Abstract

A detailed analysis of the available thermal data in Texas is performed and the new heat flow values are interpreted in terms of local and regional geology. The data include high-resolution temperature logs, old temperature-depth curves, geophysical well logs, and bottom hole temperature data (BHT). The variation in heat flow across Texas can be explained by a combination of three factors: changes in the radiogenic heat production of the basement, heat generation within sediments, and the effect of large scale aquifer flow.

A number of wells in north-central Texas, extending from the Fort Worth basin in the west to the Mexia-Talco fault zones suggest the Ouachita tectonic front represents an important thermal boundary. The heat flow values increases from 48 mW/m² in the Fort Worth Basin to 61 mW/m² exactly in the front of zone and then drops to 55 mW/m² in the interior zone. In addition to these two distinct areas, a zone of low heat flow, with values below 44 mW/m² extends from approximately 30 kilometers north of Dallas towards Oklahoma, and is linked to the low heat flow values recorded in deep Anadarko Basin and in the frontal part of the Wichita Uplift.

Natural radiation gamma logs were used to estimate the radiogenic heat contribution of the sedimentary column for different wells. In spite of the high heat generation values of the Mesozoic black shales, the total sedimentary radiogenic contribution for the wells east of Ouachita Tectonic front can be neglected. Further to the east, in the proximity of the Gulf Coast, the radiogenic heat generation could become important due to the large thickness of the sedimentary column. West of Ouachita front, the largest radiogenic heat generation is in Forth Worth basin (the contribution to the heat flow is 4 mW/m²) due to the high shale content of the sedimentary units. In the Palo Duro basin (mean heat flow of 51 mW/m²), the radiogenic contribution to the heat flow does not exceeds 2 mW/m².

The water flow is probably the cause of one anomalously low heat flow values in Balcones Fault zone. Lackland Air Force Base (heat flow 34 mW/m²) reflects the effect of water flow and not the basement heat flow, as the structure is very localized compared to the low heat flow north of Dallas.

In general the heat flow points derived from high-resolution temperature logs are consistent with the heat flow points obtained from BHT. Although the BHT data have a higher error range, the large number of BHT observations and the good coverage allow interpretation of detailed regional variations. The BHT data suggest that the low heat flow in the Fort Worth basin and north of Dallas are isolated features and that they are not linked to the low heat flow in Midland and Delaware basins, although the similar heat flow values for Fort Worth and Midland basins suggest similar kind basal heat flow. The 50 mW/m², contour level inferred from BHT data extends in the west towards Palo Duro basin, but its exact position in this area is not very well constrained because of poor coverage of the BHT data in the area in between. Therefore we interpret the 51 mW/m² value for the Palo Duro basin as a transition zone between the low heat flow in Midland Basin, and the higher heat flow immediately north of Amarillo uplift.

Location of existing heat flow values (blue crosses) in the study area and generalized structure map of Texas, showing the position of basement uplifts and intervening basins. Also shown are the Balcones, Mexia and Talco Fault Zones. Data from Herrin and Clark, (1953), Decker and Smithon, (1975), Corry et. al., (1990), Blackwell et. al., (1998), King and Simmons, (1972) (for Texas); Carter, (1993), Borel, (1995), Roy et. al. (1968) (for Oklahoma); Smith and Dees, (1982) (for Louisiana); Smith and Dees, (1982), Roy et. al. , (1980), Swanberg et. al., 1982 (for Arkansas); Herrin and Clark, (1953), Decker and Smithon, (1975), Edwards et. al. (1978), Reiter et. al. (1996) (for New Mexico). The wells used in this study are located in Palo Duro and Fort Worth Basins, Dallas area, Balcones, Mexia and Talco Fault zones (red crosses). The values show the general regional heat flow patterns.

Comments could be sent at:

Petru T. Negraru pnegraru@mail.smu.edu

David D. Blackwell blackwel@mail.smu.edu