New Mexico Geological Society Annual Spring Meeting — Abstracts

The geothermal potential of the southern Raton Basin (SRB) is evaluated using equilibrium (ET), bottom hole (BHT), and wireline (WT) temperature data. ET logs are generally from shallow wells (<600 m); interval geothermal gradients generally correspond to lithology, which is indicative of conductive heat flow. Interval geothermal gradients in the Paleogene Raton and Poison Canyon formations and in Cretaceous shales (Pierre, Carlile, Graneros) are on the order of 40-60°C/km. In contrast, interval gradients in the Cretaceous Trinidad Sandstone and in other sandy units are 20-30°C/km.

BHT data constrain the deeper thermal structure of the basin. High BHTs were measured in the Stubblefield Canyon gas field near the Colorado border; the maximum uncorrected BHT is 135 °C at a depth of 2160 m and associated geothermal gradients are 50-80°C/km. BHTs in the Las Vegas Basin (LVB) to the south are cooler (85°C at 3091 m) compared to those in the SRB to the north at similar depths. This study focuses on wells with two or more BHT readings. Four wells with multiple BHTs in the Castle Rock Park gas field show a distinct decrease in temperature between measurements in the Trinidad Sandstone and measurements in the underlying Pierre Shale. This pattern implies lateral flow of warm (~45°C) water in the Trinidad Sandstone in this area.

WT logs can provide good thermal data if used with caution. WT logs are obtained by oil companies to look for zones of fluid flow or to gauge the quality of a cement job. WT logs measured in air are noisy. WT logs measured in air drilled holes and filled with formation water prior to measurement yield thermal data of a quality similar to equilibrium logs.

Temperatures of 150°C at depths of ~3 km are present in the Colorado part of the Raton just north of the border. ET data from the Stubblefield Canyon area just south of the state line yield published heat flow values of 89-120 mW/m². If the elevated gradients derived from ET, BHT, and WT data from Stubblefield Canyon are extrapolated to depth, then a temperature of 150°C is reached at 3 km, comparable to the depths on the Colorado side of the border. The difference in temperature between the SRB and the LVB is attributed to (1) elevated heat flow associated with low velocity mantle beneath the SRB, and (2) erosion of low thermal conductivity Cretaceous shales from the LVB.