The following link was posted anonymously on the Hegnar forum - so I can't give credit where it's due. Not exactly an in-depth analysis, but it points the finger of blame at sub-standard casing rather than the actual fracking of wells.
http://www.youtube.com/watch?v=NW_xJqPjE_I&feature=player_embedded
(PS. Is it just me or does the interviewer resemble Dan Aykroyd? LOL)