From the perspective of the development history and production of oil fields in southern Sudan's 1/2/4 area, since the oil fields began to use a large number of submersible pumps in 2000, they have made great contributions to the increase of oil production. However, the vast majority of submersible pumps are currently Well production began to decline. From the perspective of production dynamics, the fluid level of the oil well is relatively high, the liquid level has not been pumped to the pump suction inlet, and the degree of sinking of the pump suction inlet is relatively large. Theoretically, it should not cause a significant drop in oil field production. In order to explain this phenomenon, from the oil well production capacity forecast, the pump design and the well fluid supply situation to analyze several issues, and find the main reason for the decline in production, make the appropriate rectification measures, so that the oil field production can be restored.
2 Well productivity forecast For submersible pump pumping, the oil well production forecast is to calculate the output of the well under submersible pumping conditions in order to select the appropriate submersible pump equipment. In combination with the actual conditions in the oil fields in the southern part of Sudan's 1/2/4 area, the following methods can be used.
Due to the low saturation pressure in the southern part of Sudan's 1/2/4 area, the gas content in the reservoir is very low or substantially free of free gas. Therefore, in the prediction of well productivity, the influence of gas on production forecast may not be considered. In other words, the seepage in the oil layer is pure liquid percolation, that is, pure oil-phase percolation or oil-water percolation. Therefore, the relationship between oil well production and downhole flow pressure follows the oil production index formula, namely: Pwf bottom flow pressure, psi; is the calculation diagram of the total dynamic pressure head of the well.
The degree is Hz, the oil pressure conversion head p(m), the sleeve pressure conversion pressure head pc(m), the friction loss of the oil pipe pressure head Ft(m), the total oil pressure head H(m), the pump inlet submergence Hb(m). Lm water column = 1.42233 psi. First, calculate the bottom flow pressure: fw - moisture content, Y - the relative density of crude oil.
Then, according to the calculation formula of the oil recovery index, the oil well output under the pumping conditions of the submersible pump is calculated: Take UN-22 well as an example. The known depth of the oil layer is Hz = force PR = 2230 psi; the density of crude oil is Â¥. = 0.86; oil pressure conversion head p = 100m; set pressure conversion pressure head pc = 0; oil pipe friction loss Ft = 100m. Calculate the well fluid density based on the water content: calculate the bottom hole flow pressure: calculated in the submersible pump Oil well production under pumping conditions: 3 Submersible electric pump selection design calculations In order to reasonably select the submersible electric pump to make it run most reliably and economically, the following principles must be followed when selecting the pump design: 1 The pump must be made Work at the highest efficiency point or near the highest efficiency point to maximize the pump efficiency; the pump displacement and the oil well productivity are matched, and the head lift must be equal to the total head pressure of the oil well; the output power of the submersible motor must be able to Meet the power requirements of the pump to lift the liquid.
First, choose the pump model based on the predicted well productivity. According to the calculation result of Example 1, the GN4000 pump can be selected. The optimal displacement range is 2400 4400 bbl/d. The maximum efficiency point displacement is the second, the total dynamic pressure head of the well is calculated, and the required number of pump stages is calculated. The total dynamic head of the well can be calculated using the following formula: According to the data given in Example 1, calculate the total head pressure of the well: Calculate the total number of stages required for the pump: Total number of stages of the pump = H/Pump single In the third stage, the shaft power of the pump is calculated: pump shaft power = single machine power X total series x well fluid density In the actual calculation, the required motor power should take into account the mechanical power loss of the suction inlet and the protector. Under normal circumstances, the mechanical power loss of each protector is 10kW, and the mechanical power loss at the inlet is 0510kW. According to the above calculation results, the motor power is 146.5kW. In addition, in practical applications, the power supply quality of the power supply network must be combined. Taking into account possible network voltage fluctuations, the motor power can be selected by 120%, so that the motor power is 176kW, and a motor with a power of 210kW can be selected.
The above result is calculated when the power supply frequency is 50Hz. If the need of frequency increase is taken into account in the future, the following relational equations can be used to calculate: - The pump displacement at 50Hz and the new frequency, bbl/d; 50Hz and the new frequency of the head, m; 50Hz and the new frequency of the motor output power, the submersible pump used in the well supporting the pump model is GN5200, the number of stages is 171; motor power is 210kW; operating frequency Calculate and analyze the well using GN5200 pump, displacement range is 2800~6000bbl/d, the best working condition point (high efficiency point) displacement is if the well fluid supply is adequate, and the pump design is reasonable, well productivity and total Dynamic pressure head and pump displacement and head matching, then the pump should work at or near the highest efficiency, production should be around 4400bbl/d (50Hz), then the degree of sunk should be about 1087.5m.
