I participate in a forum that tracks drilling, fracturing in Oklahoma. One of the "shale plays" is in the Woodford formation. Here is an explanation that Mr. Barnes posted there about how he teaches about oil shale, horizontal and hydraulic fracturing.
When I teach geology to elementary school kids, we eat our lab experiments! I can do all sorts of things with cakes, chocolate pudding and straws, biscuits, oreos, jello, etc. My theory is that we learn by looking, hearing, and touching, so whatever works for them works for me!
I am visualizing a warm giant buttery biscuit with raspberry jam in the middle. The seeds of the jam are the ceramic balls in the frac fluid holding that porosity open. The liquid part of the jam is the oil oozing out of the Woodford. The flat buttery layers of the biscuit resembles the silty/shale layering structure of the Woodford. One of those bendy straws is poked into the biscuit-1st part straight down and then the right angle and then the long part right into the jam parallel to the layers. Suck on the straw and up comes the "oil".
Using his analogy, one can quickly visualize how horizontal drilling can get to more of the oil and gas.
I made another post that is more technical and gives a better and more accurate explanation. Please follow the links there to gain a deeper understanding.