| Abstract |
The Eastern Llanos Basin is located in the Eastern region of Colombia. Geomorphologic boundaries are the Colombian-Venezuela border to the north, Macarena high and Vaupes Arch to the south, Guaicaramo Fault system to the west, and Guyana Shield to the east. This basin with an extension of 196.000 km2 is considered the most productive hydrocarbon basin in continental Colombia. From a preliminary regional map, built from downhole temperatures and average surface temperatures data, the Eastern Llanos Basin was identified as the Colombian basin with the highest geothermal gradient magnitudes, excepting the Andes (Central Cordillera) where the higher anomalies are expected where there is very little information available. The Eastern Llanos basin was chosen as a priority area to improve the data density of the geothermal gradient map and to estimate the heat flow. This work presents the geothermal gradient map of this basin, based on information from 870 wells, following the BHT method. The results confirm the geothermal gradient trend to increase towards the east and southeast of the basin, observed in the regional map. The range of variation goes from 8 to 59°C/km with an average value of about 28.8 °C/km. Thermal conductivity measurements were made directly on well core samples from different geological formations, to obtain representative values. From this, effective average conductivities were estimated in the basin, between 1.12 and 1.57 W/m°K, with a mean value of 1.32 W/m°K. Low values are probably related to high porosities. From the geothermal gradients and the effective average conductivities, heat flow values were estimated in 84 wells by following Carvalho & Vacquier (1977) methodology. The variation of the heat flow between 20 and 81mW/m2, with a mean value of 37 mW/m2, also shows a trend to increase to east and south of the basin. Values higher than 56 mW/m2 could be considered anomalous when compared with the average heat flow for Precambrian shields (42 mW/m2; σ =10). |