Research on a New Flow Measurement for Intelligent Injection Tools

Intelligent separate injection technology can achieve continuous monitoring data of layered water Injection wells. So it can find out the inefficient water circulating formation timely. Then the water injection schemes can be adjusted in real-time to ensure the high water injection pass rate. It can also increase the working efficiency of the workers’ because of its automatic mode. But its prime cost is high, which limits its large-scale industrialization application in fine layered water injection wells. The key part is the intelligent water distributor in the intelligent separate injection technology. The cost of electromagnetic flow meter accounts for 38% in the intelligent water distributor. The paper intends to research on flow measurement without flow meter to reduce the high-cost. The pressure difference equation was established for flow rate and the opening ratio of the nozzle using the dimensionless analysis method. The empirical parameters of the equation were obtained through laboratory experiments. The pressure sensors are used to monitor the pressure of water injection wells while achieving the measurement of layered flow rate. The laboratory experiments results indicate that the calculated flow rate obtained by this method coincides well with the standard flow rate. The relative error is less than 12%. Then,it provides a new flow measurement method for intelligent injection tools. The most significant feature is that the flow meter is no longer mandatory for intelligent water distributors. Due to the cheaper cost that it provides a technical support for the large-scale industrialization application of intelligent separate injection technology in fine layered water injection wells.


Foreword
Daqing oilfield is in the later stage of petroleum extraction with ultra-high water cut.Displacement field changes frequently.It leads to severe ineffective water circulation or failure to achieve the expected flow rate of layered water injection.Therefore, long-term monitoring of injection flow rate,formation pressure and other parameters are required to adjust the injection scheme effectively in real-time [1][2][3][4] .In order to control water cut and slow down the decline rate of oil production, the number of water wells and separate injection intervals in a single water well increases year by year gradually.And the testing and adjustment cycle is continuous shortening too.So the existing troops and equipment can't meet the requirements for layered water wells testing.Therefore, Daqing oilfield is actively developing intelligent separate injection technology, which utilizes mechanical-electrical

Intelligent Water Distributor
The key part is the intelligent water distributor in the intelligent separate injection technology.The intelligent distributor is composed of Mechanical structure, Electromagnetic flow meter, Pressure Gage,flow control valves, Upper cable connector, Lower cable connector,etc.Shown in Figure1.Power supply for the intelligent water distributor is sent from the ground control box and transmitted through cables to each power consuming unit.At the same time,the distributor receives operating instructions from the ground control box to measure and control the fine layered flow rate with manual or automatic allocation in water injection wells [5][6][7][8] .The cost of electromagnetic flow meter accounts for 38% of the total cost of intelligent water distributors.If flow rate measurement can be realized without flow meter,the cost of intelligent water distributors will be greatly reduced.The paper intends to construct an empirical calculation equation for pressure difference, flow rate and the opening ratio of the water nozzle using the dimensionless analysis method.The empirical parameters of the equation are obtained through laboratory experiments.When the water flows through the nozzle the pressure difference is measured by the existing pressure gauges in the intelligent water distributor.The water flow rate is calculated by the constructed equation using the pressure difference.So the pressure gauges are used to monitor the pressure of water injection wells while achieving the measurement of the flow rate.The flow meter is canceled without adding other accessories to achieve the purpose of layered flow measurement for water injection wells.

3.1.Dimensional Analysis
The theory of dimensional analysis plays an extremely important role in both scientific research and engineering problem analysis.Especially for strong nonlinear problems such as fluid mechanics, it is difficult to give analytical solutions from a theoretical perspective.Through dimensional analysis, the relationship between various variables can be correctly analyzed.A complete and correct physical equation should be composed of dimensionless terms.It can greatly simplify problems and establish scientific and accurate similarity models.
Dimensions that characterize the properties and categories of various physical quantities are called physical quantities.Dimensions can be divided into basic dimensions and derived dimensions.The bas ic dimension is independent.If the dimension of a physical quantity can be reduced to zero, that is x is dimensionless, numerical that not affected by the scale of motion and can perform transcendental function operations [10] .

Empirical Calculation Criterion Equation
2 Intelligent distributor withou flow meter The design of an intelligent water distributor without flow meter is shown in Figure .2.Two pressure sensors front and after the water nozzle are arranged in the annular sealed chamber.The two pressure sensors can perform two functions.One is to observe the changes in tubing and formation pressure for seal testing and adjustment.The other is to provide a pressure difference front and after the water nozzle to the control system.Then,the control system automatically calculates and adjusts the opening value of the flow control valve based on the targeted injection flow rate.
The factors that affect the characteristic of the water flowing through the water nozzle in the intelligent distributor without flow meter are: the density of the water ρ,average injection rate ν, opening ratio of the water nozzle α,diameter of the injection pipeline D before the water nozzle, dynamic viscosity of water μ.
The physical parameter of pressure drop ΔP when the water flows through the water nozzle can be composed of the following five independent quantities, which can be written as: 3 basic physical quantities were selected from the above 6 physical quantities: D, ν,ρ.These three quantities involve the three basic dimensions of [M,L,T].Being calculated and verified,the three basic physical quantities listed above are independent and can't form dimensionless quantities.
According to the π theorem, three dimensionless π terms can be written.Then the criterion equation can be obtained: . Based on the principle of dimensional harmony,it can be obtained: Where μ/ρνD is the reciprocal of Reynolds number (Re), it can be expressed as: Owing to ρ=γ/g and h f =ΔP/γ,where γ is the gravity of the water,g is gravitational acceleration,h f is friction head loss, it also can be expressed as: Where λ=2f 2 (α,Re) known as the friction coefficient is dimensionless quantity.It can be obtained through regression analysis of experimental data and then put into formula (5) where λ is further transformed into the flow rate through the water nozzle.The flow rate is related to the opening ratio of the water nozzle and the pressure drop of the water flowing through the water nozzle.

