In the pumping and discharging of coalbed methane, because the discharged water contains a lot of pulverized coal, in ordinary oil pumps, pulverized coal is easily deposited around the fixed valve and stuck to the valve ball and valve seat. After the oil well pump works for a certain period of time, the fixed valve fails, resulting in the sampling pump stopping working. After the pump was stopped, the fixed valve was buried more seriously by pulverized coal, which led to the failure to start the pumping unit.
Aiming at the problems existing in coalbed methane mining in Hancheng block, the common oil well pump is improved. The improved self-cleaning oil pump can automatically clean the pulverized coal deposited around the fixed valve and prolong the service life of the oil pump in the development of coalbed methane wells.
When the static liquid is impacted by the current, the sediments in it will gain energy and move, and will be suspended in the liquid and move with the current. Self-cleaning oil well pump is to use liquid flow to flush the pulverized coal (solid particles) deposited around the fixed valve, so that it is suspended in the liquid. Through the liquid absorption and liquid drainage process of the oil well pump, the pulverized coal is discharged from the oil well pump, thus realizing the self-cleaning function, preventing the fixed valve from failing due to the adhesion and burial of pulverized coal, and realizing the continuous and stable production of coalbed methane wells. Self-cleaning oil pump is mainly suitable for coal-bed gas wells containing pulverized coal and sand-bearing oil wells.
Self-cleaning oil well pump mainly consists of six parts: pump barrel assembly, plunger assembly, pump barrel extension pipe, guide barrel, liquid outlet valve and liquid inlet valve assembly, as shown in Figure 7-27. The pump barrel assembly, the pump barrel extension pipe, the guide barrel and the liquid inlet valve assembly are lowered to the designed depth in the wellbore along with the pumping string, and the plunger assembly and the liquid outlet valve assembly are lowered into the pumping string along with the sucker rod. Among them, the draft tube is the main component of the self-cleaning oil well pump, which is made of round steel by lathe and milling machine. The pass rate of pulverized coal was considered in the initial scheme, but the effect was not obvious after field application because of the large diversion hole area, insufficient sand discharge capacity and excessive sand content in well fluid. In view of the above problems, the following improvements were made: shortening the length of draft tube and reducing the flow area without affecting the passage of pulverized coal, so that the ratio of the flow area of draft tube to the valve seat is about 1.6, so that the deposited pulverized coal can be washed more fully by the liquid flow (Xiong Xianyong, 20 14).
The working principle of self-cleaning oil well pump is shown in Figure 7-28 and Figure 7-29. In the upward stroke, the plunger moves upward, the volume of the lower chamber of the plunger becomes larger, and the pressure of the lower chamber becomes smaller. Under the action of pressure difference, the fixed valve is opened, the upper and lower traveling valves are closed, and formation fluid enters the pump barrel. After formation fluid enters the pump barrel from the fixed valve, the pump barrel is gradually filled with formation fluid until the end of the upstroke. In this process, the formation fluid washes away the sediment, pulverized coal and other particles deposited at the bottom of the pump barrel through the fixed valve diversion device, so that the sediment, pulverized coal and other particles are discharged from the pump barrel with the formation fluid. In the downward stroke, the plunger descends, the volume of the lower cavity of the plunger becomes smaller, and the pressure of the lower cavity becomes larger. Under the action of pressure difference, the fixed valve is closed, the upper and lower floating valves are opened, and the formation fluid enters the upper tubing of the pump barrel through the floating valves until the end of the lower stroke, thus completing a swabbing process.
Figure 7-27 Structure Diagram of Self-cleaning Oil Pump
1-pump barrel assembly; 2- plunger assembly; 3— Liquid outlet valve assembly; 4-pump barrel extension pipe; 5— Draft tube; 6— Inlet valve assembly
Figure 7-28 Schematic diagram of the upper stroke
Figure 7-29 Schematic Diagram of Downstroke
Through the above structural design and working principle, the invention can realize the following functions: in the swabbing process, the fixed valve diversion device guides the flow direction of formation fluid from the fixed valve assembly into the pump barrel, so that the formation fluid washes and cleans mud, sand, pulverized coal and other particles deposited at the bottom of the oil well pump, and solid particles are discharged from the pump barrel through the formation fluid, thus achieving the effect of self-cleaning. A pump barrel extension pipe is added at the lower part of the pump barrel, and its inner diameter is slightly larger than that of the pump barrel. When the plunger moves to the bottom dead center, it can exceed the pump barrel by a certain length, so that the sand accumulated in the pump barrel can be taken out of the pump barrel to protect the working face of the pump barrel and prevent the pump from being stuck. There is a sand scraping groove on the plunger, which can scrape solid particles such as coal powder and sand particles entering the gap between the plunger and the pump barrel into the sand scraping groove, and take them out of the pump barrel when the plunger moves up and down, thus reducing the wear of the pump barrel and prolonging its service life (Xiong Xianyong, 20 14a).
