Resistivity Imaging Method. Well Study

Compared to resistivity image on the surface, the crosshole resistivity image has a better resolution for the target with a certain depth because its current electrode is located below the surface. This method especially meets with the requirements of deep depth and high resolution of energy and resource exploration at present.The purpose of crosshole resistivity image is to ascertain the location of abnormity body and real parameters of the stratum. The geometry image method of crosshole apparent resistivity is put forward in this thesis, which can accurately ascertain the perpendicular position of abnormity body. Based on the theory of direct-current electric field in non-full space, the apparent resistivity formula that is different from half space and full space was deduced by the image method, and all apparent resistivity was solved out, then the apparent resistivity isopleth map was drawn, in which, observation hole depth is ordinate and power-supply hole depth is abscissa. At last, several typical geologic models were simulated by three-dimensional Finite Element Method. The results show, the space shape and precise position of abnormity body can be judged from apparent resistivity isoline shape, but crosshole low resistivity body reflects high apparent resistivity abnormity and crosshole high resistivity body reflects low apparent resistivity abnormity. This method has high resolution in perpendicular direction, and can accurately ascertain the depth, but the transverse position of abnormity body can't be recognized.To further ascertain the transverse position of crosshole abnormity body, the gridding image method of crosshole apparent resistivity is put forward. After the crosshole area was divided into grids, the average value of apparent resistivity in each grid nodes was calculated. Then the recomposed apparent resistivity isopleth map after gridding was drawn, in which, well depth is abscissa and crosshole separation is ordinate. Model computing result demonstrated the transverse position of abnormity body can be approximately ascertained by this isopleth map. Crosshole electromagnetism image is one of the important means to study crosshole precision configuration. Some crosshole electromagnetism image methods were summarized at the end of this thesis, and its advantages and disadvantages were analyzed. At last, this thesis pointed out the study orientation of crosshole electromagnetism image will be instrument development, the influence of metal thimble and image method, and finally multi-component crosshole electromagnetism system will be adopted to detect the anisotropism characteristic of crosshole stratum, in order to describe crosshole precision configuration accurately.