Kadaicher can probably explain better, but i'll give a shot.
An exploratory well can become a production well. If memory is correct i believe this was the case for the Macondo well but in order to turn the exploration well into a production well BP would have brought in a different rig to re-enter the well, drill out the cement and recomplete the well. They also could have drilled production sidetracks off the initial well. Each rig requires its own drilling permit: one for exploration and another for recompletion/production. I also wouldn't be surprised if each sidetrack required a separate permit.
From what i see, there are many types of permits beyond a simple split between exploration and production drilling. For example, there are also permits for going into a production well to alter the well or infrastructure within the well, clean tubing, or inject stuff into the reservoir to stimulate production.
