What does a neutron porosity log measure?

Like a density tool, it consists of an isotopic source (now most often americium-beryllium, although at least one tool uses an accelerator source) and two neutron detectors. The tool measures the size of the neutron cloud by characterizing the falloff of neutrons between the two detectors.

What log measures porosity?

neutron log
For clean, shale-free formations, in which the porosity is filled with water or oil, the neutron log measures the fluid-filled porosity. Because gas has a much lower hydrogen density than oil or water, gas-filled porosity appears as low porosity.

How does density log work?

A density-logging tool sends gamma rays into a formation and detects those that are scattered back. At this high energy level, Compton scattering dominates. The average electron density in the volume of formation probed by the tool controls the scattered gamma ray count rates at the detectors.

How is porosity of formation calculated?

Obtaining porosities from a density log

1. Φ = porosity.
2. ρma = matrix density (see table below)
3. ρb = formation bulk density (log value)
4. ρf = 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)

How do you find effective porosity?

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.

How do you determine porosity?

Porosity = ( ( Total Volume – Volume of the Solid ) / Total Volume ) x 100%. A larger percentage means that the rock has the ability to hold more water.

What is the unit of porosity?

Porosity is also known as “pore space.” The weight of an individual soil particle per unit volume. Particle density is usually expressed in units of grams per cubic centimeter (g/cm2).

What are neutron logs?

Neutron Log is a neutron porosity log which measures the concentration of hydrogen ions in a hydrocarbon formation. When the neutrons collide with the hydrogen nuclei, they deflect back and slow down. These slowed down neutrons are detected and an apparent neutron porosity log is obtained.

What is PEF log?

1. n. [Formation Evaluation] A log of photoelectric absorption properties. The log measures the photoelectric absorption factor, Pe, which is defined as (Z/10) 3.6 where Z is the average atomic number of the formation.

Why double detector is used in density log?

To overcome the problems of mudcake and hole irregularities, the new compensated formation density logging device employs two detectors spaced at different intervals from the source. The detector at the shorter spacing is particularly sensitive to the density of material immediately adjacent to the face of the pad.

How do you calculate reservoir porosity?

The porosity of a rock is a measure of its capacity to contain or store fluids. Porosity is calculated as the pore volume of the rock divided by its bulk volume. In Eq. (1.2), f = porosity; Vp = pore volume; and VB = bulk volume.