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In-situ stress magnitude and orientation determination of Ankara Kazan district from FMI log

Karadeniz, Kutay Emre
Wellbore instability is a major problem in the oil and gas industry. Rock failures occur around the borehole when the induced local stresses exceed the rock strength. Borehole breakouts and drilling-induced fractures (DIFs) are important indicators of horizontal stress orientation. Borehole breakouts are stress-induced enlargements of the wellbore cross-section which occurs when the stresses around the borehole exceed the compressive strength of the borehole wall. DIFs are created when the stresses concentrated around a borehole exceed tensile strength of the wellbore wall. In this study, a Formation Micro Imager (FMI) log which was carried out for a solution mining project in Kazan district of Ankara was used to determine the in-situ horizontal stress magnitude and orientation determination of the site. The FMI log was analyzed to determine and differentiate the DIFs and breakouts. Laboratory and field studies were carried out to determine the mechanical properties of the formations that the well was passing through. Leak-off tests from the field studies were analyzed to determine minimum horizontal stress magnitude. Later numerical analyses of various circular cross-sections of the borehole was done using FLAC to mimic the DIFs and breakouts. An iterative in-situ horizontal stress inputs were tried in the models until matching the failures around the borehole. Later, the orientation and magnitude of the horizontal stresses around the borehole was determined using both analytical and numerical methods.