| In recent years,Kuqa foreland basin is a hotspot rearch of geological exploration which belongs to PetroChina Tarim Oilfield. The previous studies showed that the Kuqa foreland basin is generated by South Tianshan thrust to south flexural subsidence. Lower Cretaceous in Kuqa foreland basin is mainly composed of pebbly sandstone, fine sandstone and siltstone strata.Kelasu and Qiulitage structural belt have high degree of exploration,while Baicheng sag has lower degree of exploration. Through a whole study on the rearch area,Bashijiqike formation’s sedimentary facies development and the main controlling factors are defined,at the same time,this study provide theretical support for the next oil and gas exploration of favorable area.According to the current drilling results, the formation in Kuqa Depression developed Triassic, Jurassic, Cretaceous, Tertiary, Paleogene, Neogene and Quaternary from bottom to up.Among these,the Lower Cretaceous Bashijiqike formatiom is the rearch destination. Over the past decades, scientific research units and institutions have done a lot of researches in the Kuqa Depression and gained a large number of conclusions in sedimentary reservoir.These results not only bring inspiration, but also bring a lot of new thinkings.The reservoir sedimentary facies belts are complex and change quickly.There are a lot of controversies on the division of the microfacies, and the rearch of Bashijiqike formation is not deep enough.This paper choose central Kuqa Depresssion’s Bashijiqike formation as the research object.Through this rearch process,based on the modern contimental facies reservoir geology theory,sedimentology, sequence stratigraphy,ancient geography and structural geology for guidance, studied the outcrop and seismic,drilling,logging data, combined core observation,indoor thin section analysis,physical analysis,gas testing and data,we get a detailed analysis and understanding of lower Cretaceous Bashijiqike formation’s depositional systems and structural characteristics,and predicted favorable reservoir areas.This paper considered Bashijiqike formation of Central Kuqa Depression as the rearch object.Through field observation and indoor comprehensive study, the main method is to combine outcrop and drilling,macro and micro.Through studing point detail to surface comprehensive evaluation, a single fine sedimentary research to combine all the analysis data to sedimentary facies in-deepth study.Then,we get the following conclusions. (1)The rearch area has stable mirofacies in the trasverse direction,the sand bodies connected well with each other,good continuity. Mud layer is thin and discontinuous laterlly. The sand layer has large thickness in space,wide distribution,continuity,little interlayer.All these characteristics demonstrated that the rearch area has a set of high-quailty natural gas reservoir.Overall, the north part of the rearch area mainly developed braided delta facies, while the west part of the rearch area mainly developed fan delta facies.Through the study of sedimentary facies distribution law,the central Kuqa Depression’s sedimentary facies and provenance direction were confirmed.Meanwhile,the factors controlling the deposition are paleostructure,paleolandscapes,paleoclimate,ancient plants and animals etc.Among these, paleostructure and paleolandscapes are the most important controlling factors.(2)Through the in-deepth study of the provenance, depositional systems’lateral evolution, the clastic component analysis, heavy mineral portfolio analysis and palaeocurrent,we conducted a comprehensive research of Central Kuqa Depression and concluded that there were multiple directions’ provenance. Among these,the northern Tianshan has multiple provenance entrance,followed by the western Wensu uplift which is also a major provenance;(3)Throuth fine core observation we conclude that the core of the Great Northern region’s sedimentary microfacies descripted in detail, and constract with the Kela area.lt provide the basis for the division and correlation of the horizon. Completed the core sedimentary reservoir histogram. Based on this, we can get a fine study with logging on the sedimentary micro-facies of the Great Northern region.(4)Compilation three maps of Central Kuqa Depression at lower Cretaceous Bashijiqike formatiom.Progress has been made both on the sedimentary facies and depositional system. Especially,K1bs1and K1bs2sedimentary facies plane distribution have some progress compared with predecessors.(5)Bashijiqike formatiom in the study area bottom-up divided into three sections, K1bs2has the longest deposition time, it has large scale fine-grained sandstone mainly.Through the analysis of logging data, lithological characteristics etc,K1bs3has coarse particle lithology size compared to K1bs2and K1bs1.Overall,it manifested as the water to recede.K1bs3is expansion of the lake basin and developed fan delta.During K1bs2, the lake began to shrink because of strong tectonic movement and sharp raise of western Wensu uplift.It developed braided delta facies.K1bs1has slightly tectonic movement,sedimentary facies has little change compared to K1bs2. |
