Sand lift tool, system and method

A sand lift tool for use in a subterranean well can include an outer housing, an inner production tube positioned in the outer housing, and a dart received in the inner production tube. An annulus is positioned between the outer housing and the inner production tube. The dart can reciprocate in the inner production tube in response to variations in fluid flow between the annulus and an interior of the inner production tube. Another sand lift tool can include an outer housing, an inner production tube, and a sand collection annulus between the outer housing and the inner production tube. A flow area for fluid flow between the annulus and an interior of the inner production tube increases in response to an increase in a flow rate of the fluid flow.

BACKGROUND

This disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in examples described below, more particularly provides a sand lift tool and associated system and method.

Sand can accumulate in well equipment when fluids are produced from a subterranean well. For this reason, it is common practice to use well screens in an attempt to exclude sand from production tubing strings used to produce the fluids to surface. However, it is practically impossible to exclude all of the sand from the interior of a production tubing string.

Therefore, it will be appreciated that improvements are continually needed in the art of protecting well equipment from sand accumulation in production tubing. It is one of the objectives of the present disclosure to provide such improvements to the art.

DETAILED DESCRIPTION

Representatively illustrated in the accompanying drawings is a sand lift tool, system and associated method which can embody principles of this disclosure. However, it should be clearly understood that the tool, system and method are merely one example of an application of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited at all to the details of the tool, system and method example described herein and/or depicted in the drawings.

A wide array of tools, chemical treatments and techniques exist to alleviate problems experienced in well bores throughout the petroleum industry. Many of these tools and treatments provide their benefit below a well's pump. Tools such as sand screens, centrifugal de-sanders, gas separators, chemical treatment tools and other solutions do their work to keep the well producing.

Electric submersible pumps (ESP's) are often used in high volume wells because they are efficient in pumping large quantities of fluid. The pump moves the well bore fluid upward through a tubing string to be produced to the surface.

One issue that is not remedied by these products and techniques occurs as sand is produced upward within the tubing along with the well bore fluid. This is due to agitation and velocity of the fluid as it is pumped up the tubing causing the sand to be suspended within the fluid. When the pump cycles off, the suspended sand falls downward and accumulates on top of, and in, the pump.

Depending on the quantity of sand within the fluid, the sand may become so impacted in the pump that the pump will no longer function due to failure of the motor or in some cases, breaking the pump shaft or other internal components. In addition, the accumulated sand prevents a chemical treatment from being pumped from surface through the pump. The sand lift tool described herein is utilized above the pump and provides a unique method of solving these problems.

Dimensions noted herein are to offer clarity of proportional size. This disclosure is not limited to the noted dimensions. Tools may be of larger or smaller size.

In one example, the sand lift tool consists of a large (4″) tubular outer housing which is reduced on each end to a smaller diameter on each end (2⅞″). A lower connection is attached to a discharge connection of a pump below. An upper connection attaches to tubing above. An inner production tube (1¼″×20′) is fixed within the tubular outer housing. This inner tube is comprised of columnar vee wire screen.

Since the fluid flow direction is from inside the inner production tube-to-outside the production tube, the vee wire column may be configured in reverse to typical screen which is configured for use at an intake point. This allows for reduced plugging of openings (slots) as sand laden fluid is expelled through them.

The openings (slots) in the vee wire screen of the inner production tube may be of varying dimensions to accommodate different production rates and tool dimensions. In another example, the inner production tube may be comprised of a solid pipe with slotted or various other shaped openings.

The top of the inner production tube is enclosed within a bullnose which includes slotted or inclined ports. Within the inner production tube is a free moving “dart” which can travel up or down depending on fluid flow.

In some examples, a bumper assembly is affixed in place inside the bullnose at the top of the inner production tube. The bumper assembly consists of an upper cap, a lower plate and a spring connected between the cap and the lower plate. The bumper assembly serves to absorb shock as the dart is forced upward by fluid pressure when the pump is active.

A bottom of the inner production tube contains a base on which the dart rests when there is insufficient fluid flow to propel the dart upward. Both the bull nose and the lower dart base contain openings which allow for unrestricted fluid flow once sand is cleared. This provides increased flow as not all the fluid must pass through the screen to exit the tool.

