Thermal history of the Michigan Basin

Pre-Devonian strata in the Michigan Basin exhibit levels of organic thermal maturity that are higher than would be expected from present-day geothermal gradients. Previous studies have shown that elevated pre-Devonian heat flow, combined with the addition of strata at the Silurian/Devonian System boundary can successfully reproduce pre-Devonian thermal maturity values. To investigate geographic and time related variations in heat flow in the basin in more detail requires thermal maturity data covering the entire well section from wells that are geographically separated.; Reflected light measurements were made on samples produced from drill cuttings for six deep wells in the Michigan Basin. The thermal maturity values determined for these six wells are used to make tentative assumptions regarding the geographical variations in pre-Devonian and post-Silurian heat flow in the basin, and produce estimates of the missing strata at the Silurian/Devonian System unconformity.; The thermal maturity data from the six wells described above were used to constrain one-dimensional thermal models. The modeling results show that both the pre-Devonian and post-Silurian heat flows varied across the basin. The resulting heat-flow values for these six wells were then used to create heat-flow contour maps for the basin, which were then used to establish heat-flow values for use in thermal modeling of 18 other basin wells for which limited amounts of thermal maturity data are available. The modeling results for these 24 wells indicate that the Silurian/Devonian System boundary represents a major unconformity, and the depositional pattern of excess strata at this boundary suggests that the deposition occurred as a result of continued basin centered subsidence and tilting of the craton from an Appalachian orogenic event.; A method was developed to extract and graphically display lithology data from a subsurface database. The graphical display of lithology data combined with the coincident display of formation top picks and electric logs can be very useful in detecting errors in formation top picks, and instructing individuals in the recognition of electric log responses to various lithologies and specific formations. Displays of lithology data can also be useful in stratigraphic analysis providing indications of sea level and possible climate variations.