鄂尔多斯盆地南部长7页岩沉积特征和有机质富集因素研究

对鄂尔多斯盆地南部瑶科1（YK1）井延长组长7段页岩45件样品进行了总有机碳、Rock-Eval热解分析，并且对其中的15个样品进行了有机碳同位素组成分析、氯仿沥青“A”含量和微量元素分析。结果显示，长7段有机质丰度指标（TOC、氯仿沥青“A”、生烃潜量）之间具有良好的相关性，长73有机质丰度高于长71，长72有机质丰度最低；有机碳同位素指示长73层有机质类型好，以Ⅰ型为主，长72和长71层有机质以Ⅰ和Ⅱ型为主；氧化还原指标U/Th、δU和V/(V+Ni)值指示长7沉积时期水体整体为还原-强还原环境，其中，相比长72和长71的沉积环境，长 73的沉积环境还原性更强，可能达到厌氧、硫化细菌发育的程度。页岩中高P元素含量，指示YK1井长7段页岩沉积时期具有高古生产力特征。有机碳含量（TOC）与氧化还原指标和P元素呈良好的正相关关系，表明有机质含量的变化同时受控于古生产力高低和氧化还原的保存条件。因此，长7段页岩有机质富集模式可能属于“生产力模式”，即长7页岩有机质的富集是由于较高的初始生产力通过消耗水体中的氧气而形成易于保存有机质的缺氧环境。综合前人的页岩气研究成果，认为富有机质的长73层是鄂尔多斯盆地南部页岩气富集的最有利层段。

Sedimentary characteristic and organic matter enrichment factors of the Chang-7 section shale of Yanchang Formation in the south of Ordos Basin

Forty five shale core samples were collected from the Chang-7 section of Yanchang Formation of YK1 well，south of the Ordos Basin. And the total organic carbon content （TOC） and Rock-Eval prolysis of these samples were analyzed. Meanwhile，fifteen samples were selected to further conduct the experiments of the organic carbon isotopes，chloroform bitumen “A” content，and trace elements. The results show that the organic matter indexes （TOC，chloroform bitumen“A”，hydrocarbon generating potential）of Chang-7 section have good positive correlations，and the organic matter abundance of Chang-73 is higher than that of Chang-71 and Chang-72. The data of the carbon isotopes of organic matter indicates that the organic matter types in Chang-73 are dominated by TypeⅠ. The Chang-71 and Chang-72 source rocks have mixed types，which are dominated by Type Ⅰand Type Ⅱ. The redox proxies of U/Th、δU and V/(V+Ni) show that the Chang-7 deposition was reducing environment-strong reducing environment. Compared with the Chang-72 and Chang-71，Chang-73 deposition environment was more reduction，which probably was anaerobic and developed sulfate-reduction bacteria. The high contents of P element of the Chang-7 shale demonstrate a higher paleoproductivity during the depositional process of Chang-7 section，while TOC content has a positive correlation with redox proxies and P contents，suggesting that the organic matter contents of Chang-7 shale are controlled by redox condition and paleoproductivity at the same time. Therefore，the organic matter accumulation in Chang-7 section probably belongs to “Productivity Model”. That the organic matter accumulation in Chang-7 section is resulted by relatively high paleoproductivity，then the organic matter decomposition reduced the oxygen of the depositional water，this is favorable for the preservation of the residual organic matter. Integrated the former shale gas researches，the organic matter enriched Chang-73 is the most favorable target for shale-gas enrichment.