| Abstract: |
Pervasive broadband (cm-Km) 1/f-noise power-law fluctuation scaling S(k) 1/k in well-logs and abundant support for poroperm fluctuation relation ()*)log($) in clastic-reservoir well-core indicate that crustal rock is nearly everywhere permeable to percolating fluids. Percolating fluids can transport heat in parallel with thermal conduction if formation permeability is sufficiently high. We investigate the level of in-situ 1/f-noise permeability needed to bring advection of heat to levels comparable to those assumed for thermal conduction. The investigation centres on thermal gradient and neutron porosity well-logs recorded at 5,500-8,500 feet in a tight-gas province in western Colorado, USA. Formation core permeability is of order 10-20 Darcy. The thermal gradient and porosity logs are 60% spatially correlated at zero lag, but the temperature gradient log has an underlying trend towards higher gradient values with depth/temperature in the well. Well-site core poroperm data are 60% cross-correlated, validating the relation ()*)log($) for the tight gas foramtion and providing direct evidence for potential heat advection at all scale lengths. The temperature-gradient trend can be correlated with either a trend towards lower thermal conductivity with increasing depth/temperature, or with an advection term proportional to temperature. For the observed formation permeability, it is entirely possible that thermal advection is comparable to thermal conduction in the tight-gas formation. The tight-gas formation well-log data clearly suggest that higher permeability crustal rock can support advection heat transport where heretofore it has not been considered. |