Sediment Porosity Calculator

Porosity and pore volume

Porosity (n) expresses the fraction of a sediment volume occupied by voids. In a 50 cm³ specimen, a porosity of 0.37 corresponds to 18.5 cm³ of connected and isolated pore space. This directly relates to fluid storage and reagent contact area in chemical extractions, leaching tests, and contaminant desorption experiments. In batch tests, higher pore volume can dilute solutes, affecting measured concentrations and the apparent distribution coefficient for metals or nutrients.

Laboratory measurement workflow

Common workflows estimate void volume from water saturation, gravimetric moisture, or displacement methods. For saturated samples, void volume can be approximated from water mass divided by water density at the measurement temperature. Recording temperature, salinity, and drying protocol improves comparability across runs and reduces systematic bias in mass and volume readings. For partially saturated cores, compute degree of saturation separately so porosity is not confused with moisture content reported on a dry-mass basis.

Density-based estimation

The density-ratio approach uses n = 1 − (ρ_b/ρ_s). Bulk density (ρ_b) reflects solids plus pore space, while particle density (ρ_s) reflects only the mineral framework. With ρ_b=1.70 and ρ_s=2.65 g/cm³, porosity is 0.358. Quartz-rich sands often cluster near ρ_s≈2.65 g/cm³, while heavier minerals increase ρ_s and can shift porosity estimates. If you switch to kg/m³, keep both densities in kg/m³; the ratio cancels units, but mismatched units will distort n severely.

Uncertainty and quality checks

Small errors in total volume propagate into porosity. A ±0.5 cm³ uncertainty on a 50 cm³ volume is ±1%. For the 18.5/50 example, that can change porosity by about ±0.4 percentage points. Verify that V_v ≤ V_t, densities are positive, and ρ_b does not exceed ρ_s. Repeated measurements and averaging reduce random error. When results are used in mass-balance models, report figures and include calibration details for balance, pycnometer, and cylinders.

Interpreting results in context

Higher porosity generally indicates looser packing, better permeability, and greater accessible surface for aqueous chemistry, but it does not guarantee connectivity. Clay-rich sediments may show moderate porosity with low permeability due to small pore throats. Pair porosity with grain-size distribution, organic content, and saturation state when comparing samples or predicting transport behavior.

FAQs

1) What is sediment porosity?

Sediment porosity is the fraction of a sample’s total volume occupied by voids (pores). It is dimensionless and is commonly reported as a percentage for easier comparison.

2) Which method should I use?

Use the void/total volume method when you measured pore volume directly. Use the density-ratio method when you have bulk and particle densities, or when you can derive bulk density from dry mass and total volume.

3) Why can particle density vary?

Particle density depends on mineral composition. Quartz-rich samples often sit near 2.65 g/cm³, while carbonates, heavy minerals, or porous grains can shift the value and change the porosity estimate.

4) Can porosity be above 70%?

It can occur in very loose, organic, or highly vesicular materials, but it is uncommon for many sediments. Values above 70% should trigger unit checks and verification of volume and density measurements.

5) Does porosity equal permeability?

No. Porosity measures how much pore space exists, while permeability reflects how well pores connect for flow. Fine-grained sediments can have notable porosity yet low permeability because pore throats are small.

6) How do I improve measurement accuracy?

Use consistent units, calibrate glassware, record temperature, and repeat measurements. For density calculations, ensure the sample is dried to a defined endpoint and that total volume represents the intact bulk sample.