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 does density log work?
The density log measures the electron density of a formation. The logging device is a contact tool that emits gamma rays from a source. Emitted gamma rays collide with formation electrons and scatter. A detector, located a fixed distance from the tool source, counts the number of returning gamma rays.
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.
What is compensated density log?
1. n. [Formation Evaluation] A density log that has been corrected for the effect of mud and mudcake by using two or more detectors at different spacings from the source. The shorter the spacing, the shallower the depth of investigation and the larger the effect of the mudcake.
What is well logging and its purpose?
A well log is a record of the formations and any events that are encountered in the well drilling process. It is also referred to as borehole logging. The main purpose of keeping a well log is to determine the suitability of the well for its intended use.
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.
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 compressional slowness?
A technique for recording the formation compressional slowness based on the transit time between transmitter and receiver. The time between emission and reception is measured for each receiver, and subtracted to give the traveltime in the interval between the two receivers.
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.
Why do we log borehole?
Borehole-geophysical logging can provide a wealth of information that is critical in gaining a better understanding of subsurface conditions needed for ground-water and environmental studies. Geophysical logs provide unbiased continuous and in-situ data and generally sample a larger volume than drilling samples.
What is a density log?
Density logs have long been used for determing the bulk density of of the formations being logged. Today the density logging tool emits gamma rays from a source at the bottom of the tool. The gamma rays emitted by the source penetrate the rocks as the tool passes by where some are absorbed.
How many detectors are used in density logging?
In a similar way to how the sonic logging tool was improved to compensate for borehole effects, density logging now conventionally uses 2 or more detectors.
How do you find the probability density of a lognormal distribution?
Probability Density Function A variable Xis lognormally distributed if (Y = ln(X)) is normally distributed with “LN” denoting the natural logarithm. The general formula for the probability density functionof the lognormal distribution is
What does the density log of coal tell you?
In addition, the density log may provide information on the rank of the coal, that is, high-rank coal is denser than low-rank coal. The output of the gamma ray source and the gamma ray detector is sometimes confused with the natural gamma ray detector discussed in the previous section.
