河东煤田煤层“生烃作用”及其富集因素研究

The Hedong coalfield in the east margin of the Ordos Basin shows typical characteristics of the superimposed coal metamorphism and multistage coalbed methane generation. It has been confirmed as one of the most important target area of coalbed methane exploitation. Based on the study of hydrocarbon generating history and gasfield formating history of the Late Paleozoic coal measures, the specific objectives of this investigation are:.l.to recover and reconstruct hydrocarbon generating process by means of dynamic modeling of the allocation of geology, geothermal dynamics and reaction kinetics;.l.to probe into the prolific factor of coalbed methane and regular pattern of gas pool formation;.l.to study and master the production and reservoir characters of coalbed methane;.l.to identify the indicator, type and action pattern of multistage coalbed methane generation;.l.to distinguish the practical influence of hydrocarbon generation and gas pool formation caused from superimposed coal metamorphism..Based on the variation of kinetic parameters such as average apparent kinetic energy, maximum ratio of hydrocarbon generation and its corresponding main kinetic energy, main interval of hydrocarbon generation，combined with analysis of coal metamorphic process, several evident stages during a pyrogenic hydrocarbon generation of the Paleozoic coal in Hedong coalfield has been elaborated here, i.e. early pyrolysis （0.5%<Ro,m<0.8%）, metaphase pyrolysis （0.80%<Ro,m<1.65%）and terminal pyrolysis（Ro,m>1.65）. In the study area, the secondary hydrocarbon generation would be more beneficial to formation, accumulation and conservation of coalbed methane when the superimposed metamorphism of the Yanshan Period exerts the coals under the rank of 0.95%Ro,m..By means of program pyrolytic modeling, major parameters on the secondary hydrocarbon generation of coal have been described in detail, for instance, instantaneous hydrocarbon production, cumulating hydrocarbon production, cumulating amount of hydrocarbon generation, cumulating degradability and residual carbon. According to the original coalification degree of the daughter samples, the peak temperature of secondary pyrolysis changed in different styles such as lag, advance and fixation. To the coal at the metamorphase pyrolytic stage, the reactive temperature zone of hydrocarbon generation extends to the lower temperature dirction and the secondary hydrocarbon generation starts earlier due to the existence of weak chemical bond and bituminized substance. To the coals at the early and terminal pyrolytic stage, activation of secondary hydrocarbon generation needs equivalent or stronger reactive conditions than the past since the hydrocarbon generation is mainly depend on the pyrolysis of principal part of the coal structure. Based on the stage characteristic of secondary hydrocarbon generation of coal and the self-generating and self-reserving specialties of coalbed methane, the superimposed metamorphism beyond the period of hydrocarbon generating peak (Ro,m≌0.95%) offers the most effective ways to elaborate the hydrocarbon generating potential of coals..The studies of the allocation of tectonics, geotherm and coal metamorphic evolution indicate that to the Late Paleozoic coals in Hedong coalfield, the production rate of coalbed methane is observably high and the time of gas generation is relatively centralized within the sections affected by abnormal geotherm of the Yanshan Period magma. The secondary hydrocarbon generation controlled the intensity of gas generation and determined the superior conditions of accumulation and conservation of coalbed methane as well..Through comparing the geofactor differences of coalbed methane with United States, how the telemagmatic metamorphism is beneficial to raising the methane content and permeability in coal is analyzed, and its mechanism is probed into preliminarily. In China most coal ranks were low before they were superimposed by telemagmatic metamorphism, therefor under the action with high rising rate temperature of the superimposed t

针对煤的叠加变质作用和煤层气的多阶段形成特点，以华北晚古生代煤系生烃演化史和气田形成史研究为基础，恢复重建母质“二次生烃作用”过程，动态拟合地质、地球热力学与反应动力学配置关系，探讨煤层气富集高产因素和成藏规律，掌握煤层气发生率及储集特征，识别二次生烃标志、类型及作用方式，厘定叠加变质对生烃演化与煤层气成藏的切实影响。