Seidimentary System Study Of The N₁S^2-6 Sand Bodies In Chunguang Block, Junggar Basin

The Chunguang Block is located in the central of Chepaizi uplift in JunggarBasin, northwest China. Preliminary exploration activities and related research haverevealed good prospects of oil and gas exploration in this area. However, the currentunderstanding of sedimentary environment and its depositional systems of theNeogene Shawan formation has considerable differences, to some extent; it hinderedthe further process of oil and gas exploration and prospect evaluation. On the basis ofprevious study, with seismic stratigraphy and sequence stratigraphy standardizationtheory as a guide, this paper gets the following conclusion by the well-seismicanalysis as synthesis record a link, the sequence stratigraphic framework analysis ofthe skeleton line based on the sedimentary prototype recovery in the basin, theskeleton sand body identification based on the waveform analysis in the framework,the seismic facies and sedimentary facies analysis, the study of the sedimentarysystem.1) We divide the sand of Shawan formation into three types by speed-depth curveof the sand and shale: the type Ⅰ sandstone: the sandstone whose speed is less thanthe mudstone speed; Type II sandstone: the sandstone speed is basically same withthe mudstone speed; the type Ⅲ sandstone: the sandstone speed is faster than themudstone speed. And it is mainly the type Ⅰ sandstone in Shawan formation2) With well-seismic comparative analysis as the link of the syntheticseismogram (Focused on the correspondence between the lithological combinationand the waveform response characteristics), the impact analysis of the convolutionmodel and sandstone thickness to the reflection waveform, the typeⅠ sandstone ofThe second stage of Shawan formation can be identified by seismic data, using the waveform analysis. The mark of identification is as follows, the top of the typeⅠsandstone body corresponds to the trough, the bottom corresponds to the crest, thecomposite waveform dipping lower-right and the strength of the amplitude has somecorrespondence with the thickness of the sandstone. So it identifies9sand groupsinner the second stage of Shawan formation.3) Under the attributes (rms amplitude) analysis constraints in the S2-6sand sets,the scan interpretation of sand body depicts the spatial distribution characteristics ofthe S2-6sand group. And based on the skeleton sand body, combining with the resultof sedimentary basin recovery, the drilling data, the types of sedimentary facies, thefacies combination and the related deposition system, the result shows that the maindepositional systems of Shawan formation is delta-underwater fan. The detailsedimentary microfacies distribution is that Enclosed lake shed develops the deltaplain、delta front; pazalimnion shed—break belt area develops prodelta and themudstone of shallow lake、siltstone; there develops the deposit of subsea fan, whichformed in the slope of the out of break belt to the lake basin.4) The sedimentary system analysis reveals that the development of deltaseparates from the subsea fan in S2-6sand group development of Es2(it is separatedby the Bypass with10-15KM in the middle). The turbidite of subsea fan is thefavorable part of the lithologic trap development.