Drilling / Estimate Questions

Hi All,

Here are a couple of easy questions for the learned individuals among us.

1) No doubt there are a number of factors that would affect P10 to P90 quantities.
But it there any one or two major factors?
My guess having zero knowledge would be the net depth of a geological formation can be determined but the gross oil/gas intervals within the formation cannot be. And this would be the biggest factor?
Are there different factors for oil vs gas?

2) They talk about designing a new drill for the PS3 drill. This one will be to only test the Caley structure, while the previous drill was to test other areas as well.
What would be the differences?

Is there some good videos / reading out there covering this type info?

thanks