Abstract:

A number of high-yield wells has emerged in the southeast margin of Ordos Basin, which showed the potential of the Upper
Paleozoic exploration and development of coalbed methane resources. However, owning to the coal reservoir heterogeneity, great
differences of individual gas wells were observed in adjacent block groups and sometime even in the same block. Therefore, a deeper understanding of reservoir heterogeneity is needed for efficient exploration and development. Systematic studies were conducted on coal reservoir in terms of rock characteristics, physical characteristics, adsorption characteristics, and gas characteristics. The results showed that the 3, 5, 11 coal seam, with stable distribution and large thickness, is the main target for exploration and development of coalbed methane. Half-bright coal seam and semi-dark coal with high vitrinite content has better fracture resistance, whereas a low ash-lean coal was also found, with anthracite and a small amount of high grade coal identified in some sections. We found that coal rock porosity and permeability are low, showing strong adsorption, short adsorption time and the higher desorption rate. This is conducive to CBM output, however, coal measures of reservoir stimulation need to be strengthened. The average gas content is about 11 m3/ t or more, with a maximum of 19.73 m3/ t, and the average gas saturation is above 61%, indicating a greater resource and a high density of formation energy, in favor of CBM desorption output.

Key words: coalbed methane;coal reservoir, properties, gas content, Upper Paleozoic, southeast margin of Ordos Basin