Determination for 3D sedimentary basin depths from gravity anomaly data using steepest descent method

Abstract

In solving the gravity exploration inverse problems, determining the depth of the sedimentary basin played an important role in the petroleum exploration. In this paper, the depth to the basement of 3D sedimentary basin was calculated from the gravity anomaly using the steepest descent method. This method allowed minimizing the objective function based on the first derivative and adjusting the step length by the iterative method; using the variable is the depth of adjacent rectangular prism in the x, y directions with parabolic function between density contrast and the depth. The parameters in the parabolic function were determined by the nonlinear regression method based on the information of deep borehole in the Mekong Delta. This parabolic function was used to calculate the theoretical gravity anomaly for the sedimentary basin and solve the 3D inverse gravity problem on the model and on the real data. The used objective function was the mean square error function between the measured gravity anomaly and the calculated anomaly. The proposed method was tested on the model, showing that the calculated sedimentary basin depth almost coincides with the original model depth; then the method was applied to calculate the depth of 3D sedimentary basin from the local gravity anomaly in Bac Lieu province. The analysis results were consistent with previous publications, but the calculation time was significantly shortened, so this method can be extended to analyze data on a large area.