The Characteristics Of Clay Minerals In Carboniferous Source Rock And Its Thermal Response For Volcanism In Northern Xinjiang

Since the upper palaeozoic and volcanic oil-gas reservoir study has madesignificant progress, the Carboniferous in northern Xinjiang has attracted the attentionof the oil-gas exploration. The research area is localed to the middle of Asia, andbordered by Altai Mountains fold system to the nouth, Tianshan fold system to the south.In themiddle of the area is Junggar fold system, Juggar basin, Santanghu basin and Tuha basin.The geology and geochemical researchs indicate that the source rocks aremedium-good in its essentials, few can achieve very good source rocks, even thecarbonaceous mudstone. The source rocks formed in the Late early Carboniferous aregiven priority to the middle–good, whose organic matter type is Ⅲand in highmaturity. The source rocks have a higher abundance of organic matter andhydrocarbon generating potential in the Dishuiquan sag in Junggar Basin and JaminSue sag in Tuha basin. The organic matter type of the early late Carboniferous sourcerocks are Ⅲ and Ⅱ1,and the degree of maturity is maturity and high maturity. Thesource rocks in Ludong-Wucaiwan area, and the northwestern edge of the easternuplift of Junggar basin have a higher abundance of organic matter and hydrocarbongenerating potential. The organic matter types of the middle-late late Carboniferoussource rocks are Ⅲ and the minority are type I and II1, the degrees of maturity arematurity and high maturity. The abundance of organic matter and hydrocarbongenerating potential are higher in Malang sag and Tiaohu sag of Santanghu basin andBuErJin basinThe mineral composition of the source rocks are quartz, plagioclase, orthoclase, calcite and clay mineral, and the concent of clay mineral change from10%to63.6%.The kinds of clay mineral are the mixed-layer minerals of illite and smectite,illite, chlorite, kaolinite, and the mixed-layer minerals of chlorite and smectite. Thestudy of clay minerals in source rocks indicates that the relative content of illite/montmorillonite layer of clay mineral has a downward trend, while rate mixed-layerof smectite in mixed-layer mineral tend to lowe, as the age gradually grow old.The Upper clay minerals and illite crystalline degree of CarboniferousBatamayineishan Formation shows a different variation tendency with thecarboniferous strata. Thermal evolution degree is the same as the older strata, or evenmore. Frequently volcanism for the carboniferous is likely to promote the illitizationof clay minerals in argillaceous rock and the important reason of organic matterthermal evolution degree increasing by analysis of the tectonic evolution.The sourcerocks in large edge of the basin and rift valley regions when superimposed ofvolcanism, are more likely to promote the rock thermal evolution degree withdeepening.The results based on study of the geology, geochemical, and clay mineralogy of theCarboniferous source rocks show that they were in the advanced stage of diagenesis but very lowgrade of metamorphism and the degrees of maturity are generally at mature to high stages. Thefurther study suggests the very low grade of metamorphism of the Upper CarboniferousBatamayineishan Formation may affect by the volcanism.