Research On Network Well-Earth Electrical Method Multi-Parameters Detection System

In the industry of oil gas development, we can only exploit 30% of underground total reserves generally, which means there are approximately 60% of the oil still remained in the underground. In order to exploit the part of reserves rationally, we must determine its distribution in the oil reserve exactly, in other words, we need to determine the residual oil saturation and its distribution. Classical well-earth ERT testing instrument can detect the underground resistivity by the measurement of the surface electric potential. However, it can only research the distribution of the surplus oil and the edge of the water injection qualitatively and half-quantitatively. Because the dielectric constant of water exceeds that of all the rock and fossil oil far and away, the polarizability of water is so strong under the additional exciting field that we can add the induced polarization method into the field of well-earth surplus oil detection. Meanwhile, pseudo-random signal has good randomness and is easy to be dissociated from other signals and noise. At the same time, it can measure multi-frequencies apparent resistivity and the frequency of the main and others are easy to adjust which can increase the working efficiency greatly. The research on network well-earth electrical method multi-parameters detection system is based on the function of measuring resistivity in the original equipment. This system add the functions of measuring induced polarization parameters and pseudo-random parameters, meanwhile, it achieves network measuring all of which can overcome the original equipment's weakness such as signal measuring parameter, without the function of dynamic measurement. It can research on the detection of the surplus oil and the edge of water injection and provide reliable basis for tapping latent potentialities of the remaining oil.The design of the system adopts modularized thinking and based on virtual instrument technology which is convenient for function upgrading. Under the control of the software, we get the signal of the measuring electrodes by the hardware. After preliminary amplifing,passing low-pass filte,secondary amplifing and changing of amplitude the signal is sent into multi-channels ADC for quantifying. CPLD control the time sequence. Two 8 bits FIFO are composed to 16 bits for buffering. The USB ,microcontroller control the programmable amplifier,the starting and stopping of the ADC,the feedback of DAC and the transmission to computers. In the computer, the data is processed by the measuring and controlling software to achieve the resistivity,induced polarization parameters and pseudo-random parameters. At last, these results are displayed on the coordinates map and they are also stored in the computer at the same time so that it increase the accuracy and efficiency of the detection.The system is consisted by three parts which are the receiver,the relay station and the sub-stations. The system adopts the technology of multi-channels acquisition in synchronism in order to realize 18 channels acquisition. At the same time, the system can realize the functions of system calibration,control of the acquisition time,control of the electrode,measuring the earth resistance,choosing sampling frequency,control of magnification times and DC-offset compensation which are used to meet the requirements of the field work. The electrode intelligent switching of the system is finished by RS485 transmission. In order to the expansion of the electrode's number, the relay station is added into the system. Now 54 electrodes can be switched in the system which 288 electrodes are switched at most in order to meet more measurement field. Both the M and N electrodes are switched in every sub-station for the requirement of IP method. At the meantime, we can use the original well-earth ERT measurement mode by the function switches in the relay station which can achieve compatibility and expansibility of the system.For IP parameters, it achieves the switchover of the electrodes by RS485 transmission. That's to say, the intelligent switchover of M electrode change into that of MN electrodes. Because the IP signal is periodical and full of stochastic noise, we adopt digital average superposition to eliminate the noise. The paper uses the software to show the effect of the method of digital average superposition. Then the experiments verify the good processing results of this method. It also studies on the characteristics of TIP and FIP parameters and designs every block according to every characteristic. Then it gives us simulation emulations and experiments indoor in order to proof its feasibility and accuracy which meet the need of the design.For pseudo-random parameters, based on the study of the principle and the characteristic of 2~n series pseudo-random, we design the abstraction block for pseudo-random parameters. It is FFT that change the time domain signal into frequency domain for analyzing in order to extract the each basic frequency information from the pseudo-random signal. Then change each signal into time domain by inverse FFT in order to get the amplitude of each basic signal. We take three frequencies pseudo-random signal for example to show the detail process of the block function and it is proved effective by some experiments.At last, the paper gives the detail of performance adjustment,calibration test,short-noise test,the RC network experiment for TIP and FIP,water channel experiment for TIP,pseudo-random parameters experiment. Then use TIP and resistivity method contrast experiment to prove that in the model polarizability has better resolution than apparent resistivity.