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
- 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)
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
Assumptions Continue reading
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