Seal mechanism of cap rocks

Seal mechanism of cap rocks was analyzed with self-designed instrument for gas breakthrough pressure experiment.As to the same siltstone sample,breakthrough pressure was the same even though the sample length was different.Therefore,cap rock thickness does not affect capillary seal capacity in geology application.In experiment,different water pressure was imposed constantly to one end of the sample,resulting in the increase of gas breakthrough pressure,which was equivalent to the imposed water pressure.According to illustrations of overpressure formation mechanism,the overpressure had made it more difficult for gas to break through the lower tight formation and the extra pressure was equivalent to overpressure of the undercompacted formation.