Gamma kits like gamma ray tools record naturally occurring gamma rays in the formations adjacent to the wellbore. 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. The method was tested using gamma ray logs and potash assays from boreholes. Measurement of the natural gamma rays emitted by various elements in the formation. This nuclear measurement indicates the radioactive content of the formations. This gamma radiation originates from potassium40 and the isotopes of the uraniumradium and thorium series. Mscl systems rapidly and nondestructively obtain highresolution typically 1 cm to 10 cm downcore spacing geophysical and geochemical data from sediment and rock cores. The gamma ray log is widely used in the mining and groundwater industry for the identification of lithology, correlation between boreholes and clay content analyses. Gr log is used to predict the varying lithology in borehole by measuring the spontaneous emission of gr radiation. Waterbearing zones water saturation sw geopressure detection depth of invasion stratigraphic correlation the borehole environment r resistivity ohms.
Automatic gamma ray log response generated from grainsize information. The user will be able to interpret the lithology by using several logs, there are gamma ray, spontaneous potential, resistivity, and density log. Could anyone suggest any software package for lithological. Correlation gamma ray and ccl logs cardinal surveys. Thus gamma ray logs cannot be said to make good lithological logs by themselves, but in practice, gamma ray logs are compared sidebyside with stratigraphic logs. Abstract there is a theoretical basis for calibrating the gammaray log in terms of fractional clay volume vclay. Porosity may also be derived from this bulk density, if the matrix density is known. Shales and clays are responsible for most natural radioactivity, so gamma ray log often is a good. While the gamma ray log traditionally has been used primarily for welltowell correlation, it also plays a role in quantitative log analysis. This tool is stackable within the quick link ql product line or it can be run as a standalone tool. The gamma ray log is the simpler of the two and only measures the total radioactive count rate in api units. Gamma ray data can also be used for core log integration.
Design of logging program the gammaray log is the main correlation log used for. In calculating these ratios, schlumberger uses the. The service is also used as a correlation device between logs when the tool is run in combination with other tools. Stratigraphic correlation of reservoir sands across wells were achieved using the interpretation of gamma ray log motifs as individual motifs displ a specific depositional environment or groups of. Gamma ray log measures natural radioactivity of formation due to the radioactive material disintegration decay. A gamma ray log measures naturally occuring radioactive minerals. Whereas the spectral gamma ray log is able to differentiate between the different radioactive elements k. Tied to lithology, porosity, and fluid content density log dphi % porosity rhob bulk density gcm3 porosity. With dual fire capability, the tool can be run with strings with multiple guns firing on positive and negative polarity. Inpefa a well correlation tool for petrel description. Gamma ray log character is one of the primary methods used to correlate the stratigraphic section. The value is rather high and may infer that the sandstone has a considerable percentage of clay minerals.
The density tool or gamma density tool utilizes a gamma ray source placed a distance from the gamma ray detector, which measures gamma ray count that is an inverse function of the density of the coal or. The equation 1 shown below defines an igr shaliness index as a function of the gr gamma ray log signal. This is acceptable for most production logging tests. Most interpretations of spectral gamma ray logs focus on the relationships between the three elemental concentrations. Magnetic susceptibility log bi in nt, gamma ray log gr and correlation coefficient log r, in well a and well b. Realtime formation evaluation for optimal decision making. Sonic log correlate seismic data in time to well data in depth density log tool emits gamma rays detects returning scattered gamma rays gamma ray absorption is proportional to rock density measures density.
The dual fire gun gamma ray service allows gamma ray correlation to occur during explosive operations. Sedimentary facies interpretation of gamma ray gr log as. Shale is usually more radioactive than sand or carbonate, gamma ray log can be used to calculate volume of shale in porous reservoirs. Crains petrophysical handbook natural and spectral. Based on theoretical curves of vclay the following conclusions were drawn. 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 log response depends on the radiation, tool characteristics, and logging parameters. The gamma ray logs of the four wells were first placed at an equal depth in order to facilitate correlation. The most common logs used for this purpose are the gamma ray, the resistivity and the acoustic log. The log is also used for correlation between wells, for depth correlation. Nondestructive analysis, such as spectral gamma ray, provided the.
Log normalization is most often applied to gamma ray logs. A case study in the local estimation of shearwave logs. Calculation of the gamma ray index is the first step needed to determine the volume of shale from gamma ray log. The gamma ray log was the first nuclear well log and was introduced in the late 1930s. Archival gamma ray logs standardization by nondestructive core. Now that we know how the tools work, we are ready to discuss how gamma ray logs are used in log analysis. The dissimilarity matrix shows running costs for all possible matches. Jun 29, 2012 basic evaluation of south louisiana well log.
