The Global Oil System: The Relationship Between Oil Generation, Loss, Half-Life, and the World Crude Oil Resource: DISCUSSION

The global oil system is dynamic, with fundamental parameters of volume, time, and flux rate. With certain geological assumptions, these parameters are mathematically linked by the equation, half-life = (0.693 x volume)/filling rate. Reservoired conventional oil has a well-defined half-life of 29 m.y., derived from the distribution of oil generation ages. The global oil reserve is therefore directly related to the global filling rate of reservoirs. If the global system is in equilibrium, then the reservoir filling rate cannot be less than the rate at which reservoirs seep (i.e., leak to surface). Both filling and leaking parameters are poorly constrained. Total global oil generation is estimated to be about 2.7 million bbl/yr. Surface seepage data suggest that at least 0.8 million bbl/yr of this enters reservoirs, the remainder escaping directly to surface without being trapped. This seepage rate cannot be supported under equilibrium conditions by global oil reserves of the size commonly supposed. The seepage rate implies global crude oil reserves of at least 4 trillion bbl, whereas typical current estimates based upon geological analogs are 2 trillion bbl, excluding tar sands. Either (1) the global oil system is out of equilibr um, and reservoirs are draining faster than they fill, or (2) seepage rates are lower than supposed, or (3) most seepage is due to active generation and migration straight to surface, rather than leaking reservoirs, or (4) ultimate recoverable reserves are much greater than previously thought.