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Cause of geothermal temperature anomalies in Wattenberg field: unraveling the impact of hydrothermal fluid movement in the Lyons formation
Eaton, Melia M.
Eaton, Melia M.
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2024
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2025-05-26
Abstract
The Wattenberg Field temperature anomaly solidified the field as the largest hydrocarbon producer in the Denver Basin and has spurred industry interest in using the field for geothermal energy and CCUS. While the presence and impact of the hot subsurface temperature anomaly is known, the cause of the anomaly is not. This study proposes that heat from northeastern Colorado Mineral Belt intrusives was conducted to reservoir rocks in the Greater Wattenberg Area via the subsurface circulation and migration of hydrothermal fluids along field-wide fault zones. Using core description, XRF, thin section microscopy, and FESEM analysis, pervasive hydrothermal fluid-rock interaction was observed in the Permian Lyons Formation. The Lyons Formation is the host of various ore minerals that are found to have been emplaced and nucleated in-situ: 1) low temperature (125℃-175℃) sulfides pyrite, marcasite, sphalerite and galena; 2) intermediate temperature (125℃-225℃) sulfarsenides of the Co-Ni-As-S system, including gersdorffite, nickeline, and clinosafflorite; and, 3) the high temperature (>225℃) sulfide chalcopyrite. Ore mineral emplacement is accompanied by various intermediate temperature (>150℃-200℃) gangue mineral alteration types such as albitization, dedolomitization, and generation of Fe-Mg-metal-rich clays.
Spatial relationships between ore minerals of differing temperature regimes indicate that at least three episode of hydrothermal deposition occurred. By comparing the timing of northeastern CMB intrusions with the timing of dissolution-reprecipitation events in the Lyons, hydrothermal interaction is interpreted to have occurred in Wattenberg Field from the late Paleocene to late Miocene. Long-term heat conduction between hydrothermal fluids and the Greater Wattenberg Area sedimentary succession was facilitated by the high thermal conductivity of the Lyons Formation (3.56 Wm-1K-1) and maintained by the thick, insulating Mesozoic sedimentary succession – ultimately causing the Wattenberg Field temperature anomaly.
Hydrothermal fluid-rock alteration begets critical implications for CCUS and geothermal activity in Wattenberg Field. Operators should investigate potentially detrimental chemical reactions that could occur between sequestered gases, sulfides, and sulfarsenides. Geothermal system designs should account for potential dissolution and remobilization of cementing metals that could alter reservoir characteristics and release metals to the groundwater supply. Overall, understanding the distribution and impact of hydrothermal alteration will improve energy exploration strategies in the Greater Wattenberg Area.
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