An example of one-dimensional maturity modeling of the MITI Rumoi well, a stratigraphic test drilled in a frontier area of Japan, is worked out in detail to illustrate how maturity modeling should be carried out. Prior to and during modeling, an effort was made to integrate all available geological, geochemical, and geophysical concepts and data to create a single geologic model (called here the “good” model) that was as plausible and internally consistent as possible.

Where data sets were internally inconsistent or in conflict with other data, decisions had to be made about data reliability. Some vitrinite-reflectance data, subsurface temperatures, and thermal conductivity measurements were rejected for a variety of reasons. The justifications for these decisions, which influenced the results of the modeling, are discussed in detail.

Using the “good” model, we evaluated the timing and amount of oil and gas generation from coals in the Haboro Formation, the only proposed source rocks in northwest Hokkaido, Japan. Generation has occurred continually since the middle Miocene, but the fractional conversion of kerogen to hydrocarbons to date has been small. As a result, the total volume of hydrocarbons available for expulsion and migration from the Haboro source rock probably is small unless very large volumes of coal are present.

The “good” model does not represent a unique solution, however. It thus should be regarded as one of a number of viable models rather than as the only “correct” one. Alternative models are considered in a companion paper. The modeling process itself, by which and during which we learn much about the geologic system, is at least as important as the final numerical answer. Highly interactive modeling programs greatly aid in proper modeling.

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