Study On Induced Polarization Potential Decay Spectrum Logging Method And Logging Prototype Development

The original induced polarization logging used polarizability parameters to evaluate qualitatively some formation properties such as formatin water salinity, shale content and permeability, ect. However, for the complex influencing factors of polarizability, the result is not desirable. The polarizability of rocks can only indicate the ration of potential of secondary field and that of total field while excitation electric field is off instantaneously. The measured geological information is limited. Whereas potential decay spectrum of induced polarization can indicate secondary field potential decay values varying with time after excitation electric field is off. The geological information contained in the whole spectrum is much more than that contained in induced polarization logging. Study shows that the decay spectrum of induced polarization potential of rocks can be fitted into relaxation time spectrum which is similar to T₂ spectrum of NMR and is closely related to pore sturcture and permeability of rock. It has promising application prospect.The objectives of the subject: one is to investigate acquisition methods of decay spectrum of induced polarization potential on the basis of analysis and investigation of character of induced polarization of rocks through the theoretical modeling and petrophysics experiment. The acquisition methods include experimental acquisition and field logging acquisition; the other is to design the logging electrode array of decay spectrum of induced polarization as well as develop logging prototype of induced polarization potential decay spectrum. And through these studies, we finally developed a new induced polarization potential decay spectrum logging method for oil exploration and development.Through studying and analyzing the characters of induced polarization, we come to the following conclusions: firstly, the method of determining formation parameters by using induced polarization relaxation-time spectrum was proposed and had got a patents; this method is to fit the decay spectrum of induced polarization potential to relaxation time specturm, then establish the relationship between relaxation time spectrum and formation parameters through petrophysics experiment, further determine formation parameters. Secondly, the theory of ionodialysis polarization of compact rocks was proposed. It could reasonably demonstrate the phenomenon that induced polarization happened in pure sandstone. This had made up the limits of conventional knowledge.In terms of acquisition of decay spectrum of induced polarization potential, firstly we designed a kind of logging electrode array of induced polarization decay spectrum in combined structure which can acquire continuously the potential decay spectrum of formation induced polarization secondary field, one patent was awarded. The time of power supply and power failure had both reached to be 15s. The power supply effect and acquisition quality has an advantage over induced polarization logging. The polarizability decay spectrum could also be acquired. Secondly, we developed a set of logging prototype of induced polarization potential decay spectrum, and realized the continuous measurment of formation induced polarization potential decay spectrum. The prototype has the functions of power supply, acquisition automatically, AIEC and processing, etc. The field acquisited induced polarization potential decay spectrum is in consistent with theoretical spectrum and conforms to the exponential decay rule. The logging speed of prototype is 360m/h. The radial detecting depth is 0.75m. The longtitunial resolution is 0.4m. This can meet the requirements of data use and in-site operation.