Experimental studies on the hydrocarbon sealing efficiency of pelitic rocks

Laboratory experiments and petrophysical measurements were performed to determine the hydrocarbon sealing efficiency of shales and siltstones from the Norwegian Continental Shelf and Northern Germany. The investigations covered both molecular transport (diffusion) and volume flow. Diffusion coefficients for methane in water-saturated rocks measured at 150 deg C ranged between 10-9 and 10-11 m2/s and showed a clear correlation with TOC content. A significant reduction of diffusion coefficients was observed with increasing effective stress. Diffusion coefficients for molecular nitrogen were consistently higher than for methane. Permeability values of the pelitic rocks varied between 0.1 and 10,000 nDarcy (10-22 - 10-17 m2). Measurements under controlled effective stress revealed different types of stress dependence of permeability. The effect of faults on fluid transport was investigated in a dual approach. (author)