渭河盆地基底三维变密度重力反演

渭河盆地前寒武系变质基底深度反演对于盆地古生界油气勘探具有重要意义，但目前对于基底深度认识不足。盆地内各沉积层密度随深度变化且横向上亦有差异，因此采用常密度模式的重力反演不能准确得到盆地基底深度。本文根据渭河盆地综合地球物理剖面解释结果，结合不同构造单元内各地层密度，在不同水平位置利用6种密度-深度函数拟合实际地层密度。不同函数拟合误差统计结果表明，指数变密度函数更符合渭河盆地沉积层密度变化规律。利用不同位置的指数变密度函数中地表密度差及密度随深度的变化系数进行插值，进而得到了全区的地表密度差及密度随深度变化因子，据此建立了渭河盆地及邻区三维密度模型，并利用该变密度模型反演了前寒武系结晶基底深度。与常密度模式重力反演结果对比表明，三维变密度反演结果更加准确，能为盆地油气勘探提供基础数据支撑，该方法亦可为解决类似地质-地球物理问题提供研究思路。

Basement depth estimation based on gravity anomalies in Weihe Basin with 3D variable density contrast model

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 Δ_ρ0 at the surface are extracted from the fitted exponential density contrast-depth functions,and the λ and Δ_ρ0 in the whole basin are acquired by gridding the discrete λ and Δ_ρ0.Thus,the 3D variable density contrast model is obtained by combination the gridded λ and Δ_ρ0 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.