The Design Of Fluid Density Intertial Tool

The density of oil,gas and water mixture is an important decision and evaluation parameter in oil exploration and development.It provides timely and accurate basis for evaluation of formation resources and production characteristics.In recent years,tuning fork density logging which reflects the change of fluid density according to the resonance frequency of the tuning fork sensor,is a new method of downhole fluid density measurement.The difficulties are mainly reflected in the following aspects:(1)We have to determine the resonant frequency of the tuning fork sensor to calculate the density of the measured liquid.(2)In order to monitor downhole fluid dynamics the instrument that we will have designed must have on-line measurement function.Aiming at the above problems,the equivalent model of cantilever beam is introduced,the main causes of the vibration frequency variation of tuning fork sensor is analyzed,the relationship between the measured liquid density and the resonant frequency of tuning fork sensor is studied,finally the basic principle of tuning fork type fluid density measurement is expounded in this paper.On this basis,the following work is completed:(1)According to the requirement of real-time online measurement,a design scheme of closed-loop self-excited oscillation based on tuning fork sensor is proposed.(2)In order to eliminate the influence of the distributed capacitance of the tuning fork sensor and the circuit board on the test results,a charge amplifier is used as the preamplifier circuit.(3)The unlocking module is added to the frequency tracking circuit to further improve the anti-interference ability of the sensor.(4)In order to reduce the measurement error a method of the equal precision frequency measurement is adopted and the 8051 soft core is embedded in the FPGA chip to realize the complex data operation.Finally,the overall scheme of the tuning fork density logging tool is designed and the corresponding electronic circuit is developed.By adopting the above scheme and measure,the tuning fork sensor has the advantages of high resolution,strong anti-interference ability of the circuit and small measuring error.In summary,the research and work of this paper has solved several key technical problems of the tuning fork density logging tool and the developed system in 0-1.25g/cm3 density range has a good resolution and a smaller measure error.What has been done in this paper is important for breaking the foreign monopoly market and researching the tuning fork density tool of owning independent intellectual property rights.