CHARACTERISTICS OF CARBON AND SULFUR ISOTOPES IN CRUDE OIL AND OIL-SOURCE CORRELATION IN THE TARIM BASIN

Based on the fractionation of carbon and sulfur isotopes in the process of petroleum generation and evolvement,the crude oils and their sources in the Tarim Basin have been discussed.The δ¹³C of crude oil inherited the one of its biologic matrix.The δ¹³C value of marine crude oil is less than-32‰ or more than-24‰,and the δ¹³C value of continental crude oil is from-32‰ to-24‰.The organic sulfur in crude oil originates from the sulfate in source rock.But the δ³⁴S value of mature crude oil with temperature being higher than 80-120 ℃ is 3‰-4‰ lighter than the δ³⁴S value of the sulfate in source rock.The crude oils in the Tarim Basin can be classified into four types according to the characteristics of carbon and sulfur(isotopes) as well as other physical and chemical properties of crude oil.The second is 21‰-26‰ and δ¹³C value is less than-32‰.It is typical marine crude oil.The second is Permo-Carboniferous crude oil whose δ³⁴S value is 5‰-7‰ and δ¹³C value is less than-32‰.It is also marine crude oil,but the biologic matrix is poor.The third is Triassic-Jurassic crude oil whose(δ³⁴S) value is 10‰-14‰ and δ¹³C value is about 26‰.It is typical continental crude oil.The fourth is mixed oil of the above three types of crude oil.Its δ³⁴S value is between that of marine and continental oil.The mixed oil composed of Cambrian-Ordovician and Permo-Carboniferous crude oil has characteristics of marine oil,and the mixed oil composed of Cambrian-Ordovician and Triassic-Jurassic crude oil has characteristics of mixed oil facies.The mixed oil composed of Permo-Carboniferous and Triassic-Jurassic crude oil has not yet been discovered.