Evidence from illite/smectite diagenesis and vitrinite reflectance for fluid migration in Jeanne d'Arc Basin, Grand Banks offshore Eastern Canada

摘要

Illite content and the degree of ordering in mixed-layer illite/smectite (I/S) in mudrocks invariably increase with burial depth and temperature in 22 exploration wells in the Jeanne d'Arc Basin, Canada. The diagenetic evolution of I/S, however, displays significant anomalies with respect to organic-matter maturation in parts of the basin where major oil fields occur. In the Trans-Basinal Fault (TBF) area, illitization is rapid in the 30-70% illite range causing step-shaped illitization profiles. The Southern and Northern Jeanne d'Arc Basin lack the stepwise increase in % illite. In the anomalous TBF zone and on the western flank of the Central Ridge (CR) area, the random to (R1)-ordered I/S transition occurs at lower vitrinite reflectance values than in the main parts of the basin. This indicates advection of deep K+-bearing fluids along faults that advanced I/S diagenesis.In this part of the basin illitization is primarily not temperature dependent. The concentration of all major oil discoveries in the TBF zone and CR area suggests that the upward migration of hydrocarbons to the shallower reservoirs may have followed the same pathways as the illitizing fluids.