Oil in Place (OOIP)
Compute a reservoir's original oil in place (OOIP) by the volumetric method, OOIP = 7758·A·h·φ·(1−Sw)/Boi, in stock-tank barrels (STB). It combines the reservoir area (acres), the porous thickness (ft), the porosity (φ), the water saturation (Sw) and the oil formation volume factor (Boi). The constant 7758 converts acre-feet into barrels. It is the basis of any oil-field evaluation. Enter the area, thickness, porosity, water saturation and Boi.
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Oil in place (OOIP)
How much oil sits in a field? The first estimate comes from the volumetric method: OOIP = 7758·A·h·φ·(1−Sw)/Boi. The logic is geometric — multiply the area (acres) by the porous thickness (ft) to get the bulk rock volume, then by the porosity (φ, the fraction of void space) and by (1−Sw) to discount the water filling part of the pores, leaving the oil volume at reservoir conditions. The Boi factor (formation volume factor) converts that subsurface volume into surface barrels (oil shrinks as it rises and gives up gas). The constant 7758 is the number of barrels in one acre-foot. The result, in STB (stock-tank barrels), is the starting point of every economic evaluation — but it covers only the oil in place; how much will be recovered hangs on the recovery factor. Enter the area, the thickness, the porosity, Sw and Boi.
Related Tools
Reservoir Recovery Factor
Compute a reservoir's recovery factor, RF = (Np/N)·100%, the fraction of the original oil (N, or OOIP) that will actually be produced (Np). It is one of the most important — and uncertain — numbers in the industry: primary recovery (natural energy) is usually 5–15%; with secondary recovery (water/gas injection) it rises to 30–50%; and advanced methods (EOR) can go further. It defines the field's economic value. Enter the cumulative production and the original oil in place.
Recoverable Oil Reserves
Compute the recoverable oil reserves by multiplying the original oil in place (OOIP) by the recovery factor (%). While the OOIP is the total volume present in the rock, only a fraction is technically and economically extractable — those are the reserves that actually have value and enter oil companies' books. It is the number behind asset valuations and investment decisions. Enter the OOIP and the recovery factor.
Gas-Oil Ratio (GOR)
Compute the gas-oil ratio (GOR) by dividing the produced gas volume by the oil volume, in scf/STB (standard cubic feet per barrel). It is a central petroleum-production parameter: it indicates how much gas accompanies the oil, characterizes the reservoir fluid type (black oil, volatile, gas-condensate) and sizes the surface separation equipment. A rising GOR can signal gas-cap breakthrough at the well. Enter the gas and oil volumes.
Oil Formation Volume Factor (Bo)
Compute the oil formation volume factor (Bo) by dividing the volume the oil occupies at reservoir conditions by the volume it occupies at the surface (stock-tank barrels). Bo is always greater than 1 because, in the reservoir, the oil is hot and has dissolved gas, occupying more space; as it rises and loses gas and heat, it shrinks. It is essential to convert reservoir volumes into surface production. Enter the volumes at reservoir and surface conditions.
Reservoir Net Pay
Compute a reservoir's net pay (net productive thickness) by multiplying the gross interval thickness by the net-to-gross ratio (N/G), the fraction of rock with enough porosity and permeability to produce. Shale layers, tight rock or water zones are discounted. The net pay, not the total thickness, is what enters the oil and gas volume calculations. Enter the gross thickness and the net-to-gross ratio.
Extraction Yield (Solid)
Compute the yield of a solid-liquid extraction, Y = (extract mass / sample mass)·100%, the fraction of raw material extracted by the solvent. It is used in processes such as the extraction of oils, caffeine, pectin, dyes and bioactive compounds from plant matrices. The yield assesses extraction efficiency and guides the optimization of solvent, temperature, time and solid-liquid ratio. Enter the extract mass and the sample mass.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.