BIOMARKER CHARACTERISTICS AND IMPLICATION OF THE MESOPROTEROZOIC GAOYUZHUANG FORMATION IN LIAOXI DEPRESSION OF YANLIAO RIFT ZONE

The oil-gas shows found in several bore wells in Liaoxi Depression of Yanliao Rift Zone bring the Meso-Neoproterozoic marine strata in the area once again into the focus of oil-gas exploration and research. Both gas chromatography and gas chromatography-mass spectrometry are used to study the biomarkers of source rocks from Mesoproterozoic Gaoyuzhuang Formation in LLD1 well, and analyze the organic matter source, sedimentary environment, and hydrocarbon generation potential. Through comprehensive analysis, it is considered that Gaoyuzhuang Formation belongs to poor-medium grade source rocks, as organic type of Ⅱ₁, generally in mature-high mature stage with mass generation and expulsion of hydrocarbon. The carbon number distribution of n-alkanes in saturated hydrocarbon is pre-unimodal. The main peak carbon is mostly nC₁₇, with the advantage of C₂₇ regular sterane, indicating that the parent material input is dominated by lower organism. Combined with the distribution characteristics of terpanes, it is inferred that the main organic source is low bacteria algae. Moreover, the high gammacerane content and low Pr/Ph ratio reflect the main source rocks of Gaoyuzhuang Formation were formed in salt water reduction environment, with certain layers possibly in strongly reduced environment.