Organic petrology is a marginal science that is quite practicable. At present, it has developed into a routine research tool that is widely applied in petroleum exploration and assess ment. Based on several years’research of the authors, this paper presents the advances in organic petrological studies on immature source rocks, including the classification and characteristics of macerals, the composition of macerals and types of organic matter, the abundance and evolution of organic matter, oil2prone macerals, hydrocarbon generation and expulsion. All these results show that organic petrology is of considerable value pertaining to its application in the assessment of immature oil and gas. The immature source rocks consist of various macerals with obvious heterogeneity, contain different hydrocarbon-generating macerals with different oil thresholds and oil peaks, and show a two-staged evolutionary pattern of organic matter.

Isotachophoresis results indicate that the total concentrations of organic acids in Ordovician formation waters range from 9.17mg/L to 94.49mgPL and are obviously higher than those of Permo-Carboniferous formation waters. But both of them have the same compositional characteristics, i.e., acetic acid > > formic acid > propanoic acid > butanoic acid. The total alkyl phenol contents of Ordovician formation waters range from 0.57mg/L to 4.73mg/L, averaging 1.77mg/L. Among the samples for phenol detection, 47.06% samples contain less than 1.0mg/L, 35.29% samples 1.0-3.0mg/L, and only 17.65% samples more than 3.0mg/L alkyl phenol. The concentrations of organic acids and alkyl phenols in the Majiagou formation waters are of obviously heterogeneous distribution. There are several areas where the concentrations of organic acids and phenols are high in central Ordos Basin. These organic acid and phenol-high areas (organic acids >45mg/L and phenols > 2.0mg/L) are consistent with natural gas reservoir enriched areas in central Ordos Basin.