(2) Jet pump
Working principle of jet pump.
Jet pump drainage technology uses high-pressure water as power fluid to drive underground drainage and gas production device to work, and achieves the purpose of drainage and gas production through energy conversion between power fluid and produced fluid. In the process of lifting produced liquid, the liquid velocity of any cross section in the production string is greater than the minimum velocity to ensure the coal powder to rise, thus ensuring the smooth discharge of coal powder with the fluid. The suction port of the drainage gas recovery device goes down to the lower part of the coal seam to ensure that pulverized coal is not buried in the coal seam.
High-pressure water (power liquid) enters the power liquid pipeline from the power liquid tank through the wellhead, and reaches the underground pump body along the power liquid pipeline to drive the underground drainage gas production device to work. The mixed liquid of produced liquid and power liquid reaches the wellhead through the annular space formed by the power liquid pipe and the mixed liquid pipe, and enters the power liquid tank (Figure 7-30) (Zhang Lin, 2008).
Figure 7-30 Schematic diagram of concentric double-tube cavity of jet pump
2. Main structure
The equipment of jet pump drainage technology includes two parts: ground and underground.
The ground part mainly includes: power liquid tank, ground pump, frequency converter, filter, special wellhead, control and metering instruments, etc. The specific process is as follows: First, high-pressure water (power fluid) reaches the well through the power fluid pipeline and one end of the wellhead high-pressure wing through the universal electronic flowmeter. Secondly, the mixed liquid of formation production liquid and power liquid is produced from the other wing of the wellhead, enters the mixed liquid pipeline through the flowmeter, and then enters the mud, sand, water and pulverized coal separation tank. The power liquid is recycled after sedimentation and separation, and the water produced by coal seam enters the sewage pool. Finally, coalbed methane is produced from the casing and enters the gas transmission process after metering (Chen et al., 20 12).
The underground part includes: power liquid pipe, mixed liquid pipe, drainage (pulverized coal) gas generating device, screen pipe, tail pipe, etc. (as shown in figure 7-30).
3. Technical advantages
1) Sand control and pulverized coal prevention
The suction port of the underground pump barrel of the drainage gas recovery device goes down to the lower boundary of the coal seam, so as to ensure that a certain dynamic liquid level can be deeply pumped, and coal powder and mud sand will not bury the coal seam. In addition, a wire-wound sieve tube with a slit width of 1.8mm is installed at the formation fluid inlet of the downhole pump to prevent large solid particles from blocking the flow passage of the downhole pump and affecting the normal work of the downhole pump. Choosing reasonable working parameters of downhole pump according to the diameters of sediment and pulverized coal can ensure that pulverized coal and sediment can be discharged to the ground.
2) Non-eccentric grinding without moving parts
Compared with the conventional sucker rod pump drainage equipment, there are no rod parts and moving parts in the pipe string structure of jet pump drainage technology, so there is no influence of eccentric wear of the pipe rod.
3) Replace the pump without moving the pipe string.
The downhole pump core is sealed in the working cylinder. When the original well displacement can't meet the production demand or the pump core fails, the surface pumping can be realized only by adjusting the surface valve and changing the inflow of power fluid in the mixed liquid pipe. Put the replaced pump core into the power fluid pipe, restore the inflow direction of power fluid, and seal the pump core to resume production. Therefore, compared with the conventional sucker rod pump drainage equipment, the jet pump drainage equipment can replace the downhole pump without moving the pipe string, and the operation is simple, the time is short, and there is no workover operation cost (Xiong Xianyong, 20 14a).
(3) Electric submersible screw pump
Ground-driven screw pump is prone to problems such as broken rod, worn rod and pipe, and stuck drill, which restricts its further popularization and application (Liu Xinfu, 2009). In this case, the electric submersible pump, which combines the advantages of rodless oil production, downhole drive and screw pump, has been widely concerned.
Electric submersible single screw pump is used for drainage and production of coalbed methane wells in Hancheng block. The drainage and production system consists of ground part, underground part and intermediate connecting part.
