起伏观测面约束的重磁数据快速联合物性反演方法研究

Study of fast joint physical inversion methods of gravity and magnetic data with undulating observation surface constraints

重磁联合反演能够综合重磁数据特征直接获取地下密度及磁性分布,有效揭示不同岩性分布及地下构造,是矿产资源勘查的重要手段.实际地表以及沿地形起伏的航空重磁测量的观测面都是起伏的,为实现起伏观测面的重磁高效率联合物性反演,我们建立了一种起伏观测面约束下的重磁数据快速联合物性反演方法,其首先是依据最大观测高度对数据进行曲化平处理,然后利用Block-Toeplitz-Toeplitz-Block(BTTB)-FFT实现快速反演,并将换算观测面与实际观测面的空间作为约束来消除无效网格单元计算所带来的多解性,从而本方法能够实现高效率反演且不因额外的剖分单元而增加求解多解性.模型试验表明本方法在能够有效地提高多于32倍的计算效率且不损失反演计算的精度,且对于含噪数据反演也具有良好的稳定性.最后,我们将本方法应用到中国吉林省东部通化盆地三棵榆树凹陷,获得了该地区基底和火成岩分布,该地区的盆地基底平均深度约为2.5 km,同时火成岩发育主要集中在基底深度较大的区域,为下一步油气勘探提供重要基础地质信息,亦对松辽盆地东部外围新区的油气勘探部署提供重要的指导意义.

Joint inversion of gravity and magnetic can directly obtain the underground density and magnetic distribution by synthesizing the characteristics of gravity and magnetic data,and effectively reveal different lithology distribution and underground structure,which is an important means of mineral resources exploration.The actual surface of the earth and the observed surface of the airborne gravity and magnetic survey that fluctuates along the terrain are both undulating.In order to realize the highly efficient joint inversion of the undulating observation surfaces,we have established a fast joint physical inversion method for gravity and magnetic data under the constraints of undulating observation surfaces.Firstly,the data is flattened according to the maximum observed height.Then,Block-Toeplitz-Toeplitz-Block(BTTB)-FFT is used to achieve fast inversion,and the space between the converted observation plane and the actual observation plane is used as a constraint to eliminate the multiple solutions caused by the calculation of invalid grid cells.Therefore,this method can achieve high efficiency inversion without increasing the multiplicity of solutions due to additional partition elements.Model tests show that this method can effectively improve the computational efficiency by more than 32 times without losing the accuracy of inversion calculation,and has good stability for noisy data inversion.Finally,we applied this method to Sankeshu Depression,Tonghua Basin,eastern Jilin Province,China,and obtained the distribution of basement and igneous rocks in this area.The average depth of basin basement in this area is about 2.5 km,and the development of igneous rocks is mainly concentrated in the area with large basement depth,which provides important basic geological information for the next oil and gas exploration.It also provides important guiding significance for oil and gas exploration and deployment in the eastern peripheral new area of Songliao Basin.