Seismic Sedimentology Study Of Jurassic In Doshan Area,South Turgay Basin

Doshan area which covers about 824 km~2 is located in the northwestern of Aryskum graben,South Turgay Basin.The well drillings which are scarce and the distribution is uneven are deep but the target stratum structures are not complex in the area.Depend on the research of sequence stratigraphy and sedimentary petrology,the lateral resolution of three-dimensional seismic data are fully exploited to study the sedimentary characteristics of different periods and the distribution of depositional system of Doshan using the key technologies of seismic sedimentology,such as 90°phasing convertion,strata slice and frequency division.Considering the formation conditions of lithologic-stratigraphic trap and trap elements,trap prediction and evaluation for the region are done to predict the favorable exploration targets.Under the guidance of sequence stratigraphy theory and the integrated use of core,logging and seismic data,the main sequence boundary of lower Jurassic to lower Cretaceous in Doshan area is identified and divided.10 sequences,11 sequence interfaces,2 first-order sequence interfaces,2 second-order sequence interfaces and seven third-order sequence interfaces are justified and the four stratigraphic division and comparison of the upper Jurassic in study area are done.Then the high resolution sequence stratigraphy framework in the work area was established.Based on the analysis of the sedimentary facies,single well facies and seismic facies in the area,seismic sedimentology characteristics analysis of the key strata,Akshabulak group(SQ8)three fourth order sequences are done using 90°phasing convertion,strata slice,slice attribute analysis,frequency division processing and other techniques.The sensitive frequency range and optimizing sensitive attributes are determined.At least six periods channels in the SQ8 are identified.At least two periods in SQ8-1 formation representing the most widely and intense period.The channels with poor longitudinal continuity in SQ8-2 formation is thinning.The distribution of the channels where the range of water is shrinking in SQ8-3 formation is limited.Compared with SQ8-1 and SQ8-2 formation,SQ8-3 formation with the sedimentary characteristics of inheritance reflects a main transgressive process with shallow water depth in the transgressive and regressive process.There are four kinds of trap in Doshan:lithologic trap,stratigraphic trap,structural trap and composite trap where the former two types are widely distributed in Akshabulak group(SQ8)of Aryskum graben.The basis elements of hydrocarbon source condition,reservoir conditions,preservation conditions and other traps'formation are comprehensively analysed to give the preliminary assessment of the discoverable lithologic trap.The target layer of Doshan area are classified into level I,level II and level III.There are 2 traps of level I,total area 14.6 km~2,2 traps of level II,total area 9.44km~2,1 trap of level III,total area 3.26km~2.Through a comprehensive study of oil and gas analysis,four benificial exploration targets are pointed out according to construction background and sedimentary facies.