Quantifying in situ horizontal stress in the Niger Delta Basin, Nigeria

We have determined the direction and the magnitude of the two horizontal stress components (minimum and maximum) in the Niger Delta Basin, Nigeria from petroleum exploration data from the region. Faults interpreted from a high fold 3D seismic data imply a dominant normal faulting regime. It suggests that maximum horizontal stress (SHmax) is an intermediate principal stress in the basin. The magnitude of the horizontal stress is quantified by two methods: as a function of vertical stress and as a function of overpressure at depth. The scattering of SHmin values estimated from application of the Eaton (1969) method and Leak Off Test (LOT) data is indicative of the SHmin gradient varying with depth in the basin. We propose an inhomogeneous stress field and more than one source of stress in the region based on the result of multiple directions determined from the analysis of 32 borehole breakouts recorded in six wells. We suggest the occurrence of repeated earth tremors in the region is likely to be due to the reactivation of rifted continental crust linking the regional onshore faults along major lineaments.