HCIIP Formula
The HCIIP is an acronym for Hydrocarbons Initially In Place. For Oil this is STOIIP (Stock Tank Oil Initially In Place) and for Gas it’s GIIP (Gas Initially In Place).
HCIIP a function of the multiplied by the , (
POR) and Oil or Gas Saturation (Shc). All these fractions are used to discount any volume of the GRV that does not add to the Hydrocarbon volume. Furthermore HCIIP is not the volume of hydrocarbons in the reservoir, but at stock tank (at the surface) conditions. Hence the name STOIIP: Stock Tank Oil Initially In Place when talking about Oil. For gas the name is just GIIP.
To calculate stock tank conditions the temperature, composition and pressure of the fluids in the reservoir is used to calculate a Formation Volume Factor. This factor is used to express the expansion of the gas when brought to surface. For oil it is used to express the volume decrease due to gas escaping from the fluid when the pressure drops.
Please note that the HCIIP is not the volume that is eventually produced as no reservoir can be produced to the last drop of Oil or Gas. The recovery Factor is a last factor that can be used to estimate the recoverable volume of Hydrocarbons but is very much dependent on the development method for the field.
GRVStands for Gross rock volume and is the volume of rock in the trap above the hydrocarbon water contact.
NRVStands for Net rock volume and is the volume of rock in the trap above the hydrocarbon water contact with non-reservoir rock discounted. This done by multiplying GRV with . NTG is a fraction for 0 to 1.
NPVStands for Net Pore volume and is the volume of fluid or gas filled intragranular pores in the trap above the hydrocarbon water contact with non-reservoir rock discounted. This done by multiplying NRV (=GRV*NTG) with POR. The POR does need to be the average porosity in the net reservoir, usually called PORNET and is somewhere between 0 to 0.45.
HCPVStands for Hydrocarbon Pore volume and is the volume of oil or gas filled intragranular pores in the trap above the hydrocarbon water contact with non-reservoir rock discounted. This done by multiplying NPV (=NRV*POR) with Shc. This Shc is the average saturation of the hydrocarbons in the pores, usually 1-Sw (water saturation).