Sedimentary System Analysis Of Devonian Donghetang Formation In Northern Tarim Basin

Tarim basin is rich in oil and gas resources.In particular,the Donghe sandstone section developed in the Devonian Donghetang Formation in northern Tarim uplift is the important marine sedimentary reservoir with the first example of high production industrial oil and gas flow in China as well as a vital targeted section for the oil and gas exploration and development in the northern Tarim basin,even the whole Tarim basin.However,by now,the division of the sequence stratigraphy and sedimentary system of this formation is still not unified,and this leads to the confusion about the distribution of reservoir in this formation and caused significant inconvenience for the exploration and development practice of Tarim oil field.Therefore,under the guidance of the sequence stratigraphy theory,sedimentology theory and seismic sedimentology theory,on the basis of full digestion and absorption of the outcomes of massive prior studies,this paper researches into the Devonian Donghetang Formation in the northern Tarim area.Through the use of drilling,logging,core,outcrop and 2D seismic data in the study area,this paper starting from the identification of the types of single well facies,identifies the key sequence interface and stratigraphic pattern;thus determining the sequence division scheme of Donghetang Formation and establishing the sequence stratigraphic framework.Based on the above understanding of sequence stratigraphic analysis,comparative analysis of well sedimentary facies and seismic facies analysis,this paper clears the development and distribution characteristics of Donghetang Formation's stratigraphic system in the research area.Combining with the exploration practice in the northern Tarim uplift,this paper includes an objective evaluation of the favorable reservoir facies of Donghe sandstone,aiming to provide reference for future oil and gas exploration in this area.Through the above research,this paper identifies 8 types of lithofacies including the parallel bedding sandstone facies and sand grain bedding sandstone facies,3lithofacies combinations in the Donghetang Formation.Combining with the analysis of signs of sediment facies including petrological characteristics?rock's colours,sediment structures and granularity distribution,it can be concluded that shore facies is the main the main sedimentary facies in Donghetang Formation in northern Tarim basin,which is composed of two sub-facies including the shoreface sub-facies and foreshore sub-facies.Besides,this paper identifies 2 kinds of typical logging facies in Donghetang Formation.Based on the division of sedimentary facies of single well,this paper cleared the sequence interface and stratigraphic superposition pattern,thus making the stratigraphic division scheme.Donghetang Formation in northern Tarim basin consists of a three order sequence D₃SQ1,which can be further divided into four para-sequence sets with isochronous correlation significance.Shore facies sedimentary system is the main sedimentary system in Devonian Donghetang Formation in northern Tarim basin,The southeastern,northwestern,southerneastern and northeastern study area mainly developed the foreshore sub-facies,while the southwestern and central study area developed the shoreface sub-facies.