Abstract:

The prediction method for CBM reservoir production performance could be developed by combining the material
balance equation and productivity equation. When this method was developed by previous researchers，the initial adsorbing
saturation of CBM reservoir is neglected，making the previous method applicable to only the saturated or supersaturated CBM
reservoir. In this paper，the material balance equation is re-derived by taking initial adsorbing saturation into consideration，
and then the production predicting method was established，applicable to under-statured CBM reservoir. It is demonstrated
that during water drainage period，this method can predict water rate with an average relative error of 8%，and then during
gas production period，it can predict gas rate with an error of –13%，which can meet the accuracy requirement of production
engineering.

Key words: coalbed methane, material balance, production performance, production rate, prediction