JLog® Petrophysical Software - Petrophysics Software - Formation Evaluation Software - Well Log Analysis Software - Log Analysis Software - Well Log Interpretation Software - Version 8
JLog works with wireline log and LWD log data indexed to depth. Data can either be in TEXT or LAS format. If one has been using a spreadsheet for log analysis the table of data can be imported by JLog if Depth is present in one column. LAS is the preferred format since it contains more information and is available from all logging vendors.
JLog, at $US 1,595.00, is affordable software for individuals, independents and small companies that need to do log analysis from time to time. JLog is easy to use and install. There is no annual support fee or maintenance fee.
JLog is designed to identify and quantify hydrocarbons in place for conventional and unconventional reservoirs including source rock. Data and answers can be exported in LAS, TEXT and graphic file formats. The website graphics are JLog GIF files.
The workflow is straightforward with a pragmatic approach. Users work down each of 6 menus and from left to right in a linear manner. It is not necessary to always use the manual when one follows this concept - particularly if they first work through the SAND.TXT, CARB.LAS and DOLO.LAS examples shipped with JLog. This is very important - it will save time in the long run.
Here is an unsolicited comment from a JLog user: "Jlog arrived promptly on Monday and the installation was a breeze. I have been working with the program for 2 days now and it is more than I hoped for. Thank you for developing an excellent product combining realistic performance at an affordable price."
Here is an unsolicited comment from an independent geologist: "I have to say I really love your software and am sure it is going to help me find lots more oil."
Here is another unsolicited comment from a Petroleum Engineer: "I am the model of a JLog user, someone that uses the program rarely and irregularly. I like the program because it is well thought out and logical. It is a terrific piece of work .. Regards ..".
The following two remarks come from another petroleum engineer:
"I received JLog yesterday, installed it and am working through the first example now. I had called yesterday with a question, but I figured it out afterwards. The manual does a good job. It looks like a great program. Thank you for the call back."
And then: "This is a really nice program Jack. It does A LOT for the price."
JLog 8 runs on 32-bit and 64-bit Windows® XP, Vista, 7 and 8 and on Mac® OS X PowerPC and Intel architectures.
The JLog author has been working with logs for over 50 years and has been developing petrophysical software since 1986. JLog has been under continuous development since 2000.
Clayey Sand, Carbonate (2, 4 and 5 minerals), two 3-Mineral, Sand Silt Clay, Coalbed Methane, Gas Shale, Tight Oil (aka Shale Oil), Source Rock and Pulsed Neutron models make a quick estimate of hydrocarbons in place with the right data and models.
The hydrocarbon in place estimate determined by a traditional resistivity-based model can be checked with a Saturation-height function in water-wet reservoirs under suitable conditions.
Source Rock model S1 barrels of oil may represent oil reserves in Tight Oil (shale oil) rocks.
A: Tight Oil
Two tight oil Niobrara models follow. The first is based on density-neutron crossplot porosity PHIE instead of PHIT in the Archie Sw model. The second uses density porosity corrected for kerogen and pyrite.
Note how the JLog simplified brittleness indicator (pBRIT) tracks BRIT in Track 2 above. The pBRIT calibration can be used in other Niobrara formations at the same depth range that do not have acoustic data. This concept is explained in JLog Calculated Curves.pdf and the Source & Tight Oil Manual shipped with JLog.
Note the interesting correlation between Umaa and the AT90 resistivity over most of the Niobrara.
Both Niobrara models arrive at 31,000,000 BBL OIL in place per section (640 acres).
B: Gas Shale
Four JLog plots that aid in the evaluation of a Niobrara Gas Shale or Chalk follow.
The RHOmaa-Umaa plot above suggests that Quartz is more brittle (BRIT) than Calcite. See JLog Calculated Curves.pdf for the definition of the BRIT brittleness indicator.
The Young's Modulus-Poison's Ratio plot above shows how the two relate to BRIT (in the z-axis).
The plot above suggests that Passey TOC and Rwa aid in identifying hydrocarbons and kerogen in shale.
The Evaluation plot above is a small section of the previous plot where gas in place is computed with the Gas Shale model using the 3-Mineral PEF model for lithology.
C: Clastic Reservoir
The three plots that follow use different Evaluation models in conventional sand reservoir. These three plots are from SAND.TXT shipped with JLog.
The plot above uses Vclay from the GR that works well here but not in all reservoirs.
