JLog® Petrophysical Software - Petrophysics Software - Formation Evaluation Software - Well Log Analysis Software - Version 4

  • JLog affordable software for independents that is easy to use and install.

  • Clayey Sand, Sand Silt Clay, Carbonate, 3 Mineral, Coalbed Methane, Gas Shale and Pulsed Neutron models make a quick estimate of hydrocarbons in place.

  • The estimate of hydrocarbons in place determined by a traditional resistivity-based model can be checked with a Saturation-height function in water-wet reservoirs under suitable conditions.

  • JLog 4 runs on Windows® XP and Vista and Mac® OS 9 and is designed for those who do log analysis from time to time on one or many zones that have all the same characteristics such as Rw, Rmf, GRclean and so on.

  • JLog is coded in the Java® programming language so it has the potential to run on different operating systems equipped with the appropriate Java Virtual Machine (VM) and security key (dongle).

  • JLog users need access to an e-mail account should they need support.

  • JLog imports LAS and TEXT (ASCII) and exports answers in LAS and TEXT files. An increased number of curves may be in the LAS file in this version. JLog handles depth in both meters and feet and up to 63 log curves and additional calculated curves such as Rwa, Sw etc. Graphics can be saved in several graphic file formats if not too large. Graphics at 2 samples/foot up to 4,000 feet (1,200 meters) may be shaded.

    JLog User Instructions

    Section I: File Menu

  • Here data is imported, graphics printed and saved, and data and answers saved.

  • With the View button of Import... of the File menu open SAND.txt and you will see the following logs in a spreadsheet format of columns and rows. The first row contains the curve names:

    Depth MSFL LLS LLD RHOB NPHI GR PEF DT SP CALI

    The data appears in a spreadsheet arrangement below each curve name.

    If one wanted to read log values from hard copy logs they could enter values by hand and construct a similar spreadsheet and save it as a TEXT file. Each column of data must be filled in. If data is bad or missing just enter the null value of -999.250. It is not necessary to enter the log data at uniform depth increments but it is better to do so. The depth increment could be larger for a thicker pay zone than for a thin one.

    NPHI is in percent limestone porosity units here but JLog wants the units in decimal. You will have a chance to convert from percent to decimal when importing the SAND.txt data. If NPHI is in sand or dolomite porosity units JLog will convert them to limestone.

    It is useful to open the Text or LAS file to be imported with a word processor or text editor and print out a page or two so you can see the curve names and check the actual data. The hardcopy printout can be included in the hardcopy file containing the log analysis report.

  • Choose TXT as File type of Import... of the File menu. With the Import button open SAND.txt.

  • The first dialog box asks for the Logging Contractor which is Schlumberger. Choose the Schlumberger button. It is important to correctly identify the Logging Contractor so that the correct lithology overlays, neutron matrix conversions and density-neutron porosity models will be used. The BPB (Reeves) button may also apply to some Precision and Weatherford logs. Check with your logging contractor. Note the logs in the TXT File to be imported in the bottom window. Note the last line of text in the blue Jlog window that indicates the key is in place along with the DLL file in the JLog folder. Above that you will find the location of the Java Virtual Machine (JRE) in C/Program Files. Click OK. To abort the import process click Exit.

  • Next you will be asked for the SP and Caliper names. Look at the bottom window entitled Logs in TXT File to be Imported to see what logs are present. There is an SP called SP and there is a Caliper called CALI so choose the appropriate buttons which are SP and CALI. JLog will automatically push the correct button for some commonly used curves. Always check because if the correct button is not pushed the default may not match the curves to be imported. If the Caliper was named CALX you would type in CALX and choose the user button for Caliper. Note that the names are case sensitive so you cannot enter calx for a CALX name and have calx recognized. If no Caliper curve was present you would choose No caliper. JLog will choose some of the buttons for you but you need to always check the logs in the bottom window to be sure the appropriate curves are imported. Click OK.

  • Next you are asked to Select GR if present. There is a GR so choose the GR ...... ...... ...... ...... button and click OK.

  • Next you are asked to select micro log and Rxo curves if present. There is a MSFL so choose the ...... ...... MSFL button. Six dots ...... ...... denote the absence of micro log curves. Click OK.

  • Select Resistivity curve names if present. LLS and LLD are present so choose the ...... ...... ...... ...... LLS LLD button. Click OK.

  • Select Density and PEF curve names if present. Both RHOB and PEF are present so choose the RHOB ...... PEF button. Click OK.

  • Select Neutron curve names if present. There can be up to 3 neutron curves in some (Schlumberger Platform Express) data files. After all the neutrons are imported the user can select any one to work with when doing the log analysis. It is important that the actual logging contractor curve name be used. Do not use a third party made up name. For example if importing a set of logs with ZDEN density and PNLS neutron you need to edit the incoming file so the actual Atlas neutron curve name CNC is used. Otherwise you can import the PNLS neutron and Edit it with Add New Curve Names... of the Edit menu. Other Contractor neutron logs are treated as Schlumberger NPHI. Here we only have NPHI so we choose the ...... ...... NPHI button. Click OK.

