The development of unconventional reservoir explorations at the Middle Magdalena Valley Basin (MMVB) from Colombia has allowed to determine the natural radionuclides concentration and doses and its interaction with all matrices related with the hydraulic fracturing technic, associated with the local conditions (weather, industrial processes around, and soil). The main objective of this project is to evaluate the behavior of natural radionuclides in the unconventional reservoir environment at MMVB considering all conditions around, comparing the results with other cases related, generating a start point to the radioactive characterization of the area. The study area selected for this project was Kalé, the first research project for hydraulic fracturing in Colombia, locating in Puerto Wilches – Santander at the MMVB, a region recognized for the palm crops. In this case, were selected 81 sampling points for doses (natural background) around Kalé's area using portable detectors and 44 sampling points for activity concentrations using ICP-MS and gamma spectrometry, measuring natural radionuclides such as: U-238, Th-232, Ra-226, Ra-228, K-40 and Pb-210. The results obtained were compared with other cases related around the world in unconventional reservoirs from USA, Argentina and China, and additionally in relation to palm crops. The results of effective doses obtained in the Kalé's area were in a range from 0.07 to 0.39 mSv/y, well below the limit value established by the International Commission for Radioactive Protection (ICRP) of 1 mSv/y, demonstrating a very low risk of radioactive affection. On the other hand, the activity concentrations of natural radionuclides were variables according to radioisotope; for natural decay of U-238 from 18 to 80 Bq/kg, in secular equilibrium with Ra-226; for Th-232 from 22 to 103 Bq/kg, in secular equilibrium with Ra-228, whereas that K-40 showed a range from 162 to 611 Bq/kg and Pb-210 from 37 to 140 Bq/kg. The comparison with other cases around the world demonstrated that Kalé's area is very influenced for the weather, industrial processes around and specially for palm crops, in this way, the behavior of natural radionuclides at MMVB may be closely related not only to the geological conditions, but also with external processes in the area. The results of this project representing an important data to strengthen the baseline of necessary information need to the evaluation of radiometric risks in extractive processes in oil & gas in Colombia, to avoid health and environmental affections.

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