The plot above uses the 3-Mineral PEF model for lithology while the plot that follows uses the 3-Mineral Sonic model with a hypothetical gas-oil contact set at 4720 feet.
D: Carbonate Reservoir
The plot above (from CARB.LAS shipped with JLog) uses the 3-Mineral PEF model for two carbonates plus anhydrite and an override for Clay. Overrides can extend the model by use of filters calling various porosity models. This is useful for limited data sets.
The plot above (from DOLO.LAS shipped with JLog) utilizes the 5-Mineral (carbonate + clay) model from SPE 12597, McGinley & McKnight, 1984 (M&M). This model differentiates radioactive dolomite from clay or shale and uses the sonic to estimate clay or shale content. Very useful when dealing with radioactive carbonates that can be confused with shale. See JLog Workflow Example that follows much later.
E: Source Rock
The plot above (from SourceRock.JLG shipped with JLog) uses the delta log R method to estimate TOC in both weight % and volume %. This is important since it is now recognized that shale gas is associated with TOC. When lab data is available S1 and S2 may be computed from a relationship with TOC. Then S1 and S2 barrels of oil can be computed for oil source rock work.
The plot above uses a relationship (hypothetical here) between S1 and TOC to estimate free thermally extractible barrels of oil if within the oil window. This can be free oil residing in kerogen porosity or any other pore space and may represent free oil reserves in tight oil rocks.
The plot above uses another relationship (hypothetical here) between S2 and TOC to estimate present day source rock potential in barrels of oil.
The following are three quick means to identify source rock.
The two plots that follow are based on work by Meyer and Nederlof (1984).
Generally, marine source rock has increasing resistivity associated with increasing GR as seen below.
More mature source rock generally has increased resistivity, up to a point.
The plot above shows how the Passey delta log R method compares to that of Meyer & Nederlof.
Meyer & Nederlof (M&N) has the ability to quickly identify source rock when it is not possible to find a shale baseline needed for Passey delta log R method. But M&N does not estimate TOC.
The plot above shows good agreement between Passey delta log R and M&N methods for source rock identification. M&N (Source SSsh>0.0) supports the shale baseline resistivity and sonic value selections. The 5-mineral M&M model is in the far right track.
1,206,000 BBL S1 oil/640 acres are present based on reasonable hypothetical values. See the Source and Tight Oil Manual for workflow and variables selection.
JLog is designed for those who do log analysis from time to time on unconventional reservoirs and conventional reservoirs with 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 (JVM) and USB port security key (dongle). A JVM for Windows is shipped with JLog and may be installed if not already installed (most Windows machines already have a JVM). Mac has a JVM.
JLog users need access to an e-mail account should they need free support.
JLog imports LAS and TEXT (ASCII) files of unlimited length and exports answers in LAS and TEXT files. JLog handles depth in both meters and feet and up to 63 log curves and many additional Calculated Curves. Graphics can be saved in several graphic file formats. Graphics at 2 samples/foot up to 4,000 feet (1,200 meters) may be shaded. This limit does not apply to the length of logs that can be plotted, cross plotted or evaluated. Who is looking at 4,000 feet of pay anyway?
JLog plots the following Calculated Curves if the appropriate logs are present: Khoyle, phiS, phiND, RHOmaa, Tmaa, Umaa, Rwa, Rmfa, PHIT, PHIE, Vclay, Sw, Sxo, BVW, BVH, Ktimur, % VRE, ADSscf, DESscf, PoiRat, ShearM, YoungM, MHSG, MHS, Ratio, Ro, FOIL, SwFOIL, BulkM, TOC, TOC+0.8, TOCvol, S1, S2, Sfact, S1/TOC, S2/TOC, S1+S2, PI, S3, OI, BRIT, pBRIT, BRITpe, sBRIT, BRITdt, Rxo/Rt, AcImp, RefCf, Vp/Vs and Source. See JLog Calculated Curves.pdf (shipped with JLog) for explanations and descriptions of the Calculated Curves.
- No environmental corrections are applied. However RT is estimated from Schlumberger Chart Rint-9 when Rxo, LLS and LLD or equivalent curves are available. This computation is made for all logging contractors so the resulting RT may not be absolutely correct for all Rxo, LLS and LLD combinations but it will generally be a better RT estimate than LLD.
