Application of Electrokinetics for Enhanced Oil Recovery - Electrokinetics for Petroleum and Environmental Engineers - page 107

the carbonate reservoirs are lined with clay minerals they will also become
partially to preferentially water wet.
The percentages of the pore space filled with water, oil, and/or gas, at
any depth, is called water, S w , oil, S o , and/ or gas, S g , saturation, respectively.

3.2.4 Initial Reserves

Initial reserves are the amounts of oil and/or free gas in the reservoir, before
any production has taken place. For oil the definition is:

7758 Ah f ( 1 − S ) ,

(3.1) STOOIP =

w

B

oi

where: STOOIP is stock tank original oil in place, in bbls.
A is the reservoir closure area, in acres.
h is the average reservoir (net) thickness, in feet.
φ is the average reservoir decimal porosity.
S w is the average reservoir decimal water saturation.
B oi is the initial oil formation volume factor.
7758 is the acre-ft to bbls conversion factor ( (different conversion
constants will be required, for other unit systems ).
A similar relationship also exists for gas reserves.

3.2.5 Primary Oil Production and Water Cut

Wells are drilled into petroleum reservoirs to recover the oil and/or gas.
Reservoir energy determines whether an oil well will flow ( without assis-
tance ) or must be pumped. The reservoir energy is provided by dissolved
gas, mechanical compaction, and/or hydraulic pressure within the reser-
voir. As a reservoir is depleted, more than one fluid type will be produced.
For oil reservoirs, not only will oil be produced, but also associated gas ( gas
cut ) and/or water ( water cut ).

3.3 Relative Permeability and Residual Saturation

Figure 3.1 is a generic representation of an oil/water (two phase) relative
permeability determination, for a preferentially water-wet reservoir rock.
For multi-phase systems, the relative permeability is a measure of the
amount of each fluid, which can be produced from a reservoir and under