Joint Inversion Research Of Surface And Borehole Magnetic Data

With the country's modernization construction and national economic development, consumption of mineral resources increased rapidly, and the majority of our resources in shallow mines have been mined and exhausted, exploration targets have turned to the external and deep mines. Thus, in recent years, deep exploration become our geological hot spot.Years of exploitation of the old mines, the ground magnetic survey of the shallow and surface disturbance is very serious, coupled with magnetic response of deep ore bodies on the ground are weak, hard to be identified. Inversion results are often unsatisfactory by single ground-magnetic survey data inversion interpretation.Borehole magnetic measurement is an effective method of magnetite ore, and it can avoid ground and shallow magnetic body interference, achieve all-round measurement in borehole, high vertical resolution and accuracy. If borehole magnetic data is used to inverse alone, according to the various components of the vector line maps to determine the head and tail of the mine, but not avail to determinate spatial patterns and the exact location. And the magnetic measurement is restricted by drilling, the scope of its control is very limited, so a single inversion of borehole data interpretation is sometimes difficult to meet the actual needs.In order to search for deep deposits better, we must find a more effective way to combine the ground and well magnetic measurement data, so as to inverse the spatial location and forms of the underground ore accurately. This paper mainly carried out the following research work for the deep prospecting problems:1. The ground-borehole joint magnetic susceptibility imaging inversion was carried out in this article. The principle and rule for dividing the underground 3D spatial model were introduced, which divide the semi-space underground into many little cuboids, each magnetic susceptibility value of which was a constant, but could be different. In the process of imaging, use the Occam's inversion method and the pre-optimum conjugate gradient algorithm to solve the large scale linear equation group. The practical examples of single inclined plate and combined plates models were presented, performed 3D ground magnetic susceptibility imaging inversion,3D borehole 3 components magnetic susceptibility imaging inversion and 3D ground-borehole joint magnetic susceptibility imaging inversion separately, through compared and analyzed the results, we found that we could distinguish two plates with different inclines from the horizontal direction by the single ground magnetic susceptibility imaging inversion, which was with higher resolution, while the results of two similar plates from the vertical direction were different from the theoretical models. The plates could be approximately distinguished from the vertical direction by the single borehole magnetic susceptibility imaging inversion, but it was very fuzzy in the horizontal direction, and couldn't separate the horizontal positions. It was very clear and easy to distinguish two plates with different sizes and opposite inclines both in the horizontal and vertical directions with the ground-borehole joint magnetic susceptibility imaging inversion. Through the model test, we proved 3D ground-borehole joint magnetic susceptibility imaging inversion could utilize advantages of the high horizontal resolution of ground magnetic susceptibility imaging inversion and high vertical resolution of borehole magnetic susceptibility imaging inversion, and it was more clear, which was more coincident with the practical situation.2. Based on BG theory, the necessary of 3D surface and borehole magnetic joint inversion is discussed theoretically. Form of average function depends on the character of the kernel function, which is the essence of geophysical problem. Kernel functions are different in nature, its attenuation with depth is different, and will affect the character of the average function. Kernel functions which depleted in the shallow, decides the shallow nature of the average function; the other hand, the slow decay of the kernel function mainly affects the deep features of the average function. For surface magnetic measurement data, the shallow resolution is high, and the deep resolution is low; well for the borehole magnetic measurement data, the resolution near the borehole is high and low far from the borehole. Therefore, in theory, resolution of 3D surface and borehole joint inversion is much better than a single data inversion. An example of sphere model is given to prove that surface and borehole joint inversion is superior to the single surface, or borehole inversion.3. The basic principle and performed steps of 3D ground-borehole joint human-computer interactive inversion was described, the forward formula of 3D spatial ground-borehole magnetic anomaly was introduced and how to compute the forward anomaly and build 3D geological model as well as the linked precept between adjacent profiles when with the same or different integral offsets were discussed, and 3D ground-borehole joint human-computer interactive inversion for the deep prospecting of the national crisis ore mine was applied in this article.In this paper, Jianlin hill-Elphant trunk hill mining block in Daye, Hubei province was shown as an example, by sorting out the petrophysics data as well as the known geological and borehole data, we analyzed and compared the predecessors'achievements, then did 3D ground-borehole joint human-computer interactive inversion for the 6 profiles(line 17,18,19-0,21,22) and 3 borehole(ZK18-12,ZK19-1-15,Zk22-16) here, as a result, we concluded it was with obvious "step" characteristics of the iron mine in the elevation hosting position. Finally, we present 2 practical examples and proved that 3D ground-borehole joint human-computer interactive inversion was prior to single data inversion, which not only reduced the multi-plicity of the solutions, but also improved the difficulty problem in 2.5D inversion for changing geological body's form along y direction, and it was more coincident with the practical situation, so it is a very effective theory and method for deep prospecting.