4.1.Laboratory Inspection and Calibration System
The flowchart of the laboratory inspection and calibration system is shown in Figure .3.It consists of an injection system, experimental automatic control,data acquisition and processing system,oil and water automatic metering system, pressure back system, supporting auxiliary system,etc.
This system can simulate the actual working conditions on-site and monitor real-time production data.So it can intuitively evaluate the working performance of the intelligent injection distributor in the well.
Connect the intelligent water distributor without flow meter to the test-bed, it can obtain the pressure difference and flow data at different water nozzle opening ratio and then regress the friction coefficient.

4.2.Experimental Data
Ten sets data of pressure difference and flow rate are obtained for ten water nozzle opening ratio ranging from 35% to100%.Use software to perform regression analysis on the processed data.And the friction coefficient at different water nozzle opening ratio can be calculated.Then the basic expression of the flow rate can be obtained, that is: ,where Q is the calculated flow rate of water through the water nozzle, ΔP is pressure drop when the water flows through the water nozzle,α is the opening ratio of water nozzle,k,d and f are the regression coefficients regressing the friction coefficient λ with formula (5).Some regression calculation data is shown in Table 1.In order to prevent the sand plugging the water nozzle,the nozzle shape of outlet is designed with a structure of a slender rectangle connected to a large rectangle shown in Figure .4.The flow rate through the slender rectangular outlet basically covers the values used commonly for layered water injection.The flow rate through the water nozzle increases suddenly when the large rectangular outlet starts to work.The sand blockage will be removed by the impact force of the sudden increase in water volume.

Table1. Some experimental data
When the large rectangular outlet begins to work, the nozzle opening ratio is approximately 80%.Therefore, the experimental data is divided into two parts for regression analysis based on the nozzle opening ratio,which are 35-70% and 80-100%.

Analysis on Experimental Data
On the basis of fluid theory, when the water flows through the nozzle the flow rate is linearly related to the square root of the pressure difference.According to the pattern to perform the data analysis.Figure. 5 and Figure.6 show the experimental results with nozzle opening ratio of 35-70% and 80-100% respectively.The horizontal axis in the Figures represents the square root of the pressure difference front and after the water nozzle,and the vertical axis represents the flow rate passing through the water nozzle.In the Figures ,the data points represent the standard flow rate measured by the flow meter in the laboratory inspection and calibration system, the data lines represent the calculated flow rate passing through the water nozzle based on empirical calculation criteria equation.
Figure .5 shows a good linear relationship between the square root of the pressure difference and the flow rate when the nozzle opening ratio is 35-70%.And the calculated flow rate and standard flow rate coincide well.Figure .7 is a summary of the relative errors between the calculated flow rate and the standard flow rate with all opening ratio.It can be seen that the proportion of relative errors within 12% is 92.52%.And the proportion of low relative errors within 5% is 64.49%.By analyzing the data,it was found that experimental data with relative error more than 12% basically existed in experimental conditions with the opening ratio of 80~100%.
when the nozzle opening ratio is 35~70% ,the range of the flow rate through the water nozzle basically covers the values used commonly for layered water injection.So it indicates that the purpose of measuring the layered flow rate in water injection wells without a flow meter can be achieved according to the empirical calculation criterion equation.
Figure .6shows that it is a significant deviation between the calculated flow rate and the standard flow rate.The main reason is that the large rectangular outlet is working when the nozzle opening ratio exceeds 80%.The flow rate through the nozzle increases suddenly, which results in the poor linearity of flow rate.If the flow rate is necessary within the range in the injection wells, the design of the nozzle outlet shape needs to be improved.The paper constructed an empirical calculation equation of the pressure difference for flow rate and the opening ratio of the nozzle using the dimensionless analysis method.The empirical parameters of the equation were obtained through laboratory experiments.When the water flows through the nozzle the pressure difference is measured by the existing pressure gauges in the intelligent water distributor.And the water flow rate through the nozzle can be calculated using the equation.The experimental results indicate that this flow measurement method can achieve the goal of measuring the flow rate in fine layered water injection wells with the intelligent water distributor without a flow meter.
2)The successful implementation of this flow measurement method can significantly reduce the cost of the intelligent separate injection technology.And it can make the technology achieve low cost,multiple layers,continuous ,real-time measurement and adjustment for fine layered intelligent 3) The friction coefficient obtained from the experimental data in the laboratory inspection and calibration system may be different from the actual friction coefficient in the actual water injection wells.The difference may affect the value of the regression empirical parameters not the form of the basic expression of the equation.In future ,we will consider implementing real-time correction of regression empirical parameters based on actual well conditions to improve the accuracy of this flow measurement method.

Figure. 1
Figure.1 Structural diagram of intelligent water distributor 1 Upper cable connector 2 Electromagnetic flow meter 3 Flow control valve 4 Pressure gauge circuit sealing chamber 5 Lower cable connector 3. Theoretical Analysis of Flow Rate Measurement

Figure. 4
Figure.4 Schematic diagram of the water nozzle outlet shape

Figure. 5 Figure. 7
Figure.5 experimental results with nozzle opening ratio of 35~70% water injection.So it provides a technical support for the large-scale application of the intelligent separate injection technology.