| Abstract | Phetchabun basin is one of Tertiary basins in the central Thailand. The Wichian Buri oil field is located on its southern part. The field was discovered in 1988 and hydrocarbon has been produced since 1995 till now from fractured igneous rock reservoir, whose rock types have never been investigated in very details. Not many works of thin section analysis have been done and other petrophysical parameter were still not well estimated. This research focused on rock type identification and petrophysical characterization of shallow fractured igneous rock in Wichian Buri oil field. The study integrated the data of well log analyses and digital rock thin section analyses for rock types identification. The well log interpretation was performed by the Quanti.Elan model in Techlog to do lithological zoning and to find fractured igneous and sedimentary zones in a study well (WB01) . In the digital thin section analysis, the new digital camera (Olympus DP22) was used to capture the image and the ImageJ software was employed for counting minerals. Cutting samples were collected from 4 wells, and the results from two of which (WB01 and WB02) were used to correlate with well log data. For WB01, three layers of sedimentary rocks were identified, one layer of metamorphosed sedimentary rock and one layer of igneous rock were identified. By comparison with rock cutting analysis results, the igneous rock type was identified as gabbro. The fractured igneous zone could also be identified by RESD and DT logs. For tight igneous rocks GR and Vsh is 51.21 API and 48.32%, respectively. For fractured igneous rocks GR and Vsh is 31.81 API and 24.40%, respectively. The porosities of fractured igneous rock were found as: PHIDT = 5.1%, PHID = 12.8%, PHIN = 31.9%, PHIT = 22.3%. The porosities of tight igneous rock were found as: PHIDT = 11.2%, PHID = 29.0%, PHIN = 42.0%, PHIT = 35.5%. The Sw and Shc is18.9 and 81.10%, respectively for tight igneous rock. The Sw and Shc is 10.23 and 89.77%, respectively for fractured igneous rock. The fractured porosity was also calculated using mathematical model proposed by Giao and Chung (2017) for tight and fractured igneous rock zone, the value of fracture porosity are 99.96% and 99.51% by the 1D fracture model ( slab model) in z direction, 2.05% and 0.74% by the 1D fracture model (slab model) in x or y direction, 2.05% and 0.74% by the 2D fracture model (matches model) in z direction, 4.11% and 1.48% by the 2D fracture model ( matches model) in x or y direction, and 3.08% and 1.11% by the 3D fracture model (cubes model) in x, y, z direction. |