摘要
The paper studied 14 gas reservoirs in the Xujiaweizi rift Sag, Songliao Basin thoroughly and the result showed that volcanic rocks in the top of the first member of Yingcheng Formation, composed mainly of tuff and volcanic breccia with a thickness between 0 and 80 cm, were characterized by high interval transit time and enlarged borehole diameter, and locally formed a suite of good cap rocks. Consequently, a method was established for synthetically assessing gas-sealing ability of these volcanic rocks based on factors impacting on gas-sealing ability of volcanic cap rocks, such as, thickness, displacement pressure, vertical sealing of faults, viscidity of natural gases and pressure of gas reservoirs. A positive correlation was found between the reserve abundance of natural gases and the synthetic evaluation index.