They are in the 'Database/Albums' folder, but they are alpha-numeric (with multiple entries for one smart album). I don't think there is a way to identify the ones that are part of your smart album unless you know the date and time you created that album and are sure no others were made at that time.
You can test this by creating a new test library > import some images > look in that library package Database/Albums folder to see 3 pre-populated album files > create a new smart album > look in Database/Albums folder again. You will see multiple new album files in addition to the 3 pre-populated ones.
At least that is what I see on a MBP running OS X 10.8.4 and AP 3.4.5.
It might be safer, to restore your Aperture library from te last backup, before you added your smart album.
If you really want to try to delete single albums, compare the contents of the 'Database/Albums' folder in your backup to the current contents and delete the albums that have been added since then.
Interesting, I was able to confirm what you are seeing (at least partially).
That is if I create the smart album, filter on the file size and then switch file size to orientation Aperture does crash. However when I reopen Aperture it does not crash and if I look in the smart album the setting is still File Size not Orientation.
What I assume I am seeing is that the Aperture library is not being updated with the Orientation setting before the crash.
Of course what I am seeing could be due to the fact that the library I am testing this on is small, made just to test this, and with more images in the library it would take longer to crash and have time to update the smart album settings.
However it happens it doesn;t help your situation.
Now for the not so great news, smart albums do not exist in one place in the database unlike regular albums do so deleting a smart album is not as easy as going to one spot in the library and removing a file or editing a plist file.
Léonie's suggestion to restore from a backup prior to the creation of this smart album is your best bet. If you don;t have a backup try running the Aperture first aid steps. First do a repair and if that doens;t help do a rebuild. Hopefully one of those will correct the issue.
After that it will be a question of hunting and pecking in the library to try and remove enough of the smart album to get Aperture to stay open.
Or else you might try contacting Apple and trying to get through to the Aperture team and explaining this.
A possible solution.
With Aperture closed:
In Finder locate the Aperture library, select it, control click on it and select Show Package Contents. This will revel the library. Now go to the folder named Database and then into the folder called Albums.
Set the Finder window to sort on Date Modified, the file with the .apalbum extension that is at the top of the list should be the definition of the smart album in question.
To be sure open a Terminal window (Terminal is located in the Utilities folder of the systems Application folder) and open it.
Type strings followed by a space but do not hit return, now go back to Finder and drag the .apalbum file from the top of the list into the Terminal window and drop it. The path to the file should be on the line with strings with a space between them. Now hit return.
You are looking for the name of the smart album. It should be about midway through the printout in the Terminal.
Assuming this is the correct file drag it to the trash. Now start Aperture while holding down the option and command keys to get to the first aid window. Do a library Rebuild (a repair will only cause Aperture to recreate the .apalbum file) this should remove the smart album from the library.
If this works when Aperture is done rebuilding it should open OK.
Note you should have a backup of the library before doing this, between doing the rebuild and going into the library to delete files there is a chance things could get worse.