Seismites characteristics and significance of exploration and development fromcoal measure gas of Shanxi Formation in Xishan Coalfield

The geological exploration history of Shanxi Formation in Xishan Coalfield of Taiyuan City is earlier,while the exploration and development of coalbed methane(CBM) started late. Although the number of CBM wells put into production is increasing in recent years,the overall gas production did not achieve the desired effect. There are three layers of seismites developed in roof of No.2 coal,No. 3 coal and bottom of No. 1 coal in Xishan Coalfield,respectively. In order to study the characteristics and its significance of exploration and development in coal measure gas of the seismites of Shanxi Formation in Xishan Coalfield in Taiyuan City,outcrop observation,sampling and laboratory testing were carried out. The results show that:① there are 8 kinds of deformation structures in the Shanxi Formation, including synsedimentary faults, seismogenic breccia, stepped small faults, seismic fold rocks, liquefy homogeneous layer, ball-and-pillow structures, water escape structures and biological escape into caves. The three layers of seismites have different vertical sequence.② The frequent seismic events at the late early Permian in the study area inhibited the evolution of peat bogs. The balance between crustal subsidence rate and peat accumulation rate is destroyed,which reduces the accommodating space of peat bogs,thus leading to the extinction of peat bogs. Seismic events are the main reason for the relatively thin and unstable coal seam distribution in Shanxi Formation in Xishan Coalfield. ③ Seismites on the roof of No.2 coal were formed at the late of peat swamp evolution,and its total organic carbon contents are ranges from 1.22% to 13.73%,with an average of 4.51%,the seismites are a better source rock. The porosity of seismites is ranges from 2.53% to 7.81%,with an average of 4.22%,the small stepped faults and seismic breccia formed by earthquakes increased the porosity of mud shale,and it’s also provided space for occurrence and migration of coal measure gas. The brittle-mineral contents of seismites are ranges from 32.1% to 75.9 %,with an average of 50.6%,showing strong reformability. ④ In the development of coal measure gas,the No.2 coal can be combined stimulation with roof seismites,which can make full use of the advantage of coal seam gas resources and seismites fracability,and also break through the technical bottleneck of establishing flow migration and output channel.