Which downhole pump is suitable for low submerged oil well?
The degree of submergence should be determined according to the output of the oil well and the working fluid level. Before the oil enters the deep well pump, the resistance of the filter, gas anchor, sand anchor and valve must be overcome, which requires the deep well pump to enter a certain depth below the fluid surface to form a pressure.
In oilfield production, it is important to be able to acquire the reservoir status of oil wells in real time, especially for low or ultra-low permeability oil wells. In this paper, based on the reservoir percolation characteristics of the oil layer and combined with the oil well permeability, liquid pressure and oil well pressure formulas, the non-homogeneous linear differential equation for oil well pressure is derived, based on which a submergence depth model of oil well reservoirs is established. The parameter merging is applied to reduce the parameter dimension of the submergence depth model; this approach substantially reduces the parameter dimension and application complexity and effectively improves the model application range.
The model not only conforms to the reservoir percolation law of the oil layer but also applies to the balance laws of other substances with potential energy balancing ability. The application methods studied (namely, the extraction of the greatest common divisor, the weighted dichotomy and least-squares curve fitting) successively reduce the calculation error and expand the application scope. The least-squares curve fitting method causes the submergence depth error to reach the minimum of the 2-norm, and the number of iterations can be accurately assessed by the convergence speed of halving the numerical calculation error in every iteration.
This method is suitable not only for the zero submergence depth case in the initial state but also for non-zero submergence depth cases. The experimental results show that the proposed submergence depth model for oil well reservoirs accurately reflects the change laws of submergence depth and time. Combined with the proposed application methods, the corresponding submergence depth can be obtained at any time point. The model and application methods provide strong support for formulating scientific oil production plans and implementing reasonable production methods for oil wells.
Due to the special geological conditions and the imbalance between injection and production, some oil wells in the oil field have low formation pressure and poor permeability, resulting in the submergence of these oil wells being less than 200 meters. At present, the main use of oil wells with low submergence is intermittent downhole pumping or deep downhole pumping with small downhole pumps, long strokes and low stroke frequency. However, the standing valve of this conventional downhole pump uses a normally closed structure, that is, a liquid inlet method during suction.
When the submergence is small, the oil pressure is small, and the standing valve ball cannot be pushed up properly, which has the problem of difficulty in absorbing liquid. In addition, the downhole pump barrel has a low filling factor and a large air downhole pumping coefficient, which is likely to cause liquid blow, gas cutting, and gas lock. The sealing surface of the valve seat is subjected to repeated instantaneous impact force, which causes the valve seat seal to fail prematurely, shortening the inspection cycle of the downhole pump and affecting the service life of the downhole pump.
In order to solve these problems, Sanjack Group has developed a downhole pump suitable for low-submergence wells. This downhole pump is composed of downhole pump barrel assembly, plunger assembly and standing valve assembly. The structure diagram is as follows:
|1||Barrel Assembly||6||Valve Ball|
|2||Plunger Assembly||7||Cage ball cover|
|3||Standing Valve Assembly||8||Return Spring|
|4||Oil Inlet channel||9||Oil outlet channel|
|5||Inverted Valve Seat||10||Valve body|
The valve body of the standing valve assembly of the new oil downhole pump is provided with an oil inlet channel and an oil outlet channel. The valve body, valve ball, cage valve ball cover and return spring are installed in order from top to bottom in the valve body. The valve ball and cage ball cover are supported by the return spring. Because the valve body is designed with an oil inlet channel and an oil outlet channel, the infusion type liquid inlet is realized, and the problem of difficulty in sucking liquid by the oil downhole pump is solved. The valve seat is inverted in the valve body and the valve ball and cage valve ball cover are supported by the return spring. And the elastic force of the designed return spring is equal to the self-weight of the valve ball and cage ball cover. When no oil enters the inlet passage of the valve body, the valve ball and the valve seat are closed. As long as oil enters the inlet passage of the valve body, the valve ball can be separated from the valve seat.This ensures that as long as the oil well liquid level is higher than the oil inlet channel, the valve ball and the valve seat will remain open and closed, avoiding the abnormal impact of the valve ball and the valve seat due to liquid hammer, gas cutting and gas lock phenomenon. This greatly alleviates the problem of valve seat seal failure.
The new sucker rod downhole pump has a reasonable structure. It solves the problem of difficult suction of downhole pumps in wells with less submergence and the problem of premature failure of valve seat seals which greatly improved the service life of the downhole pump.