Onshore wells in Geocap
- Stein Midtvaage
Geocap 7 handles offshore wells, but has an issue with the elevation information for onshore wells. This article proposes a solution to the issue.
As reference, see https://itportal.ogauthority.co.uk/web_files/gis/Documents/OGA_WellboreStandard_2016_005_7.pdf which includes the following picture:
The issue in Geocap is that there only are fields in the well header for KB and water depth. When creating or editing a well it is not permitted to enter a negative water depth; it must be a non-negative number. This means that we cannot record the ground elevation onshore.
All well parameters must behave in the same way, regardless if the wells are onshore or offshore. If we use the “water depth” field in Geocap to mean ground level onshore or offshore in a well, then it must be a negative number onshore, where we are above MSL, because we use a positive number offshore where we are below MSL. There are several possible solutions, but I think the most elegant is to allow “water depth” to be entered as a negative number, and to add a help text that guides the user to register onshore wells with the ground elevation as a negative number in the water depth field. This for future releases.
Two workarounds are possible at the moment:
- when wells are created from a file, negative water depths are allowed;
- a negative water depth can be entered with the script command project setmember well::wd <number>.
Ground level elevation relative to datum is more important than water depth, and I therefore recommend to always enter this in the “water depth” field. When we are offshore, and use MSL as datum, they will be the same. That is what we do 99% of the time with Geocap, so for most users this problem does not come up. (I mean; when we are offshore it is not the thickness of the water column but the position of the seabed relative to zero depth - the datum - that is most important.)
This script (i.e. a Script command) will enter ground level elevation as a negative water depth. The user enters a positive number.
# set ground level elevation as a negative water depth in an onshore well
set gle [qgetdouble "Onshore well [project getname]" "Ground level elevation" 0.0]
if {$gle == ""} {
puts "Ground level entry aborted"
return
}
set wd [expr $gle * -1]
project setmember well::wd $wd
Ivar Meisingset