Qualitative analysis of clay minerals and swelling potential using gamma-ray spectrometry logs: A case study of the Bahariya Formation in the Western Desert, Egypt.

Gamma-ray spectrometry logs are verified as a qualitative analysis tool for clay minerals where clay swelling depends on the clay mineral type. The data are obtained from three random wells (Kh-24, Bassel-1X, and Hayat-1X wells) in Western Desert oil fields. X-ray diffraction, scanning electron microscopy, and gamma-ray spectrometry are performed and the swelling potential index is obtained for surface samples from the Bahariya Formation. The swelling values and the total counts of gamma radiation, equivalent Th, equivalent U, and K are plotted with correlation coefficients (r) of 0.71, 0.81, 0.62, and 0.07, respectively. The swelling percentage ranges from 33% to 110%. This swelling behavior is reflected in the great difference in the composition of the clay minerals. Active clay minerals such as montmorillonite are widely observed with mixed-layer clay, illite, chlorite, and kaolinite. The correlation coefficients clarify a strong relation occurs in the cases of total gamma radiation and equivalent Th versus the swelling index. Consequently, gamma-ray spectrometry logs provide a new approach for identifying not only clay minerals but also their swelling trend. Moreover, they help to give an expected drilling risk, such as stuck while drilling.