Study On Several Key Issues Of Logging Method In Two Directions Focused Induced Polarization

Permeability, representing the percolation capacity of fluid in rock pores, is one of the three basic evaluation parameters of the reservoir. The permeability of oil well formation could be obtained by the induced polarization logging method. Aiming at several key issues in the development of the first generation of induced polarization logging tool, further discussion was made in the thesis. The specific research results are in the following aspects.About the issues of the focused method of induced polarization and the improvement of detection efficiency, according to the focused property of electric field, induced polarization two directions focused logging method was proposed. Based on the basic structure of focused electrode system, the models of focused current ratio of shielding electrode to main electrode, instrument coefficient and radial geometrical factor were established. On the basis of these models, simulation experiments were presented by multi-physics simulation software (COMSOL). The simulation results show the correctness of these models and the prominence advantage of the two directions focused logging method in improving the depth of investigation and signal to noise ratio; in the same conditions, compared with the traditional induced polarization electrode, the depth of investigation of the axial focused electrode increased by more than54%in the range of optimal current ratio; in the same current density, the two directions focused electrode increased by more than15%than the axial focused electrode.On the basis of deriving the relationship between relaxation time and pore diameter, the optimization sampling of polarization relaxation process was further analyzed. Considering the computation and accuracy of subsequent inversion, the suitable number of discrete sampling points was determined. And the optimal distribution of discrete sampling points was obtained by the optimal quantization method combining with the probability density of polarization curve. The results of numerical inversion and actual core data show that the optimal discretization strategy could reduce the ill-posed property of discrete equations and improve the inversion accuracy and stability.For the existing relaxation time spectra inversion method, the relaxation time sequence was set in advance, which causing larger inversion error and discontinuous of relaxation time spectra. The differential evolution algorithm was introduced successfully for relaxation time spectra inversion, and a hybrid inversion method together with singular value decomposition with spectral component residual correction and differential evolution algorithm was proposed. The inversion results show that the proposed method still had high inversion accuracy in the condition of low signal to noise ratio.For the sand-shale formation, an integrate permeability estimation model with porosity, formation factor and relaxation time spectra was established. The coefficients of the models were obtained by statistical analysis of sand-shale core samples dataset. The estimation results show that the permeability estimation models with induced polarization relaxation time spectra could improve the estimation accuracy evidently. For the sake of verifying the accuracy and applicability of permeability estimation models, the different core samples datasets from both the same area and different areas were used to predict permeability. The consequences declare that the permeability estimation models with relaxation time spectra provide an effective new way for the permeability estimation.