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. As with all ussr logs, the interpretation and correction of these logs to api units is not straightforward. Muhammad shamshad gadi institute of geology university of punjab, lahore. Because the cgr is the summation of thorium and potassium sources, this curve is an improved log to estimate clay content, free of perturbations by uranium. One or more radioactive isotopes tag the various materials sent downhole. Because we use gamma ray logs as relative measures, precise calibration is not very important except as a visual log display feature. Applied to smeks field, offshore western niger delta olumuyiwa odundun1. Gamma ray log shamshad ppt materials chemical substances. The purpose of this discussion is to furnish a working reference for the interpretation of gammaray logs for uranium exploration. Natural gamma ray logs have been used systematically in iceland for the last.
Soon this was followed by the neutron log and a number of other. Thus, the principal aims of this paper are 1 to summarize the relationship between spectral gammaray logs, gross lithology and stratigraphic architecture for all sites drilled on leg 150, and 2 to critically assess the use of spectral gammaray. Because these elements are present in shale but usually absent in siliceous ss and. There are discussions and topics included which obviously are not needed for field or even office use. The scientific world journal hindawi publishing corporation. The api nuclear calibration facility is located on the campus of the university of houston, houston, texas. To understand the physical principles behind the operation of spontaneous gammaray logging tools, 2. In the field of wireline logging, there are a number of different records and reports that must be generated.
Formations under consideration are unconsolidated to poorly consolidated. Measurement of natural emission of gamma rays in oil and gas wells are useful because shales and sandstones typically have different gamma ray levels. In the junggar basin, northwest china, many high gammaray gr sandstone reservoirs are found and routinely interpreted as mudstone nonreservoirs, with negative implications for the exploration and exploitation of oil and gas. The method of interpretation of downhole magnetic measurements yielded a magnetostratigraphy within each well, allowing absolute dating and time correlations between the wells. Ppt well log interpretation gamma ray log powerpoint. Natural gamma rayneutron porosity logging by michael p. Formation evaluation and well log correlation swapnil pal imt geological technology indian institute of technology roorkee 2.
The gr identifies lithologys and stratigraphic correlations in boreholes case or uncased, liquid or air filled. The gamma ray log was the first nuclear well log and was introduced in the late 1930s. Older tools were recorded in counts or as equivalent weights of radium per ton. These include resistivity logs, as well as the creation of density, sonic, and other types of logs. Logging is a general term which means to make a record of something. Pdf total and spectral natural gammaray logs of core. Sedimentary facies interpretation of gamma ray gr log as basic well logs in central and lower indus basin of pakistan. Gamma ray log interpretation southwest exploration. Plot of gammaraythickness versus k2o gradethickness in potash zones in 7 wells near carlsbad, new mexico data set 1. Gamma ray logg ing is a method of measuring naturally occurring gamma radiation to characterize the rock or sediment in a borehole or drill hole. Detail of interpreted facies is given below and facies interpretation is given in fig.
The second data set used in this study incorporates gammaray logs and k2o analyses from the pseries of wells, in which the gammaray log was recorded in cps rather than api units. All wells were drilled with oilbase mud obm, logged with triplecombo tools, and sampled with whole and sidewall cores. Comparison of welllogging and laboratory measurements of the total gammaray natural radioactivity of the core samples from a local field well for. The natural gamma ray logging tools provide increased detection efficiency with spectral processing to significantly improve measurement precision and reduce environmental corrections. Crains petrophysical handbook basic physics natural. Crains petrophysical handbook natural and spectral. Modern gammaray detectors of the type used in this study are extremely sensitive and detect nearly all of the gamma photon interactions with. 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. Facies interpretation is based on grain size analysis using gr logs as shown in fig. Pdf sedimentary facies interpretation of gamma ray gr. The spectral gammaray log geological log interpretation. An empirical relationship between effective 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 typical of the 1960 1980 era.
Society of professional well log analysts annual logging symposium, 27th, dallas, tex. Lanewells now atlas wireline services introduced gammaray logging to the oil industry in 1939, employing an ionization chamber as a detector. The gamma ray log well logging pete 3036 fall 2012 introduction the first gammaray logs were run in 1936 by j. All modern logs are scaled in terms of the api american petroleum institute gamma ray unit. Rack5 abstract the newly installed multisensor track mst natural gamma ray activity spectrometer should provide a powerful way to. 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. Different types of rock emit different amounts and different. To learn how to interpret gammaray logs in terms of clastic lithology, shale content, grain size, and some other petrophysical properties, 3. The tool is calibrated to an api standard well resident in the university of houston, texas. Brown and steven anderson groundwater division resource planning department. Shales and clays are responsible for most natural radioactivity, so gamma ray log often. The classical approach is to use the grl to distinguish between pure sandstone and shale.
Gamma ray logging is a method of measuring naturally occurring gamma radiation to characterize the rock or sediment in a borehole or drill hole. From a spectral log that separates the different isotopes, engineers establish the vertical zones of each of the different phases of the treatment. Geophysical well logging was first developed for the petroleum industry by marcel and conrad schlumberger in 1927 figure 1. Sensitivity to the barite content of mud is eliminated by using only the highenergy gamma rays for analysis. The technique of measuring the spectrum, or number and energy, of gamma rays emitted as natural radioactivity by the formation. Geoscientists use many types of logging including corelogging, cuttingslogging, petrophysical logging and geophysical well logging. Gammaray logging through drill pipe can reduce the gammaray radioactivity by as much as 30%. The formation evaluation gamma ray log is a record of the variation with depth of the natural radioactivity of earth materials in a wellbore. Definition use of well logs information obtained from logs. These radioactive isotopes emit gamma rays that have characteristic energy levels. The main issues affecting the quality of the logs are tool calibration and drilling mud composition. During the past decade, the remarkable technology of nuclear magnetic resonance.
Before you can start interpreting spectral gammaray logs or, indeed, any kind of data, you need to ask about quality. The most common interpretation method is the simple bulk linear mixing law presented previously. The earliest detectors on logging tools were geiger counters, but these have been replaced by scintillation detectors in most modern tools. Interpretation of grls in igneous rocks has received less interest. 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. There are three sources of natural radioactivity in the earth.
Sunday, march 09, 2014 well logging pge 492 9 gamma ray tool layout. To conceptually understand when and when not gammaray logs are indicative of shaleclay concentration, 4. Comparison of natural gamma ray activity profiles from downhole logging and the mst core logger at site 911 yermak plateau1 mitchell lyle,2 james bristow,3 jan bloemendal,4 and frank r. As we have seen, this radiation is in fact emitted from three main types of source elements. Spectral natural gamma ray systems designed for kuth logging have been applied to evaluate stimulations and completions. Sedimentary facies interpretation of gamma ray gr log as. The logging operation lower the tool to the bottom 100 to 200 feet repeat section measured at the bottom then tool is raised through the entire well casing may prevent some logs from working logging speed. The sgr records the total gamma ray count from all sources, while the cgr results from the subtraction of the uranium contribution from the sgr. Gamma ray log measurement and interpretation gr is measured in api units american petroleum institute. In the analysis of spectral gamma ray data, use is commonly made of the ratios of the abundances of the main radioactive sources. Interpretation method, fraccade, fmi fullbore formation microimager, mdt modular formation dynamics tester, ofa optical fluid analyzer, powerstim and tlc tough logging conditions are marks of schlumberger.
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