petroleum

Oil Saturation Adjustment Due to Combination Drive

For the case of combination drive, both water and gas invasion zone is incorporated

in the saturation equation given as:

Determination of Present GOC and OWC from

Material Balance Equation

Step 1: Determine the bulk volume of the reservoir rock at each depth interval

Step 2: Make a plot of depth versus the bulk volume

Step 3: Calculate the cumulative water influx from the general material balance

equation (We)

Step 4: Calculate the volume of oil displaced by water (Net water influx into the

reservoir) (OW ¼ We Wp)

Step 5: Calculate the reservoir volume liberated gas (GL)

GL¼ NRsi N Np

Step 6: Calculate the expansion of the primary gas cap (Ge)

Ge ¼ mNBoi

Bgi

Step 7: Calculate the gas drive (GD)

GD ¼ GL þ Ge

Step 8: Calculate the produced excess gas (Gpe)

Gpe ¼ Np Rp Rs

Step 9: Calculate the volume of oil displaced by the gas (Og)

Undersaturated Reservoir with Water Drive

Saturated Water Drive Reservoir

Oil Saturation Adjustment Due to Water Influx

Depletion Drive Reservoir

5.8.1.1 For Undersaturated Reservoir (P > Pb) with No Water Influx

That is, above the bubble point; the assumptions made are:

Material Balance Time Concept for Pseudo Steady State

for Undersaturated Reservoir

From the expression of the isothermal compressibility in terms of effective compressibility, we can express it in terms of

total compressibility, Ct

Saturated Reservoir (P < Pb) Without Water Influx

Calculation of Oil Saturation

As hydrocarbon is produced from the porous rock, water moves to replace the

corresponding space or void left by the produced hydrocarbon because nature avoids

vacuum. In some cases, the effects of the reservoir drive mechanisms need to be

accounted for; which are presented subsequently in this chapter. Mathematically, oil

saturation is given as:

Gas Drive Reservoir

Oil Saturation Adjustment Due to Gas Cap Expansion

The volume of oil in the gas-invaded zone is represented as: