The " Oriskany Sand ", an important gas sand, has produced in excess of a trillion cubic feet of gas in West Virginia.
2.
For a polarity reversal to occur, the shale has to have a lower acoustic impedance than the water sand and both are required to have a higher acoustic impedance than the oil / gas sand.
3.
For a dim spot to occur, the shale has to have a lower acoustic impedance than both the water sand and the oil / gas sand, which is the opposite situation required for a bright spot to occur.