What does a gamma ray log tell you?

What does a gamma ray log tell you?

Gamma ray (GR) logs measure the natural radioactivity in formations and can be used for identifying lithologies and for correlating zones. As shale content increases, the gamma ray log response increases because of the concentration of radioactive material in shale.

What is spectral gamma log?

The spectral gamma ray log measures the natural gamma radiation emanating from a formation split into contributions from each of the major radio-isotopic sources. Analysis of the sources of the natural gamma radiation give us added information concerning the composition and likely lithology of the formation.

Why is gamma ray log used as a shale indicator?

Gamma-ray scans of core are also taken to reconcile core depths with log depths. In most stratigraphic and petroleum geological applications, the gamma ray log is used as a “shale log,” both to discriminate shales from “clean” formations, and to estimate the relative shale proportions in shaly reservoir units.

Which of the following from gamma ray log is best indicator of clay content of rock?

Spectral gamma ray logs are most useful in identifying the following: Clay minerals. Illite clays are rich in potassium, whereas smectite and kaolinite contain thorium. The thorium to potassium ratio can distinguish illitic from smectitic shales and so provide a correlation tool.

How do you interpret resistivity logs?

Three depths of resistivity can be logged (shallow, medium, and deep) that record the resistivity of the formation with increasing distance away from the borehole. Resistivity logs can be interpreted to infer information about the porosity of a formation, the water saturation, and the presence of hydrocarbons.

What is the value of gamma ray?

Gamma rays are electromagnetic radiation, generally in the energy range 0.1 to 100 MeV. As light, this would correspond to very short wavelengths indeed. The difference between gamma rays and X-rays is largely semantic because they overlap in energy.

What is porosity log?

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. So, the log is mainly a measure of hydrogen concentration (mostly contained by the pore fluids of the formation).

What is gamma API?

The gamma ray API unit is defined as 1/200 of the difference between the count rate recorded by a logging tool in the middle of the radioactive bed and that recorded in the middle of the nonradioactive bed.

What is mCi measurement?

One curie is a large amount of radioactivity. Commonly used subunits are mCi (millicurie), µCi (microcurie), nCi (nanocurie), and pCi (picocurie). 1 Ci = 1000 mCi; 1 mCi = 1000 µCi; 1 µCi = 1000 nCi; 1 nCi = 1000 pCi.

How do you read porosity logs?

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.

How do you read well log data?

Follow the Ko Ko Rules:

1. Tight non-reservoir: Right-Right-Right-Right.
2. Shale: Right-Right-Right-Left.
3. Low porosity (tight) reservoir: Left-Right-Right-Right.
4. Water bearing reservoir: Left-Left-Left-Left.
5. Oil bearing reservoir: Left-Right-Left-Left.
6. Gas reservoir: Left-Right-Left-Right.

What does the gamma ray log measure?

The gamma raylog measures the total natural gamma radiation emanating from a formation. This gamma radiation originates from potassium-40 and the isotopes of the Uranium-Radium and Thorium series. The gamma ray log is commonly given the symbol GR.

What is a gamma ray detector and how does it work?

Unlike all other nuclear tools (and, in fact, all other logging measurements), it is completely passive. It emits no radiation. Instead, it simply detects incoming gamma rays from the formation and (unfortunately) the borehole. Gamma rays are electromagnetic radiation, generally in the energy range 0.1 to 100 MeV.

How do log analysts look for formations with low radiation?

Log analysts look for formations with low background radiation because they have the potential to contain moveable hydrocarbons. Resistivity tools measure the formation at different depths of investigation. The resulting log presents shallow-, medium- and deep-reading curves.

Why quality control all of the spectral ray logs?

It is imperative to quality control all of the logs, for bad readings and pick-up effects, before doing any quantitative work. Most interpretations of spectral-gamma ray logs focus on the relationships between the three elemental concentrations. In particular, Th/K and Th/U are often used for petrophysical interpretation and log correlation.