CHARACTERISTICS OF BIOMARKER COMPOUNDS IN THE SOURCE ROCKS OF LOWER CRETACEOUS YIXIAN FORMATION FROM XD1 WELL IN XIUSHUI BASIN, NORTHERN LIAONING PROVINCE: Geological Implication

The gas chromatography and gas chromatography-mass spectrometry(GC-MS) are used to study the characteristics of biomarker compounds in the source rocks and analyze the organic matter source, sedimentary environment and thermal evolution degree of source rocks of Lower Cretaceous Yixian Formation in XD1 well of Xiushui Basin. The results show that the source rocks have high organic matter abundance, with II-type organic matter, which are in the mature stage. The(C₂₀+C₂₁)/(C₂₃+C₂₄) tricyclic terpane ratio of 0.66-5.06 and C₂₄ tetracyclic terpane/C₂₆ tricyclic terpane ratio of 0.38-2.25 reflect the characteristics of typical lacustrine source rocks. The Pr/Ph ratio of 0.5-1.0 indicates the reduction environment. The gammacerane/C₃₀ hopane ratio of 0.05-0.41 indicate the strong reducing sedimentary environment, with low water salinity and possible water salinity stratification during the deposition of source rocks. The relationship of Pr/nC₁₇ and Ph/nC18 shows the organic matter is mainly II₁ type, and the correlation of C₂₇-C₂₈-C₂₉ steranes reflects that the organic matter is derived from a mixture of lower aquatic organisms and higher terrestrial plants. The Ts/Tm ratio of 0.45-1.82 and C₃₁αβ22S/(22S+22R) ratio of 0.41-0.62 reveal that the source rocks are in the low mature-mature evolution stage, with the maturity of source rocks in the middle and lower parts of Yixian Formation higher than that in the upper part. It is concluded that the source rocks of Lower Cretaceous Yixian Formation in Xiushui Basin were formed in a reduction-strong reduction environment with low water salinity, the mixed source of organic matter is conducive to the enrichment of organic matter, and the Yixian Formation has good prospects for oil-gas exploration.