Multi-stage hydraulic jet pump

Abstract

A multi-stage hydraulic jet pump for use in downhole environments is described.

Description

FIELD OF THE INVENTION

The invention pertains to jet pumps, such as those used to enhance production in downhole environments.

BACKGROUND OF THE INVENTION

Single hydraulic jet pumps are well known and documented in the oil and gas industry. Such pumps are used to increase the recovery of fluids such as oil and gas when the downhole fluid pressure is lower than desired. For example, U.S. Pat. No. 7,255,175 (“the '175 patent”) to Jackson, et al. discloses a jet pump for use with a fluid recovery system.

Similarly, U.S. Pat. No. 5,372,190 (“the 190 patent”) to Coleman discloses a jet pump that is similar in design to that of the '175 patent. The disclosures of both the '190 and the '175 patents note that jet pumps have significant advantages over other types of prior art pumps, such as the ability to handle more solid materials in the flow stream.

Current art jet pumps allow the operator to pump a power fluid down the wellbore, pass the power fluid through a first converter to convert the pressure of the power fluid to velocity, a jet to inject the power fluid into a mixing chamber, where it is mixed with production fluid, and a second converter to convert the velocity of the mixed fluid into pressure.

In the event that repairs to the jet pump are necessary, the flow through the jet pump may be reversed, giving it the advantageous ability to pump itself out of the wellbore.

However, current and prior art jet pumps are not a cure-all for every instance of low bore pressure. The production fluid pressure (wellbore pressure) of the fluid must be high enough compared to the power fluid pressure, or the jet pump will cavitate. The primary mode of cavitation in jet pumps occurs when the static pressure of the produced fluid drops below the vapor pressure due to high velocities entering the mixing throat of the pump. This state will result in a choked flow condition. Additionally, the downstream collapse of the cavitation bubbles can severely erode the pump.

The risk of cavitation can be alleviated somewhat by installing a larger mixing throat, thereby reducing the velocity of the produced fluid. However, doing so has two effects: First, the larger throat changes the area ratio of the pump, requiring a higher power fluid pressure to achieve sufficient lift; and second, the higher power fluid pressure increases the jet velocity at the same time the produced fluid velocity is reduced. The increased mismatch between power fluid velocity and produced fluid velocity makes the shear zone between them more severe, which in turns increases the intensity of the turbulent vortices formed at the interface between the two fluids.

Even if the mean static pressure of the produced fluid is high enough to prevent cavitation, the cores of the vortices will be at a substantially lower pressure and cavitation bubbles will form there. Subsequent downstream collapse of these bubbles can cause erosion of the pump, even though the overall pressure level is not low enough to cause the choked flow condition. Another consequence of oversizing the pump is that it will operate well below its efficiency peak.

Accordingly, it is desirable to provide a jet pump that avoids cavitation at a higher power fluid to bottom-hole production fluid pressure differential than prior art designs.

It is further desirable to provide a jet pump that reduces the likelihood of cavitation within the pump, thereby helping to protect the pump against damage.

It is another desired result to provide a jet pump that will allow lower production fluid pressure wells to be drawn down further during production, thereby increasing the efficiency of production.

It is further desirable to provide a jet pump that requires lower power fluid pressure for a given well to provide the same level of production, thereby reducing the energy cost of production.

SUMMARY OF THE INVENTION

The invention is a two or more stage hydraulic jet pump, whereby the first stage hydraulic jet pump is used as a charge or booster pump for the second stage jet pump. In one embodiment of the invention, power fluid pumped down a tool string is divided between a first stage power fluid flow and a second stage power fluid flow.

The portion of the total power fluid flow that goes to the first stage can be controlled by the relative flow volumes created when the power fluid flow is divided. Further, an optional orifice plate can be placed in the path of the first stage power fluid flow to reduce the pressure of that flow. As those of skill in the art will recognize, such an orifice plate can be sized as desired to “tune” the first stage jet pump to best utilize bottom-hole conditions, such as bottom-hole production fluid pressure.

The first stage power fluid is further decreased in pressure and is increased in velocity by a first stage inlet converter, typically utilizing the Bernoulli principle, and is then jetted into a mixing chamber to mix with bottom-hole production fluid, producing first stage mixed fluid. Ideally, through controlling the portion of total power fluid used in the first stage, and by controlling the pressure of that fluid by use of an orifice plate, if necessary, the first stage jet pump can operate at a desirably low power fluid pressure to production fluid pressure ratio and will avoid cavitation.

Similarly to the first stage power fluid flow, the second stage power fluid flow is increased in velocity and decreased in pressure by a second stage inlet converter, and is jetted into the second stage mixing chamber. The first stage mixed fluid from the first stage jet pump outlet is also introduced into the second stage mixing chamber, where it is mixed with the second stage power fluid to form produced fluid.