- JLog is shipped with a sandstone Text file (SAND.TXT), a carbonate LAS file (CARB.LAS) and a dolomite LAS file (DOLO.LAS). SAND.TXT includes productive shaly oil sands (4,700-4,800 feet) and coals (4,900-5,000 feet). DOLO.LAS contains dolomite pay and source rock. These files can be used to self-train on JLog. Thanks to Delhi Santos and Wiltshire Geological Services of Adelaide, South Australia, for the SAND.TXT well logs. Thanks to Advantage Resources, Inc. of Denver, Colorado for the CARB.LAS well logs. Thanks to the companies that posted log data on the Colorado Oil and Gas Conservation website. SourceRock.JLG (also shipped) can be used to test the Source Rock model.
- Appropriate density-neutron crossplot porosity estimates are available for Neutron Logs including: APLC, CNC, CNCF, NPHI, NPOR, NPRL, NPRS, NPRD, SNP and TNPH.
- A wide variety of lithology crossplots with vendor and log specific overlays are available to check log quality and identify lithology. JLog includes the following lithology crossplots if the logs are available: Density-Neutron, Density-PEF, RHOmaa-Umaa, MN, MID (RHOmaa-Tmaa), Tmaa-Umaa, Sonic-Neutron and Density-Sonic. The RHOmaa-Umaa plot is used to select end points for the 3-Mineral PEF model while the MID plot is used to pick end points for the 3-Mineral Sonic model (mineral-3 from both can be Vclay). The RHOmaa-GR plot is used to pick Vclay clean and clay endpoints and test for clayey sand gas effects. The Density-GR plot is used to select coal, rock and clay endpoints. Pickett and Rxo-RT plots quickly estimate m, Rw, Rmf, Sxo and Sw. Up to 4 filters can be applied to all crossplots and histograms to view critical data patterns.
- Users can shade above/below and between log curves with 10 colors and add a short legend to emphasize important points.
- Appropriate Vclay (up to 10), Porosity, shaly sand, sand-silt-clay, carbonate, two 3-mineral lithology models and 5 Sw models allow the user to quickly estimate hydrocarbons in place. Coal Bed Methane Gas analysis uses the Clay Rock Coal model. Gas Shale analysis and Pulse Neutron models are also available. The Source Rock model estimates source rock hydrocarbon values.
- Answer curves such as porosity, Vclay, Sw and mineral volumes are calculated on the fly and are available for viewing and export in LAS and TXT files. All the Calculated Curves may be included in the saved LAS or TXT file.
- Calculated Curves such as Khoyle (carbonate permeability indicator), Rxo/RT, Rwa and Rmfa assist in identifying potential reservoirs and hydrocarbons. ADSscf and DESscf calculations in the form of a+b*Curve^c may be plotted. Coal Bed Methane Adsorption and Desorption is often related to the density log with a function or transform of this sort. Mechanical rock properties Calculated Curves are available if shear and compressional sonic along with density are present.
PoiRat- Poisson's Ratio. need DTc and DTsh.
ShearM-Shear Modulus. need DTsh and density.
BRIT (brittleness) and YoungM (Young's Modulus). need DTc and DTsh and density.
MHSG-minimum horizontal stress gradient. need DTc and DTsh. user inputs Biot's poroelastic constant and reservoir, overburden and tectonic pressure gradients.
- The plot above with Calculated Curves Rxo/Rt in Track 1 and Rwa in Track 3 identify pay while AcImp and RefCf in Track 3 can aid in seismic understanding.
- Calculated Source Rock curves include TOC, TOC+0.8, S1, S2, Sfact, S1/TOC, S1+S2, PI, S3 and OI. An explanation of these Calculated Curves and the Source Rock Eval Mineral Model is found in the separate Source & Tight Oil Manual folder. Open SourceRock.html inside with a web browser to proceed with these models.
- Net pay based on user determined cutoffs is flagged in graphics and computed in text tables for perforation selection and export.
- Hydrocarbon reserves are estimated from the summation of level by level calculations.
- JLog does not do depth shifting or curve fitting and does not allow users to program their own models (no math pack). This can be done in a spreadsheet. Data is then saved in a tab-delimited text file and imported by JLog.
- The best way to check out JLog is to scroll through the JLog User Instructions that follow. A number of features will be demonstrated but not all. Working down each menu is the best way to check out JLog capabilities. You will see various plots, models and graphics along with Windows and Mac interfaces.
JLog User Instructions
Section I: File Menu
Here data is imported, graphics printed and saved as GIF and other file types. Data and answers can be saved as TEXT and LAS files for export to other applications.
