical characteristics (depending on composition; under normal conditions, unless otherwise noted):

The third principle, based on the use of a centrifugal process, is also used to determine the density of natural gas. The design of this type of measuring device contains an axisymmetric measuring chamber in which a rotor with a constant rotation speed is installed. The gas to be analyzed is fed into a mixer in the chamber. As a result of the centrifugal force created on gas molecules when the mixer rotates, the pressure in the chamber increases. There is a linear relationship between gas density and the increase in pressure in the dosing chamber.

• Density:
  • from 0.68 to 0.85 kg/m³ relative to air (dry gaseous);
  • 400 kg/m³ (liquid).
• Auto-ignition temperature: 650 °C;
• Explosive concentrations of gas-air mixtures from 5% to 15%
• Specific heat of combustion: 28-46 MJ / m³ (6.7-11.0 Mcal / m³);
• Octane number when used in internal combustion engines: 120-130.
• 1.8 times lighter than air, so if there is a leak, it does not collect in the lowlands, but rises up

Natural gas, extracted from the depths of the earth, has no taste, color or smell. To impart an odor in order to recognize it in the air in the event of a leak, odorization is used - introducing a strong-smelling substance into the gas. Ethyl mercaptan is used as an odorant in an amount of 16 g per 1,000 m3 of natural gas. This allows natural gas to be detected at a concentration of 1% in air, which is 1/5 of the lower explosive limit™.

The described method is suitable for measuring the density of gas flows, but does not differ from the high accuracy principles described above. In the Czech lands in Prague, a new vehicle has appeared all year round, a car with a gasoline engine. The use of gas in transport began in the Czech Republic within a year. In particular, the use of liquefied gas to drive cars, buses and tractors. In those years, gas buses also operated in Krnov, Olomouc, and Mlada Boleslav.

At that time in Prague, a compressor station was installed at the Michli gas station to fill bottles with compressed gas. Under normal atmospheric conditions, propane-butane occurs in gaseous form. Relatively easily, by cooling or compressing, it can be converted into a liquid state. The easy transition between two states is very useful for practical use. Propane-butane is currently the most used gas in transportation, having been used as a vehicle fuel for decades.

The most important thermal technical characteristic of natural gas is the heat of combustion - the amount of heat released during the combustion of 1 m3 of dry gas and depending on the state of aggregation in the combustion products: water released from the fuel and formed during the combustion of hydrogen and hydrocarbons - in vapor or liquid . If all the water vapor in the combustion products condenses and forms a liquid phase, then the heat of combustion is called the highest Q in s. If condensation of water vapor does not occur, then the heat of combustion is called the lowest Q n c = 35.8.

Typically, combustion products leave boiler plants at a temperature at which condensation of water vapor does not occur, therefore, in thermal engineering calculations, the value Q n c is used, which for natural gas is close to the heat of combustion of methane and amounts to 35.8 MJ/m 3 (8,550 kcal/ m 3).

The density of natural gas (methane) under normal conditions (0°C and 0.1 MPa, i.e. 760 mm Hg) рг = 0.73 kg/m3. The air density under the same conditions is p = 1.293 kg/m3. Thus, natural gas is approximately 1.8 times lighter than air. Therefore, when gas leaks, it will rise up and accumulate near the ceiling, ceilings, and the top of the firebox.

Self-ignition temperature of natural gas tignition = 645... 700 °C. This means that any mixture of gas and air, after heating to this temperature, will ignite itself without an ignition source and will burn.

The concentration limits of ignition (explosion) of natural gas (methane) are in the range of 5... 15%. Outside these boundaries, the gas-air mixture is not capable of spreading flame. During an explosion, the pressure in a closed volume rises to 0.8... 1 MPa.

The advantages of natural gas compared to other types of fuel (primarily solid) include high calorific value; relatively low cost; lack of warehouse space for storage; relatively high environmental friendliness, characterized by the absence of solid inclusions in combustion products and a smaller amount of harmful gaseous emissions; ease of automation of the combustion process; the possibility of increasing the efficiency factor of the boiler unit; facilitating the work of service personnel.

Today, naturally occurring gas serves as the most important source of energy. All gaseous flammable compounds from the bowels of the earth are odorless and contain many impurities that affect the density of natural gas.

