The hydraulic fracturing process solves this problem by generating fractures in the rock.

Some subsurface rock units such as organic shale contain large amounts of oil, natural gas or natural gas liquids that will not flow freely to a well. They will not flow to a well because the rock unit either lacks permeability(interconnected pore spaces) or the pore spaces in the rock are so small that these fluids can not flow through them.
The hydraulic fracturing process solves this problem by generating fractures in the rock. This is done by horizontal drilling a well into the rock, sealing the portion of the well in the petroleum-bearing zone, and pumping water under high pressure into that portion of the well. This water is generally treated with a chemicals and thickeners such as guar gum to create a viscous gel. This gel facilitates the water's ability to carry grains of frac sand in suspension.