When an oil and gas reservoir is tapped with wells, oil and gas, and frequently some water, are produced, thereby reducing the reservoir pressure and causing the remaining oil and gas to expand to fill the space vacated by the fluids removed. When the oil- and gas-bearing strata are hydraulically connected with water-bearing strata (aquifers) with… Continue reading Derivation of the Material Balance Equation
Introduction
Fluid does not leave a void space behind, as it is produced from a hydrocarbon reservoir. As the pressure in the reservoir drops during the production of fluids, the remaining fluids and/or reservoir rock expand or nearby water encroaches to fill the space created by any produced fluids. The volume of oil produced on the… Continue reading Introduction
Review of Reservoir Water Properties
The properties of formation waters are affected by temperature, pressure, and the quantity of solution gas and dissolved solids, but to a much smaller degree than crude oils. The compressibility of the formation, or connate, water contributes materially in some cases to the production of volumetric reservoirs above the bubble point and accounts for much… Continue reading Review of Reservoir Water Properties
Isothermal Compressibility
Sometimes it is desirable to work with values of the liquid compressibility rather than the formation or relative volume factors. The isothermal compressibility, or the bulk modulus of elasticity of a liquid, is defined by Eq. (2.1): The compressibility, c, is written in general terms since the equation applies for both liquids and solids. For a… Continue reading Isothermal Compressibility
Formation Volume Factor
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
Solution Gas-Oil Ratio, Rso
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
Review of Crude Oil Properties
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
Viscosity
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
Isothermal Compressibility
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
Formation Volume Factor and Density
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