Study On The Tectonic Control Of No.3 Coal Seam Gas Content In Anze Area Of Qinshui Basin

Based on 2D seismic data,well logging and well completion data,using seismic software and mathematical analysis method,for seismic fine structure interpretation,buried denudation recovery,hydrocarbon generation history,structural characteristics and tectonic evolution analysis,researched the tectonic control of No.3 coalbed methane content in Anze area.52 faults include 48 high angle normal faults and 4 reverse faults,fault throw between30-140 m,fault strikes are mostly NE-SW,dip angle is between 30-65~o.There are 8 Anticlines and 5 synclines,alternating distribution in central Anze,strikes are mostly NNE-SSW and NE-SW,most of them are vertical horizontal folds.There are 25 collapse columns.According to the degree of collapse,mainly composed of a half column and a lower column in Anze area.Since late Triassic strata denudation amount total between 1800-2900 m,denudation in the west is high and east is low.In Anze area,the denudation amount of the T-J period is between400-650 m,the denudation amount of J-K period is between 950-1600 m,the denudation amount of K-Q period is between 450-750 m.Tectonic evolution of Anze area has experienced four periods:The Indosinian period is approximately N-S compressive stress field,forming W-E fold.The Yanshanian period is NW-SE compressive stress field,forming NNE-SSW fold.The early Himalayan period is NW-SE tensile stress field,forming NE-SW normal fault.The compressive stress field in the NE-SW trend in the late Himalayan epoch is uplifted and denuded.Coal seam buried history is W type,experience two stages of hydrocarbon generation,main stage of coalbed methane generation is late Yanshanian magmatic intrusion stage,the main period of loss gas is Himalaya early extensional tectonic stress stage.In Anze area,coalbed methane content is between 7.18-23.85 m~3/t,the average gas content is 16.3 m~3/t.Most faults were formed from the cretaceous to paleogene and have good lateral sealing ability;Due to the poor vertical sealing ability,early Himalayan is the main period of coalbed methane loss;In the late Himalayan epoch,the vertical sealing property has a linear relationship with coalbed methane gas content.Now,the overall vertical sealing property is very good,little influence on overall gas content.The control range of fault to coalbed methane content is within 1km.In Anze area,the coalbed methane content of upthrow plate of fault is lower than downthrow plate by 5 m~3/t.Upthrow plate storage condition is poorer than downthrow plate.Upthrow plate of the compressive strength,tensile strength,modulus of elasticity is lower,poisson’s ratio is high.Graben,reverse fault is good gas storage environment,horst is gas loss environment.The gas content is increasing from anticline to flanks to syncline.The gas content near collapse column is generally low.The higher overlying effective thickness of strata,the greater the coalbed methane content in Anze area.The gas content of area is generally higher than the average gas content,where today buried depth more than 900 m and the largest buried depth more than 3200 m depth has good preservation.