Stability Analysis of φ56mm Tandem Three-cavity Suction Pump Core Connecting Rod

The analysis of the stability of the hollow connecting rod of the 56mm series three-cavity pump in the oil field machinery Liu Jiankui (The 388th plant of China Shipbuilding Industry Co., Ltd. in Hubei Yidu 443301, will lead to the instability of the hollow connecting rod, resulting in difficulty in sucker rod down Affecting the normal operation of the oil pump.From the mechanical point of view, the stability of the hollow connecting rod was analyzed and calculated, and the relationship between the pump hanging depth and the submergence degree was given, which was helpful to the well selection and operation design of the pump.

Three-cavity pump; Hollow connecting rod; Stability; Analysis: TE933.302: A 6mm series three-cavity pump t1 (hereinafter referred to as three-cavity pump) uses a double pump series structure, in the up and down stroke, can be sucked , Drainage, with a small pump diameter, large displacement, deep pumping and other characteristics. However, the pump's unique structure causes the pump to generate an upward hydraulic feedback force during the down stroke, increasing the downward resistance of the plunger. When the force is large enough, it will cause the hollow connecting rod to buckle and bend, resulting in a sucker rod Under the influence of the normal operation of the three-cavity pump. This paper analyzes and calculates the stability of the hollow connecting rod of a three-cavity oil pump from the mechanical point of view, and gives the relationship between the pumping depth and the sinking degree of the three-cavity oil pump, which can be used to select and lower the three-cavity pump. Pump design time.

1 Three-cavity pumping pump down-stroke hydraulic feedback force analysis Three-cavity pumping pump working state in the next stroke. Under the downward stroke, the lower inlet valve closes and the upper outlet valve opens. The upper column of the upper plunger will produce an upward force F1 on the plunger (as shown in the figure, the middle inlet valve opens, the sink pressure of the pump The plunger produces a downward force F2 (for example) We call F, F2 is the hydraulic feedback force F. When F! is greater than F2, p will block At present, CB25D4, CB6A more than 1 well was first performed The experiment has achieved good results and greatly improved the economic efficiency of each well.Private 2mm hollow rods each with a centralizer worth learning, 42mm hollow rod materials and welding process pass, should be improved;It is recommended to promote the use of DN80mm screw pump Special-purpose wellhead; Using a simplified on-line operating condition monitor, the test item only needs to transmit the axial hydraulic load in real time, and the circumferential shear torque can be used.

Three-cavity Suction Pump Downward Stroke Hydraulic Feedback Force Analysis 2 Mechanical Model and Calculation Formula The three-cavity submersible pump upper and lower plungers are connected in series by a hollow connecting rod. According to the working conditions of the three-cavity oil pump and the hydraulic feedback force analysis of the down stroke, the hollow connecting rod can be regarded as an equal-section column whose one end is hinged and the other end can be moved axially. The mechanical model of the downward stroke of the hollow connecting rod is as follows.

According to the stability condition of the iso-section column, the hydraulic feedback force on the hollow connecting rod can be obtained. nw is the stability factor of the hollow connecting rod.

Hollow link stability critical load Fc is the elastic modulus, N/m2; is the center of the hollow link minimum moment of inertia m4; / is the length of the hollow link, m. the diameter of the rod, m; P is the density of the crude oil, kg/m3 H is the pumping depth of the three-cavity pumping pump, m; h is the three-cavity pumping pump submergence degree, m. The minimum moment of inertia I of the hollow connecting rod center is the foot type (5), the hollow connecting rod of the three-cavity pump is not Unsteady bending can ensure the normal operation of the three-cavity pump.

3 Calculation example Take a 3-millimeter pump 3m stroke as an example. According to the data, the three-cavity pump 3m stroke hollow rod length / = 4.3m, the hollow connecting rod diameter Dz = 0.036m, the hollow connecting rod diameter d (; = 0.028m. According to the mechanical model, check the mechanical design manual can be taken hollow connection Bar safety factor nw- 8, hollow link stability factor 1 = 20.19, hollow connecting rod material 45 steel, elastic modulus E = 2.0X 1011N/m2, assuming crude oil density P = 850kg/m3. The above data into the formula ( 5), can be obtained (HhX516.7m. Similarly, can calculate the three-cavity pump with different stroke (H - Office) values, such as Table 1. Table 1 three-cavity pump with different stroke (H stroke s / m Hollow link length // m 4 Conclusion The three-cavity pump is only suitable for wells with sufficient fluid supply.

In the design of the downhole, the pump can only work normally if the pumping depth and submergence of the three-cavity pump meet the requirements of formula (5).

As can be seen from Table 1, the three-chamber pump is not suitable for long strokes.

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