Study On Joint Interpretation Of Borehole And Ground-airborne TEM Data

The mining practice at home and abroad shows that the deep and periphery of the developed mines is an important way to find new deposits and expand the reserves of resources.In recent years,the great countries of the mining industry have intensified their efforts to explore the geological exploration of large and rich mines,and have made great progress.In Canada,Australia and other countries,Borehole TEM(Transient Electromagnetic Method)has been widely used in deep prospecting and prospecting,and many achievements have been made in the world.The Borehole TEM usually refers to a device that is launched on the ground and uses a special probe to receive transient electromagnetic response in a borehole.As the probe is closer to the ground,the more reliable information of the ore body can be obtained.Because the interference from the near surface is very small,the receiving device is closer to the deep ore body,so that it can get useful geological information in the range of hundreds of meters around the borehole,thus improving the ore finding rate and the prospecting effect.Borehole TEM has become a very important exploration method for conductive mineralization,particularly in areas where the ability of surface EM to define a target is limited either by large depth or by interfering conductive bodies such as overburden shallow sulphides and peripheral mineralized horizons.However,due to the complexity of transient electromagnetic theory in the borehole,the current data processing and interpretation methods are still qualitative and semi quantitative,which are difficult to meet the actual quantitative demand.Moreover,in the actual interpretation and inference,single borehole information can only indicate the approximate location of the ore body near the borehole,and it is difficult to provide more accurate ore body information,and depends on drilling again to carry out the next measurement and interpretation.In order to solve the above problems,a method of joint interpretation method with ground airborne Transient electromagnetic data and transient electromagnetic data in borehole is proposed in this paper.Ground airborne TEM is the configuration with the source put on the ground,receiving TEM response by flight platform to obtain target effective regional geological information quickly with higher SNR,which is especially suitable for carrying out the work in the complex mountainous terrain.Making full use of the ground source and carrying out TEM data collection and comprehensive interpretation in the borehole and air,we can get higher resolution ability both vertically and horizontally,so as to improve the reliability of interpretation.This thesis focus on borehole TEM data interpretation method,aiming at the existing problems in the data processing and interpretation to carry out related research,including analysis of the characteristics of the emitter source,study on the definition method of full field apparent resistivity of borehole TEM,Joint three component vector intersection both in air and in borehole,joint interpretation method with air and hole data based on equivalent filaments.In this paper,the numerical simulation method of ground airborne and borehole TEM is given,including the forward modeling method and the FDTD three-dimensional forward modeling method of the one dimensional model in the whole space.The distribution characteristics of magnetic source and electrical source underground and air field are analyzed.The spatial distribution of transient field in homogeneous half space and the three component transient response characteristics in one-dimensional and three-dimensional models are studied by forward modeling.The model results show that relative to the magnetic emission source,electricity emission system by increasing the transmit power,increase the available area,has deep good prospecting exploration potential,electric source borehole TEM method of three component transient response curve has a good response to the electrical interface and abnormal body.In the field,we can refer to the result of the analysis of the feature of the midfield source in the field,and choose the suitable device to carry out the measurement according to the actual situation.As the interpretation method of electric source borehole TEM,first gives the electric dipole in layered media in the underground TEM response,and then through the electric dipole superposition of the obtained electrical source under the condition of TEM response.Full field apparent resistivity is defined by the inverse function theorem,by using the monotone relation between the inductive magnetic field and the uniform half space resistivity.Calculation results of apparent resistivity of theoretical model shows that the apparent resistivity curves of different depth are different in the first part and basically the same in the last part.This reflects that the global apparent resistivity is a comprehensive reflection of the medium around the measuring point and the range of first part of apparent resistivity curves are changing with position.In this paper,the method of joint vector intersevtion both with air and borehole is put forward,and the three component intersection is carried out by air and borehole data.The calculation results of theoretical models show that the results of the combined space vector intersection are in good agreement with the theoretical models,and have higher interpretation accuracy compared with the single air data or borehole transient electromagnetic method.For the magnetic emission source,a joint interpretation method based on the equivalent filament is proposed in this paper.The theory show that the eddy only distributes in the edge or surface of conductive body excited by primary field at early time,and then move to the center because of the interaction effect of current filaments.In other words,the vortex current can be equivalent as filaments at different times.The filament of early time reflects the edge of abnormal body,and the filament of late time reflects the center.Consequently,the geometric morphology of geological target can be obtained through the inversion of different time filaments.While the field of the equivalent filament is used to fit the data in the air and in the hole,the parameters of the filament are more accurate and reliable.Joint interpretation methods are established for magnetic source system,which are fast,reliable and accurate,and it can provide technical support for further deep prospecting.