Composition and Distribution Features of Fatty Acids in Salt-Lake Immature Oils

Key words: 
• immature oil /
• fatty acids /
• ethyl ester of fatty acid /
• salt lake facies.

Abstract: The relative high abundance and important hydrocabon-generating potentiality of fatty acids in geological bodios make it necessary to investigate the composition、distrbution and presence of fatty acids in various geological bodies.The composition and distribution features of fatty acids in immature oils of diferent sedimentary environments,sach the alkaline salt lake facies in the Migang depression, Halite salt lake facies in the Wayang depression,ggpsum salt lake facies in the Xiangcheng depression and fresh water lake facies in the Nanyang depression were analysed and investigated. As a result,the fatty acids in immature oils of various salt tale depressions are compased of saturated n-fatty acids,unsaturated n-fatty acids,branched fatty acids, isoprenoid fatty acids and fatty acid ethyl eslers with different abundances The carbon number of fatty acids is between C₁₂ to C₃₀ major at C₁₆ and C₁₈ and the short-chain homologumes are predominant with a strong even／odd predommance,The unsaturated n-fatty acids are mainly composed of C_16:1△⁹ C_18:1△⁹ and C_18:1△¹¹ fatty acids,and the UFA／TFA values ranged between 0.013 to 0.091(average values:0.042).The branched fatty acids are composed of C₁₅、C₁₇ iso-anteiso-fatty acids and C₁₄～C₂₁ isoprenoid fatty acids (except for C₁₈).Thes results and the low C₁₆／C₁₈、C_18:1 values indicate that the source materials of the immature oils are mainly bacteria、algae and the bacteriol alternated products of higher plants and aquaticorganisms.Thas,the composition and distribution features of fatty acids in immature oils can be used to explain the sources of primary organic matter in these various deperssions.On the other hand,the C₁₁～C₂₅ ethyl esters of fatty acids with laoer even／odd prodominance fourd in various sedimentary environments clemonstrate that the fatty acids can present as esters in geological bodies.