Initially Undersaturated

Initially Undersaturated

1. Undersaturated Conditions (P_i > Pb)

Lets begin with:

Oil Oil In Place (N or OOIP) = Total Space Occupied by Oil at New Condition

(available pore space does not change).

Solve for N

which implies volume space created by production = expansion of remaining oil

While B_o and B_oi are available from PVT data, Np is from production data.

2. Undersaturated Conditions (P_R < Pb)

In this scenario, we explore as Pr has decreased by bubble point (Pb). Initially, all the gas was in solution, so GOR as surface equals the solution gas ratio. GOR = R_si while P_R > P_b. After saturation pressure, GOR will now consist of solution gas + solution free gas. Therefore:

Hydrocarbon Pore Volume = Oil Remaining at New Pressure (incl solution gas) + Gas Present at New Pressure

To evaluate the amount of free gas (Gfg) is in the reservoir, a material balance on the gas must be done/

Total Gas Initially = Gas Produced + Gas in Solution + Free Gas

Solve for free gas:

Substitute back into the previous equation

Re-arrange, collect “like terms“ and we achieve the following form:

Where:

= Void from production of oil

= Production of gas

= Expansion or shrinkage of oil

=Expansion of free gas

3. Inclusion of Water Production and Water Influx

Water influx can be the result of water injection for natural water movement.

N and We are both difficult to estimate concurrently. Mathematically, from above, we can solve N if we know We (or vice-versa)

Proceed to Initially Saturated (Gas Cap Present)

References:

• Northern Alberta Institute of Technology, Course Notes, PETE 2320, 2020.