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Molecules of a particular chemical species are composed of groups of atoms that always combine according to a specific formula. The chemical formula and the international atomic weight table provide us with a scale for determining the weight ratios of all atoms combined in any molecule. The molecular weight,M, of a molecule is simply the sum of all the atomic weights of its constituent atoms. It follows, then, that the number of molecules in a given mass of material is inversely proportional to its molecular weight. Therefore, when masses of different materials have the same ratio as their molecular weights, the number of molecules present is equal. For instance, 2 lbm hydrogen contains the same number of molecules as 16 lbm methane. For this reason, it is convenient to define the unit "lbm mol" as a mass of the material in pounds equal to its molecular weight. Similarly, a "g mol" is its mass in grams. One lbm mol or one g mol of any compound, therefore, represents a fixed number of molecules. This number for the g mol was determined in 1998 by the U.S. Natl. Inst. of Standards and Technology to be 6.02214199 1023. The number of significant digits shown is the accuracy to which it has been determined experimentally.
- Health, Safety, Environment & Sustainability > Health > Noise, chemicals, and other workplace hazards (1.00)
- Reservoir Description and Dynamics > Fluid Characterization > Phase behavior and PVT measurements (0.95)
- Reservoir Description and Dynamics > Formation Evaluation & Management (0.94)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.69)
- Information Technology > Knowledge Management (0.40)
- Information Technology > Communications > Collaboration (0.40)
At low pressures and relatively high temperatures, the volume of most gases is so large that the volume of the molecules themselves may be neglected. Also, the distance between molecules is so great that the presence of even fairly strong attractive or repulsive forces is not sufficient to affect the behavior in the gas state. However, as the pressure is increased, the total volume occupied by the gas becomes small enough that the volume of the molecules themselves is appreciable and must be considered. Also, under these conditions, the distance between the molecules is decreased to the point at which the attractive or repulsive forces between the molecules become important. This behavior negates the assumptions required forideal gas behavior, and serious errors are observed when comparing experimental volumes to those calculated with the ideal gas law.
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (0.73)
- Health, Safety, Environment & Sustainability > Health > Noise, chemicals, and other workplace hazards (0.73)
- Reservoir Description and Dynamics > Fluid Characterization > Phase behavior and PVT measurements (0.47)
- Information Technology > Knowledge Management (0.40)
- Information Technology > Communications > Collaboration (0.40)
Summary An accurate technique for estimating oil pressure/volume/temperature (PVT) properties using the Standing-Katz Z-factor chart has been developed. Prior work to derive tuned gas-pseudocritical-property values that provide consistent and accurate compressibility factors has been extended to oils. Data from 1,099 worldwide oil PVT reports with 11,960 density measurements have been analyzed. The oils studied have API gravities ranging from 10.6 to 63, with gas/oil ratios ranging from 5 to 4,631 scf/STB. Bubblepoint formation volume factors (FVFs) range from 0.98 to 4.58 bbl/STB. Saturation pressures ranged from 60 to 10,326 psia at temperatures ranging from 50 to 332°F with pressure differentials to 18,491 psi. The resulting work shows that oil pseudocritical properties can be correlated with molecular weight, as with gases. The resulting relationships can be used to determine saturated- and undersaturated-oil density accurately. Oil PVT properties, such as formation volume factor and isothermal compressibility, can then be derived from fundamental relationships with density. Because the new method correlates properties with the molecular weight of the wellstream, the chemical nature of the oil (e.g., whether naphthenic or paraffinic) is considered. Existing correlations (30 for bubblepoint oil formation volume factor and 17 for isothermal compressibility) have been identified in the literature. These methods are tested against the database along with the new method to determine accuracy and recommended procedures. Isothermal oil compressibility has proved difficult to correlate historically, with errors typically in excess of 30%. The proposed method significantly reduces the error in calculated isothermal compressibility in comparison to traditional methods. Introduction This paper uses a unified approach to determine oil PVT properties using methods typically reserved for gas. Equations involving the Z factor can be applied to either single-phase-gas or single-phase-oil systems to calculate density and isothermal compressibility. Since publication in 1942, the Standing and Katz (SK) gas Z-factor chart (Standing and Katz 1942) has become a standard in the industry. Several very accurate methods have been developed to represent the chart digitally. The Dranchuk and Abou-Kassem (1975) (DAK) method has been shown to provide accurate and consistent results over a wide range of conditions extrapolated beyond the data originally used in its development. The DAK method uses a form of the Benedict-Webb-Rubin equation of state (EOS) to fit 1,500 points of selected digital Z-factor-chart data originally published by Poettmann and Carpenter (1952). Data for isotherms less than 1.15 required smoothing.
