What is neutron porosity logs?
PetroWiki. The neutron-porosity log first appeared in 1940. It consisted of an isotopic source, most often plutonium-beryllium, and a single detector. Many variations were produced exploiting both thermal and epithermal neutrons. In most of the early tools, neutrons were not detected directly.
How does a neutron porosity log work?
The neutron log is sensitive mainly to the amount of hydrogen atoms in a formation. Its main use is in the determination of the porosity of a formation. The tool operates by bombarding the formation with high energy neutrons.
How do you find the porosity of a neutron log?
Obtaining porosities from a neutron log To obtain porosity, read the value directly from the log. If the log is recorded in limestone units and the formation you wish to evaluate is sandstone or dolomite, then correct the log value by using the appropriate chart in a log interpretation chartbook.
What is porosity logging?
The “Porosity” logs. There are three types of logging tools that are used to estimate the amount of pore space in a rock: the neutron, density, and acoustic velocity (or sonic) tool.
What does neutron porosity measure?
Neutron porosity measurement employs a neutron source to measure the hydrogen index in a reservoir, which is directly related to porosity. The Hydrogen Index (HI) of a material is defined as the ratio of the concentration of hydrogen atoms per cm3 in the material, to that of pure water at 75 °F.
How do you determine 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. Porosity = ( ( Total Volume – Volume of the Solid ) / Total Volume ) x 100%.
What does a neutron density log measure?
In density logs, which measure electron density and transform it into bulk density, porosity is calculated by assuming the matrix density and fluid density. Neutron log measures the ratio of count rate from the rock, which is equivalent to how much hydrogen index it has.
What is density porosity log?
What is density log and its purpose?
Density logs are useful for determining hydrocarbon density and for detecting hydrocarbon gas with low density compared to rock matrix or liquid densities. A low density implies high hydrocarbon gas content, while a high density suggests low hydrocarbon gas content.
How do you calculate porosity from particle density?
A fairly straightforward formula is used as follows: Soil Porosity = ( 1 – (Bulk Density ÷ Particle Density) ) x 100. This will indicate the percentage of the soil that contains pores.
Which log is used to measure porosity accurately?
For clean, shale-free formations, in which the porosity is filled with water or oil, the neutron log measures the fluid-filled porosity.
What are the four types of porosity?
Four basic porosity types can be recognized in sandstones: (1) intergranular (primary), (2) microporosity, (3) dissolution (secondary), and (4) fracture (Figure 2). Intergranular porosity exists as space between detrital grains.
How do you measure porosity?
One way is to measure the pore volume by sealing the sample in a pressure vessel, decreasing the pressure by a known amount, and measuring the increase in volume of the contained gas. Conversely, the grain volume can be measured and, if the bulk volume is known, porosity can be determined.
How is porosity measured?
It is defined as the ratio of the volume of the voids or pore space divided by the total volume. It is written as either a decimal fraction between 0 and 1 or as a percentage. For most rocks, porosity varies from less than 1% to 40%.
What are the two main types of porosity?
Contents
- 1.1 Total porosity.
- 1.2 Effective porosity.
What are the three types of porosity?
There are three levels of porosity: low, medium, and high.
Why do we measure porosity?
The porosity of a material is decisive when evaluating its durability and resistance to adverse conditions. The distribution of pores and their characteristics defines the permeability of the material, that is, its ability to store fluids, thus conditioning its physical and chemical properties.
How do you test the porosity of a material?
How do you calculate porosity?
How do you measure porosity of a metal?
First measure the apparent density da using a parallelepiped block of perfectly known dimensions that you can weigh accurately. da is the ratio of weight to volume. Then use the density of the metal dm and calculated the porosity Fi as Fi = 1 – da/dm.
How can porosity be measured?
6.1. One way is to measure the pore volume by sealing the sample in a pressure vessel, decreasing the pressure by a known amount, and measuring the increase in volume of the contained gas. Conversely, the grain volume can be measured and, if the bulk volume is known, porosity can be determined.
Does porosity affect neutron log response in reservoirs?
Reservoirs whose pores are gas filled may have a lower porosity than the same pores filled with oil or water because gas has a lower concentration of hydrogen atoms than either oil or water. Lithology, porosity, fluid type, and tool type affect neutron log response.
What is neutron logging?
Neutron logging involves the input of neutrons into the strata and the recording of either the reduction in energy of these particles (neutron—neutron logging) or the γ rays emitted from the strata as a result of neutron capture (neutron—γ logging). From: Encyclopedia of Physical Science and Technology (Third Edition), 2003
What are compensated neutron-porosity logging tools?
The now-standard compensated neutron-porosity logging (CNL) tool, in common use since the 1970s, is still a very simple tool. 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.
Why neutron porosity is used for gas detection?
Moreover, the shallow-reading density log frequently is an invaded-zone measurement, completely masking the gas effect on it. Because the neutron porosity is deeper reading, it is often the only log that can be used for gas detection.