A Comprehensive Judgement of the Source Direction of the Middle Jurassic of Chaonan 1 Well in the Tuha Basin and Its Research Significiance

Key words: 
• source direction /
• Middle Jurassic /
• Chaonan 1 Well /
• Tuha Basin

Abstract: The source direction of the Middle Jurasic of Chaonan 1 Well in Tuha Basin was comprehensivelyjudged through a comparative research on its lithologic characteristics of source areas and of its stratumthickness, and special distrilution of sedimentary facies of adjcent wells.The lithological difference of thenorth and south boundary mountains in Tuha Basin is clear, i.e, the southern Jueluotage Mt.is predormi-nated by acidic igneous rocks while the northern Bogeda Mt.by intermediate to basic rocks.The Clarkevalues of petrogenic elements, K, Ca, Mg, ferric family elements, Fe, Ni, Fe, rare earth elements, Sr, Ga,Rb, Ba of the Middle Jurassic mudstones of the Chaonan 1 Well were close to those of acidic igneousrocks.The two heavy mineral associations, rich in zircon and magnetite, respectively, basicatly represented those of acidic igneous rocks.The content of quartz in sandstones was over 20 %, the microcline andorthoclase were high while the anothesite low, and the volcanicdebris were mainly intermediate acidicones, which are closely related with acidic igneous rocks.It coued initally be concluded from the abovethat the clasts of Chaonan 1 Well were derived from the southern Jueluotage Mt.From Yue 1 Well, sour-thern to Chaonan 1 Well, to Xiaochao 1 Well, northern to Chaonan 1 Well, the thickness of sandstonesbecame thin, the size smaller, and the physical properties worse.The thickness of mudstones got thicker,the color darker, the content of sands less, the content of organic matter higher and the type of organicmatter better.Because the content of clay minerals, especially kaolinite,inceased and the mudstone thick-ened, the seal conditions were better.The above research result is of great significance in perfecting thejudgement method of source direction of sedimentary basins, predicting the distribution of the most fa-vorable reservoir bodies and source-reservoir-caprock associations and guiding the exploration of oils andgases.