What is Original Oil In Place (OOIP)?
Original Oil In Place (OOIP) refers to the total volume of oil estimated to be stored in a reservoir prior to any production. It is a fundamental metric in petroleum engineering used to determine the commercial viability of an oil field and to plan recovery strategies.
The Volumetric Method
The OOIP is typically calculated using the Volumetric Method, which accounts for the physical dimensions of the rock and the fluid properties within the pores. Several factors influence this calculation:
- Area (A): The horizontal extent of the reservoir.
- Net Pay Thickness (h): The vertical thickness of the rock layer that contains exploitable oil.
- Porosity (φ): The percentage of the rock volume that consists of open spaces (pores) capable of holding fluid.
- Water Saturation (Sw): The fraction of the pore space occupied by water; the remaining space (1 - Sw) is assumed to be oil.
- Formation Volume Factor (Bo): Since oil shrinks when brought from high-pressure reservoir conditions to the surface, this factor adjusts the volume to standard surface conditions.
Interpreting the Result
The result is usually expressed in Stock Tank Barrels (STB). It is important to remember that OOIP is the total oil present, not the amount that can be extracted. The Recovery Factor is later applied to OOIP to estimate how much oil is actually producible.
Formula:
OOIP Formula:
OOIP = (7758 × A × h × φ × (1 - Sw)) / Bo
7758 is the conversion factor for Acre-feet to Barrels