Hydraulic pulse valve with improved pulse control

Hydraulic pulses are produced each time that a pulse valve interrupts the flow of a pressurized fluid through a conduit. The pulse valve includes an elongate housing having an inlet configured to couple to the conduit to receive the pressurized fluid, and an outlet configured to couple to one or more tools. In the housing, a valve assembly includes a poppet reciprocating between open and closed positions, and a poppet seat, in which the poppet closes to at least partially block the flow of pressurized fluid through the valve. A pilot within the poppet moves between disparate positions to modify fluid paths within the valve. When the valve is open, a relatively lower pressure is produced by a Venturi effect as the fluid flows through a throat in the poppet seat, to provide a differential pressure used to move the pilot and poppet. An optional bypass reduces the pulse amplitude.

BACKGROUND

Fluid is commonly pumped though tubing inserted into a well to drill or to provide intervention services such as stimulation or milling of obstructions. Means for pulsing this flow have been developed for a variety of applications, including mud pulse telemetry, well stimulation, enhanced drilling, and for use in extending the lateral range of drilling motors or other well intervention tools. For example, U.S. Pat. Nos. 6,237,701 and 7,139,219, which are assigned to the same assignee of the present invention, disclose hydraulic impulse generators incorporating self-piloted poppet valves designed to periodically stop the flow of fluid at the bottom end of the tubing. Stopping the flow leads to an increase in pressure upstream of the valve and a decrease in pressure downstream of the valve.

Pressure pulsations in the tubing disposed upstream of the bottom hole assembly (BHA) provide a plurality of beneficial effects. For example, the pulsations can improve the performance of rotary drilling by applying a cyclical mechanical load on the bit and a cyclic pressure load on the material that is being cut. In combination, these loads can enhance cutting. The vibrations induced by these cutting tools in the tubing can reduce the friction required to feed the tubing into long wells that deviate from a straight bore line.

The self-piloted poppet valve also generates pressure fluctuations in the wellbore near the tool. These pressure fluctuations can enhance chemical placement in the formation and enhance the production of formation fluids, such as oil or gas. In addition, the pressure pulses can also be used to generate a signal that can be employed for seismic processing.

The valve designs disclosed in U.S. Pat. Nos. 6,237,701 and 7,139,219 generate a relatively short pressure pulse, which limits pulse energy and effectiveness. These designs are also subject to relatively high differential pressure, which causes the tools to cycle at high speed, leading to wear and breakdown, and limiting the flow and pressure available to operate other tools, such as motors and jetting tools. The pulse amplitude generated by the hydraulic impulse tools is determined by the flow rate of fluid. An independent means for controlling pulse amplitude is required in order to accommodate the varying fluid flow rate requirements of a job, which may be determined by hole cleaning requirements in wells that deviate from a straight bore line, or by the limited size of tubing available for coiled tubing well intervention.

It would thus be desirable to increase the duration of the hydraulic impulse in order to increase impulse energy and effective range. It would further be desirable to reduce the pressure differential required to operate a hydraulic impulse generator. In addition, the cycle rate should be reduced to allow seismic interpretation and pore pressure prediction when the tools is used as a seismic source. Finally, it would be desirable to include means for controlling the impulse amplitude, while maintaining pulse duration and cycle rate.

SUMMARY

The following discussion discloses a novel pulse valve that is useful for a range of wellbore intervention applications. In accord with the present novel approach, one exemplary pulse valve that is used for producing pressure pulses within a conduit includes an elongate housing. The housing has an internal passage for conveying a pressurized fluid between an inlet disposed on one end of the housing and an outlet disposed on an opposite end of the housing. The inlet is configured to couple to a source of the pressurized fluid (which will normally be conveyed through a conduit), and the outlet is configured to provide the pressurized fluid flowing through the outlet to a component (such as another tool) that is coupled to the housing. A poppet seat is disposed adjacent to the outlet and includes a constricted throat. At least one port is disposed in the throat and is coupled in fluid communication with an internal volume. A valve assembly is also disposed within the elongate housing and includes a poppet that is reciprocally movable between a closed position in which it at least partially blocks pressurized fluid from flowing through the poppet seat, and an open position in which the pressurized fluid flows through the throat of the poppet seat. A pilot that is disposed within the poppet and reciprocates between a disparate first and second positions to alter fluid communication paths within the valve assembly. A plurality of fluid passages are configured to be in various fluid communication configurations, based upon positions of the pilot and of the poppet within the valve assembly. The pilot and the poppet move in response to differential pressures developed in the valve assembly. For example, a differential pressure arises as a result of a higher pressure of the pressurized fluid within the internal passage and a relatively lower pressure produced in the at least one port in the throat and adjacent volume while the poppet is in the open position. The relatively lower pressure is produced in the at least one port by a Venturi effect as the pressurized fluid flows through the throat of the poppet seat when the poppet is in the open position.

