基于重力梯度张量数据的欧拉反演在梅山铁矿的应用

Application of Euler inversion based on gravity gradient tensor in Meishan iron mine

随着在石油勘查、矿产勘查、构造研究等地质工作中提出的应用位场异常研究规模相对较小的地质体及其细节的要求不断提高,传统重力方法在精度和分辨率方面已不能满足要求.重力梯度张量作为重力位二次导数,较之重力异常,能够更直观地反映地下密度体的赋存状态,基于重力梯度张量数据的反演能够提高地质体的定量模拟质量.但是由于受国内仪器的发展水平限制,直接获取实测的重力张量数据难度较大,目前对于重力张量数据的获取主要是通过数值计算的方法,把重力异常测量值变换成张量信息.本文是在样条理论的基础上,提出新的重力梯度张量计算方法,利用三次样条插值方法拟合重力异常,进一步地通过积分导数关系求取样条函数系数,实现了由重力异常求取重力梯度张量的数据计算.在此基础上,利用张量数据进行欧拉反演计算,对比常规欧拉反演结果,进一步分析张量欧拉反演精度.球体及水平板状体模型试验结果显示,张量欧拉反演更能有效地完成目标体的反演,其结果更加准确.最后,将张量欧拉反演应用到梅山铁矿区重力实测数据解释中,准确地反演出梅山主矿体的水平投影范围及矿体中心埋深.同时,相比常规欧拉反演,张量欧拉反演在刘家村附近、梅山村南部及黄林库-吴家洼地段显示出有更加收敛的欧拉解,这为梅山地区进一步找矿工作提供了重要的理论支撑.

With the increasing requirements of the description of geological bodies with relatively small scale of applied potential field anomaly research proposed in petroleum exploration, mineral exploration, structural research and other geological work, the traditional gravity exploration method can no longer meet the requirements in terms of accuracy and resolution. The gravity gradient tensor as the second derivative of gravity potential can more intuitively reflect the occurrence state of underground density anomaly body than gravity anomalies, Gravity inversion based on gradient tensor data can improve the accuracy of simulation of geological body. However, due to the limitations of the development level of domestic instruments, it’s difficult to directly obtain the measured gravity tensor data. At present, the gravity tensor data are mainly acquired by transforming the measured value of gravity anomaly into tensor information through numerical calculation. Based on the spline theory, this paper proposed a new method for calculating gravity gradient tensor which used the cubic spline interpolation method to fit the gravity anomaly, and further calculates the coefficient of the sampling spline function through the integral derivative relation, so as to calculate the data of high-precision gravity gradient tensor from the gravity anomaly. On this basis, Euler inversion is calculated with tensor data, and the precision of tensor Euler inversion is further analyzed by comparing the results of conventional Euler inversion. The results of sphere and plate models test show that the tensor Euler inversion is more effective to complete the inversion of the target bodies, and the results more accurately reflect the center position of the sphere and the boundary of the horizontal plate bodies. Finally, the tensor Euler inversion is applied to the interpretation of the measured gravity data in Meishan iron mine area, and the horizontal projection range and central burial depth of Meishan main orebody are accurately inverted. Furthermore, compared with the conventional Euler inversion, the tensor Euler inversion shows some more convergent results at Liujia village, south of Meishan village and Huanglinku-Wujiawa area, which provides an important theoretical support for further prospecting work in Meishan area.