When the pump is cycled off, the dart falls to the bottom of the inner production tube. Once the pump is activated, fluid is forced to move upward within the inner production tube. This will push the dart upward.

Fluid is forced out through the screen and into an annulus between the large tubular outer housing and the inner production tube. Sand particles may accumulate within this annulus allowing continued fluid flow up the inner production tube.

The action caused by movement of the dart forces fluid through the screen at a high velocity, agitating any sand which has accumulated in the annulus and flushing the screen openings (slots) keeping them clear. Due to agitation and velocity of the fluid, solid particles are suspended in the fluid and are able to be produced to the surface, clearing the sand in the annulus.

By clearing the tool of sand in each pump cycle, sand does not accumulate over time as it does in typical ESP systems. This protects the pump from damage and increases run times between expensive well workover events.

Multiple sand lift tools may be installed one above another in any length needed, with a single dart operating through the entire string. In another configuration, separate sand lift tools may be installed at varying locations within the tubing to offer additional stages of sand clearing. In wells with higher levels of sand content, placing these “booster” tools will work to keep sand suspended as fluid is moved to the surface.

Referring now toFIG. 1, an example of a system10for use with a subterranean well is representatively illustrated. In this example, a sand lift tool12is used to protect an electric submersible pump14from sand accumulation in a tubing string16. The tubing string16is generally vertical as depicted inFIG. 1, but in other examples the tubing string could be inclined from vertical.

The pump14is used to produce fluid18from the well. When the pump14is activated, the fluid18is flowed upward to surface through the tubing string16. When the pump14is deactivated, the flow of the fluid18ceases and any sand or other debris in the tubing string16above the pump14could settle onto the pump, if the sand lift tool12were not present in the tubing string.

The sand lift tool12performs its “sand lift” function by stirring up any sand that has accumulated in the sand lift tool, so that the sand is produced to the surface with the fluid18. The sand is stirred up in the sand lift tool12when the pump14is activated to flow the fluid18upward through the sand lift tool and the remainder of the tubing string16extending to the surface.

Referring additionally now toFIG. 2, a cross-sectional view of an example of the sand lift tool12is representatively illustrated. TheFIG. 2sand lift tool12may be used with the system10and method ofFIG. 1, or it may be used with other systems and methods. For convenience, the sand lift tool12is described below as it may be used in theFIG. 1system10and method.

In theFIG. 2example, the sand lift tool12includes an upper connector20, a lower connector22, an outer housing24, an inner production tube26and a dart28. In other examples, the sand lift tool12could include more or fewer components, or different combinations of components. Thus, the scope of this disclosure is not limited to the specific details of the sand lift tool12as depicted in the drawings or described herein.

The upper connector20in this example is configured for connection to the tubing string16extending to the surface. The lower connector22in this example is configured for connection to the pump14. Thus, the flow of the fluid18from the pump14enters the sand lift tool12via the lower connector22and exits the sand lift tool via the upper connector20.

The outer housing24extends between and connects the upper and lower connectors20,22. The outer housing24surrounds the inner production tube26, so that a sand collection annulus30is formed between the outer housing and the inner production tube. When the flow of the fluid18ceases (e.g., when the pump14is deactivated), sand can accumulate in the annulus30and can pass into the screen36.

The inner production tube26in this example includes an upper impact absorber32, an upper housing34, a screen36, a centralizer38and a base housing40. The dart28is able to reciprocate in an interior of the inner production tube26between the upper impact absorber32and the base housing40. The dart28is biased to displace downward by gravity, and is biased to displace upward by the flow of the fluid18when the pump14is activated.

As depicted inFIG. 2, the fluid18is flowing upward through the sand lift tool12. The fluid18flows into the lower connector22, into the interior of the inner production tube26, into the annulus30, and then upward and out of the sand lift tool12via the upper connector20.

This flow of the fluid18from the interior of the inner production tube26to the annulus30pushes the dart28upward. However, when the flow of the fluid18ceases, the dart28will descend in the inner production tube26, until it engages a shoulder in the base housing40, as described more fully below.

Referring additionally now toFIG. 3, a cross-sectional view of an example of the dart28in the inner production tube26is representatively illustrated. In other examples, other types of darts and other types of inner production tubes may be used, and so it should be clearly understood that the scope of this disclosure is not limited to the details of the dart28or the inner production tube26as depicted in the drawings or described herein.

