Research Of Complex Resistivity Logging Technique

The conventional way to determine rock water-saturation is by the formula of Archie, through ration of rock resistivity and formation water resistivity. It's hard to determine the unmeasured constant and formation water salinity through this kind of method. The application of frequency property of complex resistivity to determine rock water saturation can reduce the effect result from formation salinity and lithology, improve accuracy of water saturation calculation, the method in this paper is of great importance to the exploration and development of non-heterogeneous reservoir and complex oil zone.The rock mechanism is relatively complex, not known clearly so far. There also be some distinctive explanations for relative dielectric constant of saline rock under low-frequency which can reach to be 10 8order of magnitude(Fuller and Ward,1970)The main component of rock is matrix and fluid. When pore fluid is saline, the dielectric constant of rock under low-frequency ( 1000Hz below) is exceptional high, much greater than weighting sum of dielectric constant of common matrix and water.Many reference discuss frequency scatter of rock and other electric media through equivalent circuit model (Cole and Cole, 1941; Henkel and Collins, 1961; Knight etc,1985)。Although theoretically, if the circuit is complex enough, equivalent circuit can match the measured data, only those equivalent circuits relative to rock conductivity is of physical significance.As for complex resistivity study, there are several principles: Firstly, basically, net model is agree with measuring result. Secondly, can make a lively explanation about conduction mechanism of water- bearing rocks. Thirdly, There is a certain correspondence between conducting-net model variables and water-bearing rock parameters. Fourthly, Model selected suitable for logging interpretation.At present, the study concerning complex resistivity of rock under wide frequency in mainly carried out in laboratory, there are abundant reference and report about dielectric constant of rock complex resistivity, among them, the frequency scatter of complex dielectric constant under low frequency had been carried out in many labs world wide.Poley et al.(1978) had mentioned in article that when frequency is above 200MHz, the real part of complex dielectric constant of sandε' will not scatter and tend to be insensitive to water salinity; the imaginary partε′′can be indicator of water salinity.Knight et al (1985,1987) had studied sand rock of different water saturation, he believed that as for part-saturating or full-saturating rock, there is an apparent frequency scatter in impedance of rocks, more over, obvious difference occurred in two distinctive frequency band, the impedance difference is 6 order of magnitude. They also calculated physical parameters of equivalent circuit that modeling rock electric property through inversion.Sheman(1988)analyzed frequency scatter property of reservoir, in connection with interface polarization, dipole polarization mechanism and DC conductivity, he also gave a model to interpret frequency scatter of rock dielectric of 96MHz—1300MHz frequency band, he believed that resistivity is inseparable with dielectric constant.The above mentioned rock electric property is mostly measured by secondary, quadruple or parallel plate capacitor. When measured by conductive coil array, for different measurement, the information contained in measured signal is not exactly the same, so many researchers aim to solve the problem.As for development of the instrument, there is not any business application of current complex resistivity logging tool overseas, we have oil institute(Beijing),Xinjiang oil field, Huabei oil field, shengli oil field and Jianghan logging research institute to study complex resistivity domestically. When identifying fluid in quality, the basic data being used is low-frequency resistivity(nearly to DC) and complex resistivity value under multi-frequency. Through percentage of differenct value between resistivity and complex resistivity to determine the fluid property in rocks.Domestically, Huabei oil field had developed complex resistivity logging tool, they carried in above mentioned way, added a frequency to dual lateral logging tool so that complex resistivity logging tool come into being, it had been said that through using the tool, more than 70 wells had been logged and had achieved desirable results.The paper is mainly discuss about research of complex resistivity logging tool , to develop a new type of complex resistivity logging technique. In theoretical aspect, we have theoretical analysis about relationship between saturation and complex resistivity, frequency spectrum of complex resistivity, study on model, parameter inversion, programming and debugging of inversion software and study on rock complex resistivity; In laboratory aspect, we had completed development of complex resistivity logging tool, frequency spectrum measurement of complex resistivity in 200 cores under normal temperature, frequency spectrum measurement of complex resistivity in 80 cores, laboratory research and analysis of complex resistivity of varied saturation; In tool development aspect, we had determined frequency number and size of complex resistivity logging tool, designed electrode system, developed sample tool and designed physical simulating tool and simulating well, we had got qualified logging data in field experiment of 10wells; In aspect of data evaluation, in combined with laboratory research, we had determined interpretation parameter, model, and method.Through above mentioned study, we had realized automatic controlling and digital acquisition of laboratory system, determined frequency of complex resistivity logging tool, completed development of complex resistivity logging tool. The technique is of great innovation, it applied simulating anneal technique to solve the problem of frequency spectrum inversion of complex resistivity. In the mean time, we believed that frequency spectrum of complex resistivity is in agreement with Dias model, for the first time we suggest to evaluate saturation through frequency scatter of imaginary part (phase), we had quantified analyzed relationship between complex resistivity parameter and oil saturation.The research has showed complex resistivity logging technique is holding an advantage in identification of water-flooded zone, the tool we developed is more stable and with higher resolution compared with other tools of the same type domestically.