In particular, thk and thu are often used for petrophysical interpretation and log correlation. Lithofacies interpretation was carried out with schlumbergers petrel 2010 software package using the gamma ray, effective porosity and. The gamma ray curve gr identifies the clean sands but there is no obvious correlation to the top and base sands on the acoustic impedance log ai. A log run for the purpose of correlating between wells. Waterbearing zones water saturation sw geopressure detection depth of invasion stratigraphic correlation the borehole environment r resistivity ohms resistivity. Basically, a formation with high gamma ray reading indicates that it is a shaly or shale, when the low gamma ray reading indicates a clean formation sand, carbonate, evaporite, etc. Further postcruise processing of the log data from the fms and ghmt will be performed at lmf. Gamma ray measurement has the following applications. The spectral gamma ray log is widely used in the mining and environmental industries for the identification of lithology, correlation between boreholes, and clay content analyses. As for zone 3 the gamma ray log shows a value around 120gapi, considerable less than the other two. This arrangement allows the grt2 to be inserted anywhere within an analogue asr tool string or between the wireline adapter and tas section within a geochain tm string surface control the geochain system panel gsp with an inbuilt gamma control module. In this case, the other tracks most often include resistivity, density, neutron or sonic logs fig.
A resistivity log measures the conductivity of electrical current. Figure 2 shows the correlation oftwo well log sequences by the dynamic depth warping method. Some of the gamma rays are absorbed by the matrix, and the intensity of those arriving at two fixed distances from the source are recorded. Our gamma instruments can be fitted quickly and easily to both digital and analogue tool systems. 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.
Physical, elemental and mineralogical properties can be obtained from whole or splitslabbed core samples. It performs spectra analysis, including peak search, radionuclide identification and radioactivity determination in samples, allowing full userdefined customization and parameters setting. Published in 1991, log interpretation principlesapplications provides a thorough background of log interpretation. Inpefa a well correlation tool for petrel description and case. Effective in any environment, gamma ray tools are the standard device used for the correlation of logs in cased and open holes. Gamma rays have longer penetrations than either alpha or beta rays, and can be measured by simple counter devices, such as a geiger counter.
Measurement of natural emission of gamma rays in oil and gas wells are useful because shales and sandstones typically have different gamma ray levels. Smart reservoir depth correlation with tubingconveyed. The corresponding seismic shows a relatively poor reflection that corresponds to the top of sand. Landing is the location at which the well trajectory reaches horizontal, 90 deviation. The density log measures the bulk density of the coal reservoir and associated rocks figure 7. The gamma ray log read a value of around 150gapi for zones 1 and 2. The hlds emits highenergy gamma rays, which are scattered in the formation. The casing collar locator ccl is a magnetic device sensitive to changes of metal thickness at casing or tubing collar.
Origin and sources of gr gamma rays are bursts of highenergy electromagnetic waves that are emitted spontaneously by some radioactive elements unlike alpha and beta rays of low energy correlation curves lithology curves. Pseudo gamma ray volumes estimated from offset seismic. Spectral gamma ray distinguishes the different sources of gamma rays clay content organic content resistivity log applications determination of hydrocarbonbearing vs. Postcruise processed acoustic, caliper, density, gamma ray, magnetic, neutron porosity, resistivity, and temperature data in ascii format are available directly from the ldeobrg internet web site see the related leg data contents list. The density log is based on scattering of gamma rays emitted by a gamma ray source that is focused into the formation. What is commonly known as the gamma log, is actually differentiated into the 1 gamma ray log, and 2 the spectral gamma ray log. Create multicolumn stratigraphic charts from text information. For most engineering and geophysical applications, the gamma ray log is primarily used to extract lithologic, mineralogic, or fabric estimates. Interpretation of welllogs and well log correlation were achieved using schlumbergers petrel 2010 version software. Individual log curves are often offdepth with respect to each other. Gamma near zero means very little relationship for instance agreement with obama and preference for a dog versus a cat. The rationale behind this interpretation is that variations in the gr are related to the presence of organic matter that sequesters. Spectral gamma ray logs are most useful in identifying the following.
With an intuitive user interface using a standard web browser the polaris logging system is the easiest to operate with far less personnel training than any other mwd logging software. The regression coefficients in this analysis were found to be v s 656. The active gr ct realtime gamma ray logging tool detects naturally occurring gamma rays in the formations adjacent to the wellbore, while maintaining pumpthrough capability for ct intervention. Depth correlation before perforation is crucial in reservoir testing, to minimize the uncertainties about the reservoir being tested. Gamma ray gr measurements are available with the active realtime downhole ct services, which provide downhole measurements enabled by fiberoptic telemetry. Example of a gamma ray log solid black curve in track 1 forming the correlation curve on a density neutron log. In calculating these ratios, schlumberger uses the following cutoffs. Lithological correlations by comparison of log pattern between well locations are often performed using the volume fraction of shale calculated from the gamma ray log or sp as lithological.
