Gas material balance: Handout for course “Petroleum Engineering” (ta3440) February 2014

The material balance equation (MBE) is a tool to predict the future production behavior of a reservoir by using its past production data. It is a balance of volumes of reservoir fluids, before and after production. Important to notice is that the volume of the fluids change when they are taken from reservoir conditions (pressure p, temperature T) to standard conditions psc and Tsc at the surface. The total reservoir volume is called the hydrocarbon pore volume (HCPV) defined as VHCP = Vϕ (1 - Sw), where the product Vϕ is the pore volume (PV), V is the gross rock volume, ϕ is the porosity, and Sw is the water saturation. If we assume that there is no free water in the reservoir, the water saturation is equal to the connate water saturation Swc, which results in VHCP = Vϕ (1 - Swc).