  • Select Sonic curve name if present. We have DT so choose the DT ...... ...... ...... ...... button. JLog handles several sonic curves if present. Click OK.

  • Add more curves?. If there were more curves we can add them or we can also add a curve one more time but since there are none we choose the Do not add any more curves button. If there were more curves to be added choose the Add up to 33 more curves button and type in the new curve names that appear in the bottom window. If we wanted RHOB duplicated we would type in the the RHOB name and a 2 would be appended to the name yielding RHOB2 in the JLog file. Remember the curve names are case sensitive.

  • Identify Density units in incoming file. When we inspected the SAND.txt file we saw RHOB values expressed as 2.32, 2.45 and so on. These units are G/CC. If the values were expressed as 2320 units would be K/M3, if 20.0 then Porosity Percent and 0.20 Porosity Decimal. In the last 2 cases we would be asked for the RHOF and RHOG values used to compute the porosity because we want our density in grams/cc.

  • Identify Sonic units in incoming file. When we inspected the SAND.txt file we saw DT values expressed as 82.4 and so on. These units are in microseconds/foot (US/F). Other units might be microseconds/meter (US/M) or milliseconds/meter (MS/M).

  • Identify Neutron units in incoming file. When we inspected the SAND.txt file we saw NPHI values expressed as 30.00 and so on. These units are in limestone percent. Logging contractors do not always identify neutron porosity lithology units in their data files so check the hard copy logs for neutron lithology.

  • The following information would come from the hard copy logs. If we were importing a LAS file the information might be present in the LAS file. But not necessarily. It is always a good idea to have the hard copy logs or at least the log headers available. Default values that follow are appropriate for Jackson #1 data in SAND.txt. This information must be changed for other wells.

  • Company Name: Delhi-Santos. Well Name: Jackson #1. Field Name: Wildcat Click OK.

  • More Well Information: STATE: Queensland. COUNTRY: Australia. Click OK.

  • Mud, filtrate and mud cake Resistivities: First choose the Fahrenheit button. Rm: 1.080 at 86.0 Fahrenheit. Rmf: 0.752 at 71.6 Fahrenheit. Rmc: 1.308 at 66.2 Fahrenheit.

  • Bit Size and zoned Bit Size: Bit Size: 8.50. If there are several Bit Sizes you may enter them along with the appropriate interval.

  • Depths, Temperatures, Fluids and Units: Select feet and lb/gallon. Fahrenheit is already selected. Depths Surface: 0.00. Bottom Logger: 5727. Temperatures Surface: 80.00. Bottom Hole: 217. Fluid Density: RHOF (G/CC): 1.0. Drill Fluid Density: 9.70 lb/gallon.

  • The default JLog file name is the Well Name. File name: Jackson #1.JLG Click OK or SAVE or whatever is appropriate for your operating system when you name a new file. Be sure the .JLG file extension is present so the file can be identified.

  • Once the file is converted you will be notified. Open the resulting JLog file with Open... of the File menu to start the log analysis.

    Section II: Edit Menu

  • Here the user can add well information, add new curve names, compute Rw and add plot legends.

  • With Open... of the File menu find Jackson #1.JLG and open it.

  • Work down the first 4 menu items of the Edit menu and you will see the well data that was entered when making the JLog file. That information is saved in the Jackson #1.JLG JLog file. It is a good idea to check this data and correct it if necessary.

  • Add New Curve Names... allows the user to change the curve names. You might want to do this after importing a meaningless pseudo curve name. For example if you imported a set of Atlas logs with a PNLS neutron you can change PNLS to CNC which is a proper Atlas curve name. JLog would not recognize PNLS but will recognize CNC as far as crossplot overlays and crossplot porosity is concerned. The JLog file has to be closed to use this feature.

  • The Rw submenu contains routines for calculating fluid resistivity at reservoir depth and Sigma fluid from Fluid Resistivity or Salinity, Rw from the SP and percent formation water from wireline test samples or DST samples. Rw estimation from SP and salinity data is one of the first things done in a log evaluation.

  • The Annotations submenu contains Well Information... and allows the user to enter text for Plot Legend... .

    Section III: Logs Menu

  • Here log data is viewed, presentations for log plots are set and logs are plotted.

  • Next we should look at the data with View Log Values... of the Logs menu to check the log data.

    Set From at 4500 and To at 4520. Click OK. After a brief wait the log data will appear in a table. JLog cannot handle long depth intervals of text so if a blank window appears after a wait just shorten the depth interval.

