Describing and understanding the basement relief of sedimentary basins is vital for oil and gas exploration. The traditional method to map an interface in each spatial direction is based on three-dimensional (3D) modeling of gravity Bouguer anomalies with variable lateral and vertical density contrasts using a priori information derived from other types of geoscience datasets as constraints (e.g., well and/or seismic data). However, in the pre-exploration stage, vertical gravity, gz, which is sometimes the only available geophysical data, are typically used to recover smooth density contrast distributions under a generic set of constraints. Apparently, the use of the gz component is not sufficient to produce geologically reasonable interpretations with high resolution. To address this, we developed a novel process of hybrid inversion, combining gravity migration and inversion using the same gz dataset, to distinguish the complicated interface between basement and sedimentary basin rocks from a full-space inverted density distribution volume. First, a 3D-migrated model delineating the basic sedimentary basin structure was derived using a focusing gravity iterative migration method, where a priori information is not necessary. Subsequently, under the framework of the regularized focusing conjugate inversion algorithm, a high-resolution density contrast model was inverted for the delineation of the basement boundary by integrating the 3D-migrated density model as a priori information. We examined the method using one synthetic example and a field data case, of which a transformed resolution density matrix was developed from logarithmic space to qualitatively evaluate the practical resolutions. The high resolution of density distribution of Cretaceous basement with clear interface was achieved and verified by limited seismic data and strata markers in limited wells.
Practical Tips for 3D Regional Gravity Inversion