Page 71 - Reservoir Formation Damage

54 Reservoir Formation Damage

Tortuosity

Tortuosity is defined as the ration of the lengths, L t and L, of the
tortuous fluid pathways and the porous media:

T = L,/L (3-13)

Liu and Masliyah (1996a, b) recommend the Bruggeman (1935) equation

1 2
1
T ^ / (3-14)
for random packs of grains of porosity § > 0.2 and the Humble equation
(Winsauer et al., 1952)

1.15 (3-15)

for consolidated porous media of porosity (|) < 0.45. They point out that
the latter may have a variable accuracy and, therefore, tortuosity should
be measured.

Interconnectivity of Pores

Based on their binary images shown in Figure 3-3, Davies (1990)
classified the pore types in four groups (Davies, 1990, p. 74):

"Pore Type 1: Microspores, generally equant shape, less than 5
microns in diameter. These occur in the finest
grained and shaly portions of the sand.
Pore Type 2: Narrow, slot like pores, generally less than 15
microns in diameter, commonly slightly to strongly
curved. These represent reduced primary inter-
granular pores resulting from the reduction of
original primary pores by extensive cementation.
Pore Type 3: Primary intergranular pores, triangular in shape,
twenty-five to fifty microns maximum diameter.
These are the original primary intergranular pores
of the rock which have been affected only mini-
mally by cementation.
Pore Type 4: Solution enlarged primary pores: oversized primary
pores, fifty to two hundred microns maximum
diameter produced through the partial dissolution
of rock matrix."