Study On Coal Structure And Its Geological Factors Of Low Rank Coals In The Fukang Area,Xinjiang,China

Tectonic coal with a narrow distribution plays an important role in the outburst of coal mine gas and occurrence of coalbed methane(CBM).Accurately predicting the horizontal and vertical distribution of coal body structure has guiding effects on the exploration and development of CBM.This study focuses on the Fukang area in Xinjiang.Based on the macro characteristics of the coal cores,the tectonic coals in the study area are divided into three categories,including TYPE1(intact coal),TYPE2(cataclastic coal),and TYPE3(granulated coal and mylonitized coal).Multiple logistic regression and deep fully connected neural networks were used to test CBM wells data in the study area.Some parameters in the logging data were adopted as model input features,including C13,C24(well diameter),DT,LLD,LLS,GR,RHOB.Then the coal body structure inversion model was built and tested,and the results showed that the accuracy of the neural network model was more than 90%.Inversion of the coal body structure in the study area found that the coal seams in the lower section of the Badaowan Formation in the Fukang area were mainly developed with TYPE2 tectonic coals,the corresponding content reached more than 80%,while TYPE3 and TYPE1 were locally developed.Based on the inversion,the trend of logging curves with the different coal body structures was summarized,and the distribution of the coal body structure in the main coal seams(No.42,44,45,46 coal seams)in the study area was predicted.The results indicate that all types of coal seams are dominated by the development of TYPE2 tectonic coals.Except for the No.44 coal seam,the development areas of TYPE3 tectonic coals are mostly concentrated near the Chigang fault in the southwest of the study area,and the content of TYPE1 tectonic coals is increasing toward the northeast.Couple with the analysis of the geological controlling factors and evolution of tectonic coal in the study area,it is found that the distribution of the coal body structure of the lower seam of the Badaowan Formation is mainly controlled by sedimentation and tectonic movement,which the former is supplementary and the latter is dominant.As the sedimentary facies in the northwest of the study area changed from braided river delta facies to semi-deep-deep lacustrine facies,the increase in mud content and thickening of coal seams led to the increased resistance of the main coal seams in the northwest to structural damage.For tectonic control in the study area,the development of tectonic coals in the lower seam of the BadaowanFormation began in the late Yanshan period and reached its peak during the Himalayan period.At present,the coal seam structure of the lower section of the Badaowan Formation is mainly controlled by Fukang syncline,Fukang anticline,Chigang fault,Baiyanghe fault,Ergonghe syncline,and Baiyanghe reverse fault.