The Upper Devonian Dunkirk Shale, Western New York State – Results of Hydrous Pyrolysis Experiments

David Blood¹ and Gary Lash^2
1 University at Buffalo, Buffalo, NY
² State University of New York – College at Fredonia, Fredonia, NY

While not necessarily an exploration target in the Appalachian basin, there is much to be learned from the Upper Devonian Dunkirk shale regarding its timing of hydrocarbon generation and perhaps that of other Devonian black shales. We carried out simple hydrous pyrolysis experiments on a sample suite collected from the base of the Dunkirk shale. At the sample locality, the Dunkirk is immature to early mature (Ro=0.53%) and composed predominantly of Type II and lesser Type III organic kerogen. Black shale samples were run for 72 hrs at temperatures ranging from 305°C to 357° C; each sample was analyzed for TOC and Rock-Eval parameters. Samples pyrolyzed from 305°C to 344°C showed a modest increase in production index (PI) from 0.11 to 0.22 and, perhaps more significantly, only a minimal increase in Rock-Eval Tmax from 443°C to 446°C. However, the increase in temperature from 344°C to 357°C was accompanied by increases in PI to 0.61 and Tmax to 582°C. Similarly, the hydrogen index (HI) over the 305°-344° C range diminishes from 356 to 216; however, from 344° to 357°C, HI drops to 11. It appears, then, that organic matter of the Dunkirk shale resists conversion until a threshold level of thermal maturity is reached at which time kerogen rapidly decomposes to liquid hydrocarbons. The refractory nature of Dunkirk shale kerogen is confirmed by bulk kinetics analyses of three Dunkirk shale samples of variable Ro (0.53-0.73%) that reveal that the bulk (>80%) of the conversion reactions require activation energies in the range of 5,400-5,500 cal/mole, values that are typical of documented late-oil generators.