Abstract: Organic acids in source rocks are derived from organic matters. The different occurrence forms of organic matter and various properties of organic acid can affect the relationship between organic acids and organic matters, and further affect the separation and detection methods of organic acid. On the basis of summarizing the occurrence of organic matter and the properties of organic acid, it is proposed that organic acids in source rocks seldom exist in a single form, but have three forms, i.e., watersoluble, fat-soluble and insoluble. The free organic matters contain water-soluble and fat-soluble organic acids, while in mineralcombined organic matters, there are water-soluble, fat-soluble and insoluble organic acids. Thus, it is necessary to take stepwise separation methods to separate organic acids of different properties in free organic matters and mineral-combined organic matters. The appropriate detection methods for organic acids were selected according to their properties. For water-soluble organic acids, ion chromatography is a proper method. The fat-soluble organic acids, which were obtained by Soxhlet extraction using dichloromethane, were detected by gas chromatography-mass spectrometry. The insoluble organic acids were obtained by
acidolysis of the extraction residue and detected using infrared spectrum. The types and contents of organic acids with different properties can be comprehensively and systematically understood using these detection methods. The successful separation and detection of different organic acids are of great significance to further investigate the characteristics and evolution of various types of organic acids in source rocks, and deepen the understanding of mechanisms of hydrocarbon generation and organic-inorganic interactions in source rocks.

Key words: source rocks, organic matter occurrence, organic acid properties, stepwise separation and detection