Representation of Material Balance Equation under Different Reservoir Type

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 com￾pressibility, 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: