Monday, September 7, 2009

Comeback, DISC, and SMT depth conversion

After a hiatus of about 9 months, I am dusting off the Seismos blog. A few things have helped me come to this decision.

First, I set up a blog for my wife Dolores, former SEG assistant editor for The Leading Edge. If you are interested, here is the link: Proubasta Reader The experience of setting up and customizing her blog gave me some good ideas about how to maintain my own. Back in January 2009, I was just playing around with the blog and found it onerous to come up with daily or even weekly entries. Now I see the point is not to wait for big things to write about, but say a few words as things come up. Closer to a postcard than a book chapter.

Another push came from my being nominated for SEG Distinguished Instructor Short Course (DISC) for 2012. It still requires approval of the SEG/EAGE Executive Committees in about 6 weeks at the SEG convention here in Houston, which brings me to another push. For this approval meeting, I need to supply the DISC committee chairman, Tad Smith, with a 2 page summary of what I have in mind for my DISC. What better place for this to develop than on the blog, leading to a Seismos column in TLE (which will surely have to be published after the convention due to editorial backlog).

And finally, assuming I am approved the DISC instructor must write a book that is used as notes whenever the 1-day short course is given. So as I get the book in shape over the next few months I can track progress and interesting topics on the blog.

Enough for now about the comeback and DISC.

************************ SMT depth conversion note ******************

I'm teaching a graduate 3D seismic interpretation class this semester at U Houston (GEOL6390). The software used for this class is Seismic MicroTechnology's (SMT) Kingdom software (v.8.4). We have a generous and important 30-seat license donation that makes this popular class possible. This semester we have 26 students, limited by good hardware seats and optimum instructor-student interaction.

I am also principal investigator for a DOE-funded CO2 sequestration characterization project in the Dickman field of Ness County, Kansas.

In both cases, the issue of depth conversion comes up. For the class we have 3 assignments, the last of which is prospect generation in the Gulf of Mexico using data donated by Fairfield Industries (thank you very much John Smythe). There is one well in the project that allows for depth control. For the Dickman project we have 135+ wells and a 3D seismic volume, so a more ambitious integrated depth map is in order.

But just today I was testing various ways to track and depth convert the Mississippian horizon at Dickman. First I carefully did 2D picking in each direction, keeping an eye on the event as it passed through each well with a Miss formation top pick. Using a shared time-depth (TD) curve all the wells lined up nicely with the seismic event. Next came 3D infill picking that did a good job.

But how to convert the time structure horizon to depth? I created grids to infill a few small tracking holes due to noise and weak amplitude. It seemed logical to then depth convert the time-structure grid to depth using the shared TD curve. But strangely, this did not let me constrain to an existing polygon. Further, it required some additional gridding parameters, even though you would think it just needs to look up each already gridded time value and find the associated depth from the TD curve.  I was also hoping for the ability to cross-plot the seismic gridded depth values at all wells that have a Miss formation top picked.  From the cross-plot there is enough information to generate a v(x,y) velocity field, extending the v(z) time-depth curve, so that all known tops are matched exactly and some kind of interpolation happens between known points.  No can do, as far as I can see.

Finally, it would be nice to be able to plot the TD curve as a simple time-depth crossplot, and do this with several TD curves to investigate lateral variability.

A different, perhaps better, approach is to depth convert the seismic data directly using the TD curve (TracePAK) and then re-track the Miss event through the depth volume. SMT does not allow the tracked time horizon to be extracted through the depth volume, again strange since the TD curve is known.

The jury is still out on this one. Perhaps you have a better idea....

No comments: