Logging Sedimentary Facies And Its Coalcontrol Action Within The Sequence Stratigraphic Framework Of Coal-bearing System In Guxian Exploration Area

The traditional geological exploration has been generally unable to satisfy the needs of mining, with the process of mining-uniting of coal bed methane, shale gas and tight sandstone gas(namely "three gas" resources) of the coal-bearing formation rock. The coal-bearing formation rock, as the media of the formation and storage of "three gas" resources, plays an important role in mining. The Guxian block locates in the northwest of Qinshui coalfield, of which coal-bearing formation rock is composed of the Lower Shihezi Formation, Shanxi Formation of Permian and the Carboniferous Taiyuan Formation. With the advantage of highly abundant content, the "three gas" resources in Guxian block has great potential development. And it is necessary to deeply research the characteristics of main-mining coal seam of the coal-bearing formation rock based on previous work, which can provide a theoretical basis for the development of "three gas" resource in future.This paper makes the coal bearing formation of Guxian block as research object,then identify sequence stratigraphic framework and classify logging sedimentary facies using Logging means. This paper analyzes the thickness and distribution characteristics of main mineable coal seam in logging sedimentary facies. The main ideas of this paper can be summarized as follows:1.On the basis of environment correction and standardization for logging data in research area, this paper identifies five third sequence stratigraphic boundary and eleven fourth sequence stratigraphic boundary by using the logging method, then the coal bearing formation is classified as four third sequence and ten fourth sequence. Through comparing different wells, the fourth sequence stratigraphic framework of Guxian County is established.2.Using cross plot method, this paper analyzes the logging responses of classic rock of coarse-fine sandstone(grit stone, medium sandstone, fine sandstone)and silt-mudstone(siltstone, sandy mudstone, mudstone)which have different granularities in research area. Then using calculated particle size analysis curve, this paper achieves the method that calculates “sandstone percent removing siltstone” in the sequence using logging data quickly. Through comparing the sandstone percent between removing siltstone and siltstone, this paper thinks that the “sandstone percent removing siltstone” can reflect the change characteristics of sedimentary facies in the sequence better.3.Combining with the drilling coring data, this paper explains sedimentary facies and microfacies about single well, and summarizes the logging facies characteristics of sedimentary facies and microfacies about barrier island, lagoon, tidal flat, carbonate platform and delta plain in the study area. Considering the factors of sandstone percent, ancient terrain and so on, the author analysis sedimentary facies of fourth sequence of upper-group and under-group coal seams in the study area(PS3, PS4, PS9) where PS3 sequence is mainly developed in tidal flat-lagoon facies, PS4 sequence is mainly developed in barrier islandlagoon facies, PS9 sequence is mainly developed in delta plain facies.4.This paper concludes the coal-controlling of logging sedimentary facies under sequence stratigraphic framework in the research area, which research results show that the thickness change of the relative coal seam is controlled by sedimentary facies under fourth sequences stratigraphic framework obviously. 11 coal is mainly developed in the mud flat of tidal flat(PS3). 9 and 10 coal are mainly developed in lagoon facies behind the barrier island, then in peat flat of tidal flat(PS4). 2 coal is mainly developed in peat bog of delta plain, then in distributary bay and oxbow lakes(PS9).