Research and Application of Electro-pump Discharge Technology in Coalbed Gas Wells Ren Yuanfeng, Lu Weidong, Feng Yitang (North China Petroleum Administration Bureau, Langfang 065007, Hebei, China), needs to be improved accordingly. This article describes the gradual improvement of electric pump drainage technology including frequency conversion control technology on the basis of 12 electric-pump drainage tests for CBM wells over the past five years, making the electric pump drainage and extraction technology a relatively complete set. CBM well drainage technology.
Langfang City, Wanzhuang - North China Oilfield underground zip code ie065007.-Electronic Foreword China in the 1990s, the electric pump used for high production water CBM well drainage, due to the process is not perfect, the application effect is poor. In recent years, with the continuous increase in exploration and development of coalbed methane, a group of inclined wells, multi-branch horizontal wells, or high-productivity coal-bed gas wells have appeared one after another. Since the discharge pumping process such as tube pump or screw pump has been difficult to meet the production needs, and the electric pump has the features of large displacement, high lift, and wide application range (can be used for inclined wells and horizontal wells), it is used more frequently. In coal bed methane drainage. Compared with the oil production process, the use of electric pumps for CBM drainage has many differences. First, the electric pumps are required to have good controllability, and the displacement of the pump can be adjusted at any time according to the requirements of drainage and drainage, so as to achieve a smooth pressure reduction. The second is that the fluid discharged by the electric pump changes from an oil-water mixture to a gas-water mixture; third, the pumped fluid changes from a single-phase flow to a two-phase flow; and fourth, the production method changes from a tubing production fluid to a tubing drainage and a casing gas production. The fifth is the discharge of fluid containing sand (fracture sand, to 1 it has 2 overload 1 in load fle over (pressure 6u ow lack phase, over Hshi ring House. formation sand) pulverized coal, mud, etc. These different In order to increase the difficulty of drainage and require the use of electric pumps for drainage, relevant technical measures must be improved, such as the introduction of variable frequency speed control systems, improvement of gas-water separation efficiency, prevention of coal powder clogging, and prevention of sand cards. Based on the analysis of the characteristics of coalbed methane drainage and recovery, the principle of electric pump extraction and recovery is analyzed, and the key technologies of coal bed methane drainage, a frequency conversion speed control system and multi-stage gas-water separation technology are broken through, and the main factors influencing the effectiveness of coalbed methane drainage and recovery are achieved. Analyzed, Formulate corresponding measures, and apply them in production, after the actual application of Wuxu 3, Jiji 4, Jixi 6, Jixi 16, Wu 1, Wu M1â€•1 wells, and through continuous improvement, A complete set of coalbed methane drainage technology has been achieved and achieved good results.
2 Principles of electric pump exhaust and recovery and key technologies 21 Principles of electric pump drainage and production process The first stage of the electric-pumping process of the CBM well pump is to put submersible electric pump unit into the well through the tubing. Under the control of the inverter, the electric power passes through the transformer, The frequency converter and power cable enable the downhole motor to drive multi-stage centrifugal pumps for high-speed rotation. The fluid in the well is lifted to the ground through multi-stage rotary gas separators, multi-stage centrifugal pumps, single-flow valves, oil pipes, and gas trees. With the fluid production, the annulus liquid level continues to drop steadily, and the coal seam pressure also decreases steadily. When the coal seam pressure is lower than the desorption pressure of the coalbed methane, the adsorbed gas in the coal seam is largely desorbed. After the gas-water mixture discharged from the oil pipe is separated and metered by the ground process, the coal-bed gas enters the gas transmission pipeline and the water enters the processing station for disposal. A large amount of coalbed methane gas is mainly produced from the casing valve through the oil jacket annular space, and is metered into the gas transmission pipeline.
22 Key technologies of electric pump drainage mining According to the characteristics of coalbed methane drainage, we believe that the key technologies of the coalbed methane electric pump drainage technology are frequency conversion speed control system and centrifugal gas separation technology.
