Methods for thermal maturity estimation in shale gas source/reservoir rocks: A case study of a Devonian shale in Western Canadian Sedimentary Basin

Thermal maturity has been estimated from various methods. Because residual organic matters in shales possibly cause erroneous maturity assessment, the methods need to be applied with caution. The Devonian shales in the Horn River Basin contain little vitrinite and show too low S2 value to obtain reliable 'f max. 'I'hus; it is difficult to estimate reliable thermal maturity from the Rock-Eval pyrolysis and vitrinite reflectance analysis. These Devonian shales contain abundant solid bitumen. The reflectance of solid bitumen has been used as an alternative for maturity estimation; but it could be affected by other factors rather than thermal maturity. In this study, the vitrinite reflectance converted from the solid bitumen reflectance is in good agreement with the vitrinite reflectance from MPI-1(Methylphenantrene Index-1) values. 'Ills result suggests that the reflectance of solid bitumen is alternative maturity indicator of the Devonian shales in the Horn River Basin. The converted vitrinite reflectance (ay. 1.9%) shows that the shale samples are within the gas window TOC (total organic carbon) values range from 1.5 to 6.8 (a.y. 3.8) wt% and RC (residual carbon) contents represent up to 90% of TOC. The results indicate that most of PCs (pyrolysable carbons) have already been converted to hydrocarbon and organic pores have been developed. 'I'hus; the Devonian shales m the Horn River Basin would have good potential of gas generation and storage.