Study On Quantitative Detection And Analysis Method Of Dynamic Oil Content In Oil-water Two-phase Pipe Flow By Infrared Spectrum

Real-time and accurate detection of phase holdup of oil-water two-phase flow is a problem that needs to be solved in every link of crude oil from exploitation to transportation,it is easy to form complex local flow characteristics in the two-phase flow pipeline,which makes it difficult to effectively detect and accurately identify oil-water content.In order to solve the problem that the traditional measurement methods can’t meet the measurement requirements of high precision,non-contact,low cost,stable performance and universality at the same time,starting from the infrared spectral absorption characteristics of crude oil,calculates the spectral characteristics of refractive index,reflectivity and equivalent transmittance of oil-water two-phase flow by using the double thickness method,and investigates the spectral pretreatment methods and data modeling methods of low water cut crude oil and high water cut oil-water mixture.Through comparison,a moisture content prediction model based on ELM is proposed by adopting the combined band screening rules of CARS and SPA.Through the simulation analysis of the flow state and flow field characteristics of oil-water two-phase pipe flow under 27 working conditions,the basic characteristics of oil-water two-phase pipe flow are clarified,so as to determine the best position of spectral measurement.The water content of oil-water two-phase flow can be measured in real time by establishing an online testing system,and the structural scheme of dynamic detection device is designed,which provides theoretical guidance for field installation scheme and on-line detection application for oilfield development and crude oil measurement.To solve the difficult problems of universality and real-time measurement,taking the standard liquid as the experimental sample,establish the modeling method that can be used for the prediction of oil content of oil-water two-phase flow.With diesel oil as the volume fraction,prepare 50 volume fractions of standard solutions with oil content of 2%-100% and to measure the transmittance spectrum.A simplified double thickness model is established to peel off the influencing factors of the optical window,so as to realize the accurate interpretation of the reflectivity,refractive index and equivalent transmittance of the oil-water two-phase standard liquid.After spectral data preprocessing,original sample data set division,feature sample extraction and ELM modeling,the nonlinear model for oil-water two-phase standard liquid oil content prediction is obtained.The goodness of fit for oil content prediction can reach0.991 and the minimum root mean square error is 0.0504.The linear model with of oil content prediction of oil-water two-phase standard liquid is obtained by PCR,GA＿PCR,SA＿PCR and PLS,i PLS and Si PLS.The goodness of fit of oil content prediction can reach 0.9974 and the minimum root mean square error is 0.0212.By comparison,the ELM nonlinear modeling method based on CARS + SPA feature sample selection more suitable for the rapid and real-time prediction of oil content of oil-water two-phase liquid in.The linear modeling based on Si PLS is more suitable for high-precision prediction when the original samples are sufficient and evenly distributed.To solve the difficult problems of high precision and stability,based on the characteristics of pipe flow field,the optical spectrum measurement position of oil-water two-phase pipe flow is determined to realize the effective coupling of flow field and light field.The horizontal pipeunder different working conditions,inclined pipe with different inclination angle and vertical pipe with different inlet are simulated respectively,and the velocity distribution,pressure distribution,phase distribution,energy distribution and turbulent kinetic energy distribution of oil-water two-phase pipe flow under different working conditions are simulated.Based on the flow state and flow field characteristics of oil-water two-phase pipe flow,the optimal radial position and axial position of spectral measurement are determined.Through analysis,it is determined that the best measurement position is when the axial position of horizontal tube spectrum measurement is greater than 24 D away from the pipe inlet and the radial position is above the vertical axis.When the axial position of inclined tube spectrum measurement is greater than 23 D away from the pipe inlet and the radial position is above the vertical axis,it is the best measurement position.The axial position of vertical tube spectral measurement is between 5D to 20 D away from the inlet of the tube,which is the best measurement position,and the radial position does not need to be considered.Through the optical path simulation,it can be verified that luminous flux at the best installation position is between 48% and 96% under the condition of low water content and high water content.To predict the oil content of unknown two-phase flow,the prediction models of oil content of crude oil,mixed oil and oil-water two-phase liquid are established by nonlinear modeling method,and the performance of the model is evaluated.The K-S method is used to divide the sample set of the original sample data of crude oil,mixed oil and oil-water two-phase liquid,and the characteristic samples that can be used for modeling are selected through the CARS+SPA combination algorithm.The quantitative prediction model of oil content is established by ELM method.The average goodness of fit of oil content prediction is 0.993,and the RPD is 6.5599.The highest goodness of fit can reach 0.9963 and the maximum RPD can reach 8.2891.In order to realize the real-time on-line measurement of oil content,by improving the temperature characteristics of the prediction model,the performance of the dynamic test system is further optimized,and the device design that can be used for field test is realized.In order to realize the dynamic detection of oil content of oil-water two-phase pipe flow,a test platform and online test system are built.The dynamic test and data analysis of oil content measurement of oil-water two-phase pipe flow with different content and flow rate are carried out.It is verified that the measurement error can be controlled between 0.11% ～ 6.53%.Through the temperature fitting of refractive index and reflectivity at different temperatures,the prediction model is further optimized.After improvement,the fitting accuracy is0.9974 and 0.9981 respectively,which realizes the correction of the prediction model of oil content at different temperatures.According to the on-site working conditions,two infrared detection device schemes of oil content of oil-water two-phase pipe flow are designed to realize the dynamic on-line measurement of oil-water two-phase pipe flow.