Geothermal regime and thermal history of the Llanos Basin, Columbia
- Alberta Geological Survey, Edmonton, Alberta (Canada)
- Instituto Colombiano del Petroleo, Bucaramanga (Colombia)
The Llanos basin is a siliciclastic foreland sub-Andean sedimentary basin located in Columbia between the Cordillera Oriental and the Guyana Precambrian shield. Data on bottom-hole temperature, lithology, porosity, and vitrinite reflectance from all 318 wells drilled in the central and southern parts of the basin were used to analyze its geothermal regime and thermal history. Average geothermal gradients in the Llanos basin decrease generally with depth and westward toward the fold and thrust belt. The geothermal regime is controlled by a moderate, generally westward-decreasing basement heat flow, by depositional and compaction factors, and, in places, by advection by formation waters. Compaction leads to increased thermal conductivity with depth, whereas westward downdip flow in deep sandstone formations may exert a cooling effect in the central-western part of the basin. Vitrinite reflectance variation with depth shows a major discontinuity at the pre-Cretaceous unconformity. Areally, vitrinite reflectance increases southwestward in Paleozoic strata and northwestward in post-Paleozoic strata. These patterns indicate that the thermal history of the basin probably includes three thermal events that led to peaks in oil generation: a Paleozoic event in the southwest, a failed Cretaceous rifting event in the west, and an early Tertiary back-arc event in the west. Rapid cooling since the last thermal event is possibly caused by subhorizontal subduction of cold oceanic lithospheric plate.
- OSTI ID:
- 54894
- Journal Information:
- AAPG Bulletin, Journal Name: AAPG Bulletin Journal Issue: 1 Vol. 79; ISSN 0149-1423; ISSN AABUD2
- Country of Publication:
- United States
- Language:
- English
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