In theFIG. 3example, the screen36includes a “V”-shaped cross-section wire42wrapped helically about multiple longitudinally extending rods44. The wire42can be welded to each of the rods44in the manner of a conventional well screen. The rods44are circumferentially distributed about the dart28and the interior of the inner production tube26.

A longitudinal spacing between adjacent wraps of the wire42can be varied as desired to provide for regulation of sand and other debris into and out of the interior of the inner production tube26, to provide for sufficient flow of the fluid18from the interior of the inner production tube to the annulus30, or for other purposes. For clarity of illustration, the spacing between the adjacent wraps of the wire42are depicted inFIG. 3as being relatively large compared to a conventional well screen, but any spacing may be used in keeping with the principles of this disclosure.

Note that it is not necessary for a screen to be used as a component of the inner production tube26. For example, a tube with holes, slots, perforations or other openings could be used instead of the screen36. Thus, the scope of this disclosure is not limited to use of the screen36or any other component of the inner production tube26.

In theFIG. 3example, the dart28has a body46that is generally cylindrical in shape. However, a downwardly facing nose48of the dart28has a generally conical shape that increases in cross-sectional area in an upward direction. The conical shape of the nose48deflects the fluid18radially outward from the interior of the inner production tube26toward the annulus30. This radially outward and upward flow through the annulus30stirs up any accumulated sand or other debris in the annulus, allowing it to be produced with the fluid18to the surface.

Referring additionally now toFIG. 4, a cross-sectional view of a portion of the sand lift tool12is representatively illustrated. In this view, the flow of the fluid18has ceased, and so the dart28has descended in the inner production tube26to its lowermost position.

Downward displacement of the dart28is limited by a shoulder50formed in the base housing40. Note that this engagement between the dart28and the shoulder50does not prevent flow of the fluid18in any direction through the inner production tube26, as described more fully below. Thus, contact between the dart28and the shoulder50does not prevent the fluid18and entrained solids (e.g., sand, debris, etc.) from passing downwardly through the base housing40and lower connector22to the pump14, but the downward flow of the fluid and entrained solids is thereby regulated.

In theFIG. 4example, the base housing40has multiple inclined ports52formed through a wall thereof. The ports52are angled downward in an outward direction.

This orientation of the ports52has at least two benefits—any sand that accumulates in the annulus30up to a level of the ports52is restricted from flowing upwardly through the ports into the interior of the inner production tube26when the pump14is deactivated, and the fluid18will be directed by the ports52to flow toward the lower end of the annulus30(and will thereby stir up any sand that has accumulated at the lower end of the annulus) when the pump14is activated. However, the scope of this disclosure is not limited to any particular direction or orientation of the ports52or to use of the ports in the base housing40at all.

Referring additionally now toFIG. 5, a cross-sectional view of the dart28and the base housing40is representatively illustrated, taken along line5-5ofFIG. 4. In this view, the manner in which flow through the interior of the inner production tube26is still permitted, even when the dart28is engaged with the shoulder50in the base housing40, can be seen.

As depicted inFIG. 5, multiple gaps or recesses54are formed into the shoulder50(seeFIG. 4), so that the body46of the dart28cannot seal off against or sealingly engage the shoulder. Thus, flow is always permitted through the interior of the inner production tube26, even when the dart28is at its lowermost position.

Referring additionally now toFIG. 6, a cross-sectional view of the dart28at its uppermost position in the inner production tube26is representatively illustrated. In this view, the fluid18is flowing at a sufficient flow rate to bias the dart28all the way to the upper end of the interior of the inner production tube26.

As the dart28ascends in the inner production tube26in response to the increase in the flow rate of the fluid18, a flow area through the screen36for fluid18flow to the annulus30from an interior of the inner production tube26increases.

To prevent damage that might occur to the inner production tube26or the dart28due to impact of the dart against the upper end of the interior of the inner production tube, the impact absorber32is connected at an upper end of the upper housing34. In this example, the impact absorber32includes a biasing device56(such as, a coiled spring, an elastomer, a compressible gas, etc.) positioned longitudinally between an upper cap58and an abutment plate60.

