The Characteristics Of Origin And Oil Generation Of Black Rock Series In Chang 7 Member Of Yanchang Formation In Ordos Basin

For a long time,It is generally recognized that the black rock series,which belonged to Chang 7 member of Yanchang Formation in Ordos Basin,formed in the most developed stage of Yanchang lake basin.That black rock series are characterized by composed mainly by clastic sediments,such as mudstone,shale and siltstone and silty sand and so on,which mostly developed in half deep lake-deep lake environment.That black rock series are also the mostly critical dense oil layers in Yanchang Formation,because of its large thickness,widely distribution,and strong ability of hydrocarbon generation.In recent years,there were volcanic materials and hydrothermal jet materials found in that black rock series,so the study of relationship between sedimentary composition,volcanic materials and hydrothermal jet materials and hydrocarbon generation in black rock series,has importantly theoretical and practical significance.We have mainly got the following conclusions and understanding by adopting multidisciplinary theory,mainly include sedimentology,petrology,mineralogy and geochemistry,a series of test methods and macroscopic and microscopic,and super-microscopic observation about the rocks of wild outcrop profile and drilling cores.(1)It has long been regarded as that the "mudstone,oil shale,siltstone,silty sandstone etc",which identified by the naked eye,are normal sedimentary sandstone,but there actual lithology may be tuffaceous rocks,such as tuffs,tuffites and tuffaceous sedimentary rocks with different particle size,which size range from clay to sand.(2)There are some kinds of hydroclastites and hydrothermal exhalites,which discoveried for the first time in the Chang 73,and many combination types of hydroclastites and hydrothermal exhalites were divided by theirs material source,generation type and structural construction.The carbonite and felsic fall-out phreatomagmatic hydroclastite,which formed by fall out of fine magmatic ash,generated by hydroclastic explosion.The carbonite and felsic exhalative hydrothermal rocks,which generated by hydroclastic explosion and magma overflow and characterized by magmatic minerals and magma structure.The exhalative hydrothermal rocks also can be divided into white smoker and black smoker types.The white smoker type includes dolomitic,felsic,and siliceous exhalative hydrothermal rocks.The black smoker type includes pyrite exhalative hydrothermal rocks.They are like three types of rocks,dolomitic spherolite,dolomitic and colloidal biolite,related to white smoker and black smoker exhalative hydrothermal rocks.(3)The black rock series developed high natural gamma sandstone,which particle size,range from coarse silt to sand,and caused by radioactive mineral which related to hydroclastites and hydrothermal exhalites.The high natural gamma sandstone's log value of natural gamma-ray logging is mostly greater than 180API,which greater than adjacent mudstone and usually misunderstood as fine-grained sedimentary rock,such as mudstone,shale etc.The radioactive mineral also usually cause high radioactive background of stratum lithology.(4)The primary hydrocarbon-generating organism are like collophanite and round-shape algae,which belonged to thermophile,in Chang73.The degree of development of collophanite and round-shape algae is mainly associated with hydroclastites and hydrothermal exhalites,,followed by slowly and continually deposited tuffaceous rocks,except sedimentary rocks.(5)The carbonite blast rock and neutral magmatic rocks produce lots of heat,nutrient,radioactive element(U and Th),and generated high radioactive background of stratum lithology,lots of thermophile,black-dominated strata rich in black organic matter such as asphalt,and caused two accumulation stages,the early and the late stage in Chang 73 of Yanchang Formation in Ordos Basin.