By using the methods of hydrocarbon generation kinetics and carbon isotope kinetics, combined with geological background of natural gas pool formation, the generation and accumulation of natural gas from Yinan 2 gas pool was studied in Kuqa Depression of the Tarim Basin. Natural gas of Yinan 2 gas pool is mainly' derived from Middle and Lower Jurassic coal-bearing source rocks, and generally belongs to long time-accumulated gas. It is suggested that Yinan 2 gas is chiefly accumulated in the last 5Ma, its Ro ranges from 1.25% to 1.95%, and the loss rate of natural gas is about 25%-30%. This work not only complements and reduces the deficiency of formation model of natural gas pools which traditionally depends on the matching relation-ships between source rock, reservoir, cap rock, and trap, but also is a useful reference in the study of other gas pools.

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.