Evaluation of a Low-Resistivity Well Using the Multi-Sensor Core Logger

Abstract

The objective of this study was the reservoir evaluation and characterization of low resistivity intervals in the TAGI-І Formation of the Berkine Basin. This was achieved using a comprehensive core-based dataset acquired through Multi-Sensor Core Logger (MSCL) measurements. The dataset included P-wave velocity, bulk density, gamma ray, resistivity, magnetic susceptibility, as well as X-ray fluorescence (XRF) and hyperspectral imaging (HSI) analyses. Based on gamma ray, P-wave velocity, and density data, the core was subdivided into five lithological intervals. Among them, Intervals 1 and 2 represent the main reservoir zones. In these two intervals, resistivity values ranged from 0.22 to 4.79 ohm·m, which is considered unusually low for hydrocarbon-bearing formations. To better understand this anomaly, XRF and HSI data were integrated for geochemical and mineralogical evaluation. The interpretation revealed that the low resistivity observed in these intervals is not primarily due to high water saturation but rather the result of high clay content, particularly the presence of chlorite and illite, which are conductive clay minerals. These minerals reduce the rock’s resistivity, making fluid saturation evaluation challenging when relying solely on conventional log data. It is recommended to integrate conventional wireline logs with laboratory petrophysical analysis and advanced logging tools (e.g., NMR, dielectric logs) in future studies. Additionally, detailed clay mineral identification using XRD should be carried out to refine saturation models and improve reservoir evaluation in clay-rich, low-resistivity formations such as the TAGI-І.