Bored as heck yesterday, and was wondering about well control; when hitting high pressure pockets, or reservoirs while drilling (kicks).  Found a video which explains that the blowout preventer seals against the drill pipe and the operation proceeds. The kick is circulated out, and drilling mud & hole pressures re-balanced; which keeps everything below in tact (stable). Here's the video if interested:  
https://www.youtube.com/watch?v=G-lfa_wwpYQ