Gas Field Engineering: Properties of Natural Gas Practice Flashcards

Vocabulary flashcards covering the physical properties, composition, governing laws, and calculation methods for natural gas mixtures as presented in the PEB/PFB 4213 Gas Field Engineering lecture.

Natural Gas

A mixture of hydrocarbon gases (such as methane, ethane, propane, and butanes) and impurities (such as carbon dioxide, hydrogen sulfide, and nitrogen).

Ideal Gas

A hypothetical fluid where the volume of molecules is insignificant compared to the total gas volume, no intermolecular forces exist, and no internal energy loss occurs during collisions.

Boyle’s Law

A gas law stating that if temperature is constant, the volume of gas varies inversely with the absolute pressure, expressed as $P_1V_1 = P_2V_2$.

Charles’ Law

A gas law stating that if pressure is held constant, volume varies directly with absolute temperature, expressed as $\frac{V_1}{T_1} = \frac{V_2}{T_2}$; it also states that at constant volume, absolute pressure varies directly with absolute temperature ($\frac{P_1}{T_1} = \frac{P_2}{T_2}$).

Avogadro’s Law

States that under the same conditions of temperature and pressure, equal volumes of all ideal gases contain the same number of molecules ($2.733 \times 10^{26}$ molecules in 1 pound-mole).

Standard Conditions

Reference conditions for gas measurement defined as a temperature of $60^{\circ}F$ and a pressure of $14.73\,psia$. At these conditions, 1 pound-mole of an ideal gas occupies $378.6\,cu\,ft$.

Kay’s Mixing Rules

Calculation methods used to determine the overall physical properties of a gas mixture based on the physical properties of its individual pure components.

Mole Fraction ($y_i$)

A way of expressing gas composition defined as the number of moles of a specific component divided by the total number of moles in the mixture.

Apparent Molecular Weight ($M_a$)

A pseudo property of a gas mixture defined as $M_a = \sum y_i M_i$, where $y_i$ is the mole fraction and $M_i$ is the molecular weight of component $i$.

Gas Deviation Factor ($z$)

An empirical factor, also called the compressibility factor, used to correct the deviation between the measured behavior of a real gas and that calculated using the ideal gas law.

Pseudocritical Pressure ($P_{pc}$)

The molal average of the critical pressures of the individual components in a gas mixture, calculated as $P_{pc} = \sum y_i P_{ci}$.

Pseudocritical Temperature ($T_{pc}$)

The molal average of the critical temperatures of the individual components in a gas mixture, calculated as $T_{pc} = \sum y_i T_{ci}$.

Theorem of Corresponding States

The principle stating that the properties of gases have the same value at the same reduced temperature ($T_r$) and reduced pressure ($P_r$).

Viscosity

A measure of the resistance to flow exerted by a fluid, which for gas mixtures depends on temperature, pressure, and chemical composition.

Gas Formation Volume Factor ($B_g$)

The ratio of the volume of gas at reservoir conditions to its volume at standard conditions, commonly expressed in units of $cu\,ft/scf$ or $barrels/scf$.

Gas Expansion Factor ($E$)

The reciprocal of the gas formation volume factor ($E = \frac{1}{B_g}$), representing the volume at standard conditions per unit volume at reservoir conditions.

API Gravity

A gravity scale used for hydrocarbon liquids where a liquid with the same density as water at $60^{\circ}F$ (specific gravity 1.0) has a value of $10^{\circ}\,API$.

Hall–Yarborough Method

A method for direct calculation of $z$-factors developed using the Starling-Carnahan equation of state, often solved using the Newton-Raphson iterative technique.

Dranchuk, Purvis and Robinson Method

A method to calculate $z$-factors by fitting the Standing-Katz correlation using an eight-coefficient Benedict-Webb-Rubin type equation of state.