Abstract:The depth estimation of the Precambrian basement of Weihe Basin is of great significance for the Paleozoic hydrocarbon exploration in the basin.Unfortunately,there is lack of understanding of the basement depth.The density of each sedimentary layer varies with depth,and it also changes in the horizontal direction.Therefore,the gravity inversion conducted with a constant density contrast cannot accurately delineate the basement depth.We fit the real density contrast of the sediments with 6 different density-depth functions according to 5 integrated geophysical sections and 3 boreholes' information,which contains the density of every sedimentary layer in different tectonic units.Fitting-error statistical results of different functions indicate that the exponential density contrast-depth function is more coincide with the real density variation in Weihe Basin.Then the decay factor λ and the density contrast Δρ0 at the surface are extracted from the fitted exponential density contrast-depth functions,and the λ and Δρ0 in the whole basin are acquired by gridding the discrete λ and Δρ0.Thus,the 3D variable density contrast model is obtained by combination the gridded λ and Δρ0 in the whole area.Finally,this variable density contrast model is applied in Precambrian basement estimation of Weihe Basin,and the result indicates that the 3D density could be adopted to obtain a more accurate basement relief than the constant density contrast.This approach provides a strong basic data support for the hydrocarbon exploration in the basin and can also be very helpful for solving similar problems in other basins.
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