GENERAL INFORMATION
The PETROCK program is aimed for interpolation of unevenly sampled petrophysical data, the density or magnetic susceptibility, on an evenly sampled grid. Naturally, other data such as geochemical and geophsycal data could be used as long as it has some correlation with the underlying geology. The two main purposes of the PETROCK program are: a) to create improved maps of the spatial distribution of petrophysical parameters, and b) to create data for initial 3-D models used in potential field modeling and inversion.
The program uses moving window strategy in which the gridded values are estimated from the nearest sample points using both the average mean and the inverse distance weighted mean. The program uses the digital geological (lithological) maps to provide additional weights to points inside the same lithological unit. An additional limiting condition can be used to remove outliers from the petrophysical data inside the investigation area or inside each lithological unit. Rejection rules of rock types within lithological units are further used to define the background value for the petrophysical parameter of each lithological unit. The objective is that PETROCK gridding is more reliable than normal interpolation in areas where sampled data are not available.
The petrophysical data are read from column formatted text files. The polygon information of the geological maps is read from text files that have been converted from Mapinfo MID/MIF files into a special LIT file format using the MIF2BNA program (Pirttijärvi, 2005). Input parameters are given either manually from keyboard or using a separate text file (PETROCK.INP). Output data are saved into column formatted text files.
Please, read the PETROCK_GUIDE.PDF for further information about the program usage.
ABOUT THIS DISTRIBUTION
This distribution file contains the software (PETROCK, MIF2BNA and PETRAUS) and example data (FINKPPM.DAT) and results (FINKPPM folder) where PETROCK has been used to interpolate rock geochemical data of Finnish bedrock using a large-scale digital geolgical map of Finland.
THE DIGITAL MAP
The digital map of Finnish bedrock in scale of 1:10 million by by Geological Survey of Finland (GTK) is used in these examples. The original map data is available at http://www.gtk.fi/geotieto/kartat/kalpe/kalpe10milj.html. It has first been exported from ESRI Arcinfo SHP file format into Pitney Bowes Mapinfo MID/MIF format and the converted into PETROCK's LIT format using the MIF2BNA program. See the example of MIF2BNA conversion in the corresponding folder.
The final map data is in the 10MILJ2_KP.LIT file.
THE DATA
The data used in this example is not petrophysical but geochemical. It is taken from the Rock Geochemical Database of Finland by GTK. The original data is available at: http://www.gtk.fi/geotieto/aineistot/uusimmat/metadata/rgdb.html.
In order to use the data in PETROCK the PETRAUS program has been used to assign each sample point a lithological code based on its location on the geological map. See the example of PETRAUS in the corresponding folder.
The final lithologically weighted geochemical data is in the FINKPPM2E.DAT file.
Markku Pirttijärvi
Oulu, 7.11.2011
P.S. The BNA (digital geological map and borders of Finland) and BLN (blanking) files in this folder are used to make Surfer plots.