With the View button of Import... of the File menu one should always open TXT and LAS files to view the curve names and LAS header information such as curve names and units. Correctly structured LAS files should explain the curve names and units in the ~Curve Information block. All curves should be imported in order to enable the appropriate JLog features.
One can also open the TXT or LAS file with a word processor and view and print the header.
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. Never use Open of the File menu to open LAS or TXT files. 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.
It is generally not a good idea to change the curve names. An exception would be an input TXT or LAS file that has density only in the form of density porosity such as DPHI. You could change the DPHI name to RHOB prior to import and then convert to bulk density when importing by advising JLog of the RHOF and RHOG values used to compute DPHI. If possible, always ask for the bulk density itself in the LAS file - JLog can compute density porosity from it later on.
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 (TXT) 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. This dialog is similar to that in previous versions. There are no dramatic interface changes from version to version. 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 Atlas button refers also to Baker Atlas. The BPB (Reeves, Weatherford) button may also apply to some Precision 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 USB key is in place along with the Sxjdk.dll DLL file in the JLog folder. Above that you will find the location of the Java Virtual Machine (JRE) in C:\Program Files on Windows PC.
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. Remember, 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. A pair of 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. Note the deepest resistivity curve placed in the far right slot will be taken as RT except for laterolog curves equivalent to LLS and LLD (HRLS HRLD through RS RD in the dialog box above) where RT will be estimated as mentioned earlier. Many of the common resistivity combinations are found in the buttons above. Note how the resistivity curves with shallowest depth of investigation are on the left with the deepest depth of investigation curve on the right. Suppose the dual induction resistivity curves are RLL3, RILM and RILD and are not found in the button array above. In this case RILD would be typed in the far right user slot #6 and becomes RT. RILM is typed in slot #5 just to the left of RILD and RLL3 is typed in to the left of RILM in slot #4. The first three user slots would each remain empty with ...... . Be sure to push the user button so the three new curve names will be recognized and imported by JLog. Then Click OK.
Please note that all 6 ...... have to be removed when typing in a user curve name such as RLL3, RILM and RILD. Do not leave any dangling . when typing user curve names. For example, typing RILD.. will not be recognized as an incoming RILD resistivity. RILD must be typed for RILD induction and so on.
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 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 the units would be K/M3, if 20.0 then units are 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. We would also want to change the density curve name from DPHI to RHOB in one of two ways. First by changing DPHI to RHOB in the LAS file before import or after import with Add New Curve Names... of the Edit menu.
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.
SAND.TXT neutron porosity units are in percent so the "Neutron in percent" button is pushed by the user. JLog will push the correct button for you in correctly constructed LAS files.
Always ask the logging contractor to include the density in gram/cc and neutron porosity in limestone porosity units in the LAS file regardless of the lithology and the scales used on the hard copy logs. Also request near and far neutron counts in the LAS file. Additionally check that digitized neutron porosity units are correctly stated in the LAS file. This also holds true for density when units are not in g/cc.
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
More Well Information: STATE: Queensland. COUNTRY: Australia.
Mud, filtrate and mud cake Resistivity:
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. Depth Reference Elevation: -999.25 since unknown.
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 by JLog later on.
Once the file is converted you will be notified. Open the resulting JLog (.JLG) file with Open... of the File menu to start the log analysis. Never open a TXT or LAS file with Open of the File menu - it is just for JLG files.
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. View Log Values... can handle 1000 levels of text - it is designed to check that the log data is correctly imported. 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. That is one reason why it is useful to have the neutron in limestone porosity in the LAS file. That saves JLog from converting the neutron to limestone porosity if it is only in sandstone or dolomite 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, the color, track and scale. 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 based on RT and Rxo Pickett plots that can be made later.
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 under Track 1.
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 caused by quartz effect on the 2 logs run on a limestone compatible scale.
Set Margins... allows one to set margins that are useful for print centering with Print Graphic of the Logs menu.
To save as a graphic file: select Save As... of the File menu and push the GIF button and name the file Jackson#1Logs.gif. This GIF file can be imported by other applications to be included in a report or just e-mailed.
To print: select Print Graphic/Logs... of the File menu.
Section IV: Plots Menu
Various lithology, Pickett, Rxo-RT and User plots and Histograms are plotted implementing up to 4 filters. This helps lithology identification and estimates of Rw, Sw, Rmf and Sxo.