The frequency conversion speed control system requires timely monitoring of the liquid level in the process of coalbed methane drainage and extraction to ensure a steady decrease of the liquid level, in order to achieve a smooth pressure reduction, form a large pressure drop range, and improve the recovery of coalbed methane. The core of the frequency conversion speed control system of the electric pump is the frequency converter. The North China Electric Pump Service Center cooperates with Shandong Fengguang Electronic Instrument Factory to produce a special frequency converter for the electric pump. The inverter consists of three parts: rectifying filter, inverter circuit and CPU. It is applicable to all submersible pumps with working voltage of 600 ~ 2500V. It is equipped with frequency conversion and power frequency two operating conditions, variable frequency operating conditions can easily adjust the frequency to meet the needs of different displacements smooth decompression needs of temperature, short circuit and stall protection, can automatically record and display the downhole motor Three-phase operating current, frequency, voltage and other parameters, and thus higher than other series of inverter reliability, stable performance.
The frequency conversion speed control system of the electric pump has the following advantages: First, it can change the displacement of the pump through convenient frequency modulation to meet the requirements of the smooth liquid drop of the coal bed gas; Second, the soft start feature is obvious, only 2~5Hz at low frequency It can be started, reducing the high current impact on the power system and the pump system during start-up, and prolonging the life of the downhole unit. The third is that the operating frequency design can reach up to 65Hz, so that the electric pump can increase the production capacity by 30% on the original basis. The working range of the pump is greatly improved and the investment is reduced. Fourthly, the rotational speed is adjusted within the rated frequency range. The working torque is constant and will not affect the lift of the pump and improve the efficiency of the electric pump system. Fifth, the energy saving effect is significant. Savings of 15 to 30%, in particular, reduce the demand for grid capacity at startup.
Centrifugal gas separation technology separators are usually used as pump inlets and are fixed to the lower end of the pump. It can separate the dissolved gas and free gas in the water before entering the pump, so that the multi-stage centrifugal pump can effectively work in the gas well to achieve the purpose of improving the pump efficiency. According to indoor and field tests, when the rotational speed reaches 400r/min or more, the gas-water separation effect is good, and it basically meets the technical requirements for coalbed gas well drainage.
The structure of the centrifugal gas separator mainly consists of a shaft, a screw lifter, a low-pressure suction impeller, a guide wheel, a guide impeller, a separator rotor, a cross guide wheel, a housing, and upper and lower joints. Its working principle is: When the fluid in the well passes through the inlet of the separator, the spiral lifter is sent into the low-pressure suction impeller and the guide wheel is pressurized, then it enters the guide impeller, and the guide impeller makes the fluid suddenly change from a spiral state to a linear motion state. Into the separation chamber expansion, centrifugal force generated by the high-speed rotating separator rotor in the separation chamber fling the liquid with high mass to the inner wall of the separation chamber and enter the flow channel of the separation shell for pumping. The lighter weight gas is concentrated in the center, flows along the axis to the diverter shell, and enters the oil jacket annular space from the exhaust hole to complete the separation process.
3 The main factors affecting the pump's effectiveness and solutions The main factors influencing the pump's effectiveness are: gas, coal powder, mud, sand (fracturing sand, ground sand), corrosive media, cable location, pumping Depth and well structure, electric pump selection and other aspects.
