Low-rank coalbed methane (CBM) in Junggar Basin has recently become a new exploration frontier across Xinjiang, Northwest China. The low-rank coal reservoir mainly develops in Badaowan Fm. (J1b) and Xishanyao Fm. (J2x) coal measures, especially featuring stable distribution, great thickness and moderate burial depth, which is favorable of CBM accumulation.
The pores of Jurassic coalbed reservoirs are mainly small-micro (<100nm) and large ones, among which the large and medium sizes account for a high proportion; and macroscopic and microscopic fissures are well developed in the reservoirs, leading to a great variation of the permeability. The shallow coal reservoirs are mostly undersaturated, and the gas saturation tends to increase toward the deep coalbed. The low rank coalbed reservoirs have strong ability to adsorb and accumulate CBM. In terms of horizon, the J2x coalbed reservoir has a stronger methane adsorption and storage capacity than J1b and better physical properties, making CMB recovery easier. In terms of region, the coalbed reservoirs in Changji--Urumqi--Fukang areas in the southern margin of the basin, Cainan--Balikun coalmine regions in the eastern part as well as the hinterland of the basin reach the level with methane-rich to extremely methane-rich coal beds and have strong ability to adsorb and store CBM.
Coalbeds of the basin have gas shows in common and good gas-bearing property. The low rank CBM takes a large proportion of the CBM resource, with huge potential. In light of Langmuir’s volume, the gas provinces are classified into four types: poor CBM zone (<8m3/t), CBM-bearing zone (8-15m3/t), relatively rich CBM zone (15-20m3/t), rich CBM zone (>20m3/t). The relatively rich CBM zones cover Wellblock Qing 1 to Qi 8, Changji--Urumqi--Fukang area and slope belt of northwest margin—basin hinterland; while the rich CBM zones include eastern Junggar basin and Balikun coalmine region. These areas together with the adjacent thick coal region and hinterland have a great potential in deep CBM development.
Since 2005, Changji Liuhuanggou block in the south Junggar basin has been selected as PSC block for venture exploration, and a series of CBM projects and researches have been carried out successively. Recently the CBM extraction from Dahuangshan coal mine in the south Junggar, industrial gas flow from the exploration well in the western Baiyanghe of Fukang block, and deep CBM exploration breakthrough in Baijiahai of the east Junggar demonstrated good progress in exploration and proved the huge potential of low rank CBM development.