| Most of the traditional resistivity logging instrument measure single frequency,collecting less information of formation,ignoring the dielectric dispersion information.Complex resistivity logging instruments contain only two kinds of frequencies.In order to meet the different detection depth,the array induction logging instrument use different frequency electrical signals.The frequency response curve of the formation is collected under different electrical frequencies selected from 1 kHz to 500 kHz,and the electric spectrum information of the formation can be restored from single frequency value.The oil saturation of the formation can be evaluated by the electric spectrum under assumption that the salinity of formation water is stable.And low-resistance oil reservoirs and flooding layer can be better identifed.The electric spectrum logging probe prototype is well tested on the “Twelfth Five Plan” at Longdong.It can initially collect the spectrum of the formation of information,but the system still exists many deficiencies.The acquisition circuit needs to be further improved to faster and more precisely detecting phase sensitive.Through the frequency difference method to collect the signal data to eliminate the truncation error of DFT method,and the automatic gain method can reduce the quantization error when ADC acquire small amplitude signal,These contribute to the purpose of rapid and high accuracy and quick acquisition of the phase sensitive detector.Using the FPGA chip EP4CE22E22A7 N and DSP chip TMS320F28335 as the main controller design acquisition circuit.Select the analog multiplexer ADG1408,as the gain control circuit.Analog to digital converter AD9266,high-speed differential amplifier ADA4938-2 and other components of the digital acquisition module,the amplitude error below 0.02 mV,the phase difference accuracy can reach 0.01°,The time of acquisition and phase sensitive detection is not more than 10 ms. |
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