Main geological factors controlling high productivity of CBM wells in the Hancheng block at the eastern edge of the Ordos Basin
Coalbed methane(CBM)resources are abundant in the Hancheng block at the eastern edge of the Ordos Basin,where the structural zones are significantly different in single-well productivity,due to geological conditions.The main geological factors controlling high productivity of CBM wells in the block are identified on the basis of the characteristics of structures and coal reservoirs,controlling factors of CBM enrichment,as well as field production data.The findings are obtained in three aspects.First,CBM well productivity is mainly controlled by three factors,i.e.structural conditions,hydrodynamic conditions,and coal structures.Structural conditions control the enrichment and accumulation of CBM,hydrodynamic conditions dominate the preservation of CBM,and coal structures determine the permeability of coal reservoirs.Second,high-yield CBM wells are mainly distributed in areas with positive microstructures,high formation water salinity,and primary-fragmented coals.In the Hancheng block,such wells are found in areas with secondary structures,formation water salinity of(2-11)×103 mg/L,and primary-fragmented coals having an average thickness of 4.4 m,showing a daily production of over 1 000 m3 per well.Third,small faults or microstructures improve the permeability of coal reservoirs.Especially,fractures created in the high parts of positive microstructures are conducive to the desorption and seepage of CBM and thus the high production of CBM.Fourth,Under conditions of intense tectonic activity,gas escape channels may easily form near major faults,which is not conducive to the preservation of CBM.Tectonic movements create various structural forms and also change the coal structures.Moreover,hydrodynamic conditions are variable under different structural forms.Therefore,tectonic movements play a critical role in controlling the high productivity of CBM wells in the Hancheng block.This has a certain guiding significance for the adjustment of CBM development in the block and is also useful for CBM blocks with similar geological conditions.
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维普
