# How do you find the porosity of a well log?

Category:
science
geology

CNL (compensated neutron)

**logs**: also called neutron**logs**, determine**porosity**by assuming that the reservoir pore spaces are filled with either water or oil and then measuring the amount of hydrogen atoms (neutrons) in the pores. These**logs**underestimate the**porosity**of rocks that contain gas.

Beside this, how do you calculate the effective porosity of a log?

Total **porosity** minus clay-bound water (CBW). **Log effective porosity**. In essence, total **porosity** minus shale water, where solid minerals and the volume of shale (Vsh) constitute the matrix (non-**effective porosity**) and the remaining volume constitutes the **effective porosity**.

**logs**are

**porosity logs**that measure the hydrogen ion concentration in a formation. In clean formations (i.e. shale-free) where the

**porosity**is filled with water or oil, the neutron

**log**measures liquid-filled

**porosity**. Neutrons are created from a chemical source in the neutron

**logging**tool.

Keeping this in view, how do you find the porosity of a density log?

**Obtaining porosities from a density log**

- Φ = porosity.
- ρ
_{ma}= matrix density (see table below) - ρ
_{b}= formation bulk density (log value) - ρ
_{f}= density of the fluid saturating the rock immediately surrounding the borehole—usually mud filtrate (use 1.0 for freshwater and 1.1 for saltwater mud)

There are two basic equations used to **calculate porosity**. The first equation uses the total volume and the volume of the void. **Porosity** = (Volume of Voids / Total Volume) x 100%. The second equation uses the total volume and the volume of the solid.