Study On Depositional System Of S2-4in Chunguang Area, Junggar Basin

Chunguang block of Chepaizi uplift is located in east of the west uplift area ofJunggar basin. Because of the embossment continuous uplift for long time, whitchmake area for the monocline structure forms from north to south.Exploration for thegas and oil is quite mature in the area. Shengli oilfield drill light oil layer in the row-2well in2005. This success open the prelude to the oil and gas exploration in this area.Later exploration acquire some achievement; Chunguang block located on wide andflat tectonic belt. Because of the frequently transgression and regression, thesandstone and mudstone well develop and filled and sedimentary in the lake basinarea.This is beneficial for the development of the oil-gas trap.So Chun guang areahave great deal of exploration prospect. However, some well is failure to drill in thelater exploration,the primary reasons are that the cognition for the geologicalcondition to the formation of oil-gas reservoir is not clear.So It is essential torecognition the sedimentary condition and sedimentary system. In this paper, see thesha wan formation of the Neogene Chun guang area as the research object, combinethe study achievement of predecessor and the regional sedimentary background, putthe sequence stratigraphy, sedimentology, and waveform analysis theory as the theoryguidance to research the sedimentary system of the forth sand layer of sha wanformation group2in the Chun guang area. This research is the foundation of theforecast to the favorable traps and the next successful exploration. Complete thispaper mainly have the following understanding:(1)Base on the seismic data, combining the logging data and drilling data etc.,divide sha wan group sequence, the group is divided into three sections: sha wangroup1section、2section and3section. With "sequence interface recognition-deposition trend-packing way-sequence" thinking,through stratigraphic correlationbetween wells build the sequence stratigraphic framework.In the sequenceframework, internal identify the developing time of sand body. The S2-4is the firstsand layer of sha wan2group in the regression.(2) Use the synthetic record to calibrate strata through combining the seismic andwell. It is consistent compared with the drilling strata. The top interface of sand body correspond to by analyzing the synthetic records that the sand body in the study areainterface corresponding to seismic wave trough through analyzing the synthetic recordin study area. Three kinds wave style: zero phase wavelet, skew symmetric waveformand auricular waveform. Analyzing the lithology combination corresponding with thewave stype.In the research section, The main wave stype is right tilted symmetrywaveform, which show that the mostly sand body thickness less than1/4wavelength.With the decrease of the thickness of the sand body the seismic reflection amplitude isdecrease to annihilate.(3) Through analyzing the seismic data, in the research area the typical seismicfacies types are: short axial strong amplitude reflection, the middle amplitude-bottomconcavetop flat reflection, middle amplitude-high frequency-continuous-sheet reflex,the strong amplitude moundy reflection, weak amplitude nearly blank reflection, weakamplitude clutter reflection, progradation reflection etg. Progradation reflectionstand for the sedimentary bodies forward direction advance deposit and the flowdirection of the water.(4) Use the waveform-analysis and method as the guidance to interpret the sandbody of S2-4. With the sand body’s thickness decreased, the amplitude decrease. So itcan ensure the annihilation of sand body and boundary. Explain the sand body in thestudy area to get the plane distribution. The sand body form is the North-South zonedistribution.(5)Based on plane distribution of the skeleton sand body, combining with thedepositional environment、seismic facies、 single well sedimentary facies to analyzethe sedimentary facies of the S2-4.Study area mainly develop delta and lakesedimentary environment. the main sedimentary facies are: the braided delta plain,the braided delta front and littoral and shallow lake sand dam, slope fan and pelvicfloor fan sedimentary bodies.(6)Combined with sedimentary environment and sedimentary facies analysisestablish the sedimentary system of objective sand group. The sand group is thebraided delta-underwater fan sedimentary system. The braided delta and underwaterfan dividually develop.