Such gases lack the physical indicators familiar to humans - taste, color, smell - by which we are able to determine their presence. And yet they are characterized by characteristic indicators, such as: density, combustion temperature, heat of combustion, composition, maximum concentration for an explosion, pressure during an explosion.

Among many significant physical indicators, we can say about the density of natural gas. This is a value that is calculated as the ratio of mass to its volume and is given by the formula r = t/V. The density of natural gas under normal conditions ranges from 0.73 to 0.85 kg/m3.

Features of gas

Extracted from deposits, it consists of methane in the range of 82-98% of the total mass, often with admixtures of other hydrocarbons. It also contains non-flammable substances: oxygen, carbon dioxide, nitrogen, and Immediately after pumping from the subsoil, the gas is freed from toxic hydrogen sulfide, bringing its content to the permissible 0.02 g/m3. The highest density of natural gas is created by the content of non-flammable mixtures of N 2, CO 2, H 2 S or heavy hydrocarbons. The lowest values ​​are obtained from dry methane environments. It is well known that an increase in the indicator of a physical quantity entails an increase in the temperature of hydrate formation. Although light weight is also capable of producing hydrates. When the gas in the deposit is high, it liquefies, and such a deposit is called gas condensate.

In comparison with other types of fuel (solid, liquid), natural gas, the density of which depends entirely on its composition, is advantageous in several respects:

• low cost - as a consequence of a much easier method of extraction and transportation;
• During combustion, ash and solid particles are not formed;
• relatively high calorific value;
• there is no need for preliminary preparation of blue fuel for combustion;
• the work of maintenance personnel is significantly simplified;
• sanitary and hygienic conditions for workers are significantly improved;
• the conditions for automating technical processes are simplified.

There are cases in everyday life when the gas pressure on the upper floors of the house risks being greater than on the lower floors. This is explained by the fact that the indicator is much higher compared to a flammable environment. At altitude, the static pressure decreases greatly, and the gas pressure decreases less.

Methods for measuring density

The density of natural gas is determined in a laboratory. Due to technical and economic feasibility, it can be calculated in the following ways:

• manually;
• using tables, graphs, diagrams;
• using computers and automated devices.

The most accurate method is to place the test sample in a thin-walled glass container and then weigh it on an accurate balance. There are also special instruments that measure the density of natural gas. These are density meters of the most diverse types - vibration, pycnometric, acoustic, hydrometric, radiation and others. Among them, the Solartron 7812 and Solartron 3098 are very famous models. They are capable of providing continuous measurement in a flow. As a rule, these models are used in commercial gas metering systems.

Density of gases

Gases, unlike liquids, are characterized by low density. The normal density of a gas is the mass of one liter at 0°C and a pressure of 1 kgf/cm2. The mass of one molecule of any gas is proportional to its density.

The gas density c varies proportionally to the pressure and is measured by the ratio of the gas mass m to the volume V it occupies:

For practical purposes, it is convenient to characterize different gases by their density relative to air under the same conditions of pressure and temperature. Since the molecules of different gases have different masses, their densities at the same pressure are proportional to their molar masses.

Density of gases and the ratio of their density to air density:

Basic gas laws

A characteristic feature of gases is that they do not have their own volume and shape, but take shape and occupy the volume of the container in which they are placed. Gases uniformly fill the volume of the vessel, trying to expand and occupy as much volume as possible. All gases are highly compressible. Molecules of real gases have volume and have forces of mutual attraction, although these quantities are very insignificant. In calculations for real gases, gas laws for ideal gases are usually used. Ideal gases are conventional gases, the molecules of which have no volume and do not interact with each other due to the absence of attractive forces, and during collisions between them no other forces act except the forces of elastic impact. These gases strictly follow the laws of Boyle - Mariotte, Gay-Lussac, etc.

The higher the temperature and lower the pressure, the closer the behavior of real gases corresponds to ideal gases. At low pressures, all gases can be considered ideal. At pressures of about 100 kg/cm2, deviations of real gases from the laws of ideal gases do not exceed 5%. Since the deviations of real gases from the laws derived for ideal gases are usually negligible, the laws for ideal gases can be freely used to solve many practical problems.

Boyle's Law - Mariotte

Measurements of gas volume under the influence of external pressure showed that there is a simple relationship between volume V and pressure P, expressed by the Boyle-Mariotte law: the pressure of a given mass (or amount) of gas at a constant temperature is inversely proportional to the volume of gas:

P1: P2 = V1: V2,

where P1 is the gas pressure at volume V1; P2 - gas pressure at volume V2.

