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How Do Pumpjacks Pump Crude Oil from Deep Underground to the Surface?

2025-08-15

How do pumpjacks actually bring crude oil from deep underground to the surface? Some might answer that it's the sucker rod pump. Indeed, the sucker rod pump plays a crucial role. However, a deeper look reveals that sucker rod pumps are divided into two types: rod-type sucker rod pumps and tubular-type sucker rod pumps. In our oilfields, rod-type sucker rod pumps are commonly used for oil recovery due to various practical considerations. Let's take a closer look at this crucial piece of equipment hidden deep underground—the rod pump—and learn about its working principles and functions.


The rod-type sucker rod pump, a device used in mechanical oil recovery, is widely used in oil wells. Positioned below the dynamic fluid level in the wellbore, the rod pump transmits the pumping unit's power through the sucker rod, effectively pumping crude oil to the surface.


The rod-type sucker rod pump's ingenious design integrates the piston, valve, and inner working cylinder into a single unit, allowing the sucker rod to be directly raised and lowered. This design not only simplifies pump inspection—the pump is lifted by simply pulling out the sucker rod—but is also particularly suitable for wells with high gas volumes but low production rates. Furthermore, a test pumping operation can be performed before the pump is lowered to ensure quality and effectiveness. However, sucker rod pumps also have some drawbacks. Their relatively complex structure and manufacturing difficulties result in higher costs. Furthermore, their smaller pump diameter results in lower displacement. Furthermore, sucker rod pumps are not suitable for sand-producing wells, requiring special attention in their selection and use.


Next, we will delve deeper into the workings of deep well pumps.

During the pump's upstroke, the plunger moves upward as the sucker rod moves, lifting the liquid column above the plunger to the surface. This creates negative pressure within the pump barrel, while the high pressure outside the barrel forces the fixed valve to open, allowing liquid to enter the barrel. Simultaneously, during the upstroke, the floating valve closes, while the fixed valve opens, allowing the pump to draw in liquid and discharge it from the wellhead. During the pump's downstroke, the plunger moves downward, pulled by the sucker rod. This movement compresses the fluid within the pump barrel, causing pressure to rise.


As pressure increases, the floating valve opens, allowing fluid to flow into the tubing. Simultaneously, the increased pressure within the pump barrel forces the fixed valve to close. During the downstroke, the floating valve remains open, while the fixed valve closes, allowing the pump to discharge fluid into the tubing.


Next, we will discuss the theoretical displacement of deep-well pumps.

1. Related Concepts:

Stroke: Symbolized by S, measured in meters. During pumping operation, the polished rod (or piston) moves up and down, driven by the pumping rod. This complete motion is called a stroke. The stroke length is the distance the polished rod travels from its highest point to its lowest point.

Stroke Rate: Symbolized by n, measured in strokes/minute. The stroke count, also known as the stroke number, represents the number of up-and-down reciprocating movements of the polished rod per minute, or more specifically, the number of reciprocating movements of the sucker rod pump piston within the working cylinder per minute.

2. Theoretical Pump Displacement:

Under ideal conditions, the volume of liquid displaced by each up-and-down movement of the piston is equal to the space V it vacates, namely:

V = fp × S = (π/4) × d² × S

where fp represents the cross-sectional area of the piston, and S represents the stroke of the polished rod.

Then, the displacement per minute, Vm, can be expressed as:

Vm = fp × S × n = (π/4) × d² × S × n

where n represents the stroke count.

Furthermore, the theoretical daily pump displacement, Q, can be calculated as:

Q = 1440 × fp × S × n = 1440 × (π/4) × d² × S × n = K × S × n

where Q represents the theoretical pump displacement, and K represents the pump's displacement coefficient. Simply put, a pump's theoretical displacement is the product of the number of plunger movements per minute and the plunger volume per stroke. The theoretical daily displacement is calculated by multiplying this product by 1440 minutes.


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