Z-axis... menu item allows the user to select measured depth (MDEPTH), 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, compressional or shear sonic are present they may be selected with Which Neutron... , Which Compressional Sonic... and Which Shear Sonic... menu items.
The Litho & Source Rock 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 a 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 data which suggests either limey or slightly shaly sand. 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 during import.
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 in the 3-Mineral PEF models. Vclay can be mineral 3.
The MID... (RHOmaa-Tmaa) plot also helps identify lithology. The 3 main lithologies are quartz, calcite (cement?) and clay. This plot was used to pick endpoints for 3 minerals in the 3-Mineral Sonic model with Vclay as mineral 3 shown far above. Clay was picked at RHOmaa (RHOG)=2.90 and Tmaa=51. MID plot lithology identification is not always this good in unconventional reservoirs.
All available lithology plots should be viewed in order to determine the likely lithology.
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 such as 4700 to 4850 feet below.
The user drags one of the small square targets to change the fluid resistivity and m. Generally one wants the Sw=1 (Sw=100%) line to fall on the lower resistivity, clean data pattern. Once an appropriate Sw=1 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 porosity exponent needed to compute Sw and is often around 1.8 to 2.0 for sands and can be larger for vuggy carbonates. If there is a spread of porosity in a water zone it is possible to estimate m from the slope of the Sw=1 line. In the case of Jackson #1 with the RT-Density Porosity Pickett Plot from 4700-4850 feet one would find values around Rwa=1.5 with an m=2.0. Note the saturation exponent n=2.00.
The various Sw lines suggest a good hydrocarbon-bearing interval based on the selection of the Sw=1 line.
These Rwa and m values are recorded at Models menu/Variables/a, m, n, Rw and Rmf... . Check it to see for yourself. Set n=1.50
To filter out shaly data select GR as the first filter with Filter.../check Filter 1 and set the lower and upper GR filter values at 0 and 40.
Check the Delta Filter and set it up as follows:
LLD>=LLS+3.0. This means that only data where the LLD is reading 3 ohm.m or more than the LLS will be plotted. Since LLS=LLD in shale they will be eliminated. LLD>LLS in permeable sands and they are included.
The water zone is now separated from the oil-bearing zone due to the filters. Note with n=1.50 how the Sw lines are closer together due to a lower Sw for a given resistivity.
Note how it is possible to identify the top of the water zone at 4790 feet below the hydrocarbon bearing zone with measured depth (MDEPTH) in the z-azis.
With the Models/Variables/Density Porosity... menu item one can set RHOG=2.65 and RHOF=1.00 needed to compute Density Porosity for the Pickett Plot.
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.
Four filters in total are available. The Delta filter is very useful in some cases as seen above.
Use this characteristic to select only the permeable rock in various plots. 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 the GR and Delta filters. Be sure to click the OK bar after dragging the small target so the Sw=1 (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. Here the raw pBRIT brittleness indicator is calibrated to BRIT. A straight line is fitted through data plotted on a linear Y and linear X-axis as explained in the Source & Tight Oil Manual. A power curve fit is also available when Y and X-axis data are both in logarithmic scales.
Below RHOB and GR values are plotted to select Clay, Rock and Coal endpoints used to determine Eval lithology track
mineral volumes in the Clay Rock Coal Eval Mineral Model. Filters are all off.
Above, with Density-GR... of User submenu one 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 lithology track
mineral volumes in the Clay Rock Coal Eval Mineral Model. This is faster and easier 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.
Nine 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 and Effective 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 Ratio and Archie Sw equations 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 PEF... is appropriate for carbonates, mixtures of 3 clean minerals or 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 photoelectric 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 due to an increased PEF and U.
3-Mineral Sonic... is appropriate for the same mineral mixes as 3-Mineral PEF... but uses sonic instead of PEF. The user supplies the grain density (RHOG) and Tmaa of each mineral based on the MID plot. This model can be used when barite affects the PEF but is not always as good a lithology indicator as the 3-Mineral PEF. Mineral 3 can also be used for Vclay
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.
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. scf/ton means standard cubic feet of gas/ton of coal - scf gas volume is at 14.7 psi and 60 F (15.6 C). One ton is 2,000 pounds.
Gas Shale... uses both 3-mimeral models to estimate quartz, calcite and Gas Shale content or GR to estimate Clay and Gas Shale volumes. If the relationship between scf/ton and TOC is known then gas in place can be computed or a desorption relationship similar to that in the Clay Rock Coal model can estimate gas in place.
