Development Of Real-time Detection System For Salinity Of Water Injection Wells

Petroleum exploitation technology has always been an important indicator used to measure a country’s industrial level in the world,with the continuous expansion of China’s oil exploitation,more and more oilfields have entered the period of secondary development.At present,techniques of water flooding is used in the secondary development of most oilfields in China,and the salinity is an important index for water flooding solution to be tested.The cost of crude oil production will increase with low salinity,while the original formation structrue will be destroyed with high salinity.At present,conventional water quality detection instruments are used to detect the salinity of water drive solution on the ground,which can not go deep into the well,which to a certain extent increases the cost of crude oil production.Therefore,it is more urgent to develop a technology that can measure the salinity of crude oil and water flooding solution in real time.It is important to obtain the salinity of crude oil and water flooding solution in real time for stable production and recovery of formation pressure.For the reinjection water in the same area,the conductivity has a linear relationship with the salinity,In this dissertation,a real-time monitoring system is developed to measure the salinity of oil field by conductivity.The background and current situation of conductivity detection technology are introduced in this dissertation,and compares the measurement accuracy and range of current conductivity sensor while we analyzes the advantages and disadvantages of electromagnetic induction conductivity sensor and electrode conductivity sensor.This dissertation also introduces the measurement methods of seven electrode conductivity and traditional two electrode conductivity sensor of the electrode type conductivity sensor while RC-oscillation circuit and selectivefrequency network were introduced detailedly.Based on the analysis above the conductivity measurement methods,a method of collecting half cycle square wave signal was proposed to reduce the worse effect of electrode polarization and capacitance on the system.Secondly,this dissertation designs the software and hardware of the system in order to realize the above methods.The core processor is the microprocessor based on Cortex-M3,and the signal acquisition circuit is designed by using the characteristic that the output slope of the integration circuit is only related to input voltage.The temperature acquisition circuit is designed by considering the high temperature environment in the mine.Meanwhile,the PCB was designed in layers to reduce circuit volume.The system software which is mainly used to initialize is realized with C language.We also filter the original data and calibrate the relationship between salinity,conductivity and temperature.Finally,we test the system designed in this dissertation.We first test the hardware by testing the output waveform of power module,excitation module and signal acquisition module respectively.Secondly,a set of constant temperature control system is designed to simulate the high temperature environment in the mine,and the reliability of the developed salinity detection system in the high temperature environment of 85 ℃ is verified by experiments.Then,the relationship among the degree of mineralization,conductivity and temperature is calibrated by the precision mineralization meter,while the measuring range and accuracy of the system are detected by preparing the standard salinity solution.From the test,we get a conclusion that our salinity measurement system is smaller with higher accuracy than traditional one.The accuracy can reach ±1% in the range of 1000mg/L～10000mg/L,and our system meets the needs of techniques of water flooding.