Now, the following analysis and calculation can be performed in conjunction with the actual production conditions of the well: First, calculate the well bottom flow pressure under the current production conditions for the well as follows: Second, calculate the theoretical yield under current production conditions: Third, calculate In the current production situation, the total head pressure of the oil well and the required head lift are: the required head lift = total head pressure/stage of oil well. Finally, according to the calculated head lift, the pump characteristic curve is checked and the pump is obtained. The theoretical displacement is 1887bbl/d. It can be seen from the above calculations that although the calculated well productivity and pump displacement have an error with the actual well output, it basically reflects the situation of the well fluid supply and the working status of the pump. .
It can be analyzed in this way: On the one hand, due to the low number of pumps in the design of the pump, the theoretical head of the pump is low. Then the pump lifts the liquid to the ground and the required degree of subsidence is large, resulting in bottom-hole flow. The pressure increases, the production pressure difference decreases, and the amount of liquid produced in the formation decreases. On the other hand, because the amount of liquid generated in the formation is small and the pumping needs cannot be met, the hydraulic fluid level of the well becomes lower and the degree of sinking becomes more and more. Smaller, the actual lifting height of the pump increases, and the pump displacement decreases. At this time, due to the decrease in the degree of sinking, the flow pressure at the bottom of the well is reduced, the production pressure difference is increased, and the amount of liquid discharged from the formation is increased again. In the end, there will be a balance point. The amount of liquid in the formation and the pumping capacity will be in balance, and production data such as output, liquid level, and oil pressure will tend to stabilize. If there are changes in the oil well parameters or operating frequency, such as formation pressure and oil pressure, resulting in changes in the fluid supply capacity of the well or the displacement and lift of the pump, a new equilibrium point will appear and the well output, fluid level, etc. It will also change.
The above calculations are performed without the pump running normally. If the well fluid supply is insufficient, the output will be too low, it will cause the pump under the skirt to accelerate wear, long-term operation will lead to increased pump leakage loss, pumping efficiency is greatly reduced, so that the pump displacement and lift significantly reduced, the actual output of the well will It is much lower than the calculated value.
5 Measures Taken Through the optimization of the above submersible pumps and the analysis of their effectiveness, there are two reasons for the low output of the submersible pump wells, which is the relatively low productivity of the wells, relative to the special specifications of the submersible Insufficient fluid supply for electric pump equipment; Second, mechanical failure of the submersible pump, the pump guide vanes do not work or the pump efficiency is reduced, resulting in a decrease in the pump displacement.
The following measures have been taken to re-optimize the design of all electric submersible pump wells in the South Sudan oilfield in the 1/2/4 area: For oil wells with reduced fluid supply, redesign is used to use small-displacement submersible pumps to generate formations. Liquid volume and pumping capacity are in balance, and production data such as output, liquid level, and oil pressure will tend to stabilize. At the same time, when the output value is lower than the minimum displacement value of the pump, on the one hand, the wear of the submersible pump will be accelerated, the submersible electric pump unit will not be able to operate normally, the efficiency of the pump will gradually decrease, and the output of the submersible electric pump well will become lower and lower. On the other hand, due to the mechanical failure caused by the pump wear, it will lead to electrical failure of the submersible pump equipment, and ultimately make the submersible pump equipment can not run properly.
For oil wells with increasing fluid supply, if the pumping and kilograms have the same depth, increase the number of pump stages or increase the operating frequency, pump the liquid level to the pump inlet, and the output of the well will increase for the moment, or redesign for larger rows. Quantity of submersible pumps.
For the mechanical failure of the submersible pump, the impeller of the pump does not work or the pump efficiency is reduced. As a result, the displacement of the pump is reduced, the well is operated in time, and the electric pump is repaired or replaced.
For oil-submersible pumps where the amount of liquid supply cannot meet the minimum size, oil wells are intermittently produced.
By adopting the above four measures, the output of oil fields in the southern part of Sudan's 1/2/4 area has increased by 8%, and good economic benefits have been achieved.
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