Lobster:
A bigger hole in the shale will probably produce more flow. Cecil's advice regarding professional help is a good one. You could also run the risk of degrading water quality. The general equation governing flow is as follows.
Q=kia
Q = discharge (flow)
k = hydraulic conductivity (permeability)
i = gradient (difference in hydraulic head)
a = cross sectional area (hole in the shale)
Since "i" and "k" are physical properties that you cannot change, that leaves "a". There are too many variables without knowing the hydrogeology of your area to comment much further, but a large diameter well may produce more water. If you want to pump water, that is a different story.
