Small angle neutron scattering signature of oil generation in artificiallyand naturally matured hydrocarbon source rocks

We have demonstrated for the first time the application of a small angle ne utron scattering (SANS) technique for the precise determination of the onse t of hydrocarbon transport (primary migration) in shaly source rocks. We us ed a sequence of rocks pyrolysed in the laboratory under nitrogen at temper atures in the range 310-370 degrees C. These rocks contained several percen t of dispersed marine Type II organic matter. Geochemical analysis indicate d a peak of the hydrocarbon generation in the middle of the temperature ran ge (at 340 degrees C). We observed a sharp decrease of SANS intensity in a narrow maturity range within the geochemically determined region of the ons et of hydrocarbon generation. This decrease was a direct consequence of the SANS contrast variation caused by the invasion of the pore space by bitume n during the primary migration of hydrocarbons. A similar phenomenon was ob served for a natural maturity sequence of source rocks originating from the same location. Crown Copyright (C) 2000 Published by Elsevier Science Ltd. All rights reserved.