The following is a short description of the procedure taken from data search through interpretation of the age surfaces. The objective was to retrieve well data; i.e., position, elevation, and as many viable formation top depths.
For every state, there was research done to find well files. Wells were gathered from various sources. All wells were labeled by source. The files obtained were downloaded in the available formats.
To process to a GeoDatabase, different methods were used depending on what was needed to convert the downloaded files to a usable format. For some files, special coding had to be written in order to be able to use the files downloaded.
- Texas required FORTRAN coding and extensive sorting;
- An automated method was developed to extract tops directly from various state websites;
- Others were transformed from shp to csv to excel to geodatabase;
- Many states required to download one well at a time and create an excel file by typing the information needed.
- For a number of states the data needed had to be downloaded into several separate files because no single file would contain the different types of information we needed. These files would then be combined into a single spreadsheet using MS Access.
The wells that didn’t have positioning information or tops were deleted.
The wells with some type of position data were further processed depending of what type of positioning was available.
- If the file didn’t have coordinates in latitude and longitude but did have a projected easting and northing, the x and y were transformed into latitude and longitude.
Some important well control came from states with only Township-Range-Section location. The T-R-S data were transformed into latitude-longitude one by one; with this method the well position could have a maximum 2,400 foot error. This error was higher than desired but deemed necessary due to the well’s geographic position.
If a well listed a reference elevation, that elevation was applied to the top’s depth to calculate a Below Sea Level (bsl) depth. If no reference elevation was listed, one was calculated for the well (see #2 below).
The formation-to-age correlations are not straight forward as formation names as related to an age change as one traverses the US. Determining the age of all the formation tops in each well was done using several references and local stratigraphic charts. For the age of interest, its shallowest occurrence in a well was used. Note, only formations of the most upper/latest age of interest were used. In the deliveries we have included a spreadsheet labeled “Interpreter’s Notes” listing what formation/age correlation was used per geographical area.
For each of our age surfaces, the top depth was mapped and compared to the surrounding depths. Values which did not make geologic sense were removed and not included in the database. This interpretation and editing step was critical and led to including the most reasonable data.
Incorrect or at least not sufficiently correct depths could result in several ways. For example:
- The top/formation/location was mis-interpreted or mis-transcribed in the original files; this type error would range in the 100’s to 1000’s of feet and was easily deleted.
- Some wells listed no reference elevation so one was calculated from a high resolution DEM. However, imprecision with the DEM and the well depth datum (KB, GL, DF etc.) could cause an error range of 10’s feet. This was deemed acceptable for mapping at this regional scale, and these wells are included in the database.
- Some wells did not include top depths but only formation at the well’s TD. This would cause an error range of 10’s feet or greater. If this type error was determined to be too large, it was deleted during the interpretation and editing step.
The entire US Continental well database is been datum corrected to below sea level (bsl) depths and transcribe to Latitude & Longitude positions. All formations with corresponding depths were preserved.