Petroleum Geological Characteristics Of Carboniferous-Permian And Exploration Prospects Of The Southwest Depression In Tarim Basin

The long-term exploration and development shows the Southwest Depression in Tarim Basin has a broad prospect for oil and gas exploration,however,the research is relatively low,especially Carboniferous-Permian,which limits the progress of the exploration of the entire Southwest Depression in Tarim Basin.This paper takes Carboniferous-Permian of the Southwest Depression in Tarim Basin as the research object,and sedimentary petrology,sequence stratigraphy,petroleum geology and geochemistry as a guide.Combined with the results of previous studies and field geological survey,core observation,sample test analysis,seismic interpretation,we study the sedimentary characteristics,petroleum geological characteristics,accumulation modes and point out further exploration.(1)It solves the inconsistence of stratigraphic nomenclature system between piedmont zone and depression,divides Carboniferous-Permian into five third-order sequences.Sedimentary evolution of each sequence has inheritance,sequence 1 and sequence 3 develop narine carbonate platform facies mode,Sequence 2 and sequence 4 develop paralic mixed deposits mode,sequence 5 develops clastic depositional mode.Sedimentary evolution reflects cyclicity,showing a process of transgression-regressive-transgressive-regressive-sea completely receded.(2)The source rocks of sequence 2 and sequence 4 are widely distributed,the center of the thickness is in the Kunlun piedmont during the Carboniferous sedimentary,it migrates to south along the Kunlun piedmont during the Permian sedimentary.The depositional environment eontrolls the distribution of favorable hydrocarbon source rock,high-quality source rocks mainly develop in the diamictic coast during the late stage of regression,and brackish water lakes deposition environment.(3)The reservoirs related with Carboniferous-Permian source rocks are Carboniferous-Permian,Ordovician,Cretaceous and Paleogene;Cap rocks are Carboniferous-Permian carbonates and mudstone,Cretaceous-Paleogene gypsum rock and Paleogene shale;There are seven sets of favorable reservoir-cap combination.(4)Traps are well developed,the main types of traps are structural traps and stratigraphic and lithologic traps,different regions develop different types of traps.The migration pathways mainly include permeable formations,faults and unconformity,there are different migration pathways combination in different regions.(5)Through the accumulation model analysis,tectonic belt with exploration prospects are Fusha-Guman structural belts,the northern margin tectonic belt of Kashi Sag and Sugaite-Yingisha structure belt.And further analysis of the elements of hydrocarbon accumulation of every structure belt and exploration targets layer,provide a basis for further exploration and development.