The ground part consists of automatic console, autotransformer, ground junction box and wellhead device (Figure 7-3 1). The automatic console can use manual or automatic switches to control the work of the electric submersible pump, and at the same time protect the motor of the electric submersible pump to prevent the motor cable system from short circuit and motor overload.
Fig. 7-3 1 composition of ground part of ESP screw pump
The middle part is composed of cables and oil pipes with special structures. Transmit current from the ground part to the underground part, fix the cable and the outer surface of the tubing together in the gas well, and fix the cable, the single screw pump and the protector shell together in the underground part (Figure 7-32).
Fig. 7-32 Composition of the middle and downhole parts of the ESP.
The downhole part is the main unit of the electric submersible screw pump device, which consists of submersible single screw pump, coupling (with pump suction), protector, reducer and submersible motor, and mainly plays the role of pumping liquid (Figure 7-32).
Main connection conditions of underground part: the output shaft of underground submersible motor is connected with the transmission shaft of bevel gear reducer through spline sleeve; The reducer is connected with the protector shaft through the spline sleeve, and then connected with the pump shaft through the spline sleeve; The oil outlet of the pump is communicated with the oil pipeline through a threaded joint.
Working principle of electric submersible pump: Underground electric submersible pump is composed of rotor and stator (Rao Yu Meng et al., 20 10). Submersible motor drives screw pump shaft to rotate through mechanical reducer and coupling. The rotor and stator mesh to form a continuous sealed chamber. When the rotor rotates in the stator, the cavity moves from the inlet end to the outlet end of the pump, and the liquid in the cavity is pumped from the suction end to the discharge end of the pump, and then transported to the ground through the oil pipe, thus playing a pumping role (Li Fang, 20 1 1).
From the field application effect, ESP has the following advantages. Firstly, there is no power part when the underground system works, so the underground equipment has high reliability, long maintenance period and low cost; Secondly, compared with sucker rod pumps (such as pumping units and screw pumps). ), which is more suitable for deviated wells and horizontal wells, has obvious effect on pump sand sticking caused by sand production and pump sticking caused by pulverized coal production, reduces the number of workovers and reduces the damage of workovers to reservoirs. In addition, ESP also has the advantages of working under complex conditions such as high temperature, high gas-liquid ratio, sand production and corrosion, which can effectively solve the problem of sucker rod fracture or connector damage caused by selecting large pump diameter sucker rod pump in high-yield water wells.
The stator is the most easily damaged pump component of ESP, and the pipe string must be lifted and lowered every time the pump is repaired. One-time investment cost is high; The pump needs fluid lubrication and certain submergence; Compared with the pumping unit, the installation is more complicated. At present, it is mostly used in shallow wells (Xiong Xianyong, 20 14a).
(4) Rod pump
The difference between sucker rod pump and traditional tubular pump is that sucker rod pump is sealed in oil pipe. The sucker rod pump is divided into two parts, one is the sealed support joint connected with the oil pipe, and the other is the sucker rod pump. When running the pump, the sealed support joint goes down to the bottom hole with the tubing, and the sucker rod pump goes down to the bottom hole with the sucker rod and sits on the support joint. When the downhole pump fails due to the influence of pulverized coal, the sucker rod can be directly lifted out of the shaft for replacement, which avoids the need to take out the sucker rod and tubing of the whole well during the operation of conventional tubular pump, realizes the pump inspection with fixed string, shortens the well occupation period and reduces the operation cost.
According to different fixing methods, sucker rod pumps can be divided into top fixing and bottom fixing. The characteristic of the top fixed rod pump is that the discharged liquid can wash the pulverized coal between the top and the oil pipe in time, which has a certain effect of discharging pulverized coal. When the pump cylinder is subjected to liquid pressure, it will increase the gap between the pump cylinder and the plunger and reduce the pump efficiency, so it is not suitable for deep wells. Characteristics of fixed-bottom sucker rod pump: Because the supporting device is fixed at the bottom of the pump, the pump barrel is under external pressure, and the force condition is good, and the pump gap changes little, which is suitable for deep wells, but the pulverized coal is easy to accumulate in the annular space between the pump barrel and the oil pipe, which is not suitable for wells with serious pulverized coal production.
Rod pumps are divided into leather cups and mechanical seals according to different sealing methods. In order to ensure the stability of setting, the coalbed methane well in Hancheng block adopts double-card seal, that is, metal cup double seal. This seal not only has great anchoring force, but also realizes double insurance with double seal (Xiong Xianyue, 20 14a).