1.1 Analysis of Pump Inspection Causes:
Casing failure has produced the biggest number of Deep-Well Sucker Rod Pump issues which lead to more than 50% of all pump inspections. Among these, the major causes are the broken traveling valve cover, pump leakage, and the bleeder problems.
The traveling valve cover is the one that connects the sucker rod and the Sucker Rod Pump and at the same time assures that liquid is pumped out from the piston. The upward pull of the sucker rod, the weight of the sucker rod itself, and the friction between the pump barrel and the piston are the factors that the cover faces during production.
In theory, the piston's forces during the up and down strokes should be working along the same line and that should be the centerline of the sucker rod and pump. But in real production, because of the well deviation or vibrations caused by the bending of the lower tubing due to the alternating loads on the sucker rod, the piston is getting forces that are different from the vertical position of the pump and sucker rod centerlines, thus creating a lateral inertial load.
Combining this lateral inertial load with gravity that is not going along the ideal pump centerline, the center of gravity moves and thus the piston has to generate two moments during its downward stroke centered on the floating valve: one that is produced by gravity and the other by the lateral load.
Friction between piston and pump bushing automatically increases to maintain torque balance and that lever arm of the sucker rod's gravity, and thus the gravity-generated moment, is increased, too. These two moments alternate in each stroke, thus the fatigue strength of the floating valve is significantly increased, and there is a strong possibility that the pull rod will be opened from the floating valve.
Analysis of Pump Leakage Causes:
① The pump valve and assembly met the quality requirements of the deep wells downhole environment, but the problem is that grooves are formed on the contact surface between the valve seat and the valve ball due to deep wells, which results in the poor sealing of the valve ball and leakage;
② Sand and wax in the well badly impact the pump. Sand and wax deposit on the contact surface between the valve ball and the seat, thus causing damage and leakage;
③ Foreign objects entering the pump will cause leakage.
Analysis of Oil Flush Device Problems:
The oil flushing device problem is a havrowing issue pin breaking being the leading cause. Mostly fringing poor quality/substandard materials, the unproper process utilization and assembly are the major reasons of pins breaking in oil flush devices.
1.2 Analysis of Pump Inspection Causes Due to Tubing Problems:
① Alternating loads on the sucker rod cause longitudinal bending of the lower part. Also, the rod wears against the inner wall of the tubing, and as a result, tubing damage occurs;
② Due to well deviation the inner and outer sides of the tubing wear unevenly and as a result, there is tubing leakage. During the upstroke, well inclination causes the sucker rod to bend and rub against the tubing wall, thereby causing uneven wear.During the downstroke, the combined influences of different resistances and gravity inside the tubing result in the bending of the sucker rod which causes it to rub against the tubing wall. At the same time, the tubing also rubs against the casing wall which may eventually cause tubing wear and leakage. ③ Leakage caused by tubing creep: The forces changed during the upstroke and downstroke make the tubing creep downhole. As a result, wear between the sucker rod and the tubing wall as well as between the tubing and the casing wall increases, and finally, tubing leakage occurs. ④ After the damage of tubing, corrosive media make the worn surface even rougher, thus accelerating the wear and, as a result, the next stage will be tubing perforation. ⑤ Leakage caused by deteriorating well conditions: When the well casing is deformed, it wears the deformed area through it and this will happen for quite some time until the situation gets worse with the passage of time.
1.3 Analysis of the Reasons for Sucker Rod Problems Affecting Pump Inspection:
The research and improvement on deep-well pumping technology have been going on for years. Sucker rod breakage has been significantly reduced, however, it is still one of the main factors that adversely affect pump inspection. ① The lower longitudinal bending of the sucker rod induced by alternating loads causes stress fatigue, and eventually fracture; ② Well inclination results in uneven wear of the rod and tubing thus causing them to wear more rapidly; ③ The medium inside the oil well, which is the cause of the corrosion of the sucker rod, and in some wells with higher water cut, the surface of the tubing losing the protective effect of crude oil, thereby the wear rate of the rod and tubing inner wall increasing and so as tubing damage.
2. Measures and Suggestions for Extending the Pump Inspection Cycle:
2.1 Measures and Suggestions for Reducing Deep-Well Sucker Rod Pump Problems:
① Problem-solving methods for floating valve breaking: By adding a centralizer to the tie rod one can make sure that the downward force is in line with the pump shaft thus no torque is created and the floating valve is not subjected to a large stress which will result in the extension of its service life. ① An extended piston is introduced where the extended part connects the valve cover and the piston body. As a result, the piston's fluid outlet channel is moved upwards into the tubing which increases the fluid outlet area and decreases the resistance generated by the piston during fluid discharge. ② The oil drainer should be produced and assembled strictly in accordance with the operating procedures so as to avoid the breaking of the drainer pin. ③ Strict operational procedures should be followed to prevent such incidents as objects falling into the well.
2.2 Measures and suggestions to reduce pump inspections caused by tubing string problems:
① Corrosion inhibitors should be applied to the surfaces of the rod and tubing to form a protective film that is uniform and dense, thus wear will be significantly reduced; ② Nylon centralizers, centralizing couplings, and wellhead fittings should be used to widen the contact surface for the uneven wear and thus prevent the perforation of the tubing, which is caused by fixed-point uneven wear; the installation of shock absorbers is a solution to the problem of the breakage of the sucker rod by the inertial load; ③ A weighted rod should be used at the bottom to lower the neutral point and thus prevent the bending of the sucker rod; ④ Rods and tubing should be strictly controlled; unqualified rods and tubing must not be utilized in the well.
2.3 Strengthen Daily Management:
① Rationally change movement frequency, using long movements and low movement rates to life parts of tubing and rods;
② Regularly make hot washing, chemical dosing and take an intermittent system for wells with a poor liquid supply to lower reactive wear;
③ Strictly oversee the operations, making sure that workers follow the rules during the construction so as not to have incidents such as objects falling into the well.
① The first factor that leads to difficulty in pump inspection of oil wells is caused by Deep-Well Sucker Rod Pump followed by tubing leakage and rod breaking; In Deep-Well Sucker Rod Pump problems, most of the cases, flow valve breakage is the main reason for that;
② In case of the Deep-Well Sucker Rod Pump flow valve breakage, the use of extended pistons or the addition of a centralizer to the tie rod to lessen piston resistance is recommended;
③ The addition of corrosion inhibitors, the use of nylon centralizers, eccentric wellheads, shock absorbers, weighting the lower rod, and special rods, are a series of supporting technologies that are the most effective measures to stop the process of wear and corrosion in the tubing and rods;
④ The development of detailed management measures for different wells is the way to get the effect of pump inspection cycle prolongation.