What kind of downhole pump is suitable to non-viscous heavy oil wells?
Petroleum is a complex mixture, mainly containing various hydrocarbons, gums, asphaltenes…different component content resulting in different colors and properties of crude oil. There is an oil with the darkest color, very viscous and difficult to flow, but it accounts for 70% of the world’s oil reserves, and we generally call it “heavy oil.”
Heavy oil refers to crude oil with a viscosity of less than 50 mPa · s or greater than 100 mPa · s after degassing in an oil layer. The reason for the formation of heavy oil is very complicated. The biggest difference from ordinary crude oil is the degree of biodegradation. The higher the degree of degradation, the easier it is to form heavy oil.
API Gravity (American Petroleum Institute Gravity) is a recognized oil specific gravity index adopted by the American Petroleum Institute, which can roughly measure the quality of oil. According to the API severity index, crude oil can be divided into 4 categories: Light, Medium, Heavy, and Extra Heavy.
The viscous fingering morphologies at a particular stage of emulsion displacements are observed to follow similar development patterns as that of the partially-miscible viscous fingering behavior (existent between the commonly studied fully miscible and immiscible systems). Chemically-induced viscous fingering before and after the finger droplet development resembling the partially-miscible fluid behavior is investigated using fractal dimensions and various -classic and modified-dimensionless scaling groups. We demonstrate, through the quantitative analysis using the empirical data collected from our previous experimental study, that the finger droplet formation morphologies observed in partially-miscible injection are indicative of an emulsion hydrodynamic instability behavior. The dominant parameters responsible for such droplet formation and their relationship to fractal dimension and hydrodynamic stability are mapped in a phase diagram with the original experimental images.
At present, in the case of heavy oil well mining without viscosity reduction measures, the most commonly used sucker rod pump are valve type pump and hydraulic feedback pump. The valve-type sucker rod pump relies on the mechanical power of the sucker rod to move up and down to open and close the traveling valve, which solves the problem of slow opening and closing of the valve ball in the heavy oil well. However, the high frictional resistance of the sucker rod and the rod string leads to a reduction in the downstroke load of the heavy oil well, which causes the sucker rod to bend, break off easily, and wear and tear on the rod and tubing. The hydraulic feedback pump uses the principle of hydraulic feedback to produce a downward thrust during the downstroke, overcome the friction between the heavy oil and the sucker rod, and reduce the degree of alteration of the sucker rod. However, the closing speed of the valve ball under its own gravity slows down, and the opening of the valve ball slows down.
In order to improve the recovery efficiency of heavy oil wells, select the most suitable pump for non-viscous heavy oil wells. Sanjack Group has developed a mechanical valve type eccentric pump, which can be used without reducing viscosity. It effectively solves the problems of traveling valve delay in opening and closing, slow closing of standing valve, difficulty in sucker rod downward, and clogging of standing valve with falling objects.
The new pump is composed of upper pump barrel, upper plunger, mechanical valve, eccentric plunger joint, lower plunger, lower plunger introduction joint, lower pump barrel, and standing valve. The structure diagram is as follows:
| 1 | Upper pump barrel | 5 | Lower plunger |
| 2 | Upper plunger | 6 | Lower plunger introduction joint |
| 3 | Mechanical valve | 7 | Standing valve |
| 4 | Eccentric plunger joint | 8 | Lower Pump Barrel |
The upper plunger of this pump has a large diameter and a short length, the upper pump barrel has a large diameter and a long length, the lower plunger has a small diameter and a long length, and the lower pump barrel has a small diameter and a short length.
When pumping oil, the sucker rod drives the upper and lower plungers to reciprocate up and down in the upper and lower pump barrels.When the upper and lower plungers are going up, the mechanical valve is closed, a vacuum is formed at the lower part of the upper plunger, the pressure in the chamber formed by the upper and lower pump barrels is lowered, the standing valve is opened, and the well fluid is sucked into the upper pump barrel. When the upper and lower plungers descend, the mechanical valve opens under the action of the sucker rod thrust and the friction between the plunger and the pump barrel. The pressure in the chamber formed by the upper and lower pump barrels rises and the fixed valve closes. The well fluid is lifted to the surface through the inner hole of the upper plunger and the mechanical valve.
Because the upper and lower plungers are eccentrically connected in series, The upper plunger is a double plunger mechanical valve type structure, which relies on the mechanical force of the up and down movement of the sucker rod to open and close the mechanical valve, which solves the problems of the valve ball closing lag and air lock in the oil well.
The new tubing pump has a reasonable and compact structure, and uses a mechanical valve type segregation plunger which can solve the problem of the hysteresis of valve ball closing and gas lock in heavy oil well without taking viscosity reduction measures. At the same time, a rotatable double plunger is adopted, which not only separates the pressure bearing function and sealing function of the plunger, but also has a self-grinding function, which greatly improves the service life of the downhole pump.
