Wells – With eduction pump or plunger – Having liquid-gas separator
Reexamination Certificate
1998-07-31
2001-01-30
Bagnell, David (Department: 3672)
Wells
With eduction pump or plunger
Having liquid-gas separator
C166S265000
Reexamination Certificate
active
06179054
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention is generally related to improvements in a downhole gas separator and is more specifically directed to a slotted gas liberation system and a rough surface baffle to separate fluid and gas.
In the initial stages of oil production, the downhole well pressure is sufficient to force the well fluid upward. However, the reservoir pressure substantially decreases as fluids are removed. Once the pressure drops below a certain minimum level, the fluids must be elevated artificially. Typically, such low pressure wells utilize downhole pumping units for artificial lift and elevation of fluids. The most common downhole pump is a two-cycle downhole rod pump, and this is sometimes referred to as a “sucker rod.” The pump uses two cycle sucker rods and a simple piston, and is driven by a surface pumping unit. On the upstroke, fluid is lifted up and removed. On the downstroke, the valve or piston is returned to the bottom of its stroke. Often, a perforated gas separator is attached to the pump to separate the oil and gas and to ensure that only oil is lifted up.
It is very important to elevate the fluid and not the gas, because unwanted gas in the pump can cause major problems. First, the presence of gas in the pump decreases the volume of oil transported to the surface, since the gas takes up space that could be occupied by liquid. Therefore, gas in the pump decreases the efficiency of oil production. The second major problem with gas flowing into the pump is the possibility of a resulting condition known as gas-lock. If a barrel is completely filled with gas, it may never reach the pressure needed to open the traveling valve or raise the piston. This means that oil fluids cannot enter the barrel, and that the gas inside the barrel cannot get out. Thus, a “gas-locked” situation results, because for stroke after stroke, no liquid enters or leaves the pump. Gas lock is such a common phenomenon in sucker rod pumps that many wells cannot be produced because they contain too much gas.
The final major problem with gas entering the pump is that when the liquid is pumped up, there can only be a limited amount of gas in the pump before operational problems will develop that can result in severe damage to the pumps. This problem is usually called gas pounding. The light gas propels the heavy liquid forward. The forced pounding of liquid against the inner walls which results can severely damage the sucker rods and slowly disfigure the pump. When this happens, the whole pumping unit has to be removed out of the ground for repair and readjustment, and this decreases fluid recovery efficiency. Usually, a spiral segregator, a baffle plate, or some variation thereof is incorporated into the design of the down hole pump to decrease the amount of gas inside the pump at any given time. Typically, the amount of gas in the pump inlet's fluid flow stream can not exceed about fifteen percent by volume without damage. Thus, pumps are much more efficient in a gas free environment.
Gas separators are traditionally used to avoid these three problems, and several designs are currently in use. Often, a gas lock problem is avoided by lowering the traveling valve so that a higher compression ratio is obtained in the pump. This forces pump action more frequently since the traveling valve will open both when it hits the liquid in the pump, and also when the pump pressure is greater than the pressure above the traveling valve. If the valve is forced open more often, the pump can release more gas and take in more oil. The flaw in this technique is that it does not increase the gas separator efficiency. If the gas and liquid that enters does not separate properly, then regardless of the increased efficiency of the pump's ability to take in larger volumes, gas can still interfere with the pumping of oil to cause gas lock or gas pounding.
In order to prevent this from happening, U.S. Pat. No. 2,969,742 to Arutunoff, issued Jan. 31, 1961 discloses a motor-driven, reverse flow-type liquid-gas separator. Other examples of such motor-driven rotating type gas-liquid separators are described in U.S. Pat. No. 4,481,020 to Lee on Nov. 6, 1984 and U.S. Pat No. 4,981,175 to Powers on Nov. 6, 1984. The fluid is forced to undergo reverse flow along a spiral or helical flow path so that, in effect, there is a centrifuging of the liquid-gas mixture to separate them. Because the reverse flow technology is motorized, this type of separator consumes additional power due to work exerted to separate and lift the liquid, and thus is not very efficient.
U.S. Pat. No. 5,482,117 to Schoeppel granted Jan. 9, 1996 discloses a gas separator that has been developed to solve this efficiency problem by using centrifugal forces to separate the gas and liquid without a motor. This gas separator device consists of a stationary helical baffle within tubular housing that redirects gas flow in a non-natural direction. The baffle is placed within a conventional downhole pump, and because it is stationary, it does not consume any additional power. The liquid is forced to the outer wall, and the gas is forced into a flow path that takes it to the surface. Since the baffle surface area of each twist of the helix is not very large and surface contact with the solution is not that high, there is reliance on the centrifugal forces to separate the oil and gas. When the gas is finally released, it is liberated through tiny, little holes called perforations. Although a non-motorized gas separator is more efficient than a motorized one, there is still a gas lock problem that remains to be solved. The tiny holes can get plugged up with gas bubbles upon exit can prevent oil entry.
A similar helical spiral ramp was disclosed in Ward's U.S. Pat. No. 4,531,584 granted on Jul. 30, 1985. This gas separator provides continuous upwardly spiraling separating velocity to the entering oil and gas in order to separate at least enough gas to reduce gas lock. The gas separator relies on the continuous flow separation velocity to direct the separated oil to the oil flow outlet and the separated gas to the gas flow outlet. The internal collection tube includes a series of openings which allow for the migration of gas radially inward. The gas is then directed upward and released through small outlets. These holes can also prevent fluid entry and thus result in a decrease of oil recovery if plugged up by gas bubbles in a gas lock condition.
Since the U.S. Pat. No. 1,697,321 granted to Marsh on Jan. 1, 1929 began the trend, all the devices patented thus far have disclosed holes for fluid entry/exit openings. Recent technology disclosed in U.S. Pat. No. 5,653,286 to Schoeppel granted Aug. 5, 1997 is no exception. The apparatus is an elongated vessel that is closed on one end. It contains fluid inlets and gas vents on top that extend through the side walls. The fluid inlets are used to capture the rising fluid as it enters so that the gas separates and is forced to exit the interior chamber through the vents above. There is also a second chamber below the interior that has an opening to release gas in case any gets collected there. The longer, lower end of the tubular body with the fluid inlets is cut at an angle, and the upper end of the gas separator has an angled deflector. A deflector is a flexible spring steel that is welded to the separator and is mounted on the opposite sides of the fluid inlet. The angled deflector forms wide and narrow flow regions the help separate the liquid and the gas. The liquid tends to collect on the casing to be pushed down and the gas tends to be forced up to the more open region. However, even in this, the most current of technology, two problems remain. First, the gas is still exiting through small holes that can get plugged by gas bubbles. Secondly, the use of a smooth baffle as a gas separator is not an efficient baffle system, so the problems of gas pounding and the resulting decreased productivity remain.
SUMMARY OF THE INVENTION
In the present invention, a slotted gas
Bagnell David
Bracewell & Patterson L.L.P.
Dougherty Jennifer R.
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