Research On Detection System For Well-Earth Potential

The distribution of water-pouring and remaining oil is a hot topic in the industry of oil gas development. It is also a worldwide difficult problem. Well-earth ERT (electrical resistance tomography) technology is an important geophysical exploration method, which can provide reliable basis for tapping latent potentialities of the remaining oil. Its underlying principle is the technique by which a strong current is applied to the casing of the waterflood input well on the surface of the earth, the current forms a non-uniform field in underground layer. It reflects underground resistivity distribution by measuring the electrical potential distribution of the earth surface. Therefore, associating the distribution of the underground layer precipitation facies, lithologic characteristics and stratum water salinity, it could make qualitative and semiquantitative research on propelling front edge of water flooding and the distribution of underground layer residual oil and gas by making use of the resistivity differences.Therefore, the accurate survey for well-earth potential is the core and the important guarantee of well-earth ERT technology. This paper has conducted the thorough research on networked detection system for well-earth potential. First, proposes a scheme of multi-channel simultaneous detection system for well-earth potential with on-the-spot investigation. Based on virtual instrument technology, the paper designs a multi-channel simultaneous detection system which achieves multi-channel, large scale simultaneous data sampling and real-time transmission. Compared with the traditional instrument, it increases detection efficiency substantially and has been applied to oilfield production successfully. The system adopts multi-channel simultaneous sampling ADC to sample with 18 fully differential input channels at the same time in order to suppress the electromagnetic noise and improve efficiency of field work; introduces the bipolar and differential inputs, analog LPF(low pass filter), FIR digital filter and linear accumulated digital averaging technology to suppress noise and improve SNR(signal-to-noise ratio). In view of measurement signal overshoot phenomena, the system uses a stationary signal extraction method to avoid huge errors, improve accuracy of measurement. When SP (spontaneous potential) in the earth superposes on the measurement signal, it reduces the dynamic measurable scope. So the design adopts feedback compensative method to exclude the influence of SP and covers a wide dynamic measurable scope. In fieldwork, the electrodes are sparsely and distantly disposed, therefore the system must detect all electrodes grounded situation before working, and spectrum analysis method is used for judging it correctly. The technique of USB2.0 is used to solve the problem of bulky multi-channel data transmission to achieve high-speed data transmission between hardware and PC. The operations of entire system such as control, data acquisition, analysis, display and storage are completed based on test and control software in PC. It has favorable modifiability and expandability and shows decided superiority and strong vitality of virtual instrument technology. The paper makes the detailed elaboration to the key techniques of the...