| The study area is located at the massif of Weihe river east uplift belt that in the southeast of the Ordos,which to the south of Weihe uplift structure belt,east to Hencheng big fracture.Coal measures strata in this area from bottom to top respectively in the carboniferous Benxi group,upper carboniferous Taiyuan formation and Shanxi group of lower Permian,in which the Benxi group generally do not contain coal.Through the research of perm carboniferous coal-bearing sedimentary system of demonstration area in north Weihe,found that the sedimentary of Taiyuan group is mainly for the lagoon,tidal flat,barrier island deposition and epicontinental sea carbonate platform deposits,of which found the alternating mudstone,sandstone,limestone and coal deposits,the sedimentary facies types is rich.The sedimentary type of Shanxi formation relatively single,which develops a suit of fluvial-dominated delta deposition,mainly for the delta plain and delta front subfacies,while the former delta is undeveloped.Taiyuan formation in the study area can be divided into three long-term cycles,i.e.in general,the early regressive,middle late transgression and regression.Shanxi group also can be divided into early water subsidence period,medium water invasion period and the water subsidence in late period.Coal seams have an uneven distribution in the upper carboniferous Taiyuan group and lower.Permian Shanxi.group,and of which the number 3,5,11 are the main minable seam of coal seam.When shallow water near to the sea level,alluvial fill contributes to the development of peat bog,and then thus formed larger coal thickness and good continuity of 5 coal bed.Some coal distribution limited even as lenticular reservoir,it is because of the sea level falling,condition variation in the formation of coal.The average of 3,5,11 coal seam gas content are:14.24m3/t,14.78m3/t and i6.14m3/t,air content overall increased with increasing depth.Three sets of overall coal seam gas saturation is between 45%-95%.Among them,the Hencheng tectonic units containing gas saturation is 45%?95%,Heyang tectonic units of gas saturation are generally less than 50%.In different parts of the air content are positively correlated with the gas saturation.Based on the study of the coal measures strata sedimentary system and the coal reservoir characteristics,from the main minable seam sedimentary phase change,coal thickness,coal lithological changes and characteristics of coal seam roof and floor to block,etc,analyze the influence of sedimentation on coal bed methane enrichment.Found that,as a result of migration on the delta plain distributary channel that wash and cut the coal seam,the continuity of coal seam is poorer than that of the lagoon,tidal flat environment,besides the limited distribution.The erosion of the coal seam by the distributary channel sand body lead to its porous structure,ash and parting content increased,which influences the coal reservoir physical parameters directly,results in the decrease of hydrocarbon showings.the coal bed developed in the tidal flat,lagoon,barrier island sedimentary system,sometimes because of the turbulent sea,discontinuity occurs in mudstone sedimentary,swamp coal seam will be relatively thinning,content of ash and sulfur content are relatively larger,while air content lower.Given all this,coal bed methane development blocks of the three sets of main coal seams in the study area is in the east area of Baima town. |
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