Gas lock has plagued the oil industry since the first ball and seat pump was installed. This century-old problem causes a reduction in fluid production and increases maintenance and equipment costs. In many cases, wells having too much gas or containing fluids with many light ends, which would flash upon being subjected to the relative vacuum of the upward-traveling pump, would not pump fluid at all. The pump would soon be destroyed within the barrel due to lack of fluid lubrication. Either way, until the introduction of the DARTT® VALVE, which is specifically designed to operate in the gas environment, the gas lock problem could not be effectively eliminated. Now, the addition of a DARTT® VALVE to the pump will eliminate gas lock.

To discuss gas lock meaningfully, it is necessary to review the normal operation of the pump and describe the abnormality of gas lock.

NORMAL PUMP OPERATION

In normal pump operation, the plunger of the pump is in the down position and begins to move upward. The traveling valve within the plunger is closed, and a low pressure area is formed in the void where the plunger had been. The higher pressure (may require high fluid level) just outside of the pump forced the standing valve to open. With the standing valve open, the void within the pump is filled with fluid. When the plunger reaches the top of the stroke and starts downward, the pressure inside of the pump exceeds the pressure outside of the pump, and the standing valve is forced closed. This forms a closed chamber within the pump barrel, with the standing valve at the bottom and with the traveling valve at the top.

As the plunger continues downward, it attempts to compress the liquid, which is non-compressible; thus causing pressure within the closed chamber. which pushes against the bottom of the traveling valve ball, exerting a force to open the ball. When this force is great enough to exceed the force pushing on the traveling valve ball from the fluid column above the pump, the traveling valve ball opens. As the plunger continues downward, the fluid within the chamber escapes through the open traveling valve into the column of fluid above the pump. When the plunger reaches the bottom of the pump, the traveling valve closes and the plunger again starts upward. This creates a relative vacuum within the pump barrel, opening the standing valve, and allowing fluid from the well to enter the pump.

GAS LOCK - WHAT HAPPENS

In the real world, "normal" pump operation is unusual and when it does happen, it does not continue for long. One of the common occurrences which prevents normal operation is gas lock. During gas lock, the plunger of the pump is in the down position and begins to move upward. The traveling valve within the plunger is closed and a low pressure area is formed in the void where the plunger had been. The higher pressure just outside of the pump forced the standing valve to open. With the standing valve open, the void within the pump is filled with gas instead of fluid. When the plunger reaches the top of the stroke and starts downward, the pressure inside of the pump exceeds the pressure outside of the pump, and the standing valve is forced closed. This forms a closed chamber within the pump barrel, with the standing valve at the bottom, and with the traveling valve at the top.

As the plunger continues downward, the volume within the closed chamber decreases and forces the gas within the closed chamber to become compressed. Since gas can be compressed, this gas merely becomes compressed and does not push against the bottom of the traveling valve ball hard enough to cause a force to open the ball. Since this force is not great enough to exceed the force pushing on the traveling valve ball from the fluid column above the pump, the traveling valve ball never opens and the gas within the closed chamber remains there. When the plunger reaches the bottom of the pump, the traveling valve is still closed, and the plunger again starts upward. But this time, instead of creating a relative vacuum within the pump barrel, the compressed gas within the closed chamber merely becomes less and less compressed. No relative vacuum is formed to open the standing valve and no fluid from the well enters the pump barrel. This cycle is repeated until the pump literally wears out from the friction of the un-lubricated plunger against the pump barrel. At this time, the pump must be pulled and replaced.

DARTT® VALVE - THE CURE FOR GAS LOCK

What went wrong in the "gas lock" cycle? Once we identify what went wrong, then we can work to fix it. Well, what went wrong was that the gas was allowed to remain within the pump, instead of forcing it on up through the pump as if it were normal fluid. The gas stayed within the pump because the traveling valve never was forced to open. So, to fix the problem, we must open the traveling valve every time the plunger begins its downward stroke and keep it open throughout the entire downward stroke. Also, insufficient relative vacuum between the interior of the pump and the well existed to force the standing valve to open. Therefore, to fix this problem, we must cause more relative vacuum to be formed as the plunger travels within the upward direction. Both of these problems work hand in hand with one another, the one causing the next, which causes the next, and so on.

Accordingly, the solutions to these two problems must also work hand in hand, one preventing the first problem, thus preventing the next problem, and so on.

What would logically work to prevent these two problems would be a device of some sort which would positively open the traveling valve on the down stroke and which would positively close the traveling valve on the up stroke. Absolutely closing the traveling valve on the up stroke would create the best possible relative vacuum between the pump interior and the well; thus, doing the best job possible to force the standing valve to open in the upstroke. Positively opening the traveling valve in the down stroke would empty the pump and prevent gas compression within the pump. This correctly and perfectly sets the stage for filling the pump once again in the following up stroke.

Since pressure is presented in pounds per square inch, the force which the pressure exerts against the traveling valve to open it should logically be increased. if one were to cause the natural pressure within the pump to push against an area which is larger than the small area within the seat below the traveling valve, and then use this larger force to force the ball to open. The DARTT® VALVE makes use of this simple principle of hydraulics: the pressure pushing against a larger area to make a larger force, to positively force the traveling valve to open every time the plunger begins its downstroke. The DARTT® VALVE keeps the traveling valve open with this force throughout the entire down stroke.

In the up stroke, with the inside of the pump now empty, the traveling valve and the three cascade valves within the DARTT® VALVE positively shut and form a nearly perfect relative vacuum within the pump. The pressure differential between the inside of the pump and the outside of the pump in the up stroke now causes the standing valve to open, positively filling the pump with whatever is within the well.

This sequence of operations changes the standard plunger pump from one which can only pump fluid to one which can also pump gas. Now, we recognize that the operator would go broke trying to pump gas, but with the DARTT® VALVE installed within his pump, he could literally pump gas. The key here is to pump the gas long enough to prime the pump, sucking in gas and then gas/fluid emulsion, and finally fluid; thus preventing gas lock. Any time later in the life of the well if gas were to return to the flow to a great extent, the pump would continue to pump just as it should, regardless of the gas content in the well.

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