Isotachophoresis result indicates that the total organic acids concentration of Ordovician formation waters range from 9.17mg/l to 94.49mg/l and are obviously higher than those of Permo Carboniferous formation waters.But both of them have the same composition characteristics of acetic acidformic acid>propanoic acid>butanoic acid.The total alkyl phenol contents of Ordovician formation water range from 0.57mg/l to 4.73mg/l

and the average concentration is 1.77mg/l.Among the samples of phenol detection

47.06% samples are less than 1.0mg/l

and 35.29% samples are 1.0～3.0mg/l

and only 17.65% samples are more than 3.0mg/l.The concentration distribution of organic acids and phenols in the Majiagou formation waters occurs obvious heterogeneity.There are several higher organic acids and phenols concentration areas in the central part of Ordos Basin.High organic acid and phenol concentration areas of formation water(organic acids>45mg/l and phenols>2.0mg/l) are consistent with natureal gas reservoir enrichment areas in the central part of Ordos Basin.