鄂尔多斯盆地南部三叠系页岩和侏罗系富油煤生烃动力学差异及其原位共采的温度条件

Differences in hydrocarbon generation kinetics between Triassic shale and Jurassic tar-rich coal and temperature conditions for in-situ co-production, southern Ordos Basin

  • 摘要: 鄂尔多斯盆地上三叠统延长组7段(长7段)中−低成熟度页岩占该段总面积的90%以上,下侏罗统延安组富油煤资源量约为1 414亿 t,长7段页岩和延安组富油煤原位热解转化共采技术是实现煤与页岩内蕴油气资源协同开采的重要途径。针对页岩和煤生烃动力学特征已开展了大量研究,但页岩和富油煤的地球化学特征和生烃动力学特征差异尚不明确,制约着富油煤原位热解开发和资源潜力准确评价。基于对长7段页岩和延安组富油煤的地球化学特征对比分析,选取成熟度相近、有机质丰度不同的4个页岩样品和焦油产率不同的4个富油煤样品,比较了页岩和富油煤的热解生烃转化率和活化能分布特征;并将试验所得的动力学参数外推至原位转化条件下,探讨了页岩和富油煤原位热解页岩油、煤焦油共采的可行性及其温度条件设置。结果表明:长7段页岩和延安组富油煤均具备生油条件,且长7段页岩的生油条件优于延安组富油煤。在成熟度相近条件下,页岩的活化能主频值随有机质丰度增大而增大,富油煤的活化能主频值随焦油产率增大而降低,且页岩的活化能分布范围较富油煤集中。在原位转化条件下,相近成熟度页岩主要生烃期对应的模拟温度随有机质丰度增大而增大,相近变质程度富油煤主要生烃期对应的模拟温度随焦油产率增大而降低,且长7段页岩(TOC=5%~38%,Ro=0.68%~0.71%)主要生烃期对应的模拟温度范围(226~443 ℃)涵盖延安组富油煤(Tar∙d=7%~15.3%,Ro=0.67%~0.72%)主要生烃期对应的模拟温度范围(282~435 ℃)。因此,对于鄂尔多斯盆地长7段页岩和延安组富油煤而言,当热解温度达到长7段页岩主要生烃期对应温度时,即可实现页岩油和上覆煤焦油的原位共热解开采。

     

    Abstract: The area of shale exhibiting middle- to low-maturity constitutes over 90% of the total shale area within the seventh Member of the Yanchang Formation (Chang 7 Member) in the Ordos Basin. Additionally, the tar-rich coal resources of the Lower-Jurassic Yan’an Formation are estimated to be approximately 141.4 billion tons. In-situ conversion and co-production technology is an important way to realize synergistic exploitation of the Chang 7 Member shale and Yan’an Formation tar-rich coal. Previous studies have been conducted on the hydrocarbon generation kinetics of shale and coal, but the differences in geochemical and hydrocarbon generation kinetic characteristics between shale and tar-rich coal are still unclear. This restricts the accurate evaluation of in-situ conversion conditions and resource potential of tar-rich coal. Based on the comparative analysis of geochemical characteristics of the Chang 7 Member shale and Yan’an Formation tar-rich coal, this study selected four shale samples with similar maturity and different organic matter abundance, as well as four tar-rich coal samples with similar maturity and different tar yields, to compare and analyze the pyrolysis hydrocarbon generation conversion rate and activation energy distributions of shale and tar-rich coal. The kinetic parameters obtained from laboratory conditions are extrapolated to the in-situ conversion conditions, the feasibility and in-situ conversion temperature conditions of shale oil and tar co-production are analyzed. The results show that both the Chang 7 Member shale and Yan’an Formation tar-rich coal have the conditions for oil generation, with the shale demonstrating superior potential compared to the tar-rich coal. Under conditions of similar maturation, the activation energy of shale increases with organic matter abundance, whereas the activation energy of tar-rich coal decreases with higher tar yield. Furthermore, the distribution of activation energy for the Yan’an Formation tar-rich coal is more dispersed than that of the Chang 7 Member shale. In terms of in-situ conversion, the temperature corresponding to the main hydrocarbon generation stage of shale with similar maturity increases with the increase of organic matter abundance, while the temperature for tar-rich coal decreases with higher tar yield. The temperature range (226-443 ℃) corresponding to the main hydrocarbon generation stage of the Chang 7 Member shale (TOC=5%-38%, Ro=0.68%-0.71%) covers the temperature range (282-435 ℃) corresponding to the main hydrocarbon generation stage of the Yan’an Formation tar-rich coal (Tar∙d=7%-15.3%, Ro=0.67%-0.72%). Therefore, the in-situ pyrolysis co-production of the Chang 7 Member shale oil and Yan’an Formation tar can be achieved when the pyrolysis temperature reaches the temperature corresponding to the main hydrocarbon generation stage of the shale in the Ordos Basin.

     

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