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Drilling reciprocating mud pump, commonly known as the "heart" of drilling, its main function is to circulate drilling mud downhole to remove cuttings from the drill bit during drilling and to power downhole power-driven drilling tools . Pump outlet flow rate is an important parameter that affects drilling efficiency. It is also a parameter that must be optimized in the optimized drilling process. The pressure at the outlet of the pump is very high (usually 20-25MPa), and the mud with high sand content is transported. Ordinary flow meter to measure its flow directly there are two problems; First, the problem of high-pressure seal, the second is mud deposition and clogging problems. Therefore, direct measurement is more difficult.
According to the working principle of the reciprocating pump, the volume of liquid delivered per unit time (ie, the theoretical average flow rate Q of the pump) and the pump piston cross-sectional area S .. the stroke length of the piston 1 and the reciprocating piston The number of times (called the number of pumps or pump number) n. S and I are the structural parameters of the pump, for a given pump is a constant volume, so if you can measure the pump n of n. You can calculate the pump outlet flow.
Key words: flow measurement, mud flow, reciprocating pump, indirect measurement, 1. Pumping number measurement
Because the reciprocating pump's stroke is proportional to the rotational speed of its drive shaft, the number of pump pulses can be calculated by measuring the rotational speed of its drive shaft,
1.1 The working principle of the speed sensor The speed of the pump drive shaft is measured by Hall speed sensor. The structure principle and wiring diagram of Hall speed sensor are shown in Fig. 1 and Fig. 2, respectively.
The stator of the sensor has two Rao groups A and B which are perpendicular to each other. The Hall pieces Ha and Hb are stuck on the center line of the winding. The rotor is a permanent magnet. The excitation motors of the Hall elements Ha and Hb are respectively connected with the winding A And B are connected, their Hall electrodes are connected in series as the output of the sensor.
The following derives the sensor output Hall electromotive force expression. When the permanent magnet rotor rotates, it deforms in the air gap between the rotor and the stator into a barotropic magnetic field that changes sinusoidally with time. The magnetic flux density Bh passing through the Hall element Ha is set to be the same as the winding A spatially with the rear Ha90º , So the magnetic flux density Ba at the winding A is the alternating magnetic field inducing the alternating electromotive force Ea in the winding A by Lenz's law and Ea will generate alternating excitation power in Ha;
Since the Hall element H a itself is also in a magnetic field, a Hall electromotive force will be generated on the Hall electrode;
L1 is the inductance of winding A, R1 is the loop equivalent resistance of winding A and Hall element Ha, K1 is the sensitivity of the Hall element, which is a parameter related to the material and structure of the Hall element.
Similarly, the Hall element Hb space position ahead of Ha90o, while the winding B ahead Hb90 º, the same can be introduced Hb Hall potential Ehb generated so that the total output sensor electromotive force is
It is proportional to the measured speed.
1.2 Speed ​​sensor on-site installation In order to use the speed sensor to measure the speed of the pump drive shaft can be installed on the pump drive shaft pulley or sprocket to drive the rotor speed sensor rotation, this installation is easy and does not affect the pump The normal work.
2. Pump outlet flow calculation Measured after the pump n, can be based on the reciprocating pump structure and mode of action to calculate the theoretical average flow Q export.
For single-cylinder single-acting pump, the theoretical average flow rate is
Q = Sln (m3 / min) = Sln / 60 (m3 / s)
Where; S for the pump piston area; l piston stroke length.
For multi-cylinder single-acting pump, set the cylinder number M, then the theoretical average flow rate
Q reason = MSln (m3 / min)
For the multi-cylinder double-acting pump, the piston reciprocates once, each liquid cylinder delivers liquid twice and the volume is (2S-S ") where S" is the piston rod cross-sectional area, then the theoretical average flow of M cylinders is
Q = M (2S-S ") ln (m3 / min)
In the actual measurement found that the reciprocating mud pump work, due to the suction valve and the exclusion valve is not closed in time, the valve, piston and other honey out of a high-pressure liquid loss of the humble; pump cylinder or liquid containing gas and other reasons, The actual average flow rate of the pump Q is lower than the theoretical average flow rate
Q = aQ theory
Depending on the size of pump work, generally take 0.85-0.95.
3. Conclusion In this paper, the method of indirectly measuring the pump outlet flow rate by measuring the pump's impulse is simple and easy to avoid the problem that the sensor is subjected to high pressure and liquid corrosion in the direct measurement, and the disassembly and assembly is convenient and easy to maintain. The actual Measurement found that when the pump fullness is not high or not constant, the method of measuring the error will increase, so when the measurement accuracy is high, the test should be used to rate the other non-contact measurement methods.
Reciprocating mud pump outlet flow measurement method
Abstract This paper presents a method for measuring the pump outlet flow indirectly by measuring the pump's stroke number. The principle of using the revolution sensor to measure the pump stroke is presented. The calculation formula of pump outlet flow is given.