potentially, if it's economic enough. The typical shale wells that you see being drilled have very high initial rates, but then fall dramatically. They are a totally different well profile than the wells offshore (where shale is not being targeted).
Will shale ever be targeted offshore? Maybe, in a world where oil is $150/barrel and we're all still demanding it. A few things are holding back hydraulically fracking offshore:
1) Freshwater - The current "recipes" need freshwater, and do not work with salt water. Fracking uses a lot of water. This seems solvable, but currently not a lot of research in this area.
2) Sand - A TON of sand is required to keep these fracks open - we are talking truck load upon truck load of sand (sometimes over 100 truck loads). How does this happen in an offshore environment? The logistics would be quite tricky (and expensive).
3) Equipment - Typically, onshore drilling rigs drill the well, and then move off the location and the fracking unit comes onto the location. The fracking unit can be as big or bigger than the drilling unit spread. To translate this to an offshore environment would be logistically impossible - we would basically need specialized "fracking drill ships" to equivocate this. To date, these don't exist (but could potentially exist in the future).
4) Institutional Know-How - for how big these companies are, it's quite surprising that the big players haven't had much success fracking - ExxonMobil, Chevron, ConocoPhillips, BP, Total, Shell - all of these guys do some fracking, but it's not really their core business (offshore is). The fracking revolution was built on the backs of the smaller industry players (and these guys don't do offshore well). In tech parlance, this would be loosely equivalent to why Microsoft/Yahoo/Oracle have never really done startups well (just buy the ones that do well).
It's important to note that fracking we see in the news are a totally different target than conventional oil wells. So the permian basin, which is "so hot" right now, had conventional targets that were tapped out in the 1980's/1990's. The shale wells being drilled are entirely new wells at different targets, so you wouldn't use the fracking techniques that we hear about to extend the life of an existing well - you would drill a totally new well.
To give you an idea of the costs involved, an offshore deepwater drill ship in the Gulf of Mexico has a rig rate (all in) of about $500k/day. An onshore rig in the permian basin drilling shale wells is probably around $50k-$75k. It's a 10x difference (why is why countries like Brazil, Venezuela, etc. have struggled during this latest "boom").