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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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.
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.
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