排出能力を考慮したポテンシャル油根源岩評価法

抄録

In petroleum exploration, source-rock evaluation has become universally popular on the basis of the properties of kerogen. Here, a novel approach for potential oil source-rock evaluation that also takes expulsion into account was attempted using the one-dimensional maturity model MATOIL. Apparent oil saturations were calculated from the MATOIL output using some assumptions. Through comparison of the calculated saturations with an assumed critical oil saturation for oil expulsion, the sensitivity of the position of the top of the oil expulsion window to the type of kerogen, the concentration of kerogen, and the basement heat flow was examined.
Oil-prone (Type I or II) kerogens generate more oil and yield higher apparent oil saturations than gas-prone ones (Type III). The apparent oil saturation increases with the concentration of kerogen. Even though a source rock contains Type III kerogen, it can get the oil saturation high enough to expel the generated oil, if the kerogen concentration is fairly high. Increasing heat flow makes the top of the oil expulsion window shallower and lowers the maximum oil saturation.
In a given geological setting, the initial concentration of kerogen necessary for oil expulsion can be predicted for a given type of kerogen. Because expulsion may control the type of accumulation (oil or gas), source-rock evaluation should take the concept of the expulsion into account.