    Notice the RT values computed from MSFL LLS LLD in column 8. These RT values will be used for Pickett plots and the evaluation unless the user selects another curve for resistivity. Note NPHIls in column 12. ls has been appended to denote limestone lithology. We need the neutron in limestone decimal porosity units for cross plotting and the computation of density-neutron crossplot porosity.

    In the upper split window you will see some well information.

  • The Setup Logs Tracks... menu item has options for log presentations. Click OK when finished. Experiment here to see which presentation best fits your log data, screen width and print paper size.

  • Plot Which Logs?... allows the user to decide which logs to plot, where and how. If Logarithmic scale is checked the log will always plot in Track 2. Logarithmic scale is not appropriate for logs that contain values at or below zero. You may need to scroll to reach the OK button at the bottom of the dialog box. The Backups checkbox gives the option to plot the logs and calculated curves without backup curves. This can tidy up a messy plot that has a lot of backup curve activity. Click OK when finished.

  • With 1/500 of Plot Logs...plot from 4700-4850. Click OK when finished. This is the pay zone and the water zone just below. The oil/water contact is somewhere within the shale starting at 4790 feet. Rw is around 1.0 to 1.5 ohm.m and Rmf is about 0.450 at reservoir temperature.

  • This is how the default setting of the logs would look if the user makes no changes to setup, presentation and which logs to plot.

  • Go back to Shade Between... menu item.

    Check the first Shade checkbox. Select red Color in the first row opposite the checked box.

    Between Left Log select LLS and Right Log select LLD.

    Shade Legend type in PERMEABLE.

    We are shading between LLS and LLD and coloring it red thus suggesting the resistivity separation is due to permeability. Click OK.

  • With 1/500 of Plot Logs... of the Logs menu plot from 4700-4850. Click OK when finished. Notice the red color between the LLS and LLD in Track 2 and the PERMEABLE legend after the small red box.

  • Go back to Shade Left or Right... menu item.

    Check the first Shade checkbox. Select orange Color in the first row opposite the checked box. Click To Left of. Select GR. Under Value enter 50. Under Legend enter CLEAN SAND. Click OK.

  • With 1/500 of Plot Logs... plot from 4700-4850. Click OK when finished. Notice the orange color below GR values of 50 and the CLEAN SAND legend after the small orange box.

  • These two shading techniques illustrate a way to convey your ideas to others prior to log analysis. You need to know something about the rocks and the log response to the rocks to make this meaningful. Note GR Right Scale is now 150 and CALI Right Scale is 11. These scale changes assist in the presentation. Since there is very little movement on DT perhaps a 100-50 scale would be more appropriate.

  • Shade Stratigraphy... can be used to show sand, silt and clay intervals by shading a single curve that relates to stratigraphy and lithology. In the example that follows Yellow<35 and Orange<70. Coal is defined by 0.0 < RHOB < 2.20 set under Models/Eval Mineral Models/Coal Detection... . Shade Between... has been used to shade yellow when RHOB is to the left of NPHIls.

  • Set Margins... allows one to set margins that are useful for print centering with Print Graphic of the Logs menu.

  • To print; select Print Graphic/Logs... of the Logs menu.

    Section IV: Plots Menu

  • Various lithology, Pickett, Rxo-RT and User plots and Histograms are plotted implementing up to 4 filters with a log or calculated curve such as Rwa in the z-axis. This helps lithology identification and estimates of Rw, Sw, Rmf and Sxo.

  • Z-axis... menu item allows the user to select a log such as GR or a calculated curve such as Rwa to be plotted in the z-axis scaled in either color or numbers from a user determined minimum to maximum value. GR in the Z-axis is often useful.

    Tfluid and RHOF may be needed for some plots and later for the evaluation.

  • When more than one neutron and more than one compressional sonic are present they may be selected with Which Neutron... and Which Sonic... menu items.

  • The Litho submenu allows the user to plot a variety of lithology crossplots which aids in lithology and porosity estimation, selection of the correct evaluation model and determining if logs are affected by bad hole.

  • The Density-Neutron... is the key lithology plot for lithology estimation. This plot above shows an increasing GR as data moves away from the Sandstone (ss) line. Note the cluster of yellow which suggests either limey or slightly shaly sand represented by the yellow boxes. The RHOmaa-Umaa... plot will resolve this lithology question. The Density-Neutron plot can also be used to pick RHOB and NPHIls values for the Sand Silt Clay model as well as Sand and Silt grain density.

  • Note the porosity scales for the 3 major lithologies: ss, ls and dolo. Total porosity (PHIT) is computed from equi-porosity lines running through the 3 porosity scales. Neutron logs are designed to correctly estimate porosity in 100% water saturated limestone. The sandstone and dolomite lines vary with the logging contractor, neutron detection method and tool type. This is why it is important to correctly identify the logging contractor and the proper neutron curve name.

  • The RHOmaa-Umaa... plot helps to resolve the lithology question in the RHOB-NPHIls plot. The 3 main lithologies are quartz, calcite (cement?) and clay. Some heavy minerals (siderite?) are also present in thin beds. This plot will be used later to pick endpoints for 3 minerals with Vclay as mineral 3.

