Study on forming conditions and main controlling factors of CBM reservoirs in Yonglong Mining Area of Huanglong Coalfield

Huanglong Jurassic coal field belongs to the typical low-rank CBM-bearing zone.Coal exploration data shows that there are certain exploration potentials of CBM in the west,but the condition of CBM reservoir formation is not clear.Based on the above,this paper studied the CBM reservoir forming conditions in the western area of Huanglong Coalfield from three aspects:CBM geology,coal reservoir characteristics and gas reserving condition,taking Linbei area of Yonglong Mining Area in the west of Huanglong Coalfield as an example.The main controlling factors of CBM reservoir formation in the study area were analyzed.The results showed that the Yan’an Group in western area of Huanglong Coalfield was characterized by low coal metamorphism,thick coal seam,moderate burial depth and good gas bearing property,but the permeability of coal reservoir was poor.The CBM enrichment was mainly affected by the depth of burial and hydrodynamic conditions,and the influence of structure and cap layer was small.The depth of 500～700 m was the best depth of coalbed formation in the study area.In the late period of coal formation,the Yanshan movement was affected by many stages of tectonic movement.The original biogenic gas and thermogenic gas were dissipated.Since the Cenozoic,the coalbed had received shallow surface water and atmospheric precipitation,and received secondary biogas was the key to CBM accumulation.The formation of CBM reservoirs in the study area was typical of the late-stage biotallogenetic accumulation model of basin-margin.