According to coal lithotypes, the bottom, parting, roof, and 15 coal samples were collected by finely partitioning the M9 seam from the Renjiazhuang Mining District, Ningxia, China. Conventional chemical analysis, optical microscopy, scanning electron microscopy equipped with energy-dispersive X-ray spectrometry, X-ray diffractometry, inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry, and atomic absorption spectrophotometry techniques were used on these samples to research the vertical variation between geochemistry and mineralogy in the high-sulfur coal. The weighted average content of total sulfur calculated from 15 coal samples is 3.07%, which belongs to the high-sulfur coal. However, the contents of morphological sulfur of 15 piles are significantly different: the contents of pyritic and organic sulfur are observed to range from 0.02 to 1.55% and from 1.88 to 3.91%. The results show that these differences are mainly controlled by marine conditions and the contents of organic matter and kaolinite. The mineralogy of the M9 coal is dominated by kaolinite, followed by dolomite, and it also contains minor amounts of illite, feldspar, pyrite, siderite, hematite, chalcopyrite, calcite, and marcasite. Moreover, pyrite is the main sulfide in coal, and agglomerated chalcopyrite and granular galena are partially visible. The forms of pyrite include fine-grained, spherical, irregular block-shaped, and clumps. Trace elements are mainly carried by pyrite and ash so that physical coal cleaning can be applied to partially remove them, while thalassophile elements Na, Ca, and Mg are closely related to organic sulfur, indicating that the coal blending can be used to decrease their contents.
The geological sequestration of CO 2 in coal seams holds significant implications for coalbed methane development and greenhouse gas mitigation. This paper examines the principles, influencing factors, and evaluation methods for geological CO 2 sequestration in coal seams by analyzing relevant domestic and international findings. Suitable geological conditions for CO 2 sequestration include burial depths between 300 and 1300 m, permeability greater than 0.01 × 10 −3 μm 2 , caprock and floor strata with water isolation capabilities, and high-rank bituminous coal or anthracite with low ash yield. Geological structures, shallow freshwater layers, and complex hydrological conditions should be avoided. Additionally, the engineering conditions of temperature, pressure, and storage time for CO 2 sequestration should be given special attention. The feasibility evaluation of CO 2 geological storage in coal seams necessitates a comprehensive understanding of coalfield geological factors. By integrating the evaluation principles of site selection feasibility, injection controllability, sequestration security, and development economy, various mathematical models and "one vote veto" power can optimize the sequestration area and provide recommendations for rational CO 2 geological storage layout.
The research of sulfur content and logging parameters in coal seams is of great significance for accurate mining and efficient utilization of coal. Taking 81 coal samples collected from the Upper Paleozoic in North China as an example, coulometric titration and chemical reagent methods were used to determine the contents of total sulfur and morphological sulfur in coal seams, and correlation analysis and multivariate linear fitting methods were used to analyze the relationship between total sulfur in coal and the shape and peak value of logging curve. The results show that the content of total sulfur in the Upper Paleozoic coal seams ranges from 0.19% to 12.36%. The morphological sulfur in coal is mostly pyrite sulfur, followed by organic sulfur and sulfate sulfur. The logging curves of the deep lateral resistivity log (LLD), natural gamma ray (GR), short-distance gamma gamma (CGS), and spontaneous potential (SP) in coal seams from Shanxi Formation are funnel-shaped, toothshaped, box-shaped, and flat-shaped, respectively. The shapes of LLD corresponding to a few coal seams with a sulfur content of less than 3.0% are finger-shaped and bell-shaped, and GR is finger-shaped. The GR, CGS, acoustic (AC), and density (DEN) curves corresponding to Taiyuan Formation coal seams with a total sulfur content more than 3.0% (S t,d ≥ 3.0%) are mainly box-shaped, and the LLD curve corresponding to high-sulfur coal seams is mostly tooth-shaped. The LLD, GR, CGS, and AC curves are second only to funnelshaped, and the DEN curve is tooth-shaped. The LLD, GR, AC, CGS, and DEN curves of coal seams with a total sulfur content less than 3.0% are mainly box-shaped. GR, AC, and DEN curves are next to tooth-shaped, LLD is bell-shaped, and CGS curve is fingershaped. The total sulfur content in coal has a negative correlation with LLD and CGS values and a positive correlation with GR, AC, DEN,and SP values. The prediction model of total sulfur in coal is established by using a multivariate linear fitting method through geophysical logging parameter values, which can provide a method for comprehensively quantifying the change of total sulfur content in coal seams.
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