It follows that:

P1 * V1 = P2* V2 or P * V= const (at t = const).

This postulate is formulated as follows: the product of the pressure of a given mass of gas and its volume is constant if the temperature does not change (i.e. during an isothermal process).

If, for example, we take 8 liters of gas under pressure P = 0.5 kgf/cm2 and change the pressure at a constant constant temperature, then the following data will be obtained: at 1 kgf/cm2 the gas will occupy a volume of 4 liters, at 2 kgf/cm2 - 2 liters , at 4 kgf/cm2 - 1l; at 8 kgf/cm2 - 0.5 l.

Thus, at a constant temperature, any increase in pressure leads to a decrease in the volume of gas, and a decrease in the volume of gas leads to an increase in pressure.

The relationship between gas volume and pressure at a constant temperature is widely used for various calculations in diving practice.

Gay-Lussac's and Charles's laws

Gay-Lussac's law expresses the dependence of the volume and pressure of a gas on temperature: at constant pressure, the volume of a given mass of gas is directly proportional to its absolute temperature:

where T1 and T2 are the temperature in Kelvin (K), which is equal to the temperature in °C + 273.15; those. 0°C? 273 K; 100 °C - -373 K, and 0 °C = -273.15 °C.

Consequently, any increase in temperature leads to an increase in volume, or, in other words, the change in the volume of a given mass of gas V is directly proportional to the change in temperature t of the gas at constant pressure (i.e., during an isobaric process). This position is expressed by the formula:

where V1 is the volume of gas at a given temperature; V0 is the initial volume of gas at 0°C; b - coefficient of volumetric expansion of gas.

When different gases are heated by the same number of degrees, the relative increase in volume is the same for all gases. Coefficient b is a constant volume increment for all gases, equal to 1/273 or 0.00367 oC-1. This coefficient of volumetric expansion of gases shows by what part of the volume occupied at 0°C the volume of the gas increases if it is heated by 1°C at constant pressure.

The relationship between pressure and temperature is subject to the same pattern, namely: the change in pressure of a given mass of gas is directly proportional to the temperature at a constant volume (i.e., with an isochoric process: from the Greek words “isos” - equal and “horema” - capacity) , which is expressed by the formula:

Pt = P0 (1 + bt),

where Рt is the gas pressure at a given temperature; Р0 -- initial gas pressure at 0° C; b - coefficient of volumetric expansion of gas.

This dependence was established by J. Charles 25 years before the publication of J. L. Gay-Lussac and is often called Charles’s law. The dependence of volume on temperature at constant pressure was also first established by Charles.

As the temperature of a gas decreases, its pressure decreases, and at a temperature of -273.15 °C, the pressure of any gas is zero. This temperature is called absolute zero temperature. In this case, the chaotic thermal movement of molecules stops and the amount of thermal energy becomes equal to zero. The given dependencies, expressing the laws of Charles and Gay-Lussac, make it possible to solve important practical problems in the preparation and planning of underwater dives, such as, for example, determining the air pressure in cylinders when the temperature changes, the corresponding change in air reserves and time spent at a given depth, etc. . P.

Ideal gas equation of state

If the relationship between volume, pressure and temperature is linked together and expressed in one equation, then the equation of state of an ideal gas is obtained, which combines the Boyle-Mariotte and Gay-Lussac laws. This equation was first derived by B.P. Clayperon by transforming the equations proposed by his predecessors. Clayperon's equation is that the product of the pressure of a gas of a given mass and its volume divided by the absolute temperature is a constant value that does not depend on the state in which the gas is located. One way to write this equation is:

In this case, the gas constant r will depend on the nature of the gas. If the gas mass is a mole (gram molecule), then the gas constant R is universal and does not depend on the nature of the gas. For a gas mass equal to 1 mole, the equation takes the following form:

The exact value of R is 8.314510 J mol -1 K-1

If we take not 1 mole, but any amount of gas having mass m, then the state of an ideal gas can be expressed by the Mendeleev-Claiperon equation, convenient for calculations, in the form in which it was first written down by D.I. Mendeleev in 1874:

where m is gas mass, g; M is molar mass.

The ideal gas equation of state can be used for calculations in diving practice.

