Significant breakthroughs have been made in exploration of deep coalbed methane (CBM) in China

demonstrating promising prospects for future development. However

due to the complex geological conditions and the high d

ifficulty in CBM development

the existing basic theoretical researches cannot fully explain the deep-seated issues such as the enrichment mechanism and development prospects of CBM. The research progress of global CBM exploration and development shows that the enrichment and accumulation conditions for CBM in deep reservoirs are superior to those in shallow layers. However

the deepening research on deep CBM faces a series of challenges

including multiple genetic types with unclear genetic relationship

undetermined mechanism and key controlling factors of deep CBM accumulation

lack of discrimination criteria for enrichment modes and critical accumulation conditions of CBM

difficulties in predicting and evaluating high-yield sweet spots and fully applying the exploration experience of deep CBM in the eastern Ordos Basin to other regions. To solve the problems

the Whole Petroleum System (WPS) theory and the hydrocarbon accumulation model with dynamic field are introduced to expound the differences

correlations

and united symbiotic relationships between conventional and unconventional coal-formed gas reservoirs in petroliferous basin

in an attempt to provide new theoretical and methodological guidance for the prediction and evaluation of high-yield and rich CBM areas. The preliminary research results on CBM in major petroliferous basins of China indicate that during the evolution process of the Coalbed Whole Petroleum System (CWPS)

the free hydrocarbon dynamic field is conducive to the enrichment and accumulation of CBM in an adsorbed state

whereas the confined hydrocarbon dynamic field is conducive to the enrichment of free gas in coal seams. In the free hydrocarbon dynamic field of coal seams

the amount of adsorbed gases increased with the increasing of burial depth and decreased after reaching a peak

while the free gas content has begun to increase. In the confined hydrocarbon dynamic field

the amount of gas trapped in coal seams in a free state continues to increase with the increasing of burial de

pth

and then decreases until it tends to disappear after reaching its peak. Vertically

the lower part of the free hydrocarbon dynamic field and the upper part of the confined hydrocarbon dynamic field (organic matter accumulation degree ranges from 0.50 % to 2.75 % ) are most favorable for multiphase enrichment and high production of CBM. The buried depths of the high heat flow basins of the eastern China

medium heat flow basins of the central China

and low heat flow basins of the western China are from 1 000 m to 3 600 m

1 500 m to 7 500 m

and 3 000 m to 8 500 m

respectively. In these favorable fields

the total amount of coal resources is about 80 596×10

8

t

and the in-situ and recoverable resources of CBM are 115.91×10

12

m

3

and 56.5×10

12

m

3

respectively

showing broad prospects for development.