Interpretação paleodeposicional da formação cabeças a partir de dados gamaespectrais de poços da área do Parque dos Gaviões, Bacia do Parnaíba

Abstract

The use of spectral gamma ray logs helps in the interpretation of depositional environments and paleoenvironmental reconstitution. In order to obtain the spectrometry range in wells where these U, Th and K curves were not originally acquired, an inexpensive methodology for acquiring spectral gamma ray (SGR) data was developed using cutting samples, in which the emitted natural radiation was measured. For this study, a portable spectrometer range, cutting samples from four wells and logs data obtained from oil wells, which cross the Cabecas Formation, Devonian of Parnaiba Basin, Parque dos Gavioes region were used. Seven of these already have the SGR log acquired through wireline logging. Spectral gamma ray measurements were acquired from these cutting samples. The use of the Th / U, Th / K and U / K ratios allowed for a better correlation between the laboratory curves and those acquired in wireline campaigns The intervals were interpreted, where the Th / U > 7 ratio as the sedimentary inputs characteristic of catastrophic floods, oxidizing condition, typical of the continental environment, weathered soils and shallow marine environment. Based on the frequency of these contributions the Cabecas Formation was divided in three intervals, the intermediate interval has a higher frequency of these floods, was interpreted as having been deposited in the most proximal environment. The other intervals, lower and upper, in general, show incursions with a ratio Th / U > 7, were interpreted as a more distal environment.This work methodology opens a great perspective for geoscientific studies, as well as for cost reduction for oil, mining or water companies that need to obtain these K, Th and U curves, since these measures, of low operational cost, they can be performed on cutting samples from any well, from any basin, providing greater strength and refinement to stratigraphic studies, optimizing oil exploration and production