Example. Determine the volume occupied by 2.3 kg of hydrogen at a temperature of + 10 °C and a pressure of 125 kgf/cm2

where 2300 is gas mass, g; 0.082 - gas constant; 283 - temperature T (273+10); 2 is the molar mass of hydrogen M. From the equation it follows that the pressure exerted by the gas on the walls of the vessel is equal to:

This pressure disappears either at m > 0 (when the gas almost disappears) or at V>? (when the gas expands without limit), or at T > 0 (when the gas molecules do not move).

Van der Waals equation

Even M. V. Lomonosov pointed out that the Boyle-Mariotte law cannot be true at very high pressures, when the distances between molecules are comparable to their own sizes. Subsequently, it was fully confirmed that deviations from the behavior of ideal gases will be significant at very high pressures and very low temperatures. In this case, the ideal gas equation will give incorrect results without taking into account the interaction forces between gas molecules and the volume they occupy. Therefore, in 1873, Jan Diederik van der Waals proposed making two corrections to this equation: for pressure and for volume.

Avogadro's law

Avogadro put forward a hypothesis according to which, under the same conditions of temperature and pressure, all ideal gases, regardless of their chemical nature, contain an equal number of molecules per unit volume. It follows that the mass of equal volumes of gas is proportional to their molecular mass.

Based on Avogadro's law, knowing the volumes of the gases under study, you can determine their mass and, conversely, by the mass of the gas you can determine its volume.

Laws of gas dynamics

Dalton's law. The pressure of a mixture of gases is equal to the sum of the partial (partial) pressures of the individual gases making up the mixture, i.e., those pressures that each gas would produce separately if it were taken at the same temperature in the volume of the mixture.

The partial gas pressure Pr is proportional to the percentage C of the given gas and the absolute pressure Pac of the gas mixture and is determined by the formula:

Pr = Pa6с С/100,

where Pr is the partial pressure of gas in the mixture, kg/cm2; C is the volumetric gas content in the mixture, %.

This law can be illustrated by comparing a mixture of gases in a closed volume with a set of weights of different weights placed on a scale. Obviously, each of the weights will exert pressure on the scale regardless of the presence of other weights on it.

Ministry of Education and Science of the Russian Federation

Federal State Budgetary Educational Institution of Higher Professional Education

"Russian State University of Oil and Gas named after. I.M.Gubkina"

A.N. Timashev, T.A. Berkunova, E.A. Mamedov

DETERMINATION OF GAS DENSITY

Guidelines for performing laboratory work in the disciplines “Technology of operation of gas wells” and “Development and operation of gas and gas condensate fields” for students of specialties:

RG, RN, RB, MB, MO, GR, GI, GP, GF

Edited by Professor A.I. Ermolaeva

Moscow 2012

Determination of gas density.

Guidelines for carrying out laboratory work / A.N. Timashev,

T.A. Berkunova, E.A. Mamedov - M.: Russian State University of Oil and Gas named after I.M. Gubkina, 2012.

Methods for laboratory determination of gas density are described. The basis is the current GOST 17310 - 2002.

The guidelines are intended for students of oil and gas universities in the following specialties: RG, RN, RB, MB, MO, GR, GI, GP, GF.

The publication was prepared at the Department of Development and Operation of Gas and Gas-

zocondensate deposits.

Published by decision of the educational and methodological commission of the Faculty of Development

Bottoms of oil and gas fields.

Introduction

Physical properties of natural gases and hydrocarbon condensates are used

are used both at the design stage of development and site development

densities of natural gases, and in the analysis and control of field development,

operation of the system for collecting and preparing products from gas and gas condensate wells. One of the main physical properties to be studied is the density of the gas fields.

Since the gas composition of natural gas fields is complex,

consisting of hydrocarbons (alkanes, cycloalkanes and arenes) and non-hydrocarbons

components (nitrogen, helium and other rare earth gases, as well as acidic components

nents H2 S and CO2), there is a need for laboratory determination of density

sti gases.

This methodological instruction discusses calculation methods for determining

determination of gas density using a known composition, as well as two laboratory methods for determining gas density: pycnometric and the method of flow through a capillary

1. Basic definitions

1.1. Density of natural gas at atmospheric pressure

The gas density is equal to the mass M contained in a unit volume of the substance

va. There are gas densities at normal temperatures P 0.1013 mPa, T 273 K and

Where M is the molecular mass of the gas, kg/kmol; 22.41 and 24.04, m3/kmol – molar volume of gas, respectively, at normal (0.1013 MPa, 273 K) and standard

(0.1013 MPa, 293 K) conditions.

