chocolate imperial stout

Ok, so I read the forums alot and this is my first post. I have been brewing about 8 years and I have been doing all grain almost 2 years. I brewed by first imperial stout about 2 months ago. Everything seems to be going good but I noticed some bubbles starting to form on the top of the beer in the carboy. The bubbles didnt start to show up until about 2 weeks in the secondary. I did add bourbon and oak chips in the secondary when i transfered from the primary. I was wondering if this normal. I guess that the bubbles come from the oak chips. Any insight on this would be great. Thanks!

Yep, the oak chips are providing nucleation points.