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.
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Density-log porosity
The density log is one of the main tools for measuring porosity in a well. A radioactive source emits gamma rays that interact with the electrons of the rock; the denser the rock, the more rays get scattered, and the fewer photons come back to the detector, which reads out as the bulk density (ρb). Porosity follows from φ = (ρma − ρb)/(ρma − ρf): the real rock (ρb) is a mixture of the solid matrix (ρma, ~2.65 for sandstone, ~2.71 for limestone) with the fluid filling the pores (ρf, ~1.0 for water, lower for oil or gas). The more pore space filled with light fluid, the further the bulk density falls below the matrix value — and that drop measures porosity directly. Combined with the neutron log, it also helps identify the fluid type and the lithology. Enter the matrix, log and fluid densities.
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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.
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.
Sintering Relative Density
Compute the relative density of a sintered body, RD = (bulk density/theoretical density)·100%, the fraction of the maximum density (of the fully dense, pore-free material) the piece reached. It is the central measure of the degree of sintering: advanced ceramics aim for RD above 99% (almost pore-free) for maximum strength and properties. The residual porosity is 100% − RD. Enter the bulk (sintered) density and the theoretical density.
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.
Planting Density Calculator
Calculate plants per hectare from row spacing and plant spacing. Essential for agricultural planning.
Slurry Volumetric Concentration
Calculate the solids volumetric concentration in a slurry, C_v = (ρ_m − ρ_w) ÷ (ρ_s − ρ_w), from the mixture density ρ_m, the solids density ρ_s and the water density ρ_w (kg/m³). Volumetric concentration is the fraction of total slurry volume occupied by solids — the fundamental hydraulic-transport parameter. It is the inverse of the mixture-density calculation: in practice the slurry density in the pipe is measured (with a nuclear gauge, measuring gamma-ray attenuation through the pipe) and, knowing the water and solid densities, the solids concentration being transported is computed in real time. Volumetric concentration defines a dredge's or pipeline's PRODUCTION (solids volume transported = flow × C_v), and it is the parameter the operator seeks to MAXIMIZE (more solids per pumped water = more production and less energy per tonne) without exceeding the limits that cause clogging or excessive wear. Typical dredging volumetric concentrations are 10-30%; in optimized pipelines, up to 40-50%. Concentration control is the heart of hydraulic-transport operation. Enter the mixture density, the solids density and the water density.
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.