Stratigraphic Control of Temperatures in the Wattenberg Field, Denver Basin, Colorado
The Wattenberg Field has been reported as a thermal hot spot, but a new geothermal gradient map of Colorado does not show it to be anomalous with respect to other areas of the Denver Basin. We have reanalyzed bottom-hole temperature (BHT) data from logs from over 2500 wells in the Wattenberg Field to investigate the modern temperature structure of the gas-producing formations in this field and to evaluate the potential for electricity generation with water from the depth of existing wells. BHT data were corrected for the effects of drilling using standard correction techniques to give estimates of the undisturbed formation temperatures. An initial analysis of the data indicated no coherent temperature structure in the field, but an apparent statistical negative correlation of geothermal gradient with well depth. This correlation was found to be probably without significance as upon closer examination the BHT data had no correlation with depth, but gradient is inversely proportional to depth. Attempts to find correlations among the BHT data and other parameters were unsuccessful, until remarkably strong correlations were found between BHTs and depth for wells that were completed in the Sussex and the driller’s Dakota units of the Pierre Shale. Wells that were completed in other units showed no significant correlations. The Sussex and Dakota essentially bracket the main producing units in the Wattenberg Field, but differ from other units in that they are outside the overpressured zone that characterizes the main production. We speculate that gain and loss of drilling fluid in the overpressured zone causes disturbances to the BHTs not corrected by standard techniques. The corrected temperatures in the Sussex and Dakota are valid and may be interpolated through the intervening units using stratigraphic information. Temperatures in the producing zone range from about 100-120°C (210-250°F) at depths ranging from 2100-2600 m (6900-8500 ft). Using binary technology with small modular power plants, water from this zone could be used to produce electricity to power production operations in this field, probably with power to spare. The origins of reports of the Wattenberg Field as a hot spot were probably based on unreliable temperature data. Vitrinite reflectance data and consideration of gas maturation require higher temperatures than at present: higher past temperatures could have been associated with greater burial depth and/or higher heat flow.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009