The Radioactive Anomaly In The Deep Strata And Its Impacts On Source Rocks' Evolvement In Southwest Ordos Basin

Combining the prospecting theory of oil and gas with that of uranium, through the induction and statistics of well data and the test of rock cores in southwestern Ordos basin, the distribution, the characteristics, the genesis, and the impacts on hydrocarbon-generation of the deep radioactive anomaly are mainly studied in this paper, by means of well logging interpretation, lithology, petrographical, uranium traceback and mathematical analysis and so on.The study shows, with the feature of enrichment of uranium, three parts of significant deep radioactive anomaly exists in chang 7: chang 7~1, the top and the bottom parts of chang 7~3 member. They are regulated in distribution and probably also relates with each. Several factors for the genesis of the radioactive anomaly are analysed in the research. Firstly, the volcanoc ash tuff in Yanchang formation is probably an extremely important uranium source for the enrichment of uranium in studied area. Further more, besides the syndepositional origin model, the uranium enriched in this area, might also form in the synsedimentary stage and mineralize in the epigenetic phase. The uranium has once migrated later, the orientation of which was perhaps related with the hydrogeologic cycle, the deposition and the injected paleofluid caused by tectonic disturbance. More important, there are some indispensable advantages for the enrichment of uranium, such as, the intensive tectonic disturbance of the southwest part in Late Triassic, the massive sand body of the relic upper Yanchang formation, the turbidite of hackberry facies, and the paleoclimate and so on. Finally, the impacts that the deep radioactive anomaly on generating rock, are mainly thermocatalysis and radioactive catalysis, which have improved the evolution of the hydrocarbon generation of the oil source rock of chang 7 member.Probing into the deep radioactive anomaly and its effects on the embracing rocks, is conductive to the comprehension on some scientific issues, such as a source of shallow uranium deposits, the deep paleo-uranium deposits, and the mechanism of the oil-uranium association. Besides, it provides a new idea for the research of accumulation and distribution patterns for multi-energy mineral deposits, which is rather important in scientific study.