Material Balance for Gas Reservoir

For gas reservoirs, the material balance concept can be applied to determine gas in place and expected gas reservoir reserve.

Gas Production = Expansion of Free Gas In Reservoir

equation 1 Gp


  • Dry gas reservoir
  • No external energy support like water drive.


Gp = gas production (std cu-ft)

Bg = gas formation volume factor (res cu-ft/std cu-ft)

G = gas in place (std cu-ft)

Bgi = initial formation volume factor (res cu-ft/std cu-ft)

Gas formation volume factor (Bg)

equation2 bg Continue reading

Solution Gas Drive Mechanism Explained in Material Balance Equation

Material balance equation can be applied for any drive mechanism and this article demonstrates how to apply the material balance equation in a solution drive mechanism. For a solution drive mechanism, there are 2 cases. The first case is when reservoir pressure is above a bubble point and the second case is when reservoir pressure is below a bubble point.

Solution Gas above Bubble Point

Start with a full material balance equation.

Figure 1 - Full Material Balance Equation

Figure 1 – Full Material Balance Equation

Assumptions Continue reading

Material Balance Equation in Reservoir Engineering

Material balance is a mathematic way to express mass conservation in a reservoir and a simple key principle is “what reservoir is produced must be replaced by other mass.

Volume Produced = Volume Replaced

Volume Produced comes from Gas Production, Oil Production, and Water Production.

Volume Replaced comes from volume expansion, water in flux and water/gas injection.

Figure 1 shows the relationship of the material balance.


Figure 1 – Concept of Material Balance

Let’s take a look at each component of equation. Continue reading