Evaluating 3D models from potential fields data across oil producing blocks in pre-salt campos basin, Brazil

Three-dimensional potential fields models are being tested in the Brazilian pre-salt region of the Campos Basin, where a noticeable magnetic anomaly with oval outline was identified. The study area is relevant for tests, as 3 abandoned pioneer wells with depths varying between 5500 and 7100m were re-drilled and marked the presence of oil, one of which is a commercial producer. These wells cut through several sedimentary formations of the basin, including shales with intercalations of carbonates and sandstones. Thick layers of salt were crossed, and intercalations of volcanic and carbonates are present below the salt. Oil samples were identified at the top of a volcanic sheet at 7100m depth. Some 3D inversion models of both the magnetic susceptibility distribution and density contrast fit the observed data. To reduce the non-uniqueness of potential field models, inversions were constrained by well logs, geological and other existing geophysical data. Several parameters were considered during the inversion procedure including cell dimensions, data quantity, reference models, assigned uncertainties, depth weighting, wavelet compression of sensitivity matrix, choice of regularization parameter. A Multiphysics approach was found to facilitate the selection of the best models. The results evidenced anomalies of density and magnetic susceptibility associated with the volcanic rocks that display variations laterally and in depth and satisfactorily explains the oval magnetic anomaly.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)