  • The Pickett submenu allows the plotting of RT, Rxo or any other resistivity curve vs. porosity to estimate Rw, m and Rmf at reservoir conditions. Here we will use RT to obtain Rw in the water zone and an estimate of Sw.

  • With Pickett Porosity... menu item select the porosity model to be used in the Pickett Plot. Try Density porosity here.

  • With Pickett Plot... menu item the user can make the Pickett Plot over a user defined interval.

  • The user drags one of the small square targets to change the fluid resistivity and m. Generally one wants the 100% line to fall on the lower resistivity, clean data pattern. Once an appropriate 100% line is constructed the user clicks on the OK bar at the bottom of the plot and the resulting fluid resistivity and m are recorded. m is the Archie cementation exponent needed to compute Sw. In the case of Jackson #1 with an RT-Density Porosity Pickett Plot from 4700-4850 feet one would find values around Rwa=1.5 and m=2.0.

  • The various Sw lines suggest a good hydrocarbon-bearing interval based on the selection of the 100% Sw line.

  • These Rwa and m values are recorded at Models menu/Variables/a, m, n, Rw and Rmf... . Check it to see for yourself.

  • With the Models/Variables/Density Porosity... menu item one can set RHOG and RHOF needed to compute Density Porosity.

  • Rmfa can be estimated with the Pickett Plot by selecting Pickett /Rxo instead of Pickett /RT and making the plot over the 4800-4850 foot interval. Rmfa=0.45 for and m=2.0 are reasonable. Click on the OK bar at the very bottom when finished.

  • To filter out shaly data select GR as the first filter and set the lower and upper GR filter values at 0 and 60.

  • 3 other filters are available. The Delta filter is very useful in some cases. For example the LLS and LLD curves track each other in the shaly intervals and LLD>LLS in the permeable sands. Use this characteristic to select only the permeable rock in various plots.

    Turn off all filters and check the Delta Filter 3 and set it up as follows: LLD>=LLS+3.0. This means that only data where the LLD is reading 3 ohm.m greater than the LLS will be plotted. Since LLS=LLD in shales they will be eliminated. Note how the water zone is now separated from the hydrocarbon bearing zone.

    Try some Litho plots with the Delta Filter.

  • Rxo-RT Plot... is a way to estimate Rw and Sw without a porosity log. It works well in carbonates.

    Rwa=1.4 when Rmf=0.45. Note the use of a GR filter. Be sure to click the OK bar after dragging the small target so the Sw=100% line passes through the water data. After the user clicks on the OK bar at the bottom of the plot the resulting Rwa is recorded. See the a, m, n, Rw and Rmf... menu item of the Models/Variables submenu to check for yourself.

  • User Defined Plot... of the User submenu plots one log or calculated curve vs. another in either linear or logarithmic scale. RHOB and GR values are plotted to select Clay, Rock and Coal endpoints used to determine Eval Track V mineral volumes in the Clay Rock Coal Eval Mineral Model.

  • Density-GR... of User submenu plots density vs. GR in linear scale. RHOB and GR values are plotted here to select Clay, Rock and Coal endpoints used to determine Eval Track V mineral volumes in the Clay Rock Coal Eval Mineral Model. This is faster than setting up the User Defined Plot... above.

  • RHOmaa-GR... of User submenu plots RHOmaa vs. GR in linear scale. Both RHOmaa and GR values are plotted here to select clean and clay endpoints as explained by Robert Elphick years ago. This is faster than setting up the User Defined Plot... above. The clean and clay values can be used in VclayGR and VclayRHOB-NPHIls of Which Vclay?... later. This plot is also used to check for hydrocarbon effects.

  • The Histogram... menu item allows one to make a histogram of a log or calculated curve in a user defined color and in a user defined number of bins. This can be useful when scaling log curves for the User Defined Plot... .

    Section V: Models Menu

  • Mineral Models, Vclay, Porosity, Sw and Variables that affect those models are selected. Overrides allow the user to squeeze more out of a limited data set. Logic is available to identify coal and to utilize sonic porosity in bad hole.

  • Six Eval Mineral Models are available.

  • 1-Mineral (clean or shaly) is a shaly sand model appropriate for SAND.txt. The Indonesian and Dual Water Total Sw equations could be used here in addition to Archie.

  • 2-Mineral (carbonates) is appropriate for carbonates. The user supplies the grain density (RHOG) of each carbonate. Typically this would be 2.71 for limestone and 2.85-2.87 for dolomite. Both density and modern neutron logs such as NPHI, CNC and TNPH are required for this model. An old NEUT in counts/sec would not be suitable unless it had been recalibrated to limestone porosity units. The Archie Sw equation could be used here. This model is appropriate for CARB.las. If a compressional sonic is available Khoyle (carbonate permeability indicator) may be plotted to assist in the identification of permeable carbonates. Reference: Hoyle, W. R. and Bowler, J., 1998, Wyllie Revisited with Respect to Carbonate Permeability: The Log Analyst, Jan-Feb 1998.