1 Rotary two-stage gas separator reduces the effect of gas on the pumping effect in the pocket 0 particles smaller coal sucking pump M water carrying out) linging reserved. Gas can seriously affect the performance of downhole multi-stage centrifugal pump. Research shows that when the ratio of gas to liquid to the centrifugal pump is greater than 10%, the head of the centrifugal pump will be reduced; under the high-speed rotation of the impeller, the dissolved gas will be gradually released, and the gas will appear as the inlet gas continues to increase. The lock causes the pump fluid to suddenly rise or fall, even without liquid, and the pump efficiency is greatly reduced. In order to prevent the coal bed methane from entering the pump and reduce the impact on the pump work efficiency, the following measures can be taken: First, a rotary double-stage gas separator is used. The length of the separator is increased from 600 mm to 1200, and the gas is separated through a stage and then entered again. The separation is continued at the first level. The purpose is to relatively prolong the time for the fluid to enter the pump and to release as much dissolved gas and free gas as possible in the separator. This measure works well. The second is to increase the frequency to 75~85Hz in a short period of time. The speed of the rotor of the separator is increased to improve the separation effect of the rotary gas separator. Third, the pump is pumped into the pocket below the coal seam. The gas out of the coal bed flows out of the annulus under the action of gravity separation; the fourth is the separation. The flow deflector covers the flow direction of the liquid, and the liquid enters the separator from the bottom to the top. The suction inlet is changed to the liquid. The liquid enters the separator from the top down. The inlet gas is separated by gravity and flows out from the annulus to reduce the amount of pump gas. The fifth is to select a reasonable pump type to avoid the use of large-displacement pumps in wells with low fluid yield, resulting in long-term operation of the pump at low speeds. The separator has poor gas separation at low speeds.
32 Influence of corrosive media and solutions Some CBM well fluids often contain highly corrosive sulphides, carbon dioxide, pulverized coal, and high salinity. These corrosive media erode downhole parts of electric pump sets. Severe, often with pitting, perforation, and erosion surfaces of different sizes. In order to reduce the influence of corrosive media, the following methods can be used to solve the problem. First, parts and connecting screws that directly contact with the medium in the pump and separator should be made of stainless steel; second, motors, protectors, pumps, and separators. High-temperature paint shell; third is the use of stainless steel suede cable.
33 Pulverized Coal, Sand, Slurry, and Scale Effects and Solutions Most coal-bed gas wells contain pulverized coal in the water, fracturing wells also contain fracturing sand, and multi-branching horizontal wells will discharge a lot of water at the beginning of discharge. mud. With the operation of the pump, the amount of impurities such as pulverized coal, mud, and scale adhering to the impeller in the pump will increase, leading to a reduction in the area of â€‹â€‹the flow passage, a greater frictional resistance, a higher motor current, and a lower pump displacement. In severe cases, even if the pump is clogged or pumped, the operating efficiency of the pump will obviously be gradually reduced and the pump period will be shortened.
In order to prevent the inhalation of pulverized coal and coal dust, we installed two 60-80 mesh stainless steel screens on the outside of the air-water separator so that the larger particles of coal dust and fracturing sand cannot be sucked into the pump. . At the same time, the single-flow valve and the pressure relief valve are no longer installed in the upper part of the centrifugal pump. The purpose is to stop the pump for a few minutes when the pump displacement is found to be in use. The pressure difference between the internal and external water of the column is used to reverse the flow of the liquid in the column. The pulverized coal inside and outside the filter is washed away to prevent the filter from being smudged. Practice has proved that these measures are effective.
3.4 Influence of cable on annular liquid surface monitoring and its elimination In the process of drainage, echometers are frequently used to monitor the annulus liquid level in order to determine a reasonable drainage system. When the liquid level is measured, it is sounded through the casing and is transmitted to the downhole. When it encounters sound reflection of the tubing section hoop or liquid surface, the ground equipment receives the reflected sound wave. If the cable card is not tight or loose, the sound waves encounter reflections from the cable, affecting the accuracy of the liquid level. In addition, if the cable is close to the side of the sleeve valve, the cable and cable clips also reflect sound waves, affecting the liquid level. It is required that the cable must be firmly clamped and fixed. At the same time, when the wellhead is installed, the oil pipe is rotated to turn the side of the fixed cable away from the casing valve.
3.5 Impact of pumping depth and wellbore structure and countermeasures Coalbed methane drainage requires that the pressure be reduced as much as possible. Generally, it is required to reduce the liquid level to the coal seam, and some require bare coal seams. This requires the pump to be below the coal seam or coal seam. For a perforation or screen completion well, the pump can be placed in an inlet pocket with a pocket length of more than 100 m. Complete the hole for the naked eye, to prevent the collapse of the pump, generally down to the top of the coal seam. Therefore, consider the casing size based on the regional water production and the size of the pump to be pumped. If the outside diameter of the downhole unit does not match the size of the casing, the pump cannot meet the drainage requirements.
