Abstract: The reservoir of Chang-6 formation in Ansai oilfield has high content of acid sensitive minerals. The result of acid sensitivity evaluation shows that it belongs to medium-weak acid sensitivity. So for a long time acid treatment was considered to have no feasibility. On the basis of the abundant experimental studies, the organic acidizing field test is performed, obtaining a good result of stimulation. This proves that the acid treatment is feasible in this reservoir. This paper analyzes the defects in acid sensitivity standards from the rock/ acid reaction mechanism and experimental methods and points out existing results from acid sensitivity evaluations cannot be as the judged bases for performing acid treatment in this reservoir.

Key words: standard, sandstone, acidizing, organic acid, evaluation