Source Rock... uses resistivity and a sonic, density or neutron porosity log to estimate Total Organic Carbon (TOC) based on the Passey delta log R technique. S1 and S2 (mg hc/g rock) may also be estimated from this TOC if lab data is available for calibration.
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.
Override Porosity will apply to Pickett Plot Porosity when making a Pickett Plot so be careful.
Which Vclay?... allows a selection of Vclay indicators needed to calculate Indonesian and Dual Water Total and Effective 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 such as VclayRHOmaa-Tmaa (no sonic) 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 (JLog needs to know if the Curve is in decimal porosity or not). 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.
Five 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.
The Ratio model is normally used for clean carbonates with an exponent of 0.625 that can be modified with caution. The model does not need a knowledge of m and n. Although it is designed for use with PHIT it can be used with a Vclay indicator and PHIE for reserve calculations.
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. This can be useful if there is more than one curve in the incoming LAS or TXT file that can be used for RT or Rxo.
Section VI: Eval Menu
The evaluation hydrocarbon reserves are estimated here after the appropriate model and variables are set earlier. 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 or Calculated 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 such as drainage area, formation volume factor and recovery factor.
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 from Jackson#1.JLG. 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 model and variables information can be saved with Save As... of the File menu. Choose Eval in TEXT button to do so.
Eval colors and names for minerals and fluids are set with Paint Minerals & Fluids... of the Eval menu. Gas-Oil contact depth and gas colors and names can be set here to color gas above oil.
Eval presentation is set with 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, Sxo, BVW, BVH, Ktimur, Ro (100% wet resistivity), FOIL and SwFoil 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.
See JLog Calculated Curves.pdf for a description and an explanation for the growing number of Calculated Curves.
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 PEF 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 PEF 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. Rw=1.50.
Note Calculated Curves Rwa and Ktimur permeability in Track 2. Ktimur is computed with E=6.0 and C=62500.
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 - the Khoyle carbonate permeability indicator (Calculated Curve) can help. Both override porosity models are Constant=0.0.
Note how SHALE and ANHYDRITE overrides above extend the 2-Mineral lithology model in the lithology track at the far right.
The 3-Mineral PEF model comes next. The 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 permeability is present.
The 3-Mineral Sonic model is next and is similar to the 3-Mineral PEF model except the MID plot is used to select the three lithology endpoints from RHOG and Tmaa.
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.
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.
The Gas Shale model determines gas reserves from a relationship between desorption or total gas in scf/ton and a log or a Calculated Curve. 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... . GR, 3-Mineral PEF and 3-Mineral Sonic lithology models may be used if the appropriate logs are available.
First the GR, the only model available before JLog version 6 will be described.
Enter the GR clay and GR gas shale values. The equation used to compute Gas Shale volume displayed in Eval Lithology track is displayed in the dialog.
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.
7. Here is a 3-Mineral PEF example.
8. For the Gas Shale... 3-Mineral PEF example Quartz and Calcite names and default values are used. GAS SHALE RHOG=2.85 and U=11.0 are estimated from the RHOmaa-Umaa plot shown earlier.
9. At this point the lithology model for the Eval Lithology track is set up just like it would be in a 3-Mineral PEF Eval model.
TOC should be calculated using the Passey method in the Source & Tight Oil Manual since a simple hypothetical relationship between scf/ton gas and TOC is to be used. LOM=10.5, RT=10 and sonic=75 baseline values as shown above in Example Evaluations/B: Gas Shale are again used for this model and set up under Plot Which Calculated Curves?.../TOC in the normal way.
10. With Eval/Net Gas Shale Pay... enter the scf gas/ton to TOC relationship, 640 acres drainage area and select a TOC filter so only TOC>1.0 is used to compute gas in place. TOC baseline resistivity and sonic values are set up under Plot Which Calculated Curves?... .
The relationship between scf/ton and TOC is scf/ton=30*TOC. TOC is a Passey model Calculated Curve that is explained in the Source & Tight Oil Manual. The TOC filter below is applied so gas in place will only be calculated when TOC>1.0.