A pressure pulse is produced each time that the poppet moves to the closed position to at least partially block pressurized fluid flowing through the throat of the poppet seat and into the outlet. Those skilled in the art will recognize that at least partially blocking the flow of a fluid in a conduit will generate a “water-hammer” pressure pulse that results from the conversion of the kinetic energy of the moving fluid into the potential energy of pressurization and compression of the fluid. The amplitude of this pressure pulse is directly proportional to the speed of the fluid at the time the flow was at least partially interrupted. The pressure amplitude is highest in relatively incompressible fluids such as water, but useful pulses are also generated in more compressible fluids, such as oil or mixtures of liquid and pressurized gas. The pressure pulse propagates upstream in the conduit at the speed of sound in the fluid. The total energy of each pulse is proportional to the time required for the valve to at least partially close.

The movement of the pilot between the first and second positions reconfigures fluid communication paths in the valve assembly, to apply the differential pressures that cause the poppet to move between the open and closed positions. The movement of the poppet between the open and closed positions also causes changes in fluid communication paths in the valve assembly. The changes apply the differential pressures that cause the pilot to move between the disparate first and second positions.

The poppet seat optionally includes a bypass path that enables some of the pressurized fluid to continue flowing through the outlet of the pulse valve when the poppet is in the closed position. This continuing flow thus reduces the amplitude of the pressure pulses produced by moving the poppet to the closed position, compared to the amplitude resulting from fully blocking the flow of pressurized fluid through the outlet. The bypass path can comprise one or more grooves in the poppet seat, or one or more ports in the poppet seat. The grooves or ports are in fluid communication with the internal passage conveying pressurized fluid and are not sealed by the poppet when the poppet is in the closed position. As a further alternative, the bypass path can comprise an annular opening between the poppet and the poppet seat, which is not sealed by the poppet when the poppet is in the closed position.

When the poppet is at least partially closed, a differential pressure is also produced between a lower pressure in the outlet and a higher pressure in the internal passage in which the pressurized fluid is conveyed. This differential pressure is applied through fluid paths in the valve assembly to cause the pilot to move between the disparate first and second positions.

One of advantage of this pulse valve arises because the elongate housing is configured so that all of the pressurized fluid entering the inlet flows through the outlet. In contrast with some earlier pulse valves, none of the pressurized fluid is dumped through a port in the house sidewall into a borehole surrounding the housing.

Another aspect of the present novel approach is directed to a method for producing pressure pulses. The method generally includes steps that are consistent with the functions implemented by the components of the exemplary pulse valve discussed above.

The benefits of using a pulse valve like the present exemplary device for interrupting all or most of the drilling fluid flow to a drill bit to create pressure fluctuations or pulses in a borehole are well known. These benefits include the following:When the pressure below the bit rapidly decreases to less than the rock pore pressure, a brittle rock formation is encouraged to fracture due to the differential pressure across the surface of the borehole;A reduced pressure below the bit produces a downward force on the bit that increases the load on the cutters, improving their cutting efficiency; andRapidly changing pressures produce a “water hammer effect” or impulse that is transmitted to the drill bit and its cutters to also improve the cutting efficiency and fracturing of the rock by the bit.

Other benefits of using a pulse valve are described in commonly assigned U.S. Pat. No. 6,237,701 and include:Increased rate of drill bit penetration;Early identification of potential gas kicks; andDownhole seismic signal generation while drilling.
Additional applications of the negative pressure pulse in borehole applications other than drilling include:De-scaling of tubulars; andFormation cleaning.

Further, the design of this novel pulse valve and its enhanced functionality enables it to be used for the following exemplary purposes: (1) the use of long duration pulses to pull a coil into a long deviated well; (2) the use of long duration pulses to enhance chemical placement in a long section of wellbore; (3) the use of long duration pulses to remove formation damage from the formation surrounding the wellbore; (4) the use of the hydraulic pulse valve with a down hole motor to enhance weight transfer to a milling or drilling bit in a long deviated well; (5) the use of the pulse valve to enhance weight transfer with other down hole tools such as latches and valve actuators; (6) the use of the pulse valve to increase the movement of sand in a deviated well and to reduce the time needed to clean sand from a well; (7) the use of the pulse valve to enhance the placement of gravel packs in a long extended well; and, (8) the use of the pulse valve to increase the effectiveness of jetting tools for removal of hard fill and scale.

This application hereby specifically incorporates by reference the disclosures and drawings of each commonly assigned issued patent identified herein.

