Experimental investigation of the compositional variation of petroleum during primary migration

Acyclic alkanes were preferentially expelled with compositions depending on source kerogen and partial evaporative loss from the open experimental system expulsion. No substantial molecular fractionation within various compound classes or preferential primary migration of n-alkanes relative to acyclic isoprenoids occurred. Cyclic triterpanes and aromatic hydrocarbons were found only in small concentrations in the expelled bitumen indicating preferential retention relative to acyclic alkanes. Palmitic (C16) and stearic (C18) acids occurred as dominant compounds in the initial and residual bitumen. In the expelled bitumen they constitute virtually the only fatty acid species, indicating that expulsion efficiency is strongly dependent on concentration and generation intensity.