Drillhole Import - LAS Data

The Drillhole system provides the ability to import LAS format files into a Drillhole project.

To Import LAS Format Files:

  1. On the DH-Data menu, click Import > LAS File(s). The Drill Hole - Import LAS Data dialog is displayed.

  2. Using the LAS File(s) to import browse button, locate the LAS file to import.

  3. From the Point database name tag drop-down list, select the name tag and specify the desampling/averaging interval (cm).

  4. Then, using the drop-down list, select the interpolation method. Click the OK button to import the LAS format file.

Drillhole - Import LAS Data dialog options

LAS File(s) to import

Select one or more LAS files for import. All files will be imported into the selected database.

Point database name tag

Select the point database name tag. The full database name is created by appending this tag, along with an underscore, to the drill hole project name. For instance, for the drill hole project "Tutorial", and the name tag is "geophysics", then the database "Tutorial_geophysics.gdb" will be opened (if it already exists) or created.

Desampling/ Averaging interval (cm)

Imported data is desampled to this interval on import. If data already exists for this hole, it too will be resampled to this interval. The first and last depths are decreased and increased, respectively, to the nearest even multiple of the input interval.

If the drill project is using feet instead of meters, this value is input in inches (in). Data will always be converted to the drill project's coordinate system (either meters or feet). In a LAS file, the units of length are recorded (for instance) in the "STRT" parameter, as "STRT.M" or "STRT.F".

If this value is left blank, then the data is imported "as is", with no averaging or desampling.

Interpolation Method

Both Minimum curvature and Akima interpolation methods define a second-order cubic spline to interpolate dummy values. Minimum curvature produces the smoothest possible interpolation, but may create undesirable over-shoot in some areas, while Akima interpolation tends to be less smooth, but does not suffer from unreasonable over-shoot. Prediction uses a maximum entropy prediction algorithm to predict the missing values such that they will have noise characteristics similar to the original data; when choosing this option, you can force the two ends of each line to be continuous and maintain periodicity. This is specifically needed for applying FFT filters. Linear is a standard straight-line technique, and Nearest assigns the value of the nearest non-dummy point.

Application Notes

The LAS import currently supports version 2.0 LAS files only.

Log File

A log file "LASImport.log" is created during the import process to alert the user to instances where pre-existing data is modifed, or if the imported data is averaged or de-sampled. In addition, it notes if imported field names must be modified to form valid Geosoft channel names. Errors, caused by such things as invalid formats or data in the LAS file, terminate the process, and the log file will not automatically be displayed.

Pre-importation testing

Before data is imported, tests are performed to determine if differences between any pre-existing data’s depth intervals, the LAS depth interval, or the specified import depth interval will result in overwriting, averaging or interpolation of existing or imported data, in other words, any time the results of the import may not be exactly as expected. If these differences are found, then a warning message is displayed, and you have the option of skipping the current file. A log file with information on the discrepancies is produced each time, but is not displayed. If you wish to view the results, open "LASImportTest.log", which will give similar information as is returned in the "LASImport.log"file.

Importing Data to a New Table

Data is always imported at the specified depth interval, or if the interval is not specified, the data is imported "as is".

The following procedures are followed according to whether the LAS depth interval is the same or different than the specified depth interval.

  • If the intervals are the same, the data is imported "as is". Dummy values in the data (e.g. gaps between valid items) are not interpolated, and remain in the data.

  • If the specified interval is greater than the LAS depth interval, the values are averaged over the new intervals.

  • If the specified interval is less than the LAS depth interval, values are interpolated according to the interpolation option selected above. In this procedure, the dummies are ignored for the purpose of interpolation, so the output data has no gaps.

Merging Data to an Existing Table

The following merging process is followed if data already exists for hole in the database into which data is being imported.

  • If the data interval between existing data is constant and consistent throughout the data (e.g. no gaps, repeated values, etc.), and if the input interval is larger than the existing interval, then the existing data is averaged over the new data intervals, and the new average values.

For example: If the original data is sampled at 0.1m, and the new data interval is 0.5 m, the following occurs:

Original Depths

Original Data

New Depths

New Data

5.5

3

5.5

2.5

5.6

2

5.7

*

5.8

*

5.9

5

6.0

*

6.0

5.0

6.1

3

6.2

7

6.3

2

6.4

*

6.5

*

6.5

5.5

6.6

*

6.7

9

6.8

*

In the above example, the new data value for 5.5 averages all values such that 5.25 <= old depth < 5.75., and the new data value at 6.0 averages all values such that 5.75 <= old depth < 6.25. Note that the lower ends are inclusive, while the upper ends are exclusive

  • If the data interval between existing data is not constant, or if the input interval is equal to or less than the existing interval, then the data is interpolated, according to the selected interpolation option.

  • For example: If the original data is sampled at 0.5m, and the new data interval is 0.1 m, the following occurs when the "linear" interpolation option is selected:

    • Original Depths

    Original Data

    New Depths

    New Data

    5.5

    2.5

    5.5

    2.5

    5.6

    3.0

    5.7

    3.5

    5.8

    4.0

    5.9

    4.5

    6.0

    5.0

    6.0

    5.0

    6.1

    5.1

    6.2

    5.2

    6.3

    5.3

    6.4

    5.4

    6.5

    5.5

    6.5

    5.5

    6.6

    *

    6.7

    *

    6.8

    *

  • Data values before the first valid data point, and beyond the last, get dummies (*).

    If the input depth interval differs from the original data depth interval, or from the imported data interval (step), then new minimum and maximum depths are calculated to bracket the minimum and maximum depths of both the original and imported data. In addition, these values are guaranteed to be integral multiples of the interval itself, so, for instance data with an interval of 0.5 would never increment like 6.1, 6.6, but rather 6.0, 6.5 etc.

    Specifics of the data merging process are written to the log file.

    Reading the Well Identifier

    LAS files provide several identifier tags for identifying the well. The following procedure is used for determining the name to put into the collar table:

    1. First, if any of "UWI", "WELL" or "API" is given as "N/A", it assumed to be "undefined" below:

      1) If all of the above ("UWI", "WELL" and "API") are undefined, and there is a "HOLE ID" in the "LAS_SECTION_OTHER" block, use that, else...
      2) if the "UWI" is defined, and is NOT equal to "N/A" use it, else...
      3) if the "WELL" value is defined and is NOT equal to "N/A", use it, else...
      4) if the "API" value is defined and is NOT equal to "N/A", use it.