The Recovery Of The Paleoproductivity In The Period Of Chang 7 In Ordos Basin And Its Control Factors

"Hydrocarbon-rich sag" has become a hotspot in research of oil and gas in our country.The high quality hydrocarbon source rocks are the material basis of the formation of hydrocarbon-rich sag, in recent years, which has been taken seriously by many scholars. A large number of studies have shown that the formation of high-quality hydrocarbon source rocks is controlled by the paleoproductivity and environment of organic matter’s preservation, and the productivity is more important than the environment of organic matter’s preservation, so the research of the paleoproductivity has important significance in exploring the formation mechanism of high-quality hydrocarbon source rocks and the formation of the hydrocarbon-rich sag environment.Ordos basin is rich in mineral resources, oil and gas resource, this has a very close relationship with the hydrocarbon-rich sag of the basin。In this study,taking the Well Yan 56 in northern of Tianhuan depression and the outcrop in southern basin as research objects, tested and analysis the organic carbon, density, porosity, saturated hydrocarbon chromatogram and sporopollen fossil of the sample, and combined with logging data calculation method of organic carbon, qualitative evaluateding and quantitative recovering the lake paleoproductivity during the period of the formation of high-quality hydrocarbon source rocks in Yanchang formation, According to the sporopollen test results recoveried the ancient climate conditions;and combined with the geochemical characteristics of the deposits of the geological event, discussing the control factors of the paleoproductivity and its influence on high-quality hydrocarbon source rocks.Qualitative evaluating the paleoproductivity reling on the experiment test and log data calculate the organic carbon, the evaluation results of the two methods are consistent, the organic carbon of logging data calculated are similar with the actually measured value, and the longitudinal trend of the organic carbon is consistent. selecting suitable well profile, according the method of logging data calculation, calculating the organic carbon, then analysing the lateral evolution characteristics of organic carbon. Quantitative calculating the paleoproductivity when the Chang 7 high-quality hydrocarbon source rocks formed for the first time in the article, the results all show that the paleoproductivity in the period of high quality hydrocarbon source rock developed is higher, compared with other parts of domestic, it is obviously much higher. And comparing the results of qualitative evaluation and quantitative calculation, the two conclusions are consistent.According to the results of the quantitative calculation, combining lake’s nutrition type established by predecessor, making off the lake’s nutrition type in this period. According the data by tested and calculated with logging data, Analyzing high-quality hydrocarbon source rocks of organic carbon planar distribution characteristics, and lake’s paleoproductivity distribution characteristics in chang 73. Combining with the existing research results of tufa deposition, hydrothermal fluid activity at the bottom of the lake and radioactive anomalies, studing the spatial distribution characteristics between the event deposits and the paleoproductivity, and finding that there has a good corresponding relationship between them, the result shows that there is a connection between them. And based on the geochemical analysis of the event deposits, studing their effect to the formation of paleoproductivity, then discussing their influence to the formation of high-quality hydrocarbon source rocks.Comprehensive research shows, the paleoproductivity was higher in the period of the formation of high-quality hydrocarbon source rocks, the lake was eutrophic nutrient type-super nutrient type, the formation of the higher paleoproductivity in this period, was the result of the comprehensive influence by these factors, such as, the lake’s larger space, the suitable climate, and the development of geological events. These factors provide broad space for biological growth in the water, suitable climatic conditions, energy and nutrients, prompting the breaking out of the biology, and produced higher paleoproductivity, supplying basis material for the formation of high-quality hydrocarbon source rocks with sufficient.