Chang 8 oil reservoir set in northwestern Ordos Basin is characterized by low permeability，complex controlling factors and distribution rule of reservoir parameters. So it has become an urgent problem for reservoir evaluation and production. On the basis of fine logging interpretation for wells，oil saturation distribution rule and its controlling factors were analyzed, and well loggingmulti-well evaluation technique based on multi-subject combination was applied to low permeability reservoirs. Thus the method for characterizing the degree of oil concentration and hydrocarbon abundance by using logging data was established, and the idea that the collocation relationship between hydrocarbon generating ability of source rocks and oil concentration degree of reservoir controls the distribution of rich oil gathered blocks was put forward. Based on the clue of source rock-reservoir collocation, the oil enrichment rule of low permeability reservoirs was studied and the oil enrichment areas were chosen. The study is important to evade the risks of quick productivity construction of low permeability reservoirs, and it can also accelerate the process of exploration and development and enhance the whole benefit.