  • 3-Mineral is appropriate for carbonates, mixtures of 3 clean minerals and a mixture of 2 minerals plus clay. The user supplies the grain density (RHOG) and U of each mineral. Density and modern neutron logs such as NPHI, CNC and TNPH along with photoelctric capture cross section (PEF, PE) are required for this model. An old NEUT in counts/sec would not be suitable unless it had been recalibrated to limestone porosity units. Mineral 3 can be Clay and a shaly sand Sw equation could be used with Vclay from mineral 3. This model is appropriate for SAND.txt and CARB.las. Barite in the mud may create problems with this model.

  • The Clay Rock Coal model uses the density log and GR to estimate gas in place from a scf/ton Desorption=a+b*Curve^c relationship. a, b and c are estimated from coal core desorption data related to a log curve which is usually the density. The relationship is determined by spreadsheet curve fitting of lab desorption data to the log Curve (usually density). A density vs. GR User Plot determines the 3 Clay, Rock and Coal endpoints.

  • The Sand Silt Clay model uses Density and Neutron values determined from the Density-Neutron crossplot along with Sand and Silt grain density values. Density Porosity is estimated from the log density value and user Sand and Silt grain density selection. Vclay is estimated from the 3 mineral volume solution based on the 3 mineral density-neutron values input by the user.

  • Gas Shale...uses GR to estimate Clay and Gas Shale volumes. A desorption relationship similar to that in the Clay Rock Coal model estimates gas in place.

  • Pulsed Neutron... uses Sigma and a porosity log or curve to estimate hydrocarbons in place for Clean or Clayey reservoir rocks.

  • Coal Detection... is available and may be triggered by any one of 3 user selected logs. A Coal count can be presented in the Eval Net Pay summary.

  • Porosity/Mineral Override... Overrides are available and are designed to squeeze more from the logs. Vclay is set to zero and Porosity is selected when an override is called. I often use this feature when evaluating carbonates with a minimal set of logs by setting Override 1 as 50 less than GR less than 1000 gray SHALE. I use Override 2 as 2.88 less than RHOB less than 1000 cyan ANHYDRITE for anhydrite. The Constant override porosity model with porosity=0.0 is appropriate for both.

    Care must be taken not to override permeable radioactive carbonates. Everything that is radioactive is not shale.

  • Which Vclay?... allows a selection of Vclay indicators needed to calculate Indonesian and Dual Water Total Sw for 1-Mineral (clean or shaly) and Sigma Clay Sw in the Pulsed Neutron model. Vclay will be the minimum of the clay indicators which are computed at each depth. Nothing has yet been selected here. If a Vclay curve is unavailable it will not appear as a clay indicator. Any curve may be selected for VclayCurve. Here the caliper is selected for VclayCurve as in some cases the hole is at bit size in clean sands and badly washed out as clay content increases. Clean and clay values are set under Variables of the Models menu.

  • Porosity & Sw Models... :

    Porosity can be selected from models such as Sonic Wyllie, Density-Neutron and so on. One can also select a Curve to be the porosity log (the porosity curve should be in decimal porosity for use in JLog). If no porosity logs are present it is possible to set porosity to a constant value. Porosity may be limited to a maximum value which is useful in bad hole where porosity may read too high and result in false shows. Here Density-Neutron porosity is selected

    Two clay models relating Vclay and porosity are available. The Laminated model is selected.

    Four Sw models are available. The Indonesian Sw model is selected. The Dual Water Total model has also been selected for comparison which can be very useful for final Sw model determination as both will be plotted.

  • Bad Hole Sonic Porosity... is available if there is a sonic log. Since the sonic is often the most robust of the porosity tools it can be called for use in bad hole situations. For example in an 8.5 inch hole you might want to use the Sonic Porosity AFF Model whenever the hole was greater than 12 inch. To do this just check Bad Hole Trigger 1 and set 12 less than CALI less than 100. Whenever the caliper (CALI) is greater than 12 inches the sonic will be used for porosity. The CALI is not likely to read greater than 100. You can show where the sonic has been used on the Eval graphic plot by checking Show Eval Sonic Porosity Flag which will appear as a green mark in the Sw Track when you Plot Eval.

  • The Variables submenu is used for setting variables such as a, m, n, Rw Rmf and GR clean and GR clay for Vclay from GR. Which RT..., Which Rxo... and Which Sigma... allow selection of any curve for RT, Rxo and Sigma.

