Determination of clay minerals in Brunei's outcrops and spatial variability of the radioisotopes

Shale with the presence of clay minerals is one of the problematic formations to be encountered in the oil and gas industry. Drilling into these formations will be a challenge since shale sloughs and clay swells. Clay minerals impact hydrocarbon production and drilling operations due to clay hydration. Thus, the main objective of this paper is to identify the clay minerals from Brunei Darussalam outcrops based on the cross plot of thorium and potassium from the components of the radioisotopes of spectral gamma ray logging (SGRL). The majority of the outcrops in Brunei Darussalam contains montmorillonite which swell in contact with water. Geostatistical methods are implemented to gather spatial data over an area of interest. Variogram therefore is used to describe and characterize the variability of the radioisotopes by fitting a model to the experimental semi-variogram. The estimation of the measured values at any unknown location are then calculated by the kriging process. Semi variogram and corresponding kriging maps for thorium, uranium, and potassium components were prepared. The result indicated a good spatial similarity and areas with the highest number of the radioisotopes of spectral gamma ray logging presented the relationship of the radioisotopes in the surrounding area.