new coat same model...., page-4

My intent is not to be facetious, but I think you mean that "Gas Sand is the best type of reservoir as it is COARSER (holds more) with better porosity and pressure".

Sand has high primary porosity (space between grains) because it is coarse. It also has very good connectivity between pores spaces. Shale, on the other hand, is very fine grained and has very poor primary porosity with poor connectivity (so even if the pores are full of gas/oil, it can't get out). Shale reservoirs rely of secondary porosity such as fractures. "Fraccing" is a method of artificially fracturing shale etc to release primary porosity and increase connectivity.