3D depth‐to‐basement and density contrast estimates using gravity and borehole data

Abstract

We present a gravity inversion method for simultaneously estimating the 3D basement relief of a sedimentary basin and the parameters defining the parabolic decay of the density contrast with depth in a sedimentary pack assuming the prior knowledge about the basement depth at a few points. The sedimentary pack is approximated by a grid of 3D vertical prisms juxtaposed in both horizontal directions, x and y, of a right‐handed coordinate system. The prisms' thicknesses represent the depths to the basement and are the parameters to be estimated from the gravity data. To estimate the parameters defining the parabolic decay of the density contrast with depth and produce stable depth‐to‐basement estimates we impose smoothness on the basement depths and proximity between depth estimates and known depths values at boreholes. We apply our method to synthetic data from a simulated complex 3D basement relief with two sedimentary sections having distinct parabolic laws describing the density contrast variation with depth. Our method retrieves the true parameters of the parabolic law of density contrast decay with depth and produces good estimates of the basement relief. Inversion results obtained using gravity data from the onshore and part of the shallow offshore Almada Basin (Brazil) show good correlation with known structural features.