Page 47 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

Basic Principles, Definitions, and Data 35

The correlation for compressibility of oil was given as:

co = (a, + %Rs + a,T + a4r, + a5Yo)/a,P (5-33)
where a, = - 1,433.0
a, = 5.0
a, = 17.2
a4 = - 1,180.0
as = 12.61
as = 105

Vazquez and Beggs also presented an equation for viscosity of undersaturated
crude oils that used the correlations of Beggs and Robinson:
Po = ~ob(p/pb)” (5-34)

C; = 1.187
C, = - 11.513
C, = - 8.98 X lo-’

The improved correlations of Vazquez and Beggs were incorporated by
Meehan in the development of programs for hand-held calculators. These
programs were presented in a series of articles in the Oil and Gas Journul [34-33].
Reference 34 contains the programs for calculating gas gravity, dissolved gas-
oil ratio, oil formation volume factor and oil compressibility. Reference 35
contains the program for calculating oil viscosity.
See References 36-40 for a list of books devoted to the use of programs for
handheld calculators and personal computers.
Properties of Fluid-Containing Rocks

Porosity
The porosity, 4, is equal to the void volume of the rock divided by the bulk
volume and is expressed as a percent or fraction of the total bulk volume of
the rock. Oil-bearing sandstones have porosities which often range from 15%
to 30%. Porosities of limestones and dolomites are usually lower.
Differentiation must be made between absolute and effective porosity. Absolute
porosity is defined as the ratio of the total pore volume of the rock to the total
bulk volume of the rock whereas effective porosity is defined as the ratio of
the interconnected pore volume of the rock to the total bulk volume of the rock.
Factors affecting porosity are compactness, character and amount of cementa-
tion, shape and arrangement of grains, and uniformity of grain size or distribution.
In problems involving porosity calculations it is convenient to remember that
a porosity of one percent is equivalent to the presence of 77.6 barrels of pore
space in a total volume of one acre-foot of sand.
Pore Volume

The pore volume of a reservoir is the volume of the void space, that is, the
porosity fraction times the bulk volume. In conventional units, the pore volume,
V,, in reservoir barrels is: