CONSTRAINING MAXIMUM HORIZONTAL STRESS USING WELLBORE BREAKOUTS -- A CASE STUDY FROM ORDOVICIAN TIGHT RESERVOIR OF NORTHEASTERN OUED MYA BASIN, ALGERIA

Abstract

In this study, we interpret the maximum horizontal stress (SHmax) azimuth from the breakout positions of wellbore and attempt to constrain the SHmax gradient based on the interpreted breakout width. A cumulative of 110 m of breakouts were deciphered within the Ordovician Hamra Quartzite interval of the Oued Mya Basin from a 138 m of acoustic image log. These breakouts were ranked as “A-Quality” following the World Stress Map ranking guidelines. We infer a mean SHmax orientation of N28°E ± 8°. Following the frictional faulting mechanism and stress polygon approach, measurement of minimum horizontal stress (Shmin) from minifrac tests and observations of compressive failures from acoustic image log provided strong constraints on the SHmax magnitude in the reservoir interval in the absence of core-measured rock strength. Interpreted breakout widths exhibit a range between 32.6° and 90.81°, which indicated a SHmax range of 24.4–34.7 MPa/km. The average breakout width of 62.58° translates to a narrower SHmax gradient range, varying between 27.2 and 31.2 MPa/km. The relative magnitudes of the principal stresses indicate a strong strike-slip tectonic stress state. Considering all the uncertainties, we infer a SHmax/Shmin ratio of 1.41–1.81 within the Ordovician interval.