Study of Subtle Oil/Gas Reservoirs Exploration in Changling Sag of Songliao Basin

By using the theory of sequence stratigraphy, this paper establishes a standard for sequence classification and sequence framework in Changling sag, Songliao basin. Accordingly, we distinguish eight supersequences (second-order sequence) and thirty-five third-order sequences. T₁ and T₂ were recognized to be mfs (condensed section), and T₃, T₄, T₄¹, T₄² and T_g to be supersequence bounding surfaces. The study of the sedimentary systems formed in these five periods revealed the formation mechanism and spatial distribution of sedimentary bodies. Meanwhile, we also studied the distribution and oil-bearing characteristics of sedimentary reservoirs. On the basis of the study of oil/gas distribution in the sequence framework, we found that oil-/gas-bearing beds are mainly distributed in lowstand systems tract. The statistical study of well testing results shows that 48.2% of oil beds are in lowstand systems tract, 26.8% in trangressive systems tract (TST) and 25.0% in highstand systems tract. For the exploration purpose, the encountered lithologic traps and polygenesis traps are divided into four types: river course stone, frontal sedimentary leafy sand body, fault-lithology and structure-lithology sand body. Hence, this paper draws up the method for subtle reservoir exploration and finally makes the prediction of the subtle oil/gas reservoirs and the suggestions for the exploration plan in Changling sag.