Yulin - Yan'an Area, Ordos Basin Jurassic Sedimentary System Of Research, The Main Sand Body

Ordos basin is the second largest basin in our country, and the largest basin containedthree energy sources of petroleum, gas and coal. Because there are main source rocks ofTriassic, and the river deltas of later Triassic and Jurassic, massive low infiltrativelithologic hydrocarbon reservoirs are filled in the strata. The Zhiluo formation ofMesozoic exist massive sandbody. This paper studies the genetic stratigraphic units, the space configurations ofsedimentary systems and the space distribution of sedimentary sandbody in the base offield outcrops and information of drilling and logging by way of sedimentology andsequence stratigraphy, interpreting the significations of the space distribution ofsedimentary sandbody to reservoir. The conclusion contains the follows: 1, The division of the vertical sedimentary sequence lead to conclusion that there arebraided river facies in the early sedimentary of Yan'an formation, and transited tomeandering river facies, lacustrine facies and lacustrine delta facies and in the upper ofYan'an formation. The genetic stratigraphic units such as brained channel, meanderingchannel, crevasse channel and crevasse fan, subaqueous distributary channel, delta frontand mouth bar, etc are recognized. 2, The analysis of sedimentary sandbody shows that there are three sediment sources distributed on northeast, west, southwest to the studied area in Yan'an depositional stage. The Yan'an formation is a secondary order sequence from lower system tract to higher system tract. 3, There are mainly fluvial facies formed in Zhiluo formation, changing from the early brained river in warm and moist climate, the middle and late meandering river and lacustrine deposition in dry and middle dry climate. 4, The sediment sources of Zhiluo formation are like with what of Yan'an formation. The Zhiluo formation is a secondary order sequenc from lower system tract to higher system tract in general. 5, The signification of Jurassic sandbody is expressed in the prediction of gas and oil reservoir. The favorable areas of gas and oil reservoir are distributed inclines in sides on palaeochannel, the incised valleys at the bottom of Yan'an and Zhiluo formation are the passages of the migration of oil and gas, the traps are consisted of distributary channel, lacustrine mudstone above and pinches of sandbody. But because the trap condition in east in studied area is poor, the favorable regions are distributed in the west and southwest of the studied area.