- Asia (0.68)
- North America > United States > Texas (0.47)
Abstract Accurate prediction of gas compressibility factor is essential for the evaluation of gas reserves, custody transfer and design of surface equipment. Gas compressibility factor (Z) also known as gas deviation factor can be evaluated by experimental measurement, equation of state and empirical correlation. However, these methods have been known to be expensive, complex and of limited accuracy owing to the varying operating conditions and the presence of non-hydrocarbon components in the gas stream. Recently, newer correlations with extensive application over wider range of operating conditions and crude mixtures have been developed. Also, artificial intelligence is now being deployed in the evaluation of gas compressibility factor. There is therefore a need for a holistic understanding of gas compressibility factor vis-a-vis the cause-effect relations of deviation. This paper presents a critical review of current understanding and recent efforts in the estimation of gas deviation factor.
- Africa > Nigeria (0.94)
- North America > United States > Missouri (0.28)
- Overview (1.00)
- Research Report > New Finding (0.46)
Abstract An accurate technique for estimating oil PVT properties using the Standing-Katz Z factor chart has been developed. Prior work to derive tuned gas pseudo-critical property values which provide consistent and accurate compressibility factors has been extended to oils. Data from 1,099 worldwide oil PVT reports with 11,960 density measurements has been analyzed. The oils studied have API gravities ranging 10.6–63 with gas-oil ratios ranging 5–4,631 scf/STB. Bubblepoint formation volume factors range from 0.98–4.58 Bbl/STB. Saturation pressures ranged from 60–10,326 psia at temperatures ranging 50–332 °F with pressure differentials to 18,491 psi. The resulting work shows that oil pseudo-critical properties can be correlated with molecular weight as with gases. The resulting relationships can be used to accurately determine saturated and undersaturated oil density. Oil PVT properties such as formation volume factor and isothermal compressibility can then be derived from fundamental relationships with density. Since the new method correlates properties with the molecular weight of the wellstream, the chemical nature of the oil (ie naphthenic, paraffinic, etc) is considered. Existing correlations (30 for bubblepoint oil formation volume factor and 17 for isothermal compressibility) have been identified in the literature. These methods are tested against the database along with the new method to determine accuracy and recommended procedures. Isothermal oil compressibility has historically proved difficult to correlate with errors typically in excess of 30%. The proposed method significantly reduces the error in calculated isothermal compressibility when compared with traditional methods. Introduction This paper uses a unified approach to determine oil PVT properties using methods typically reserved for gas. Equations involving Z factor can be applied to either single phase gas or single phase oil systems to calculate density and isothermal compressibility. Since its publication in 1942, the Standing and Katz (SK) gas Z factor chart has become a standard in the industry. Several very accurate methods have been developed to digitally represent the chart. The Dranchuk and Abou-Kassem (DAK) method has been shown to provide accurate and consistent results over a wide range of conditions extrapolated beyond the data originally used in its development. DAK used a form of the Benedict-Webb-Rubin EOS to fit 1,500 points of selected digital Z factor chart data originally published by Poettmann. Data for isotherms less than 1.15 required smoothing. Therefore the data used for fitting the DAK equation encompassed the following ranges: 0 Ppr 30 and 1.05 Tpr 3.0. In 2005, Sutton showed that the DAK equation could provide accurate results at pseudoreduced pressures well beyond 30. In this paper, the DAK equation is tested at pseudoreduced pressures up to 80 and pseudoreduced temperatures as low as 0.4. A general gas Z factor chart, such as the one developed by Standing and Katz, is based on the principal of corresponding states. This principal states that two substances at the same conditions referenced to critical pressure and temperature will have similar properties. These conditions are referred to as reduced pressure and reduced temperature. Therefore, if two substances are compared at the same reduced conditions, the substances will have similar properties. In the context of this paper, the property of interest is the Z factor and physical properties that can be derived from Z factors. Mathematically, the SK chart relates Z factor to reduced pressure and reduced temperature. .............................................................................. (1) where ................................................................................ (2) ................................................................................. (3)
- Asia > Middle East (0.93)
- Africa (0.93)
- North America > United States > Texas (0.68)