For natural gases consisting of hydrocarbon and non-hydrocarbon components (acidic and inert), the apparent molecular mass M k

determined by the formula

where M i is the molecular weight of the i-th component kg/kmol; n i is the mole percentage of the i-th component in the mixture;

k – number of components in the mixture (natural gas).

The density of natural gas cm is equal to

i is the density of the i-th component at 0.1 MPa and 293 K.

Data on individual components are shown in Table 1.

Density conversion under different temperature and pressure conditions

0.1013 MPa (101.325 kPa) in Appendix B.

1.2. Relative gas density

In the practice of engineering calculations, the concept of relative

nary density equal to the ratio of gas density to air density at the same values ​​of pressure and temperature. Normal or standard conditions are usually taken as reference, with the air density being

responsibly amounts to 0 1.293 kg / m 3 and 20 1.205 kg / m 3. Then the relative

The natural gas density is equal to

1.3. Density of natural gas at pressures and temperatures

Gas density for conditions in the productive formation, wellbore, gas

wires and apparatus at appropriate pressures and temperatures determine

is calculated according to the following formula

where P and T are the pressure and temperature at the place where the gas density is calculated; 293 K and 0.1013 MPa are standard conditions when located cm;

z ,z 0 – gas supercompressibility coefficients, respectively, at Р and Т and stan-

dart conditions (value z 0 = 1).

The simplest way to determine the supercompressibility coefficient z is the graphical method. The dependence of z on the given parameters is pre-

shown in Fig. 1.

For a one-component gas (pure gas), the given parameters are determined

divided according to formulas

inclusive, and all other components are combined into a remainder (pseudocom-

component) C5+ or C7+, in this case the critical parameters are determined by the form

At 100 M from 5 240 and 700d from 5 950,

M s 5 – molecular weight of C5+ (C7+) kg/kmol;

d c 5 – density of the pseudocomponent C5+ (C7+), kg/m3.

Table 1

Indicators of natural gas components

One of the most important physical properties of gaseous substances is their density.

DEFINITION

Density is a scalar physical quantity, which is defined as the ratio of the mass of a body to the volume it occupies.

This quantity is usually denoted by the Greek letter r or the Latin letters D and d. The unit of measurement for density in the SI system is considered to be kg/m 3 , and in the GHS - g/cm 3 . Gas density is a reference value; it is usually measured at air pressure. u.

Often, in relation to gases, the concept of “relative density” is used. This value is the ratio of the mass of a given gas to the mass of another gas taken in the same volume, at the same temperature and the same pressure, called the relative density of the first gas to the second.

For example, under normal conditions, the mass of carbon dioxide in a volume of 1 liter is 1.98 g, and the mass of hydrogen in the same volume and under the same conditions is 0.09 g, from which the density of carbon dioxide by hydrogen will be: 1.98 / 0. 09 = 22.

Relative gas density

Let us denote the relative gas density m 1 / m 2 by the letter D. Then

Therefore, the molar mass of a gas is equal to its density relative to another gas, multiplied by the molar mass of the second gas.

Often the densities of various gases are determined in relation to hydrogen, as the lightest of all gases. Since the molar mass of hydrogen is 2.0158 g/mol, in this case the equation for calculating molar masses takes the form:

or, if we round the molar mass of hydrogen to 2:

Calculating, for example, using this equation the molar mass of carbon dioxide, the density of which for hydrogen, as indicated above, is 22, we find:

M(CO 2) = 2 × 22 = 44 g/mol.

The density of a gas can be determined independently in laboratory conditions as follows: you need to take a glass flask with a stopcock and weigh it on an analytical balance. The initial weight is the weight of the flask from which all the air has been pumped out, the final weight is the weight of the flask filled to a specific pressure with the gas being tested. The difference in mass obtained should be divided by the volume of the flask. The calculated value is the density of the gas under these conditions.

p 1 /p N ×V 1 /m×m/V N = T 1 /T N ;

because m/V 1 = r 1 and m/V N = r N , we find that

r N = r 1 ×p N /p 1 ×T 1 /T N .

The table below shows the densities of some gases.

Table 1. Density of gases under normal conditions.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2