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

Sandstones of Surma group comprise the ma in reservoir of Titas gas field and have gamma ray inte nsities 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 t he fact that the sandstones are clean, the reason for the high gamma ray for these sands appears to be mineralogical. The highgamma raybackground is considered to be due to potassium feldspar concentrationof up to 18 % and this is enhanced by the presen ce 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 i n these sandstones can result in the assignment of high V shalevalues and low porosity during log analysis and productive zone may be underestimated.