3.6 Factors to be taken into account in the selection of electric pumps In the CBM drainage and extraction, electric pump selection and oil extraction are very different. First of all, according to the regional production of water to determine the maximum amount of water under a certain head, the electric pump to meet this requirement during normal operation. When supporting equipment, first consider the maximum density of the effluent. As the water contains more impurities such as pulverized coal, sand, and drilling fluid, its density reaches 1.0g/cm3 or more, and the load increases with respect to the production well under the same conditions. Therefore, when selecting a centrifugal pump, the axial power of the pump must be estimated based on the maximum density of the discharged liquid, so as to ensure that the configured motor is not a small marathon. Secondly, consider the use of a centrifugal pump with a rated displacement higher than the actual production requirement, because the drainage and the oil extraction media will affect the pump displacement. After field measurement and analysis of relevant technical parameters, we obtained a set of feasible empirical formulas for electric pump selection. According to this, the electric pump supporting equipment not only satisfies the production requirements, but also makes the equipment reach a reasonable match. The formula is as follows.
Q: The rated displacement of the pump selected, m3/d; Q: The maximum fluid production required by the freshman production, m3/d P axis = Q amount H amount P water/KP axis - centrifugal pump shaft power, kW; H amount A rated head, m; P liquid a maximum density of discharge liquid, calculated according to 1.1g/cm3; K-coefficient (3) with the rated power of the motor P machine with a rated power of the motor, kW; n machine one Motor operating efficiency, generally 90% (4) Frequency converter rated power P frequency = P machine / 0.85 P frequency A frequency converter rated power, kW; (5) power transformer rated capacity P variable = P frequency / 0.75COS = P frequency / 0. P variable power transformer rated capacity, IKVA; COS order a transformer active power factor, generally 0. 0.75 - that the transformer power supply must be wealthy with the load 4 row Application site bookmark application3 Since 2003, we have applied electric pump drainage technology to Wuxi 1, Ji 4 test, Ji test 6, Ji test 16, Wu test 3, Wu M1 - 1 and other coal bed methane wells, and through Continuous improvement and improvement to adapt it to fracturing and completion of wells, cave completions, horizontal multi-branch coalbed methane wells in different regions and different coals, and to solve high-production wells Drainage problems. The on-site application is shown in Table 1. It is believed that as the exploration and development workload of CBM wells increases, the role of electric pumps in coalbed methane drainage and extraction will become increasingly significant.
Table 1 Field application of electric pump drainage gas recovery process Well number Area Completion mode Pump depth (m) Hydraulic fluid level (m) Maximum daily output Cumulative water production (m3) Gas (m3) Water (m3) Ji 4 Daning Yiji County fracturing 1003. 5 Conclusions The process technology research shows that the electric pump is an ideal drainage equipment that can be well adapted to the technical requirements of various CBM wells. The following conclusions were obtained through field tests.
For high-yield CBM wells, the use of electric pumps for large-displacement and strong drainage will help shorten the time for drainage, accelerate the pressure reduction rate, and reduce the cost of drainage as soon as possible to obtain high gas production.
Frequency conversion speed-regulating electric pump is an ideal drainage equipment. Because it has a large speed adjustment range, the liquid production volume can be adjusted in a wide range, which is conducive to a smooth control of the liquid-dropping speed, thereby achieving a smooth pressure reduction.
For a single well gas test, the electric pump is a high input, high cost drainage method. If it is used for large-scale development, it can greatly reduce the cost and increase the economic benefits of drainage.
The electric pump unit has a complex structure and is difficult to maintain under field conditions. It should be equipped with spare equipment to shorten the time required to maintain the pump when checking the pump and maintain the continuity of the exhaust pump.
In order to prolong the period of the pump inspection and reduce the cost so that the electric pump can operate efficiently for a long time, the electric pump unit should be optimized based on the specific conditions of the well.
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