Heterogeneous Carbonate Characterization using Integration of Petrophysical Analysis to Different Rock Type Approaches, A Case Study in the Carbonate of Upper Sabil and Harash Formations, Intisar-D Field, Concession 103 Sirte Basin, Libya

Abstract The integrated subsurface study of the Intisar-D oil field in the Sirte Basin focused on Paleocene carbonate reservoirs, specifically the Harash and Upper-Sabil Formations. Petrophysical properties—shale volume, porosity, and water saturation—were derived from wireline logs and validated using standard core data via Techlog software. Despite the fair to good quality of the data, difficulties were caused by the lack of sonic logs in several wells, especially in areas where washout affected the density and neutron logs. Upper-Sabil emerged as the primary reservoir, characterized by a very clean carbonate reservoir with porosity ranging from 25% to 35%. In contrast, the Harash Formation displayed variable shale content, transitioning from clean in the upper part to increased shaleness in the lower part (Harash TST), with porosity between 15% and 30%. Original Oil Water Contact (OOWC) depths varied (9418 to 9442 TVDSS) due to permeability differences. Reservoir quality was primarily influenced by the texture of reservoir facies, with diagenesis impacting the porosity-permeability relationship. Facies logs were contributory in modeling reservoir properties, and machine learning techniques provided valuable insights for permeability prediction. In offering a comprehensive understanding of subsurface conditions, this case study guides reservoir management and development strategies for the Intisar-D oil field. Despite data quality challenges, the integration of wireline logs, core data, and advanced software enhances the reliability of findings, contributing valuable insights for the field's future exploration and exploitation endeavors.