Study On Depositional System Of N₁s₂²of The Shawan Formation Of Neogene In Chunguang Block Of Junggar Basin

Junggar Basin is a large Mesozoic-Cenozoic sedimentary basins in China,andChepaizi area is located in the northwest of that. Junggar Basin is a a relatively highdegree of exploeration basin,and Shengli Oilfield obtained light oil in the Shawanformation of pai2well in drilling Chepaizi in2005,that led to the process of theChungguang oilfield exploration.The followed exploration results indicated that the oilof Chunguang oilfield had excellent features-shallow layer, very light, highproductive etc.It showed that there are still huge potential to be excavated. Chepaizi islocated at a nose and gentler slopes,in the same time the water level of the lake inChepaizi is not very deep, the most depositional system developed here are the riversand lakes.Because the frequently advanced and retreated water, sandstone andmudstone were well developed, that conducive to the development of lithologictraps.There is good prospects for oil and gas exploration after comprehensiveanalysis.This paper take the Shawan formation of Chepaizi area as the object in theresearch, using theory and methods of sequence stratigraphy, sedimentology, andwaveform analysis theory, the sequence stratigraphy framework of Shawan formationwas established, and the sandbody were interpretated in that framework. Combinedwith the depositional environment, the sand body planar maps and the seismic attributeof sand body,the sedimentary system were detected and the favorable sandbodydistribution zone were pointed out. The main results achieved in this paper were asfollows:1) Comprehensive using of drilling, seismic and well logging data, the sigle wellsequence stratigraphy interface of five wells in the study area were divided, and fivewell combained sections across the whole region were described.After that, thesequence stratigraphy dividing method is clear. Using of the T-R sequence mode, theShawan formation is divided into three sequences, that were correspond to the N1s1,N1s2, N1s3segments of Shawan.2) The well data was analyzed combained with the seismic data through the synthesis seismogram.It is believed that the top of sandbody top was correspond to thetrough of the seismic wave, and the means of identification of the sandbodys wereestablished. Six kinds of waveform were summarized up.3) The seismic facies types of Shawan formation were as follows: Mediumamplitude in continuous parallel reflection, clutter reflection with weak amplitude,Medium amplitude continuous reflection and hummocky reflection. the foresetreflection indicates the palaeocurrent direction, which is the direction of thedifferentiation of sandstone and mudstone in the same time.4) The sand body in the study area were scanning based on the waveformestablished above. The sandbody distribution of N₁s₂²was certained, and thedepositional system were analyzed combined with the depositional environment. Theresults of the analysis were: the delta-fronts, beach bars and Turbidite fans weredeveloped in the study area.The beach bar sandbody were derived from the earlydeposition of sands, that was because that early deposited sands were carried by thelake waves and then deposited in the direction of the coast line.And they showed ashummocky reflection in the seimic section in the direction vertical to the sourcedirection. The Deep-wate fans were developed in the semi-deep lake to deep lakeenvironment that were derived from the early deposited sediments on the slope break.Which was the effect of earthquakes, storms etc.Those sediments liquefied first, andcarried by gravity and deposited in sag of the lake across the slope. The deep-waterfans overplayed each other that could be called as overlap fan or deep-water fan groups.5) The target layer of sedimentary facies model was established according to thedepositional system and sedimentary facies of N₁s₂²combained with the depositionalenvironment, and the favorable facies of lithologic traps were pointed out.