KB or GL?

For this entry, i’ll relay some recent ‘excitement’ which gripped our Data Support internal e-mail group. As you see from the following exchange, it can take us some time, investigation and research to reach a answer a seemingly simple question. 5 people in our Support, Data and Design teams worked on this:

Support-Olga:  In deviated survey what is the depth referenced from? KB or Ground Elevation? Or from something else?

Data-James:          KB

Support-Olga: Then why do I not have it in the customized exporting setup?

Data-James:          Good question – I’m not sure. The depths are most definitely measured from KB. You may want to forward this question about a geoSCOUT dialog box to the design group for an explanation.

Support-Olga: Hello Design group! Could you please clarify the issue below? Thank you!

Design-Marc: Not sure why it’s not there (before my time).  It will be part of the Header information in the 7.9 new version of the viewer.  It is also currently present in the header information of the “Standard (with Header)” option.  The export seems to have the KB included as a field, but I didn’t find an example that actually had it populated.

Support-Olga: According to the client, it is NOT referenced from KB. Could you please confirm what the depth is referenced from? KB or Ground Elevation?

Data-Steve: We’ll take a look at some surveys to confirm, but here’s a quick reference I found on the internets.


Depth Reference

The point in a well from which depth is measured. alternatively, the depth reference is the point at which the depth is defined as being zero. it is typically the top of the kelly bushing or the level of the rig floor on the rig used to drill the well. the depth measured from that point…

Data – James: Directional surveys are measured relative to KB. Just to confirm this, I reviewed a few dozen original survey files and they were universally measured from KB.

Support – Olga: <The Client> is not saying that our data are in error. He called to ask a question and said that he does not think that the data is referenced from KB. I had the same issue about a month ago and Sean first said that it was referenced from KB and then he said that it was referenced from Ground Elevation. I would appreciate if you could investigate on the issue.The user did not give any specific examples, it was just a general question.

Data-James: This is my basis for saying surveys are referenced to KB: When I reviewed dozens of original directional survey files, they all either indicated outright that the depths referenced to KB or the final station point MD matched the MD for the well. If GL was the reference on the survey, the last station point MD should be several meters shallower than the well’s MD. Since well MD is relative to KB, if the last station point MD matches, KB is the reference.

Design-Mark: I will discuss this on Monday with Sean.  There is a notation in the SLX file that Olga showed me that indicates that Sean found a reference about GL being used, but I’ve never seen an example of this.  Nearly all surveys I’ve seen, as James mentions, specifically reference KB…they’ll actually report measured depth as “m KB”.  For the ones that didn’t, it’s pretty clearly implied.

I think we can safely say that KB is the standard reference.  Any survey that uses ground-level elevation as its depth reference is going to be extremely rare, at least in Canada or the US.  But as said I’ll talk to Sean about it.

Design – Sean: My notation was based on review of the original design document for the Virtual DiSDA product (Ernie Montgomery, 1983) which specified that the standard for capture and reference would be GL.  Sometime around April 1987 references appear for KB as an optional element in the data gathering chain.

Support-Olga: So what should I advise the client then? What the depth is referenced from the deviated surveys that we have in geoSCOUT? KB or Ground Elevation?

Design – Sean: Sorry for the confusion, but it took a few more readings of this whole e-mail chain to realize what the problem was.  I want to thank Marc for helping me to figure out what we were dealing with here.

1)      All Directional Surveys are now referenced from KB, and have been since we acquired the database when we acquired Virtual Computing Services back in 1997.

2)      In the early 1980’s this was not the case, and the original design of the DiSDA database was defined around GL.

3)      It is possible that Virtual may have missed converting a few surveys to KB from GL when they converted to the KB standard.  If a client finds a survey where they are questioning the accuracy of the data we need to treat it like any other Data Issue.

4)      The export item that triggered the original question was included for backwards compatibility with old surveys that clients may have had on hand.  It allows us to export the data using GL as the reference.

5)      In the 13 years since we first acquired Virtual this is the first time that this question came up, so you can understand how we had to dig through a fairly large amount of old documentation to come up with the final answer – sorry for the delay/confusion on this.

So, If we ever get asked this again, we’ve got the answer.


About James Brownbill

I've been with geoLOGIC since 1998 and in my current role as Manager of the Data group since 2005. Blogging is new thing for me and I will either succeed in making stories of Oil and Gas data interesting or I wont.
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