Purchase of an open document does not constitute license for republication in any form, nor does it allow web posting without prior written permission. The gamma log often is used to define lithology and correlate geologic units between boreholes. Interpretation of porosity and fluid constituents from. The time constant and logging speed therefore influence both the bed resolution and the amount of noise recorded on the gamma ray log. These include resistivity logs, as well as the creation of density, sonic, and other types of logs. Spontaneous potential sp and gamma ray logs are discussed first, as their primary use is correlation and their. Application of this method of interpretation is useful in uranium, oil and other minerals exploration when gamma ray logging is used.
Measurement of natural emission of gamma rays in oil and gas wells are useful because shales and sandstones typically have different gamma ray levels. A morrow sandstone resistivity image interpretation. The spectral gammaray log geological log interpretation. Spectral gamma ray measurements offer several advantages. Our gamma instruments can be fitted quickly and easily to both digital and analogue tool systems. It is a wireline logging method used in mining, mineral exploration, waterwell drilling, for formation evaluation in oil and gas well drilling and for other related purposes. Gammaray logging has evolved from a qualitative estimation of the variation of natural radioactivity with depth in a borehole, using a geigermuller detector, to a sophisticated quantitative logging technique which yields information on the identification and amount of the radioelements present, as well as data on the likely geologic history. Gamma rays have significantly high penetrations and can be measured by simple devices such as geiger counters or scintillation detectors on logging tools. Lwd tool includes two gamma ray detectors and a thermalneutron detector that have different depths of.
Spectral gamma ray logs are most useful in identifying the following. In the field of wireline logging, there are a number of different records and reports that must be generated. Field gammaray patterns and stratigraphic reinterpretation. The right half of the image shows a density neutron log with gamma ray gr and caliper cal in track 1.
Preeg2 abstract neutron and density logs are important borehole measurements for estimating reservoir capacity and infer. Scintillation counters are relatively small devices, which means that the gamma ray tool can have a high vertical resolution. The gamma ray tool was the first nuclear log to come into service, around 1930 see fig. In particular, thk and thu are often used for petrophysical interpretation and log correlation. To understand the physical principles behind the operation of spontaneous gamma ray logging tools, 2. To learn how to interpret gamma ray logs in terms of clastic lithology, shale content, grain size, and some other petrophysical properties, 3. Pdf interpretation of gammaray logs of the stratified. Gamma rays have longer penetrations than either alpha or beta rays, and can be measured by simple counter devices, such as a geiger counter.
The latest variant on the gamma ray log is the spectral gamma ray log. Because elements excited by neutrons emit characteristic gamma rays, such spectra can be analyzed for elemental concentrations. Before you can start interpreting spectral gamma ray logs or, indeed, any kind of data, you need to ask about quality. Gamma ray log lithology log measures natural radioactivity. Nuclear log interpretation is simply the practice of solving toolresponse mixinglaw equations with the judicious application of some assumptions and. Hudson abstract the relation of formation factor to resistivity of formation water and intergranular permeability has often been investigated, and the general consensus is that this relation is closest. Magnetic susceptibility and natural gamma ray intensity are useful parameters for establishing highresolution lithological correlations at a basin scale. Spontaneous potential and natural gamma ray logs the spontaneous potential sp curve and the natural gamma ray gr log are recordings of naturally occur ring physical phenomena in insitu rocks. While the gamma ray log traditionally has been used primarily for welltowell correlation, it also plays a role in quantitative log analysis. The formation evaluation gamma ray log is a record of the variation with depth of the natural radioactivity of earth materials in a wellbore.
If highprecision spectral gamma ray measurements are needed, reduced logging speed is required. Interpretation of gamma ray logs of the stratified oil shale seam in the attarat um ghudran deposit, central jordan article pdf available in oil shale 334. As with all ussr logs, the interpretation and correction of these logs to api units is not straightforward. Sedimentary facies interpretation of gamma ray gr log as basic well logs in central and lower indus basin of pakistan. The purpose of this discussion is to furnish a working reference for the interpretation of gamma ray logs for uranium exploration. The image orientation is marked at the top of the image log, with south in the center 180 degrees and north to the right and left zero and 360 degrees. Through this log we can determine the caving size and wash outs. Neutron porosity logs measure the number of pores in drilled section.
