Material balance

Material balance is a fundamental concept in reservoir engineering that expresses mass conservation in a reservoir. The material balance equation is the simplest expression of the conservation of mass in a reservoir. The equation mathematically defines the relationship between the initial hydrocarbon in place, the volume of hydrocarbons produced, and the volume of hydrocarbons remaining in the reservoir. The material balance equation can be used to determine the initial hydrocarbon in place, predict an overall recovery factor, and determine reservoir drive mechanisms.

The material-balance equation mathematically defines the different producing mechanisms and effectively relates the reservoir fluid and rock expansion to the subsequent fluid withdrawal

Here is the generalized material balance equation:

Where:

• G_fgi, N_foi, and W are the initial free gas, oil, and water in place, respectively
• G_p, N_p, and W_p are the cumulative produced gas, oil, and water, respectively
• G_I and W_I are the cumulative injected gas and water respectively
• E_g, E_o, E_w, and E_f are the gas, oil, water, and rock (formation) expansivities

Note that the equation can be simplified for specific cases , such as gas reservoirs (where the water term and water formation volume factor can be ignored) or oil reservoirs without water drive (where the water term can be ignored).

External links

http://petrowiki.org/Material_balance_in_oil_reservoirs
http://www.ipt.ntnu.no/~kleppe/TPG4150/matbal.pdf
https://topdogengineer.com/material-balance-introduction/