Pdf sedimentary facies interpretation of gamma ray gr. Well log analysis for reservoir characterization aapg wiki. The geologists picks for the clean sand and pure shale lines are the two vertical black lines in track 1. The palaeodepositional environments in the field were deduced by combining gamma ray log trends with core data. Crains petrophysical handbook natural and spectral gamma. Radioactive isotopes of elements continuously decay to more stable forms and emit radiation of several types. Although the api scale goes from 0 to 200 api, it is more common to see 0 to 100 api and 0 to 150. The depth measurement was considered in true vertical depth subsea tvdss value. The volume of shale expressed as a decimal fraction or percentage is called v shale. The relationship applies for gamma ray tools that count gamma rays of all energies, as well as for tools that use energy discrimination to selectively count gammas from potassium, uranium, and thorium. Correlation between wells, determination of bed boundaries, evaluation of shale content within a formation, mineral analysis, gr log can be run in both open and cased hole all rocks contain some radioactive material, although marine shales have a higher gamma ray emission level than sandstone, limestone and dolomite. The gamma ray log, like other types of well logging, is done by lowering an instrument down the drill hole and recording gamma radiation variation with depth. Correlating gamma ray logs that were run with various types and sizes of detectors is a bit of an art.
The bulk density is derived from the energy of the returning gamma rays. 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. Welllogging correlation analysis and correlation of well. Comparison of magnetic and gamma ray logging for correlations. Rescaling can involve an equal linear shift of the two scale endpoints, or a stretch or squeeze of the data values between the two scale end points or between two arbitrary log values. Lithological correlation by wireline logs for aquifer 3d visualization. Depth shifts depth matching crains petrophysical handbook. Furthermore, because the gamma ray log responds principally to fluctuations in the formations mineralogy, rather than physical properties such as lithification, it is particularly useful for making regional, interhole.
Ql40grccl casing collar locator mount sopris instruments. A case study in the local estimation of shearwave logs brian. The direct correlation between facies and a variety of other log shapes relative to the. 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. The results show that there is a closer correlation between the gamma ray emission and the high frequency 1. Gamma ray logs are particularly helpful because shales and sandstones typically have. It is not unusual for a correlation to be off by 1 to 3 feet. Gamma ray logs are helpful for quantifying shaliness, welltowell correlation, depth correlation between open and casedhole logs, and for correlation between logging runs. Create stratigraphic lithology columns from text information. Inpefa is a petrel plugin which aids the correlation of wireline log data, and the identification of stratigraphic packages by picking out.
Sedimentary facies interpretation of gamma ray gr log as basic. The formation evaluation gamma ray log is a record of the variation with depth of the natural radioactivity of earth materials in a wellbore. The procedure is easy and straightforward, and might give reasonable results for some deep reservoirs. The emitting elements of primary gamma radiations include potassium 40, uranium, and thorium which are associated with rocks forming minerals in variable amount. 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. Rocks and most type of soils emit gamma ray gr in varying amount. As such, gamma ray logs from different wells within the same field or region can be very useful for correlation purposes, because similar formations show similar features. Two lithological correlation groups are represented. One serious trap to avoid is the heres the last log we ran syndrome. The polaris logging system is a complete allinone package for mwd data management and reporting. Because uranium content is nearly constant, we can rescale the total gr to a more useful shale indicator by normalizing. Presented results showed a very good correlation between logs, core data. Log interpretation principlesapplications schlumberger. Inpefa is a petrel plugin which aids the correlation of wireline log data, and the identification of stratigraphic packages by picking out lithological trends in well data.
Welltowell log correlation using knowledgebased systems. Software petrel was used in order to make a correlation between the wells, after. A neutron log measures compton scattering in proportion to the number of hydrogen atoms. This is due to the negative correlation of the gamma ray log with the swave log, as seen in tables 1 and 2.
Pseudo gamma ray volumes estimated from offset seismic cseg. Crains petrophysical handbook log curve normalization. Red curve in track 1 is normalized gr grn, black curve is original gamma ray in a radioactive sand. Different types of rock emit different amounts and different spectra of. Active gr ct realtime gamma ray logging tool schlumberger. Effective in any environment, gamma ray tools are the standard device used for the correlation. 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 of mobilisation of these radioelements in. The grt2 hp gamma ray tool is a standard scintillation detector type production gamma ray tool housed within an inline asr1 body. In this paper, the correlation between the gamma ray and the radio bands is investigated. Gamma ray logging is a method of measuring naturally occurring gamma radiation to characterize the rock or sediment in a borehole or drill hole. It only needs to record the response of the gamma ray log for a nearby known shale body and a nearby known clean rock. Archival logs saved in cpm could be standardized in petrophysical software. In addition, a well to well correlation and reservoir quality assessment were undertaken.