Water Saturation (Archie)
Compute a reservoir's water saturation (Sw) by Archie's equation (with a=1, m=2, n=2), Sw = √(Rw/(φ²·Rt)), from the formation-water resistivity (Rw), the rock's true resistivity (Rt) and the porosity (φ). It is the fundamental petrophysics equation: it relates the resistivity measured by electric logs to the fraction of pores filled with water — and, by complement (1−Sw), with hydrocarbons. Enter Rw, Rt and the porosity.
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Saturação de água (Archie)
Como saber se uma rocha lá embaixo contém óleo ou só água, sem trazê-la à superfície? A genialidade de Gus Archie (1942) foi perceber que a resistividade elétrica da rocha responde: a água salgada conduz eletricidade, o óleo e o gás não. Sua equação, Sw = √(Rw/(φ²·Rt)) (com os expoentes usuais a=1, m=2, n=2), calcula a saturação de água — a fração dos poros ocupada por água — a partir de três medidas: a resistividade da água de formação (Rw, conhecida da salinidade), a resistividade verdadeira da rocha (Rt, lida pelo perfil de indução) e a porosidade (φ). Uma Rt alta com porosidade boa indica poucos poros condutores — ou seja, pouca água e muito hidrocarboneto (1−Sw). É a equação mais usada da petrofísica, fundamento da interpretação de perfis elétricos de poço. Informe Rw, Rt e a porosidade.
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Leverett J-Function
Calculates the Leverett J-function, which normalises capillary pressure by interfacial tension, contact angle and the square root of the permeability-to-porosity ratio. It collapses capillary pressure curves from samples with different properties onto a single rock-type curve. Enter the capillary pressure, interfacial tension, contact angle, permeability in millidarcy and porosity.
Density-Log Porosity
Compute a reservoir rock's porosity from the density log, φ = (ρma − ρb)/(ρma − ρf), where ρma is the matrix (mineral) density, ρb the bulk density read by the log and ρf the pore-fluid density. It is one of the most used petrophysical methods to estimate porosity in wells, since the bulk density drops as the pore volume (filled by less dense fluid) increases. Enter the matrix, bulk (log) and fluid densities.
Absolute Permeability by the Timur Correlation
Estimates the absolute permeability of a sandstone from porosity and irreducible water saturation, when no core sample is available for laboratory testing. The Timur correlation (1968), fitted on 155 Alaskan sandstone samples, is k = 0.136 × porosity^4.4 ÷ irreducible saturation², with permeability in millidarcy. The result tells how well the reservoir can flow: below 1 mD the formation is considered tight, between 10 and 100 mD it is moderate and above 500 mD it is excellent. The convention that causes most errors here is the unit: the constants 0.136 and 4.4 were fitted with porosity and saturation in percent, not as fractions — entering 0.22 instead of 22 drops the result by several orders of magnitude, which is why both fields ask for percent. Enter the effective porosity and the irreducible water saturation.
Shale Volume from Gamma Ray (Larionov)
Estimates the shale volume of a formation from the gamma ray log, the first step in any petrophysical well evaluation. The calculation normalizes the zone reading between the cleanest sand and the most radioactive shale in the interval, giving the gamma ray index IGR = (GR − GR min) ÷ (GR max − GR min), and then applies the non-linear Larionov curve, Vsh = 0.083 × (2^(3.7 × IGR) − 1). The result is the fraction of rock volume occupied by clay, as a percentage: intervals above 30 to 40% are usually discarded as reservoir, and the value later feeds the porosity and water saturation corrections for shaly sands. The Larionov curve for Tertiary, poorly consolidated rocks was adopted, which is the usual one in young sedimentary basins; for Mesozoic or older rocks the literature uses Vsh = 0.33 × (2^(2 × IGR) − 1), which returns far larger volumes for the same IGR. Enter the zone gamma ray reading, the minimum reading and the maximum reading of the interval.
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.
Saturation Flow
Calculate the saturation flow of a signalized approach, S = S₀ × N, multiplying the base saturation flow per lane S₀ (vehicles/h per lane, typically ~1800–1900) by the number of lanes N. The result, in vehicles/h, is the maximum rate of vehicles that can cross the stop line if the signal stayed green continuously and a queue existed — the queue discharge rate during green. It is a central parameter in signal design and intersection capacity, adjusted by lane width, grade, turning and parking factors. Enter the base saturation flow per lane and the number of lanes.
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.