    Section VI: Eval Menu

  • The Jackson #1.JLG evaluation is made and hydrocarbon reserves are estimated. Results are displayed graphically and in text on the screen with a reservoir summary. Calculated curves such as Rwa and Rmfa may be plotted along with logs. Eval answers including Vclay, Porosity and Sw are computed at each depth level and may be saved in LAS and TEXT files along with the reservoir summary in TEXT for report writing. The LAS file can be imported by other applications for further use.

  • Working from top to bottom in the normal JLog manner the Net Pay... menu item allows one to estimate predominately Oil or Gas reserves or None. Vclay, PHIE (effective porosity) and Sw (water saturation) cutoffs are set. If the Archie Sw model is used the Vclay cutoff has no effect. When Eval calculations meet the cutoff conditions Net Pay and Net Reservoir will be counted. The Net Pay flag appears in the Sw Track of the Eval plot. These Net Pay intervals might be perforated if not too close to water.

  • It is possible to filter Net Pay on a log curve. Perhaps Net Pay should only be counted if the GR is less than or equal to (<=) 25. In this case the Net Pay if box is checked and 0.0000 <= GR <= 25.0000 would be input. From: and To: depths would be input over the interval where this filter applies.

  • In the next dialog are a number of factors needed to compute reserves.

  • Calculate Quick Net Pay... does exactly that. Input the From: and To: interval and you will rapidly obtain a Net Pay and Net Reservoir summary based on the models and variables you have selected.

  • Here is a typical Quick Net Pay summary. Notice the estimate of barrels of oil recoverable at surface based on the user input of drainage area, formation volume factor and recovery factor.

  • The Evaluation included the following models and variables. VclayGR with clean=8 and clay=105. Density-Neutron Porosity, Laminated clay, Indonesian Sw, Rtclay=26, Rw=1.4, Rmf=0.45, m=n=2 and a=1.0.

  • View Eval Answers... lists all the variables and equations used in the evaluation along with a Net Pay and Net Reservoir summary and level by level answers. This information can be saved with Save As... of the File menu. Choose Eval in TEXT button to do so.

  • Eval colors and presentation are set with Paint Minerals & Fluids... and Setup Eval Tracks... of the Eval menu.

  • Plot Which Calculated Curves... of the Eval menu sets up the plotting of various calculated curves such as phiS, phiND, RHMA, Rwa, Rmfa, PHIT, PHIE, Vclay, Sw and Sxo if the appropriate logs are available. phiS is sonic Wyllie porosity computed from the matrix travel time estimated from the matrix density (RHMA) determined from the density-neutron crossplot. phiND is density-neutron crossplot porosity. PHIT is total porosity determined from the porosity models selected from Porosity & Sw Models... of the Models menu while PHIE is the resulting effective porosity after Vclay correction. Vclay will be the minimum of the clay estimators from Which Vclay?... of the Models menu. Rwa=Rt*PHIT*PHIT. Rwa a is a good quick look hydrocarbon indicator. Rmfa=Rxo*PHIT*PHIT. Rmfa can identify hydrocarbons in clean formations with changing and fresh Rw values. Often Rmfa in the hydrocarbon zone will be about twice that in the water zone.

  • The Eval graphics plot is made with Plot Eval of the Eval menu with standard and user defined depth scales.

  • Note the black bar at the left edge of Track 3 which flags Net Pay in the Eval plot above. Note also the shading between the RHOB and NPHIls curves which show the quartz and shale effect on these 2 logs.

  • Sw-PHI... and Sw-PHI with Perm... identifies the best reservoir and perhaps estimates permeability. Permeability here should be thought of as qualitative not quantitative. PHI denotes porosity.

  • And here is the Sw-PHI with Perm... plot for the 3-mineral Eval plot below.

  • Note the data cluster bounded by 500 and 1,000 Ktimur permeability lines. They identify the better reservoir which generally has higher Rwa values.

  • Next comes a 3 Mineral Eval plot similar to the Jackson #1 Eval plot above that is derived from SAND.txt. Here Vclay comes only from mineral 3 volume (RHOG=2.90 and U=6.5) from RHOmaa-Umaa plotted earlier. Quartz and Calcite RHOG and U defaults are used.

  • Here is the Quick Net Pay... summary for the Eval plot above.

  • Next comes a 2-Mineral Eval plot generated from the CARB.las file with NPHI as the neutron log. CARB.las is a set of Schlumberger Platform Express (PEX) logs so NPOR, TNPH and NPHI neutrons are available in decimal limestone units (V/V). The CARB.las file was imported using import curve names for PEX. This LAS file contains many of the necessary variables such as Rm, Rmf etc. Rw=0.022 and Rmf=0.109 at reservoir temperature are used for this evaluation. The first two overrides are used starting with default values to depict SHALE and ANHYDRITE. The shale value was changed to 100 because porous zones with mudcake have high GR just below 100. Care should be taken when setting GR overrides so one does not eliminate porous, permeable carbonates. Both override porosity models are Constant=0.0.

