Fractures and Breakouts Analysis from Borehole Image Logs: Preliminary Results for Interpretation of Stress History and In Situ Stress State |
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| Authors: | Gil Young Kim Buyanbat Narantsetseg |
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| Institution: | 1. Petroleum &2. Marine Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, South Koreagykim@kigam.re.kr;4. Department of Earth System Sciences, Yonsei University, Seoul, South Korea |
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| Abstract: | Fractures and borehole breakouts from image data acquired from Logging-While-Drilling (LWD) were identified and analyzed using GMI Imager software. Conductive (e.g., dark-colored images) and resistive fractures (e.g., light-colored images) were identified on the images. Breakouts occurring along the borehole wall in the direction of the minimum horizontal stress were also investigated. For fracture analysis, we investigated dip and direction of fractures on the resistivity images acquired from two sites in the Ulleung Basin, East Sea. Dip angles at two sites are 42° and 62.5° on average, respectively. Dip direction shows preferred orientation northerly. From fracture analysis, the maximum horizontal stress direction may be the NW-SE direction. This pattern likely reflects regional stress regime of this area. We also analyzed borehole breakouts on the LWD image data (borehole radius and density data) acquired from Site U1378, IODP Exp. 334 off Costa Rica. We estimated present-day in situ stress orientation from borehole breakouts. Breakout orientation of slope sediments at Site U1378 indicates that maximum horizontal principal stress direction is oriented northwest-southeast. This direction is probably related to plate motion in this area. This study presents preliminary results in order to interpret not only stress history of the Ulleung Basin but also in situ stress state of continental slope off Costa Rica in near future. |
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| Keywords: | Borehole breakout fracture GMI Imager image log data |
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