Factors Contributing to High Gamma-Ray Levels in Early Miocene Bhuban and Boka Bil Sandstone Reservoirs of Titas-15 Well

Abstract

Sandstones of Surma group comprise the main reservoir of Titas gas field and have gamma ray intensities of 60-90 API units which are
more than the average sandstone gamma ray level. The sandstones of Titas-15 may thus be considered moderately high gamma ray sand.
Petrographic study has been used to identify the sources of radioactivity. Considering the fact that the sandstones are clean, the reason for
the high gamma ray for these sands appears to be mineralogical. The high gamma ray background is considered to be due to potassium
feldspar concentration of up to 18 % and this is enhanced by the presence of radioactive heavy minerals, particularly zircon. Contributions
to radioactivity from organic matter, clays and lithic grains are minor. A failure to recognize the source of radioactivity in these sandstones
can result in the assignment of high Vshale values and low porosity during log analysis and productive zone may be underestimated.