The plate60is configured to engage the dart28and to be deflected upward against the biasing force exerted by the biasing device56when the dart displaces to the upper end of the inner production tube26. In this manner, the kinetic energy of the dart28is more gradually converted into potential energy in the compressed biasing device56, so that damage to the dart and the inner production tube26is avoided.

Multiple inclined ports62are formed through a wall of the upper housing34. The ports62are angled downward in an outward direction, similar to the ports52in the base housing40described above.

Note that the dart28in itsFIG. 6uppermost position does not obstruct any of the ports62in the upper housing34. Instead, the dart28is positioned in a tubular portion of the upper housing34longitudinally between the ports62and the impact absorber32.

It may now be fully appreciated that this disclosure provides significant advancements to the art of protecting well equipment from sand accumulation in production tubing. The sand lift tool12is uniquely configured to stir up any sand accumulation in the tubing string16when the fluid18flows upwardly through the tubing string, and to allow back flow through the pump14when the fluid flows downwardly through the tubing string.

One problem in artificial lift operations is handling solids during production. During shut down, sand in the production stream falls back onto the pump14and creates a solid plug in the pump, thereby causing a failure when the pump is turned back on. This failure is costly to operators. Operators need a solution to be able to back spin the pump14and treat through the pump with chemicals from the surface.

The sand lift tool12does not stop sand above the pump14, but regulates the rate of sand going back into the pump when the pump is shut down. This reduces plugging and allows for chemical treatment from the surface through the pump.

When the pump14turns on, the differential pressure created by the pump pushes the dart28off of the base housing40and into the upper housing34. Fluid18and entrained solids flow through the screen36to the surface.

When the pump14is turned off, the dart28falls back to the base housing40. Fluid18and entrained solids begin to flow back through the screen36in a reverse direction (as compared to when the pump is turned on). The dart28and the screen36regulate the rate of fluid and solids flow back through the pump14. Because the sand lift tool12has no seal, an operator can chemically treat through the pump14from the surface and use back spin of the pump impeller to clear obstructions from the pump.

When the pump14is turned back on, the centrifugal force of the impeller creates turbulence, which lifts the fluid18and entrained solids up though the screen36to the surface.

In one example, a sand lift tool12for use in a subterranean well can include an outer housing24, and an inner production tube26positioned in the outer housing24. An annulus30is positioned between the outer housing24and the inner production tube26. A dart28is received in the inner production tube26. The dart28can reciprocate in the inner production tube26in response to variations in fluid18flow between the annulus30and an interior of the inner production tube26.

The inner production tube26may include a screen36. The screen36can comprise a wire42wrapped about multiple longitudinally extending rods44.

The inner production tube26may include a base housing40and multiple inclined ports52formed through a wall of the base housing40. The base housing40may be connected to a lower end of a screen36.

A shoulder50formed in the base housing40may limit downward displacement of the dart28through the inner production tube26. Fluid18flow between the dart28and the shoulder50may be permitted when the dart28is engaged with the shoulder50.

The dart28may displace upward in the inner production tube26in response to the fluid18flow from the interior of the inner production tube26to the annulus30. The dart28may displace downward in the inner production tube26when the fluid18flow ceases. Downward fluid flow through the inner production tube may be permitted when the dart28is at its lowermost position in the inner production tube26.

The inner production tube26may include an upper impact absorber32configured to limit upward displacement of the dart28. The upper impact absorber32may comprise a biasing device56positioned between an abutment plate60and an upper cap58of the inner production tube26.

The inner production tube26may include an upper housing34connected to a screen36, and multiple inclined ports62formed through a wall of the upper housing34. The dart28may be positioned in the upper housing34longitudinally between the upper impact absorber32and the ports62when the dart28is at an upper limit of displacement in the inner production tube26.

In another example, a sand lift tool12for use with a subterranean well can comprise: an outer housing24, an inner production tube26and a sand collection annulus30between the outer housing24and the inner production tube26. A flow area for fluid18flow between the annulus30and an interior of the inner production tube26increases in response to an increase in a flow rate of the fluid18flow.

The sand lift tool12may include a dart28positioned in the interior of the inner production tube26. The dart28may displace upward in response to the increase in the flow rate of the fluid18flow. The dart28may displace downward in the inner production tube26when the fluid18flow ceases.