Abstract: In order to get objective and general result of caprock sealing ability, the authors put forward to the caprock sealing ability comprehensive evaluation method by using the index of permeation velocity of gas through mudstone caprock, and give, according to the Darcy law, the method of getting parameters and evaluation process.Based on thoroughly studying the macroscopic characterize and microcosmic sealing ability of the K₁d₂ mudstone caprock in the east of Daqing placanticline. The method has been used to evaluate the gas sealing ability of K₁d₂ mudstone cap-rock in the east of Daqing placanticline. The result tested in Zhaoshen 1-Fangshen 4-Fangshen 5-Fangshen 1-Wang 9-12-Wang 903 and its west show that the K₁d₂ mudstone caprock has the best sealing ability. In contrast results from the Zhaoshen 3-Chao 2-Sanshen 1 and its south and in Qing 2-Wushen 1-Sishen 1-Chuan 3 show that the K₁d₂ mudstone cap-rock has the middle sealing ability. In the south of Ershen 1-Chaoshen 2-Zhaoshen 2, the K₁d₂ mudstone cap-rock has bad sealing ability. In other areas, the K₁d₂ mudstone cap-rock has good sealing ability.

Key words: the east of Daqing placanticline, mudstone caprock, permeation velocity, gas sealing ability