Thermal maturation, as displayed by the vitrinite reflectance and coal rank maps above, increases southward in the Kansas part of the Western Interior Coal Basin. The most prolific gas generation in coals occurs at medium-volatile bituminous rank. Kansas coals are less thermally mature (generally high-volatile bituminous ranks) and hence contain less gas.
A north-south projection of the Rock-Eval Tmax maturation parameter for shales from well cuttings and cores in the Forest City basin, Bourbon arch, and Cherokee basin (see diagram at right) also indicates a southward increase in thermal maturation. At a given depth, there is less maturation in the Forest City basin than further south in the Cherokee basin. This may be caused by higher heat flow in southeastern Kansas, or northward movement of higher-temperature waters out of the Arkoma basin onto the cratonic platform during the late Paleozoic Ouachita orogeny.
These trends in maturation indicate that operators attempting to produce coalbed gas in the marginally mature strata in the Bourbon arch and Forest City basin should concentrate on the deepest coals, which should have better gas content.
(After Saulsberry and others, 1996)