Month: June 2023

The formation volume factor (Bo), which is also abbreviated FVF, at any pressure may be defined as the volume in barrels that one stock-tank barrel occupies in the formation (reservoir) at reservoir temperature, with the solution gas that can be held in the oil at that pressure. Because both the temperature and the solution gas increase the volume of… Continue reading Formation Volume Factor

The amount of gas dissolved in an oil at a given pressure and temperature is referred to as the solution gas-oil ratio (Rso), in units of SCF/STB. The solubility of natural gas in crude oil depends on the pressure, temperature, and composition of the gas and the crude oil. For a particular gas and crude oil at… Continue reading Solution Gas-Oil Ratio, Rso

The next few sections contain information on crude oil properties, including several correlations that can be used to estimate values for the properties. McCain, Spivey, and Lenn present an excellent review of these correlations Reservoir Fluid Property Correlations.19 However, these crude oil property correlations are, in general, not as reliable as the correlations that have been presented… Continue reading Review of Crude Oil Properties

The viscosity of natural gas depends on the temperature, pressure, and composition of the gas. It has units of centipoise (cp). It is not commonly measured in the laboratory because it can be estimated with good precision. Carr, Kobayashi, and Burrows have developed correlation charts, Figs. 2.6 and 2.7, for estimating the viscosity of natural gas from the… Continue reading Viscosity

The change in volume with pressure for gases under isothermal conditions, which is closely realized in reservoir gas flow, is expressed by the real gas law: Sometimes it is useful to introduce the concept of gas compressibility. This must not be confused with the gas deviation factor, which is also referred to as the gas compressibility factor. Equation (2.17)… Continue reading Isothermal Compressibility

The gas formation volume factor (Bg) relates the volume of gas in the reservoir to the volume on the surface (i.e., at standard conditions psc and Tsc). It is generally expressed in either cubic feet or barrels of reservoir volume per standard cubic foot of gas. Assuming a gas deviation factor of unity for the standard conditions, the reservoir volume… Continue reading Formation Volume Factor and Density

Everything up to this point applies to a perfect or ideal gas. Actually there are no perfect gases; however, many gases near atmospheric temperature and pressure approach ideal behavior. All molecules of real gases have two tendencies: (1) to fly apart from each other because of their constant kinetic motion and (2) to come together… Continue reading Real Gas Law

Because the density of a substance is defined as mass per unit volume, the density of gas, ρg, at a given temperature and pressure can be derived as follows: where Mw = molecular weight Because it is more convenient to measure the specific gravity of gases than the gas density, specific gravity is more commonly used. Specific gravity is defined as… Continue reading Specific Gravity

Ideal Gas Law Relationships that describe the pressure-volume-temperature (PVT) behavior of gases are called equations of state. The simplest equation of state is called the ideal gas law and is given by where p = absolute pressure V = total volume that the gas occupies n = moles of gas T = absolute temperature R′ = gas constant When R′ = 10.73, p must be… Continue reading Review of Gas Properties

The ratio of the volume that a fluid occupies to the pore volume is called the saturation of that fluid. The symbol for oil saturation is So, where S refers to saturation and the subscript o refers to oil. Saturation is expressed as either a fraction or a percentage, but it is used as a fraction in equations. The saturations of all… Continue reading Fluid Saturations