THE EVOLUTION OF THE DEAD SEA FLOATING ASPHALT BLOCKS: SIMULATIONS BY PYROLYSIS

The asphalts found as floating blocks on the Dead Sea and deep-seated in wells differ from all other asphalts of the area, mostly by their more abundand and much better preserved n-alkance. Since biodegradation was found to be the main alteration process through which crude oil was alterd into aphalts, such well-preserved n-alkanes are unexpected. A hypothesis of secondary generation of theise alkanes was tested bny pyrolysis simulations of asphalt at 300d̀C during periods ranging up to 60 days. The abundance and distrubution pattern of the n-alkanes in the simulated asphalts after 14 days of heating resembles that of the floating asphalt blocks and that found at a depth of 3,500 m. In addiation to saturated hydrocarbons, aromatics and gases were also formed at the expense of resins and asphaltenes. The H/C ratio was balanced by the formation of pyrobitumen and by a gradual decrease of the H/C ratio in the residual resins and asphaltenes. The gas formed contained about 60 to 80% methane with an isotopic composition of-41 to 42%%. The hydrocarbon content of the simulated asphalt (gas and liquids) increased from about 15% at the stariting material to about 60% after 60 days of heating.

The recognition that asphalts in the Dead Sea basin are secondarily subjected to alteration upon burial might be of economic importance. Asphalts buried to a depth at which maturation conditions are close to that reached in the pyrolysis simulation at 300d̀C after about 60 days may be counted on as source material for hydrocarbons.