11. The Calculate Quick Gas Shale Net Pay summary follows.
12. Eval/Plot Eval at 5 inch/100 feet (1/240)... gives the following plot.
The Source Rock model includes calculations of S1 (free thermally extractable hydrocarbons) and S2 (present day source potential) converted to BBL Oil knowing API oil gravity. A hypothetical example of S2 calculation based on data from Passey et al. follows. The separate Source & Tight Oil Manual is available for this model. Just open SourceRock.html in Source & Tight Oil Manual with a web browser
Before working with the JLog Source Rock model and associated Calculated Curves it is recommended that one read Passey, Q. R., Creany, S., Kulla, J. B., Moretti, F. J. and Stroud, J. D., 1990, A Practical Model for Organic Richness from Porosity and Resistivity Logs: American Association of Petroleum Geologists Bulletin, v. 74/12, p. 1777-1794.
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 the lithology track of the Evaluation plot. PHIE is in Track 4.
If a clay indicator is selected with the Sigma Clean Sw model then Clay, Mineral-1 and are PHIE in lithology track of the the Evaluation plot. PHIT is in Track 4.
If no clay indicator is selected with the Sigma Clean Sw only Mineral-1 and PHIT are displayed in Track 5 (lithology track) and PHIT in Track 4.
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 FOIL User Manual is available for the use of the FOIL model - just open satheight.html in FOIL User Manual with a web browser.
JLog Workflow Example
Here is an example of the workflow one might use to evaluate the dolomite pay in DOLO.LAS.
Import DOLO.LAS with File/Import in the normal way. This is a well written LAS file with NPHI, NPOR and TNPH in decimal limestone porosity units. With File/Reverse Depths... make a new JLG file since the LAS depths run from bottom to top and we want depths from top to bottom.
Plot the logs above with Logs/Plot Logs. The increased negative SP suggests the formation water in the dolomite above 8070 is a bit more saline than that in the wet sands below 8070. It is clear from the lower RXOZ/AHT90 ratio that there is pay above 8060.
Next identify lithology from a variety of cross plots.
Select NPORls with Plots/Which Neutron... since 3 are present in DOLO.LAS.
With Plots/Litho & Source Rock make the Density-Neutron plot above. It appears that radioactive quartz sand and clean dolomite are present.
The RHOmaa-Umaa plot above suggests radioactive quartz, calcite and dolomite are present with perhaps a little anhydrite or heavy mineral. Note the position of the M & M mineral mix called Other just below Dolomite. Other is a mixture of Dolomite and Clay and may be adjusted in JLog.
The MN plot above suggests permeable dolomite and the very high GR data is due to clay and shale. Quartz is somewhat radioactive in places. MN plots are very useful in identifying clays and shales as they stream to the lower left.
The Tmaa-Umaa plot above suggests radioactive quartz and clean dolomite and calcite are present.
At this point lithology is established and it is evident that pay is present. The porosity and lithology logs appear to be well-calibrated.
Next some of the variables will be quantified and pay confirmed.
With Plots/Pickett/Pickett Porosity... select Density-Neutron. Check "Draw Pickett Plot Bulk Volume Water (BVW) lines.".
The Pickett Plot (filtered on SP and GR) suggests Rw=0.075 (36,940 ppm NaCl) at 179.5 F at 8050 and m=2.10. Low Sw and low BVW confirm pay.
Rmf appears to be around 0.32 at reservoir temperature. This compares to Rmf=0.28 when the surface Rmf=0.748 at 63.5 F is converted to 179.5 F at 8050. m=2.10 appears to be reasonable.
With Models/Eval Mineral Models select 5-Mineral (carbonate + clay)... and leave default mineral values.
Next, with Models/Eval Mineral Models/Porosity/Mineral Override... set Override 1 to 8190 - MDEPTH - 8201 - green - BAD HOLE and Constant porosity to 0.0. This will prevent a false show in bad hole.
With Models/Variables/a, m, n, Rw and Rmf... set a=1.0, m=2.1, n=2.0, Rw=0.075 and Rmf=0.32.
With Eval/Net Pay... use default cutoffs and oil for 40 acres drainage.
Eval/Calculate Quick Net Pay... yields 1,444,000 BBL OIL in place/40 acres at reservoir conditions.
After Eval/Paint Minerals and Fluids... we have the following with Eval/Plot Eval and 5 inch/100 ft (1/240).. From: 8000 to 8200. Note the Anhydrite just below the pay that could also be a heavy mineral that sits right above the quartz sandstone. An examination of the cuttings might help here. Note also that Clay comes from the sonic-derived M & M model - not from the GR.
This workflow example demonstrates the steps one might make to evaluate DOLO.LAS.
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Revised 11 May 2015.