Study On Joint Inversion Of Borehole And Surface Gravity For Apparent Density

The gravity surveying in borehole can measure the characteristics of the gravity field subsurface.Since the gravity measurement points in borehole are close to the ore body,combining the borehole and the surface gravity anomalies for apparent density inversion can greatly improve the inversion results of the ore body.It is an important method to enhancethe reliability of mineral exploration and oil and gas exploration.To this end,this thesis relies on the national key research and development plan "underground and borehole geophysical exploration technology and equipment" to carry out borehole gravity inversion and joint apparent density inversion of borehole and surface gravity to provide technical support for gravity exploration in boreholes.In order to study the response characteristics and detection ability of the three-component borehole gravity,the thesis developed a numerical calculation method for gravity threecomponent anomalies in boreholes of arbitrary density based on the "point element method".According to the geological characteristics of real ore bodies,a variety of orebody models were designed.According to the numerical simulation results,the characteristics of three-component borehole gravity anomalies of all orebody models were analyzed and summarized.Effects of the thickness of the ore bodies and the position of the ore bodies relative to the borehole on the borehole gravity anomalywere discussed.The resolution capability and effective detection range of the three-component borehole gravity for the side ore body were also studied.In this thesis,the objective function of three-component borehole gravity was constructed based on correlation coefficient.The deformed n-dimensional golden section algorithm based on single correlation coefficient search was used to realize joint apparent density inversion of the three-component borehole gravity.On this basis,joint apparent density inversion of borehole and surface gravity was realized.Accoding to the numerical simulation results of borehole gravity,the weighting problem of the surface gravity term and the borehole gravity term was studied.The inverse distance weighting technique was proposed to weighting these two items and able to improve the inversion efficiency.By using the developed inversion software,the joint apparent density inversion of borehole and surface gravity was carried out for various orebody models.The model trial results demonstrate that the studied method can better realize the three-dimensional apparent density inversion of relatively complex ore bodies.In particular,joint apparent density inversion of borehole and surface gravity can greatly improve the three-dimensional density apparent inversion accuracy of subsurface ore bodies.Based on the forward modeling,this thesis mainly studied the joint apparent density inversion of the three-component borehole gravity and the joint apparent density inversion of borehole and subsurface gravity.model calculation results show that the inversion performances,especially the vertical resolution,are improved and the multiplicity of inversion is reduced.