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. Because these elements are present in shale but usually absent in siliceous ss and. Silica content and gamma ray logs in volcanic rocks valgardur stefansson, steinar thor gudlaugsson, and asgrimur gudmundsson orkustofnun, grensasvegur 9, 108 reykjavik, iceland key words. The energy levels of the gamma rays are characteristic of their source isotope and form distinctive spikes on a gamma ray emission spectrum, although in practice these spikes. The potassiumthorium crossplot is useful for the recognition of clay minerals and distinction of micas and kfeldspars. Before you can start interpreting spectral gammaray logs or, indeed, any kind of data, you need to ask about quality. Interactive petrophysics part iii burmesegeologists blog. The counts recorded on a standard gamma ray log are the sum of all gamma rays, most of which are emitted by potassium40 and isotopes in the uranium and thorium series. The first gamma ray logs were run by lane wells in 1936.
Now that we know how the tools work, we are ready to discuss how gamma ray logs are used in log analysis. Structural interpretation fault recognition gamma ray response to grain size 48. Clay and shale formations exhibit greater amounts of gamma radiation. Most interpretations of spectralgamma ray logs focus on the relationships between the three elemental concentrations. 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. Normally, your reservoir will give low gamma ray reading. Gamma ray tool response an empirical relationship between potassium content and gamma ray api units is reproduced below for the standard gamma ray logging conditions of 8 borehole, 10 lbgal mud and 3 58 scintillation nai detector type tool. Welllogging correlation analysis and correlation of well. Gamma ray logs are used primarily to distinguish clean, potentially productive intervals from probable unproductive shale intervals. Geological survey editorial standards and nomenclature. The service companies have charts and computer programs that can help in the selection of logging speeds to achieve specific precisions.
The sp curve records the electrical potential voltage produced by the interaction of formation connate water, conductive drill ing fluid, and certain ionselective rocks. The count rate is also smoothed by the logging speed of the tool as it is raised through the borehole. Pdf geological interpretation of spectral gamma ray sgr. Scribd is the worlds largest social reading and publishing site. The principle gammaray log shapes are frequently used for interpreting sedimentary cycles or depositional facies. Use of geophysical logs to estimate the quality of ground water and the permeability of aquifers by j. Crains petrophysical handbook natural and spectral. Many of these isotopes are unstable and decay to a more stable form, while emitting radiation of several types. We present a correlation parameter established from a simultaneous analysis of the susceptibility and the gamma ray logs within each well. Kgsgeological log analysisresistivity image logging.
The geotech gamma ray logging system gr is a portable, handoperated geophysical instrument used in exploration for uranium, potash, and base metals, as well as for petroleum and ground water. But first, you need to understand the reasons we run any well logs. Spwla 54th annual logging symposium, june 2226, 20 1 determination of formation organic carbon content using a new neutroninduced gamma ray spectroscopy service that directly measures carbon jorge gonzalez, richard lewis, james hemingway, jim grau, erik rylander and ryan schmitt, schlumberger. A sample spectrum for total gammaray measurements of the core samples from a local well logging. Radioactive isotopes of elements continuously decay to more stable forms and emit radiation of several types. Then, by looking at how the curve deflects relative to each other, you can tell the difference between oil, gas and water. Spwla 54th annual logging symposium, june 2226, 20 1 multidetector lwd sigma logging principles, petrophysical applications, and environmental effects edwin ortega, and carlos torresverdin, the university of texas at austin, william e. A majority of the elements are found in a variety of isotopic forms.
The gr identifies lithologys and stratigraphic correlations in boreholes case or uncased, liquid or air filled. To make it work, you need to have gamma ray log, resistivity logs, density and neutron logs plotted on the same log plot respectively. The ecs sonde, which is a short, simpletouse logging tool, measures and processes gamma ray spectra, or the number of gamma rays received by the detector at specific energy levels. The method was tested using gamma ray logs and potash assays from boreholes. A final class of neutron logs, neutroninduced gamma ray logging, records the energy spectra of the induced gamma rays. Gamma ray log shamshad ppt free download as powerpoint presentation. Crains petrophysical handbook crains rules for visual. Sedimentary facies interpretation of gamma ray gr log as. Spontaneous potential sp and gamma ray logs are discussed first, as their primary use is correlation and their primary interpretive target is gross lithology the. Gamma ray logging is a method of measuring naturally occurring gamma radiation to characterize the rock or sediment in a borehole or drill hole. Pdf sedimentary facies interpretation of gamma ray gr log. So, there you go the six ko ko rules in well log interpretation. Lithostratigraphic reinterpretation of the main subsurface gammaray data of 14a1 welllog through composite gammaray log of outcrops.
