1 Working principle of electromagnetic flowmeter
Electromagnetic flowmeter based on the principle of Faraday electromagnetic induction [1], Figure 1 shows the basic working principle of the electromagnetic flowmeter. When the conductive fluid flowing through the measuring conduit is moved with the flow velocity v as the magnetic field line with the cutting magnetic flux density B, as shown in FIG. 1, the voltage U generated by the induced electromotive force E detected between the pair of detecting electrodes can be expressed as follows: Said:
U=K·B·D·v (1)
In the formula, U is the signal voltage between two detection electrodes, V; B is the magnetic flux density, T; D is the inner diameter of the measurement catheter, m; v is the average flow velocity, m/s; K is the proportionality constant.
The instantaneous volumetric flow Q (m3/h) measured by measuring the catheter is:
Q=( π· D)/(4·K·B)·U (2)
Since the measuring tube has a fixed inner diameter and the excitation current is constant, the magnetic flux density B is also constant. Therefore, U and Q have a linear relationship. Therefore, the volume flow rate is proportional to the signal voltage between the electrodes. This value is measured and converted by the circuit. Out of volume flow Q.
2 electromagnetic flowmeter features
The electromagnetic flowmeter is a high-precision downhole flow measurement instrument, which calculates the flow rate by measuring the flow rate of the conductive liquid in the probe tube of the instrument by internal magnetic or external magnetic method. It has no mechanical moving parts nor throttling parts, so it is almost in measurement. No pressure loss, simple operation, good reliability, high measurement accuracy (measurement accuracy can reach 0.5% relative measurement error, special calibration or special manufacturing accuracy can be higher), zero drift, wide range, start row With small amount and no sand, the measurement results are not influenced by the temperature, viscosity, density, pressure, and liquid-solid ratio of the fluid. When the conductivity changes within a large range, it will not affect the measurement results.
3 electromagnetic flowmeter logging data interpretation method
In view of the above characteristics, electromagnetic flowmeters are widely used in the measurement of oil-well and well-well conducting liquid injection profiles or in the detection of wells, such as the measurement of a series of well logging items such as water absorption profile, water search, and leak detection [2].
Electromagnetic flowmeters are instruments that directly measure fluid flow, so the measured flow can be read directly. When turbine flowmeters are used to obtain flow, they first need to undergo a large number of linear regression and formula calculations. The calculations are cumbersome and the accuracy is not high, which makes it difficult to interpret the data.
Calculate the scalar by formula:
Δ f=fi-fo
In the formula, Δ f is the standard deviation; Fi is the measuring frequency value; Fo is zero frequency.
Then by looking up the table to get the number of words per square, you can get the ground traffic value:
Q= Δ f/k
In the formula, Q is the ground flow value; Δf is the standard deviation; k is the number of words per square. This shows that the use of electromagnetic flowmeter to calculate the fluid flow, the method is simple and high precision. Because the electromagnetic flowmeter is a full-section sampling measurement, that is, each fluid particle passes through the working magnetic field and cuts the magnetic force line to generate the induced current electromotive force, instead of only measuring the velocity of the local cross section, the accuracy of the logging data is greatly improved. It provides a reliable basis for the dynamic monitoring of oil and water wells in the oil field.
Logging data processing and interpretation use developed microcomputer software, which has high reading accuracy, easy operation, accurate calculation, and reliable interpretation.
4 Application of Electromagnetic Flowmeters in Production Logging
4.1 Application in Water-absorption Profile Logging
The water absorption profile logging series made up of electromagnetic flowmeters is not affected by isotope contamination and isotope distribution. The water absorption capacity of the constrained layer can be calculated, and the "macroporous stratum" and the lost layer can be quantitatively identified. The interpretation accuracy of the water absorption profile logging data [3].
For example: Figure 2 is a five-parameter water-absorption profile log from Well 33-XX. The log was blocked at 2690m, and the 10th, 11th, and 12th layers were not measured, but the electromagnetic flowmeter logs show that these 3 Absorbed by the barrier layer, the absolute water absorption is 74.6m3/d, and the relative water absorption is 41.2%.
4.2 Application in Engineering Water Search and Leakage Logging
The engineering water-logging logging series composed of electromagnetic flowmeters has a small start-up displacement and is not influenced by well conditions such as well inclination and sand discharge in the well. It can identify all primary and secondary effluent layers and the accuracy of quantitative interpretation of logging data. high.
The series of engineering leak detection logs composed of electromagnetic flowmeters has high accuracy in the quantitative calculation of logging data, especially in the application of leak detection logging in oil wells, and is not influenced by the quality of injected water. A single logging tool can find one or Multiple leaks, find the location of the leak is accurate and reliable.
5 Conclusion
In the actual logging, the electromagnetic flow downhole logging tool not only eliminates the effects of factors such as well inclination, well fouling, and formation pollution, but also solves the problem of quantitative interpretation of water absorption and loss of water from the small displacement, and also makes it difficult for the resistance layer and the plug. The problem of quantitative interpretation of water absorption and spiting in the subsurface layer is solved, the instrument has high measurement accuracy, and the data interpretation method is simple and practical.
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