The Genetic Mechanism of Inertinite in the Middle Jurassic Inertinite- Rich Coal Seams of the Southern Ordos Basin

also an important geological information carrier of coal forming environments.In the southern section of the Ordos Basin,the No.4 inertinite-rich coal seam of the Middle Jurassic Yan’an Formation in the Binchang Coal field was selected as an example to study the genetic mechanism of the inertinite.In this study,the results obtained from experimental tests of coal rock,including principal and trace elements,stable carbon isotopes,scanning electron microscopy,inertinite reflectance,sporopollen and free radical retorting methods,were analyzed.Then,the findings were combined with the previous understanding of the oxygen content in the atmosphere and ground fire characteristics,in order to discuss the genesis mechanism of inertinite in the No.4 coal seam.The obtained research results were as follows:(1)During the coal forming period of the No.4 coal seam,the overall climate had been relatively dry.There were four relatively dry-wet climate cycles in the No.4 coal seam,which were controlled by the eccentricity astronomical period.The inertinite content were relatively high during the dry periods;(2)The temperature range suitable for microorganism activities during the oxidation processes was between 0 and 80℃.The simulation results of the free radical concentrations showed that the maximum temperature of fusain in the No.4 coal seam during the process of coalification had not exceeded 300℃,which was significantly higher than the temperature range of microorganism activities.Therefore,these were not conducive to the activities of microorganism and formation of inertinite during the coal-forming period;(3)The genesis temperature of the inertinite in the No.4 coal seam was calculated according to the reflectance of the inertinite,which was lower than 400℃.This result supported the cause of wildfire of the inertinite and reflected that the type of wildfire was mainly ground fire,along with partially surface fire.Moreover,the paleogeographic location,climatic conditions,atmospheric oxygen concentration,etc.of the study area showed that the conditions for wildfire events were in fact available;(4)There were dense and scattered fusinite observed in the No.4 coal seam,and the thickness of cell walls were found to differ.It was speculated that this was related to the type of wildfire,combustion temperatures,combustion timeframes,and different initial conditions of the burned objects during the coal forming periods.

The classification and significance of fine-grained deposits of micro-laminae rich in unconventional oil and gas resources

In this study,an in-depth analysis of the types,characteristics,and formation mechanisms of microlaminae and microscopic laminae was conducted in order to precisely examine the link or intersection of stratigraphy and petrology.This study was essentially a sedimentary examination of the minuteness-macro and micro-tiny layers between laminae and pore structure,as well as the types of structures and sedimentation.The results of this study bear important basic subject attributes and significance,as well as practical value for the basic theories and exploration applications of unconventional oil and gas geology.The quantitative data were obtained using the following:field macroscopic observations;measurements;intensive sampling processes;XRD mineral content analysis;scanning electron microscopy;high-power polarizing microscope observations;and micro-scale measurements.The quantitative parameters,such as laminae thicknesses,laminae properties,organic matter laminae,and laminae spatial distributions were unified within a framework,and the correlations among them were established for the purpose of forming a fine-grained deposition micro-laminae evaluation system.The results obtained in this research investigation established a basis for the classification of micro-laminae,and divided the micro-laminae into four categories and 20 sub-categories according to the development thicknesses,material compositions,organic matter content levels,and the spatial distributions of the micro-laminae.The classification scheme of the micro-laminae was divided into two categories and 12 sub-categories.Then,in accordance with the comprehensive characteristics of spatial morphology,the micro-laminae was further divided into the following categories:continuous horizontal laminae;near horizontal laminae;slow wavy laminae;wavy laminae;discontinuous laminae;and lenticular laminae.According to the structural properties of the laminae development,the micro-laminae was divided into the following categories:single laminae structures;laminated laminae structures;interlaminar structures;multiple mixed laminae structures;cyclic laminae structures;and progressive laminae structures.The research results were considered to be applicable for the scientific evaluations of reservoir spaces related to unconventional oil and gas resources.