The main issues affecting the quality of the logs are tool calibration and drilling mud composition. Gamma ray gr record intensity of radioactive source clay minerals as major component presented in mineralogical composition of rock section. The gamma ray log read a value of around 150gapi for zones 1 and 2. The top of the sequence contains a thin sand body with high permeability based on the gamma ray and sp logs. Well log interpretation gamma ray log 1 well log interpretation gamma ray log earth environmental science university of texas at arlington 2 gamma ray log the gamma ray tool measures natural radiation from the rock which primarily comes from k, sr, u, th. The average grade of a bed is then determined by dividing by the overall bed thickness, which can also be obtained from the gamma ray log. Caliper log caliper log use to measure the hole size. The measurement is used to locate shale beds and quantify shale volume. Geophysical characterization and borehole geophysical. The image log section corresponds to the interval marked as image on the gamma ray log. The rationale behind this interpretation is that variations in the gr are related to the presence of organic matter that sequesters radioactive minerals responsible for the gr signal.
The radioactive particles like uranium, potassium, thorium are very fine grains. Its measure the intensity of natural radioactivity of rocks. Ppt well log interpretation gamma ray log powerpoint. This starts out exactly the same as the standard gross gamma ray count log. Common applications of the spectral gamma ray log are in the estimation of clay mineral volumes and types, and the recognition of fractures that have had uranium salts precipitated in them by groundwater systems. Open hole wireline logging gr api gamma ray tool the gamma ray log typical applications determination of reservoir thickness lithology indicator correlation between wells estimation of shale volume principle of measurement the gr log is a recording of the count rate of at gamma emissions from rock formations adjacent to the borehole. Photo electric effect pe is in track 2 with neutron porosity phin and density porosity phid spread across tracks 2 and 3. Gamma ray log interpretation southwest exploration services. In this enhancement to natural gamma ray logging, the energy levels of incoming gamma rays are counted in a series of energy windows, and an algorithm converts the energy spectrum to count rates for potassium %, thorium ppm, and uranium ppm. High gamma ray reading most probably indicates shale zones or non reservoir rocks.
In the analysis of spectral gamma ray data, use is commonly made of the ratios of the abundances of the main radioactive sources. Interpretation of gamma log data is done based on the relative low and high count rates. Ip has a lot of builtin tools like curve editing, merging, depth shifting, histogram and crossplotting for quality controlling the log curves, i will not explain detailed on these things that it will depend on individual log. Gamma ray log interpretation southwest exploration. In well logs, in addition to the concentrations of the three individual radioactive elements, a total standard gammaray curve is usually.
Second, once you have located your reservoir, then you want to. It was hailed as a great advance over the sp log because its value does not depend on mud or formation water resistivity. Crains petrophysical handbook natural and spectral gamma. This week, i would like to explain about environmental corrections on gamma ray gr and density rhob curves. Gamma ray log shamshad ppt materials chemical substances.
Hudson abstract the relation of formation factor to resistivity of formation water and intergranular permeability has often been investigated, and the general consensus is. Gamma ray response as a proxy for grain size variation in gr log character is interpreted to be a proxy for grain size and so enable these logs to play a major role in the sequence stratigraphy analysis. Spectral gamma logging evaluate shale organic content and well placement with azimuthal borehole coverage the spectralwave spectralazimuthal gamma ray sensor provides azimuthal gamma ray borehole images, precise total gamma ray, and realtime potassium, uranium, and thorium k, u, th data. The gamma ray log is combinable with all tools, and is almost always used as part of every logging. It was updated by indiana geological survey igs personnel on may 9, 2012 to add new data and to include existing locations of wells with sample only designations rotary cuttings or cores that were formerly excluded. Gamma log records the natural gamma radiation emitted from rocks penetrated by the borehole. Boundary of permeable and non permeable zone is recorded by sp log. The log trend is boxcar with only minor gradations in texture. These measurements allow for more accurately defining the clay content, mineralogy, and matrix properties of. It looked similar to an sp log and was easy to use in correlating zones from well to well. How to easily read a well log in 5 minutes or less using. Examples of gamma ray log interpretation using this method are given.
Author links open overlay panel adeel nazeer a shabeer ahmed abbasi b. A log of gamma radiation in counts or api units will give a positive indication of the type of lithology. Pdf on jan 1, 2016, jolanta klaja and others published geological interpretation of spectral gamma ray sgr logging in selected boreholes find, read and cite all the research you need on. With these rules, you are able to read any logs in no time, and figure out your own. Gamma logging tools asl gamma tools consist of a robust pressure house, containing a sensitive scintillation detector and high temperature electronics which sends pulses representing detected gamma radiation to surface. In most stratigraphic and petroleum geological applications, the gamma ray log is used. Well logging correlation analysis and correlation of well logs in rio grande do norte basin wells. To conceptually understand when and when not gamma ray logs are indicative of shaleclay concentration, 4. There are discussions and topics included which obviously are not needed for field or even office use. The tool consists simply of a highly sensitive gamma ray detector in the form of a scintillation counter. Comparison of magnetic and gamma ray logging for correlations.
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