The size of the environment would depend on the species and what it ate, from what I have read on animals in general, herbivores need a much larger territory as to not eat all the vegetation in the area,and a carnivores territory is dependent on the main source prey.
example of a herbivore dinosaur enclosure would have to be rather large, I would say for that is small you would need a the enclosure to be at least 8 football fields minimum and that is a rough guess, that way you can provide various plants to see see what type it eats the most of and what makes them sick and so forth.
as for a small carnivorous dinosaur you would maybe need a enclosure the length of at least 2 football fields maybe 3, since you would more than likely providing the food for it in the event of studying it by placing livestock in the enclosure (not chained down) so you can study it's hunting habits.
and in the event they do escape you can have a collar with a device that that would eject a fast acting poison or something if it gets outside of a certain range.