Application of material balance method to productivity forecast in coalbed methane reservoir

Aimed at the production characteristics of coalbed methane wells, a performance prediction mathematical model based on material balance method is established for fractured vertical well and horizontal well, in which the adsorption of coalbed methane, coal swelling/shrinkage and effective stress are concerned, equivalent well diameter model is introduced, pseudo pressure function is combined. The performance prediction can be achieved based on few available data by mathematical model. The change of relative permeability is analyzed. The parameters needed and calculated amounts are decreased. The individual well deliverability can be effectively enhanced through adopting horizontal wells rather than fractured vertical wells under the same geologic conditions and the productivity is about 2.3 times of vertical wells. The lead time is shortened. The applicability of horizontal wells and fractured vertical wells should be analyzed based on economic evaluation.