Relationship of Geological and Geothermal Field Properties; Midcontinent Area, USA, an Example

Abstract

Quantitative approaches to data analysis have become important in basin modeling and mineral-resource estimation in the last decade. The interrelation of geological, geophysical, geochemical, and geohydrological variables is important in adjusting a model to a real-world situation. Revealing the interdependences of variables can contribute in understanding the processes interacting in sedimentary basins. It is simple to compare spatial data of the same type but more difficult if different properties are involved. Statistical techniques can be used to ascertain the relations of standardized spatial data. In this example, structural configuration on five different stratigraphic horizons, one total sediment thickness map, and four maps of geothermal information were compared. The structural maps were highly related because all had undergone about the same deformation with differing degrees of intensity. The temperature gradients (1) derived from borehole logging measurements under equilibrium conditions with the surrounding rock and (2) derived from unequilibrated bottomhole temperatures (BHT) are mainly independent of each other. This was expected and confirmed for the two temperature maps at 1000 ft which were constructed using both types of gradient values. Thus, it is evident that the use of BHT without correction to equilibrium conditions does not reflect the geothermal regime of themore » area. Nevertheless, it seemed useful to determine to what degree unequilibrated temperatures could reflect relationships to the geological conditions. Comparing all maps of geothermal information versus the structural and the sediment thickness maps it was determined that all correlations are moderately negative or slightly positive. These results are clearly shown by the cluster analysis and the principal components and support the assumption that the temperatures within the sediment are related closely to the lithological properties (rock conductivity) of the stratigraphic units.« less