Geochemical Characteristics of Oil Sand Extracts in Different State from Sandstone Reservoirs: nalkaneones——A case study from Yanchang Formation of Triassic in Ordos basin

Key words: 
• reservoir /
• nalkaneones /
• hydrocarbon in different state /
• Yanchang Formation

Abstract: Ordos basin is an important MesozoicCenozoic petroliferous basin in West China. Xifeng Oilfield, in the southwest of Ordos Basin, was discovered in recent years. The crude oil reserve in this oilfield is about 100 million tons. Chloroform fractions of free oil and bound oil，which are extracted from six oil sands of Yanchang Formation in Xifeng oilfield, have been analyzed by GC/MS. The nalkaneones in six samples show an strong odd carbon number predominance, carbon number ranging from C13 to C31. This study shows that thermal evolution(maturity) has an effect on the evolution of nalkaneones. The nalkane2ones distribute in bound oil with low maturity, whereas nalkane3, 4,5,6(or more)ones distribute in free oil with high maturity. That is, with the increase of maturity, the carbonyl group distribution of nalkaneones shifts to the higher homologues isomers. The origin of these nalkaneones has been attributed to microbial production from nfatty acids from bacteria, seaseed and higher plant lipid by βoxidation and decarboxylation. The distribution characteristics of nalkaneonesin different state hydrocarbon can be used in dating petroleum accumulation.