Research on law of magnetic anomaly variation with depth in fire area of Ordos Coalfield

Abstract

By comparing the change law of magnetic susceptibility of Ordos coal rock at normal temperature and during the temperature increase: as the temperature increases, the magnetic susceptibility also increases, and the composition of coal rock before and after heating is analyzed by X-ray diffractometer. It is found that the main reason for this change is that the ferromagnetic mineral composition of coal rock is changing during the heating process. This is used as the basis for the magnetic anomaly changes in the coalfield fire area. According to the theory of the gravitational potential field and magnetic potential field of the classic point, the coal bed fire area is used as a typical physical model to determine, and the Poisson formula method is used to determine the gravitational potential and magnetic potential. The second-order derivative of the cuboid gravitational potential is derived from the Poisson relationship, and the forward relationship of the magnetic anomaly of the coal field fire zone is obtained by integration. The magnetic anomaly characteristics of the coalfield fire zone model are calculated and simulated using Matlab. The results show that: as the depth increases, the extreme value of the magnetic field strength exhibited by the target body continues to decrease; the mutation rate of the intensity decreases continuously as it approaches the range of the anomaly; as the burial depth of the coalfield fire increases, the extent of magnetic anomalies has also continuously expanded to surrounding areas.

Keywords

• coal field fire
• magnetic anomaly
• magnetic susceptibility
• mutation
• buried depth
• spontaneous combustion
• fire control