Design Of A Circuitry For Microresistivity Imager For Oil-based Mud

Microresistivity imaging of geologic formations penetrated by borehole is an important means of oil exploration.Since the oil-based mud has many advantages,in recent years it has been widely used as a drilling fluid.However,the oil-based mud is non-conductive which makes the water-based fliuds imager could not be used.For this reason,related agencies of domestic and foreign are studying to develop a logging instrument to operate in the oil-based mud environment.At present abroad has launched several resitivity imagers for oil-based mud and has been commercialized,However,domestic is mainly in the development stage,there is no mature product launched.The paper designed a circuitry for microresistivity imager for oil-based mud,and a series of tests are carried out on the circuit.The main work of the paper is as follows:1)The research background,application field and development status of micro resistivity scanning logging are investigated.Understand the principle of micro-resistivity scanning logging and the difficulties encountered in the oil-based mud environment.By studying the influence of frequency and electrode size on the measurement,a multi-frequency measurement method is proposed.The advantages and disadvantages of the loop between the plate and the loop inside plate are compared and analyzed.The design of the circuit is determined by the structure of the loop inside the plate.The impedance measurement method is studied,and the impedance measurement is carried out with the idea of vector voltammetry.2)Complete the hardware design of the measurement system.The measuring system consists of six acquisition board circuits,a motherboard circuit and a communication board circuit.The acquisition board is the core of the measurement circuit,The board contains DDS excitation source,amplitude phase detector and so on.The acquisition board can independently perform the measurement work and return the digital signal directly for which it has a good stability and anti-interference ability.The motherboard can coordinate the work of each acquisition board and collects the digital signals returned by the acquisition board and feeds the data into the computer via the communication board.Finally,through the Altium designer completed the design and implementation of the circuit board.3)Complete the hardware-circuit-related program design and design data communication frame structure.Calculation of The modulus and phase of the apparent impedance are studied and then give the formulas.Design of the host computer software to achieve the preservation of data,processing of data and display results.4)Test the system,The measurement system is capable of 40 measurements per second.It can be measured on the nominal resistance of 500?-5M?.In repeatability measurements show that in the linear range,The mean square error of the modal measurement is less than 0.34% and the mean square error of the phase measurement is less than 0.43 °.The test results of the measurement system are consistent with the professional impedance analyzer Agilent 4294 A in the RC layer simulation test.The test shows that the circuit designed in this paper can be applied to the measurement environment of oil-based mud,and has the characteristics of fast measurement speed,large dynamic range,high measurement accuracy.