  • Note how SHALE and ANHYDRITE overrides above extend the 2-Mineral lithology model in Track V lithology.

  • The 3 Mineal Eval plot computes Anhydrite volumes above. RHOG=2.90 and U=15.0 are used in place of Quartz for ANHYDRITE. Defaults are used for LIME and DOLOMITE.

  • Sw-PHI... and Sw-PHI with Perm... identifies the best reservoir and perhaps estimates permeability. Ktimur and Khoyle in the z-axis suggest some permeabilty is present.

  • Next comes a Clay, Rock, Coal model with 3 mineral volumes calculated from RHOB and GR endpoints selected in the RHOB vs GR User Defined Plot... or the Density-GR... plot shown above in Section IV: Plots Menu. For each coal SCF*10^3 is posted at the left edge of Track 4 and coal thickness (Thick) at the right edge.

  • The Quick Coal Net Pay Summary looks like this with a hypothetical Scf/ton relationship to RHOB:
    Depth increment = 0.5000 feet.
    Net Pay = 20.5000 feet.
    Net Pay/Gross Ratio = 0.2040 from 4900.0000 to 5000.0000 (100.5000) feet.
    Coal detected when one of the following conditions is satisfied: 0.00 < RHOB < 2.20.
    87.03*10^6 net cubic feet of gas in place at surface conditions/40.00 acres.
    RHOB density curve in gram/cc used to compute tons in scf/ton Gas.
    Scf/ton= 20.0000 + 200.0000 * RHOB ^ -4.2000.
    DAF=(Scf/ton)/(Coal decimal volume) when more than 1% Coal.

  • Next comes a Sand, Silt, Clay model with 3 mineral volumes calculated from RHOB and NPHI endpoints selected in the Density-Neutron Plot shown above in Section IV: Plots Menu. This is not a good example but we will use it. The Sand Silt Clay lithology mix exhibits a boomerang or banana pattern based on the 3 minerals. This model is designed to allow silt to be included as a reservoir which may result in more Net Pay. The model seems to move in the right direction with an additional 300,000 barrels of oil in place over the 1-Mineral (clean or shaly) shaly sand model evaluation made earlier.

    After selecting Sand Silt Clay... Model the following endpoints are used: Clay: NPHI=0.30 RHOB=2.50. Sand: NPHI=0.22 RHOB=2.20. Silt: NPHI=0.15 RHOB=2.45. Sand Grain Density=2.65. Silt Grain Density=2.71. Indonesian Sw with Rtclay=26, Rw=1.4, Rmf=0.45 and m=n=2.0 and a=1.0.

  • The Quick Net Pay Summary looks like this:
    Net Pay if Vclay<0.5000, PHIE>0.1000 and Sw<0.5000.
    Net Reservoir if Vclay<0.5000 and PHIE>0.1000.
    Depth increment = 0.5000 feet.
    Depth increment = 0.5000 feet.
    Net Pay = 70.0000 feet.
    Net Reservoir = 136.0000 feet.
    Net Pay/Gross Ratio = 0.3491 from 4650.0000 to 4850.0000 (200.5000) feet.
    Net Reservoir/Gross Ratio = 0.6783 from 4650.0000 to 4850.0000 (200.5000) feet.
    Average Net Pay porosity = 0.2049.
    Average Reservoir porosity = 0.1865.
    Net Pay porosity feet = 14.3425.
    Net Reservoir porosity feet = 25.3671.
    Average net pay: hydrocarbon saturation = 0.6898 Sw = 0.3102, Net Hydrocarbon feet = 9.8928.
    3069932.25 net barrel oil in place at reservoir conditions/40.00 acres
    2361486.43 net barrel oil at surface conditions with 1.3000 oil formation volume factor.
    1180743.22 net barrel oil recoverable at surface conditions with 0.5000 oil recovery factor.

  • The Gas Shale model determines gas reserves from a relationship between a log and desorption. This relationship needs to be determined from lab and log data. If an average scf/ton is known that can be used. Gas Shales generally have high GR, lower bulk density and higher resistivity than other shales. This results in a higher Rwa (porosity*porosity*Rt). A GR log is needed to estimate Gas Shale volume.

    Step by step Gas Shale model instructions follow.

    1. Import data in the normal way with File/Import.

    2. After checking data import with Logs/View Log Values.... and Plot Logs select Models/Eval Mineral Models/Gas Shale... . Enter the GR clay and GR gas shale values. The equation used to compute Gas Shale volume displayed in Eval Track V is displayed in the dialog. No other Models items are needed so they are grayed out.

    3. Eval/Net Gas Shale Pay... enter the scf gas/ton relationship, drainage area and select a filter to define Net Pay.

    4. The rest of the evaluation is carried on in the normal way. Use Eval/View Eval Answers... over 10 feet to check models in the upper split window.

