How do you find the porosity of a well log?

The most common method of determining porosity is with Well Logs.

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1. ϕ_sl is the porosity from the sonic log (log measurement) , fraction.
2. Δt_sl is value of the acoustic transit time measured by the sonic log, μsec/ft.
3. Δt_ma is value of the acoustic transit time of the rock matrix measured in the laboratory, μsec/ft.

What is porosity in well 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.

How do you find the porosity of a density log?

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.

How do you find the porosity of a neutron log?

Φ = porosity. ρ_ma = matrix density (see table below) ρ_b = formation bulk density (log value)



Obtaining porosities from a density log.

How do you read well log data?

https://youtu.be/
The first thing when you look at a well log you should look at the very top to see what logs will run on log number one we see in the lithology. Track track one a spontaneous.

What is oil well porosity?

Porosity consists of the tiny spaces in the rock that hold the oil or gas. Permeability is a characteristic that allows the oil and gas to flow through the rock.

What is DT in well logging?

DT. Short-spacing delay time ( t) µs/ft.

What is formation porosity?

Porosity is defined as the ratio of the volume of pores to the volume of bulk rock and is usually expressed as a percentage.

What is sonic porosity?

The sonic or acoustic log measures the travel time of an elastic wave through the formation. This information can also be used to derive the velocity of elastic waves through the formation. Its main use is to provide information to support and calibrate seismic data and to derive the porosity of a formation.

How do you find the porosity of a rock sample?

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 slowness in sonic logging?

ADVERTISEMENT. A sonic log is an acoustic log that emits sound waves which start at the source, travel through the formation, and return back to the receiver. The travel time from the source to the receiver is called slowness and as a result sonic logs are sometimes referred to as sonic slowness logs.

What is electric logging?

Electric logging consists of lowering a device used to measure the electric resistance of the rock layers in the downhole portion of the well. This is achieved by running an electric current through the rock formation and measuring the electrical resistance that the current encounters along its way.

What is fluid logging?

Detailed Description. Fluid-resistivity logs record the electric resistivity of water in the borehole. Changes in fluid resistivity reflect differences in dissolved-solids concentration of water. Fluid-resistivity logs are useful for delineating water-bearing zones and identifying vertical flow in the borehole.

What is compressional slowness?

Compressional slowness (DTCO) and shear slowness (DTSM) are two fundamental parameters that have many applications in petrophysical, geophysical, and geomechanical operations. These two parameters can be obtained using a dipole sonic imaging tool, but unfortunately this tool is run in just a few wells of a field.

What is dipole sonic log?

A sonic array tool in which sources are dipoles as opposed to radially symmetric monopoles, so that it generates both P- and S-waves in formations. Analysis involves mode identification and analysis of dispersion curves and yields both P- and S-wave velocities.

How do I read sonic logs?

https://youtu.be/
Remember that gas in the formation will tend to slow the sonic waves resulting. In the log reading more than true porosity.

What is sonic log in geophysics?

Sonic logging is a well logging tool that provides a formation’s interval transit time, designated as , which is a measure of a how fast elastic seismic compressional and shear waves travel through the formations.

How does density log work?

Density logging tools. A density-logging tool sends gamma rays into a formation and detects those that are scattered back. Typical logging sondes use a Cesium-137 source, which emits gamma rays of 0.66MeV. At this high energy level, Compton scattering dominates.

How do you read gamma ray well logs?

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The gamma ray log is scaled in gamma API units of radioactivity. With high readings causing a deflection of the curve to the right and low radioactivity causing a deflection to the left thus.

What do resistivity logs measure?

Resistivity logging is a method of well logging that works by characterizing the rock or sediment in a borehole by measuring its electrical resistivity. Resistivity is a fundamental material property which represents how strongly a material opposes the flow of electric current.

What is the resistivity formula?

Resistivity, commonly symbolized by the Greek letter rho, ρ, is quantitatively equal to the resistance R of a specimen such as a wire, multiplied by its cross-sectional area A, and divided by its length l; ρ = RA/l. The unit of resistance is the ohm.

Which value does a resistivity log record?

The resistivity log. Resistivity logs measure the ability of rocks to conduct electrical current and are scaled in units of ohm-meters.

What is Archie equation?

1. n. [Formation Evaluation] A particular relation proposed by G.E. Archie between the formation factor (F) and porosity (phi), in which F = 1 / phi^m, where the porosity exponent, m, is a constant for a particular formation or type of rock.

How do you use Archie’s equation?

The Archie Equation

1. S_w = [ (a / F^m)*(R_w / R_t) ]^(1/n)
2. S_w: water saturation.
3. F: porosity.
4. R_w: formation water resistivity.
5. R_t: observed bulk resistivity.
6. a: a constant (often taken to be 1)
7. m: cementation factor (varies around 2)
8. n: saturation exponent (generally 2)

How do you find the saturation of an exponent?

The exponent, n, in the relation of water saturation, S_w, to resistivity index, I (I = S_w^–n) for a sample of rock. It expresses the effect on the resistivity of desaturating the sample, or replacing water with a non-conductive fluid.

Why Archie equation is important?

Archie’s equation immediately transformed resistivity well-logs from a qualitative indication to the presence of gas and/or oil in sandstone and carbonate formations to a quantitative determination of the hydrocarbons in place.

What is cementation factor?

The cementation factor, sometimes referred as cementation exponent or porosity exponent, has been accepted as a measurement of the degree of cement and consolidation of the rock, as well as it is a measure of the tortuosity of the pore geometry of current flow.

What is saturation exponent?

The saturation exponent models the dependency on the presence of non-conductive fluid (hydrocarbons) in the pore-space, and is related to the wettability of the rock. Water-wet rocks will, for low water saturation values, maintain a continuous film along the pore walls making the rock conductive.

What is water saturation?

1. n. [Formation Evaluation] The fraction of water in a given pore space. It is expressed in volume/volume, percent or saturation units. Unless otherwise stated, water saturation is the fraction of formation water in the undisturbed zone.

How do you calculate connate water saturation?

Connate water saturation is the amount of the water which adsorbs on the surface of the grains of the rock or on the walls of the porous pore channels (immobile with the traditional displacement methods) divided by the pore volume.

How do you calculate saturation of water?

The basis of Archie’s equation (Archie, 1942), conventionally used to calculate the water saturation of a formation, is that the conductivity of the formation is a function of the conductivity of the fluid content in its pore space and therefore the equation can be written in terms of conductivity as:(1) S w = [ ( a ∗ …