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致密砂岩储层中蕴含的天然气资源潜力巨大,且在煤系地层中普遍分布,对储层致密化机制的认识关系到这类油气资源的有效勘探和开发.本文通过恢复煤系有机质在生物化学作用阶段和热成熟阶段的生气过程,发现煤系有机质在生气过程中产生了大量的CO2,其体积可达烃类气的50%～70%,远远超过现今煤系成因天然气藏中的CO2含量(0～5%).通过地质实例分析,发现缺失的气态CO2相当一部分以固态碳酸盐形式在储层孔隙中沉淀下来.据估算,理想条件下1m3准噶尔盆地侏罗系煤通过微生物和热力作用产生的CO2,若完全转化为碳酸盐胶结物,体积高达0.32m3,由此可见,该过程对煤系砂岩储层致密化起重要作用.由于煤生成烃类气和CO2的动力学过程具有不同步性,在弱成岩阶段和高过成熟阶段存在两期CO2规模产气期,与多期烃类气规模产气有所区别.研究指出,通过对具体地区致密储层天然气性质分析,可确定烃类气充注时间和CO2关键生成期匹配性,从而确定致密储层烃类充注和成藏机制,这对于确定致密储层充注机制与模式具有科学和实际意义.需要强调的是,储层致密化过程是有机-无机、水-岩-烃复杂相互作用的综合结果,本文仅指出该过程的重要性,CO2与地层水离子结合转化为自生矿物的时空关系尚待深化探讨.
The potential of natural gas resources in tight sandstone reservoirs is huge and widespread in coal measures, and the understanding of reservoir densification mechanism is related to the effective exploration and development of such resources.In this paper, through the restoration of coal-based organic matter in biochemistry During the gas-forming process and the gas-forming process, it was found that coal-based organic matter produced a large amount of CO2 during gas generation and its volume was up to 50% -70% of the hydrocarbon gas, far exceeding that of CO2 (0 ~ 5%) .According to geological example analysis, it is found that a considerable part of the missing gaseous CO2 precipitates in the pores of the reservoir as a solid carbonate.It is estimated that 1m3 Jurassic coal in the Junggar Basin under ideal conditions can be precipitated by microorganisms and If the CO2 generated by the thermal action is completely converted into carbonate cement and the volume is as high as 0.32 m3, it can be seen that this process plays an important role in the densification of coal-bearing sandstone reservoirs.Because the kinetics of coal-derived hydrocarbon gas and CO2 There are two periods of CO2-scale gas generation in the stage of weak diagenesis and over-maturation, which is different from the multi-stage hydrocarbon gas generation.Research shows that through the study on the characteristics of tight storage The analysis of natural gas properties can determine the matching of hydrocarbon gas charging time and key CO2 generation period, so as to determine the mechanism of hydrocarbon charging and accumulation in tight reservoirs, which is of scientific and practical significance for determining the filling mechanism and mode of tight reservoirs It should be emphasized that the densification of the reservoir is a comprehensive result of the complex interaction of organic-inorganic, water-rock-hydrocarbon. This paper only points out the importance of this process and the spatio-temporal relationship between CO2 and formation water ion conversion into authigenic minerals Yet to deepen discussion.