Page 50 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

38 Reservoir Engineering

where q = volume rate of flow, cc/sec
k = permiability, darcies
h = thickness, cm
p = viscosity, cp
p, = pressure at external boundary, atm
p, = pressure at internal boundary, atm
re = radius to external boundary, cm
rw = radius to internal boundary, cm
In = natural logarithm, base e

For the flow rate, q, in the barrels per day of a liquid [19]:

(5-42)

where k is in darcies, h is in ft. pressures are in psia, p is in cp, and the radii
are in consistent units, usually feet. For the laminar flow of a gas in MscfD [20]:

(5 43)

where T is in OR, z is the dimensionless compressibility factor, and the other
terms are as defined in Equation 5-42.

Capacity
Flow capacity is the product of permeability and reservoir thickness expressed
in md ft. Since the rate of flow is proportional to capacity, a 10-ft thick
formation with a permeability of 100 md should have the same production as
a 100-ft thick formation of 10 md, if all other conditions are equivalent.

Transmissibility
Transmissibility is flow capacity divided by viscosity or kh/p with units of
md ft/cp. An increase in either reservoir permeability or thickness or a decrease
in fluid viscosity will improve transmissibility of the fluid in the porous system.

Resistivity and Electrical Conductivlty

Electrical conductivity, the electrical analog of permeability, is the ability of
a material to conduct an electrical current. With the exception of certain clay
minerals, reservoir rocks are nonconductors of electricity. Crude oil and gas are
also nonconductors. Water is a conductor if dissolved salts are present so the
conduction of an electric current in reservoir rocks is due to the movement of
dissolved ions in the brine that occupies the pore space. Conductivity varies
directly with the ion concentration of the brine. Thus, the electrical properties
of a reservoir rock depend on the fluids occupying the pores and the geometry
of the pores.
Resistivity, which is the reciprocal of conductivity, defines the ability of a
material to conduct electric current:
rA
R=- (544)
L