    5. The Calculate Quick Gas Shale Net Pay summary looks like this:
    Constant Depth increment of 0.5000 feet
    Net Pay = 100.0000 feet.
    Net Pay/Gross Ratio = 0.5540 from 2680.0000 to 2860.0000 (180.5000) feet.
    Gas Shale detected when one of the following conditions is satisfied:
    0.00 < DEN < 2.47.
    11450.951*10^6 net cubic feet of gas in place at surface conditions/640.00 acres.
    DEN density curve in gram/cc used to compute tons in scf/ton Gas.
    Scf/ton= 518.0000 + -194.0000 * DEN.

    6. Eval/Plot Eval at 5 inch/100 feet (1/240)... gives the following plot.

  • The Pulsed Neutron model determines Sw from Sigma and works best in high formation water salinities.It is necessary to have both sigma from the pulsed neutron and a porosity log to solve for Sw in the Sigma Clean Sw model. A clay indicator such as GR is needed to find Sw in the Sigma Clay model. The clay indicator reduces total porosity to effective porosity in the usual way. Effective porosity (PHIE) is used in the Sigma Clay Sw model while total porosity (PHIT) is used in the Sigma Clean Sw model as in Archie Sw model because PHIE=PHIT. If a clay indicator is selected with the Sigma Clay Sw model Clay, Mineral-1 and PHIE are displayed in Track V of the the Evaluation plot. PHIE is in Track IV. If a clay indicator is selected with the Sigma Clean Sw model then Clay, Mineral-1 and are PHIE in Track V of the the Evaluation plot. PHIT is in Track IV. If no clay indicator is selected with the Sigma Clean Sw only Mineral-1 and PHIT are displayed in Track V and PHIT in Track IV.

    Step by step Pulsed Neutron model instructions follow.

    1. Import data in the normal way with File/Import.

    2. Sigma, Ratio, Near and Far counts and other Pulsed Neutron curves are placed in the 33 extra curves slots. When the "Add more curves?" dialog comes up push the "Add up to 33 more curves." button and add the necessary pulsed neutron curves including Sigma. Remember: the curve names are case sensitive and usually are upper case.

    3. If Rw or formation water salinity is known Sigma Formation Water (Zw) can be found with Edit/Rw/Fluid Resistivity Calculator... .

    4. After checking data import with Logs/View Log Values.... and Plot Logs. You may wish to make Sigma-GR Plots/User plots to determine Sigma Matrix (Zma) and Sigma Clay (Zclay).

    5. Models/Eval Mineral Models.../Pulsed Neutron.

    6. Models/Which Vclay?... for a Vclay indicator in the normal way.

    7. Models/Porosity & Sw Models... . Select porosity and Sw models.

    8. Variables/Zw, Zma, Zhyd and Zclay... . Plus appropriate Variables for Vclay and Porosity models are selected.

    9. Models/Variables/Which Sigma?... to select the Sigma curve from which Sw is computed.

    10. At this point a Sigma-Porosity User plot might be helpful to estimate Sigma Hydrocarbon (Zhyd).

    11. The rest of the evaluation is carried on in the normal way. Use Eval/View Eval Answers... over 10 feet to check models and variables in the upper split window.

  • The FOIL (Cuddy et al, 1993, SPWLA Symposium, Paper H) Saturation-height Function shown below estimates BVW based on height (H) above Free Water Level (FWL). BVW(FOIL)=A*H^B where A and B are constants. Sw can be computed at any H: Sw=BVW(FOIL)/Porosity. JLog uses effective or total porosity.

    FOIL constants A and B are suitable only for the petrofacies unit represented by the higher quality sands above. See Worthington 2002, Geological Application of Well Logs, AAPG Methods in Exploration Series No. 13, Chapter 7, for an excellent review on the use of Saturation-height Functions and the definition of a petrofacies unit. FOIL is for advanced users. A separate User manual is available for the use of the FOIL model.

    JLog is a trademark of Bowler Petrophysics, Inc. Mac and Mac OS are trademarks of Apple Computer, Inc. Java is a trademark of Sun Microsystems, Inc. Windows is a trademark of Microsoft Corporation.

    To order or for more information: contact Jack Bowler, Bowler Petrophysics, Inc., 730 17th Ave., Suite 835, Denver CO, 80202 USA. Phone: 303 860 1641. e-mail: jack@bowler-petrophysics.com.

    Single JLog 4 license price is US $ 1,595.00 domestic and international. Handling and shipping charges depend on location. Support is free by e-mail. No maintenance fee.

    JLog is shipped on CD with a USB port security key.

    Payment is made in advance of shipment. If JLog does not solve your log analysis problems $1,595.00 will be refunded if JLog and the USB port security key are returned within 30 days.

    Version 2 and 3 users may upgrade to version 4. Contact Bowler Petrophysics for price that depends on present version and location for handling and shipping charges. The version 2 and 3 USB security key will work with version 4. JLog 4 will read JLG files from previous versions.