The Tight Sand Reservoir Characteristics and Gas Source in Coal Measures: A Case Study of Typical Areas in China

Table 5

Potassium contents of coals and shales.

Lithology	Place and time	Average K content (%)
Shale	Shales in large basins around the world [55]	3.24
Shale	27 shales in China [55]	2.67
Shale	2 shales in the Jurassic in the Tarim Basin [21]	2.64
Shale	Shales in the Permian in the Sichuan Basin [51]	0.86
Coal	Coals in China [56]	0.214