Most of the domestic oilfields have entered the period of high water cut. Conventional plunger pumps are one of the major oil recovery methods. Due to factors such as high sand content, high water content and high temperature steam heavy oil exploitation, polymer injection and strong corrosive media environment and poor well conditions, the average time for piston pump repair is shorter and shorter, and some are even less than 30 Day you need to check the pump, seriously affecting the comprehensive economic benefits of oil field development. The reasons for the failure of the plunger pump in each oilfield are different, and are combined into the following factors: oil well water discharge, sand production, composition of injection, degree of salinity, bottom hole temperature, corrosion rate of effluent, well structure and Plunger pump itself structure, plunger and pump cylinder surface treatment and surface materials. The main reasons for failure are:
Sedimentation of sand grains in the pipe string: when the sand volume of the oil well is large and the water content is high, sand in the formation oil is mixed in the formation water. Since the carrying capacity of different media is proportional to the viscosity of the medium, the viscosity of the crude oil is far greater than the viscosity of the formation water. The formation water has poor sand carrying capacity at the same flow rate, and some sand particles will sink under gravity, Cause card pump and sand buried. Before the pump is completely stuck, the relative movement of the plunger and the barrel can cause scratches on the surface of the plunger and the inner surface of the barrel. Large amounts of scratches can reduce the pump efficiency.
Wear and corrosion double role: If the sand into the barrel and plunger between the plunger and pump cylinder surface wear increased, if the surface layer of the substrate exposed after wear and tear, due to the well electrolyte of the electrolyte and weak acid, the core extremely easy Corroded and worn. In addition, the general pressure difference between the two ends of the piston is 7-14MPa, in the high pressure drop, sand-containing liquid will produce hydraulic cutting plunger and pump cylinder, exacerbate wear and tear.
Plunger and pump cylinder fouling: If the injection of water untreated recycling, coupled with some oilfield water injection has been unable to meet the enhanced oil recovery and the use of polymer injection, so that downhole fluid composition becomes more The more complex and the more mineralized it is, the more likely it is to scale on the plunger and barrel. When deposits on the surface of the plunger and pump cylinder become denser and the adhesion becomes stronger, the hazard increases. In some areas, the typical plunger pump pickup cycle has been reduced from 300 days to 30 days due to fouling.
Suction pump structure: Ordinary sucker pump in the structure without any sand scraper measures, and the plunger end has a cone surface, sucker pump reciprocating process, making the sand directly to the piston and cylinder clearance settlement, And sucker rod on the sand control tank only with sand and sand scraping performance, the sand tank grit removal is not considered, after the sand tank sand control, the same will cause the piston pump cylinder wear.
Surface Treatment and Material Selection of Pistons and Cylinders: Investigations have shown that the selection of the pump plunger and barrel surface preparation processes and materials can significantly change the service life of the pump. The plunger and pump barrel are a pair of friction pairs. Studies have shown that the friction coefficient between the plunger and barrel surface material and the sand particles can also affect whether the sand particles will get stuck in the gap between the plunger and the pump barrel.
Versailles Versailles Ball wear and tear corrosion: sucker rod through the swimming valve and the piston connected to the reciprocating motion of the piston valve cover makes the valve carrying a load of varying sizes of asymmetric stress in the valve opening and closing process, continuous The impact caused the valve wall wear and fatigue damage. As the outlet of well fluid, the gas mask is affected by the erosion and erosion of the liquid flow due to the change of the direction of the liquid flow, eventually resulting in failure of the fracture. Versaille seat due to long-term fluid and solid erosion, can also lead to sealing surface failure.
Piston and pump cylinder clearance: plunger and pump cylinder with the reciprocating movement of the clearance fit. The relative movement of the pump barrel and the plunger relies on the sealing effect of the small clearance between the mating surfaces, and at the same time, this slight clearance ensures that there is always a certain amount of liquid loss between the plunger and the pump barrel for lubrication and cooling. For certain well conditions, the pump gap is an important technical parameter of the pump, the size of the pump gap directly affects the efficiency of the pump, affecting the pump cycle.
Downhole tube string partial wear and corrosion: due to various factors lead to tubing, sucker rod, centralizer, sucker rod coupling and other wear and corrosion, if wear and corrosion products such as iron slag, tubing coating flaking deposition in the pump On, resulting in card pump and Versail not leak after sealing.
Pumping depth: deepening of the well pump will make the pump to withstand the load increases, making the plunger and pump cylinder pressure and friction increases, the fluid on the plunger and pump cylinder hydraulic erosion will Increase, coupled with the above other factors, pump failure will speed up.
Well body structure: As the pump cylinder length of about 4-9 meters, if the hanging pump section shaft is not vertical, such as horizontal wells, inclined shafts or dogleg at the cylinder may be deformed or partial contact with the plunger and the barrel Will increase the plunger and pump barrel between the local wear and corrosion.
Downhole temperature and pressure: Downhole temperature has an indirect effect, such as affecting the plunger and pump cylinder corrosion rate, affecting the speed of scaling, and even affect the deformation of the cylinder easy.
Can be seen from the above, plunger pump failure due to many reasons, should be based on the specific well to identify the main reasons and take appropriate measures.
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