Because of the first stage mixed fluid has been, effectively, “pressure boosted” by the first stage jet pump, the second stage power fluid may be maintained at a higher pressure than the first stage power fluid, allowing the second stage jet pump to output produced fluid with a higher pressure potential than would be achievable by a single-stage pump without risk of cavitation.

By using a two stage pump the first stage increases the pressure of the first stage mixed fluid over that of the bottom-hole production fluid to the second stage inlet. Further, since the first stage has been optimized to minimize cavitation at a low bottom hole pressure, the wellbore can be drawn down further than normal when compared to the single stage pump. This in effect may allow for increased production from the oil well or in dewatering a gas well.

In wells where the bottom hole pressure is too low to normally apply a jet pump the invention will allow a broader application of this form of artificial lift.

Tests indicate that by charging or boosting the inlet pressure to the second stage the efficiency of the overall system is increased under some operation conditions. This reduces the amount of pressure and therefore the amount of energy required to use hydraulics to produce a given well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one embodiment of a multi-stage jet pump of the present invention.

FIG. 2 is a perspective view of a bottom hole assembly adaptable to accept one or more jet pumps.

FIG. 3A is a top view of a bottom hole assembly of FIG. 2.

FIG. 3B is a angle sectional view of a bottom hole assembly of FIG. 2, defined by the angle section A-A of FIG. 3A.

DETAILED DESCRIPTION

Referring to FIG. 1, a cross-sectional view of one embodiment of a multi-stage jet pump of the present invention is shown. In a preferred embodiment, bottom hole assembly 210 of FIG. 2 is utilized to position the multi-stage jet pump 10 of FIG. 1, and to split the power fluid received at power fluid intake 212 into first stage power fluid conduit 214 and second stage power fluid conduit 216. (See FIG. 3B).

Referring to FIGS. 1 and 3B, power fluid in first stage power fluid conduit 214 continues down to first stage power fluid inlet 18. The pressure of first stage power fluid flow 14 may be reduced by a restrictor, such as orifice plate 20. The pressure of first stage power fluid flow 14 is “converted” to velocity by reducing its cross section at first stage reduction 22.

Power fluid in the first stage then passes through first stage jet inlet 24 and first stage jet 26, then into first stage mixing chamber 28. Bottom hole production fluid enters the multi-stage jet pump 10 through production fluid inlet 30, and is directed into first stage mixing chamber 28 via first stage mixing inlet 32. The resulting first stage mixed fluid is then directed into second stage mixing chamber 34 via second stage mixing inlet 36.

Power fluid in second stage power fluid conduit 216 is directed through bottom hole assembly 210 to second stage power fluid inlet 16. Power fluid in the second stage is “converted” to velocity by reducing its cross section at second stage reduction 38, then passes through second stage jet inlet 40 and second stage jet 42 to enter second stage mixing chamber 44. The velocity of the resultant produced fluid is “converted” to pressure by expansion of its cross-sectional area as it exits multi-stage pump 10 at pump outlet 46.

Those of skill in the art will recognize that it is possible, though not necessarily desirable from an engineering standpoint, to omit the bottom hole assembly 210, and to divide the power fluid flow to the first and second stages within the multi-stage jet pump 10. Similarly, it is possible to modify the bottom hole assembly 210 to further divide power fluid to feed three or more stages. Such modifications can be implemented without departing from the spirit of the invention.

Referring to FIG. 2, a bottom hole assembly for configuring a multi-stage jet pump is shown. Bottom hole assembly 210 comprises upper receptacle 220, lower receptacle 222, first and second connecting tubes 224 and 226, and pump cavity tube 228. As previously discussed, internal fluid conduits providing power fluid to the first and second stages are reflected in FIG. 3B.

FIG. 3A is provided for illustrative purposes only, and shows a top view of the bottom hole assembly 210 of FIG. 2 for the purpose of indicating the angular section A-A′ depicted in FIG. 3B.

Those of skill in the art will recognize that variations on the above description can be made without departing from the spirit of the invention, and that the above description is made generally and is not intended to limit the scope of the invention.

Claims

1. A multi-stage jet pump, comprising a first stage jet pump, a second stage jet pump, and a production fluid inlet, wherein a first portion of power fluid is provided to said first stage jet pump, a second portion of said power fluid is supplied to said second stage jet pump, and wherein the output of mixed power fluid and production fluid from said first stage jet pump is mixed with additional power fluid in said second stage jet pump.

2. The multi-stage jet pump of claim 1, additionally comprising a pressure reduction device in said first stage jet pump, wherein said pressure reduction device reduces the pressure of said first portion of power fluid.

3. The multi-stage jet pump of claim 2, wherein said pressure reduction device is an orifice plate.

4. The multi-stage jet pump of claim 1, additionally comprising a bottom hole assembly, wherein said bottom hole assembly divides said power fluid into said first portion of power fluid and said second portion of power fluid.