After the dry gas reservoir with low and extremely-low permeability

but without identified edged and bottom water has been produced for a period

the formation pressure of different areas decreases inhomogeneously

while the gas saturation (S

g

) changes slightly

which can not be used to describe accurately the distribution of remaining gas.Therefore

the formation pressure in production process is usually used to describe qualitatively the distribution of remaining gas.According to the state equation of real gas and the definition of recoverable gas reserve

the functional relation between produced degree of recoverable gas reserve (K) and formation pressure (P) has been established

by which the formation pressure distribution during production process can be transformed to the distribution of produced degree of recoverable gas reserve

realizing the quantitative description of remaining gas distribution.