Research On Response Characteristics Of Dielectric Logging Based On Cavity-backed Electrically Small Antenna

In the case of high resistivity fresh water layer or low resistivity oil layer,the dielectric constant is more effective than resistivity or conductivity to identify reservoir fluid,especially to distinguish oil and water layers,judge water flooded layer,and analyze pore fluid and rock matrix,the dielectric logging is the most effective method.In this thesis,the new generation of Dielectric Scanner logging tool of Schlumberger Company is simulated to optimize the size and structure of the antenna element,determine the antenna material properties.And the logging response characteristics of the tool by numerical calculation are studied.These researches provide a theoretical basis for the development of domestic broadband dielectric logging tool.The main research contents and achievements are divided into the following four parts.The first part studies the basic theory of dielectric logging.Firstly,dielectric dispersion physics is applied to verify that the working frequencies of Dielectric Scanner are 20 MHz,200 MHz,400 MHz and 1.1 GHz.Secondly,the response charts of the antenna under four working frequencies are made.The results show that: in half space formation,at low frequency,the phase shift response of the magnetic dipole is more sensitive to the conductivity in the two polarization modes.At high frequency,both amplitude and phase are sensitive,but the phase changes too fast,resulting in multiple solutions.The second part simulates and optimizes the size and structure of the antenna element on the instrument.Firstly,in CST microwave simulation software,the cavity-backed electrically small antenna and loop antenna models are constructed,and the accuracy of the two antenna models is verified by comparing the response results and far-field diagram of the two antenna models.Secondly,the control variable method is used to optimize the size and structure of the antenna.In the third part,the dispersion characteristics of the phase and amplitude with different receiving and transmitting distance in different formations are studied.The results show that:the amplitude ratio of S21 in different formations decreases with the increase of the distance between the transmitter and receiver,but its dispersion characteristics do not change.In the other formations except the air,the difference phase dispersion curves of antennas with different spacing are almost the same,and their dispersion curves increase linearly with frequency.And in these layers,the response characteristics of horizontal polarization antenna with different spacing are similar to that of vertical polarization antenna,but the S21 amplitude of horizontal polarization is higher than that of vertical polarization,and the larger the transceiver spacing is,the higher the frequency is,the greater the amplitude difference is.In the water layer,the amplitude ratios of the vertical and horizontal polarization antennas have no dispersion characteristics at high frequency,so the water layer can be judged by whether the measured values at 0.4GHz and 1.1GHz are approximately equal.The fourth part studies the influence of formation environment on the logging response of Dielectric Scanner.The results show that: the antenna response is more sensitive to high conductivity and low dielectric constant.And the influence of mud cake thickness on logging tool response varies with the difference between mud cake and formation electrical properties.What's more,the influence of mud cake conductivity on antenna detection depth is greater than that of mud cake dielectric constant.Besides,when the frequency is less than 0.1GHz,the electrical properties(relative permittivity and conductivity)of the mud cake have no effect on the response of the antenna.When the frequency is greater than 0.1GHz,the larger the relative permittivity of mud cake is,the less sensitive the phase is to the conductivity of mud cake.