Identification of Bitumen With Pyrolysis Analysis on Core/Cuttings and NMR Relationship in Middle Marrat Reservoir Rock
Authors:   Geolog International, Shoeibi Ahmad , Al-Hashash Meshari ,   Kuwait Oil Company, Al-Ajmi Saad ,   Kuwait Oil Company, Odreman Allan Stefanci ,   Kuwait Oil Company, Sanclemente Milton ,   Geolog International B.V., Bonetti Antonio ,   Geolog International B.V.
Published: November 2024

The main objective of this study is to show the correlation between the bitumen presence identified using Pyrolysis analysis in core/cuttings and the petrophysical data from NMR logs in the Jurassic Marrat Formation in Kuwait. Since the presence of bitumen in the reservoir represent a flow barrier and is causing additional formation damage, the identification of the bitumen intervals has become critical for well completions and for the development strategy of Middle Marrat reservoirs in North Kuwait. In this study, several core and cuttings samples from Middle Marrat were analyzed with geochemical methods, especially XRD and pyrolysis analyses, in order to provide the characterization of the minerals and of the organic matter, including the determination of bitumen presence. Thanks to the instrument’s compact size and robustness, the analyses could be performed onsite. Additionally, NMR logging was employed in many of the corresponding well intervals. The comparison between porosity from the NMR log and porosity from the density log was used as an indication of the presence of solid bitumen. The results of five wells in the same field are presented in this paper. In each reservoir section, the pyrolysis analysis was applied to the core, cuttings, or both. The measurement was hindered by drilling fluid organic contaminants, affecting S1 and, in some cases, also S2 peak determination in cuttings samples drilled with oil-based drilling fluids. Contaminated samples could, however, be cleaned with the use of organic solvents, which guaranteed the efficient removal of the contaminants while retaining the insoluble part of the bitumen. The post-treatment pyrolysis analysis revealed the amount of this residual bitumen. At the same time, petrophysical interpretation of the NMR and basic openhole logs showed the presence of bitumen in the same intervals in which pyrolysis analysis identified the bitumen. However, in one of the wells, the NMR tool failed while logging, and in another one, the logging was canceled due to hole restrictions. This scenario is not uncommon due to well complexity and instability, leaving the surface analysis of cuttings/core as the only method able to detect the bitumen intervals in the reservoir, even in the presence of oil-based mud. This research represents the first characterization of the Middle Marrat reservoir, including bitumen detection by means of pyrolysis on cuttings/core, integrated with NMR logs interpretation. The correlation between the two techniques validated the pyrolysis approach, substantiating the possibility of using it alone when logs are not available. The resulting bitumen intervals identification can be the key to successful reservoir management, implementing completion strategies that maximize flow contribution from the greatest possible extent of net pay.