Mineralogy Characterization for Exploratory Eastern Offshore Field in India-Busting XRF and Cutting Lithology Myths: An Eye Opener for the Industry

The Indian sub-continent is known for its intricate lithology, making it crucial for operators to obtain precise results for their reservoir rocks. This paper presents a methodology with a case study where an operator struggled to achieve detailed mineralogy over several attempts. It ultimately demonstrates that relying solely on cuttings data and using XRF lithology data is unreliable. The process of attaining confident mineralogy is highlighted through elemental analysis, along with an explanation of why using only XRF analysis of cuttings fails to represent reality. Data from a pulsed neutron tool, which performs in situ elemental analysis by bombarding the formation with neutrons and interacting the resulting gamma-ray spectra, were compared with X-ray fluorescence (XRF) on cuttings collected at 5-meter intervals from the same open-hole section. The two methods were evaluated for consistency in elemental composition. Contrary to expectations, significant discrepancies were found between XRF results and pulsed neutron data. The study highlighted limitations in XRF due to potential sample contamination and surface handling issues. Regression and Big Data analysis were used to compare results from multiple zones in the open-hole section, examining relationships between data from both technologies. This paper contributes to the scientific community by addressing the misconceptions about XRF, which is often considered conclusive due to measurements on cuttings, and underscores the importance of pulsed neutron mineralogy tools. Best practices for using both methods for the most reliable reservoir characterization were documented, improving confidence and reliability in the reservoir characterization for the subject exploration field.