This Summary has been provided to introduce a few concepts in a simplified form that are further described in detail below in the Description. However, this Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

DESCRIPTION

Figures and Disclosed Embodiments are not Limiting

Exemplary embodiments are illustrated in referenced Figures of the drawings. It is intended that the embodiments and Figures disclosed herein are to be considered illustrative rather than restrictive. No limitation on the scope of the technology and of the claims that follow is to be imputed to the examples shown in the drawings and discussed herein. Further, it should be understood that any feature of one embodiment disclosed herein can be combined with one or more features of any other embodiment that is disclosed, unless otherwise indicated.

The characteristics and operation of the hydraulic pulse valve are best understood by examining its four sequential operational steps as illustrated inFIGS. 2A through 2D. A cross-sectional view of an exemplary hydraulic pulse valve with the poppet closed taken along section line A-A ofFIG. 1Ais illustrated inFIG. 2A. As shown therein, the valve basically includes a body10, a valve cartridge12, and a poppet seat13. Body10includes an inlet adapter15, a housing16, and an outlet adapter17. The inlet and outlet adapters have threaded ends for serial connection into the bottomhole assembly as a part of a string of downhole tools. Valve cartridge12includes both stationary components and moving components. The stationary components include an upper manifold18, a cylinder20, and a lower manifold22. The stationary components of the cartridge assembly and poppet seat13are clamped tight axially between inlet adapter15and outlet adapter17. The moving parts of the cartridge include a piston assembly23, and a pilot24. The piston assembly moves axially between upper and lower shoulders inside the cartridge assembly. Major and minor outer cylindrical surfaces of the piston form slidable seals against the internal bores of the cartridge. Variable upper annular volume50and variable lower annular volume60are thus created between the piston and cartridge shoulders. The pilot moves axially between upper and lower shoulders within the piston assembly. Major and minor outer cylindrical surfaces of the pilot form slidable seals against the bores of the piston. Variable upper annular volume42and variable lower annular volume52are thus created between the pilot and piston shoulders. The piston and cartridge assemblies may comprise several pieces to facilitate efficient and low cost manufacturing of the pulse valve, generally as described in U.S. Pat. No. 7,139,219. The piston and cartridge assemblies shown inFIGS. 2A through 2Dhave been simplified to facilitate understanding of the function and operation of the hydraulic pulse valve. At the lower end of the piston assembly is a poppet25that moves in and out of poppet seat13to open or close the pulse valve in response to changing pressure conditions within the pulse valve and changes in the path of fluid communication within the pulse valve caused by the moving pilot.

The hydraulic pulse valve is supplied with fluid from tubing connected at inlet adaptor15. The fluid flows though a passage26in the center of inlet adapter15, through passages27in upper manifold18, and into an annular volume28that is disposed between housing16and valve cartridge12. Fluid flow is directed to the inside of lower manifold22though ports29. InFIG. 2A, the pulse valve is shown in the closed position, with poppet25obstructing the fluid flow through a Venturi flow restriction30in poppet seat13, thus preventing fluid from flowing into outlet passage31in lower adaptor17. Poppet seat13further incorporates multiple flow passages32, which communicate with annular volume33and flow passages34in lower manifold22and volume35between piston assembly23and the lower manifold. Flow passages36in poppet25communicate with an inside volume37of piston assembly23and through a central passage38in pilot24. When the poppet is in the closed position, as shown inFIG. 2A, there is little or no flow downstream of the pulse valve, and the pressure is relatively low in flow restriction30, outlet passage31and in tools disposed in the string below and distal of the pulse valve. This low pressure is communicated through passages32into annular volume33, and through passages34into annular volume35. The low pressure is further communicated through passages36into volume37and into central passage38. In this pilot position, ports62in pilot are aligned with ports63in the piston assembly, thus communicating low pressure into upper variable volume50. Meanwhile, high pressure in annular passage28is transmitted through radial ports46in cylinder20to volume47and through radial ports48in piston to volume49in the pilot. In this pilot position, lower variable volume60is exposed to the high pressure in annular volume49through radial ports66in the piston. The large differential pressure between variable volumes50and60causes piston assembly23(including poppet25and pilot24) to move upwardly and open the pulse valve, to enable fluid flow through outlet passage31, as illustrated inFIG. 2B. The arrangement of ports and the principle of operation of the moving parts are similar to those described in U.S. Pat. No. 7,139,219.

FIG. 2Bshows the hydraulic pulse valve with the poppet open, and pilot24still in the lowest position within piston assembly23. Since the poppet is open, fluid is now able to flow from inlet passage26into outlet passage31through ports27, annular passage28, and ports29. Accordingly, the differential pressure (i.e., the difference between the fluid pressure at inlet passage26and outlet passage31) is relatively low and is only the result of the resistance to fluid flow through the internal passages and openings of the pulse valve, such as annular passage28and ports29and27. However, flow restriction30in poppet seat13is shaped like a Venturi, causing the fluid flow to accelerate through the throat of the poppet seat. The static pressure in the throat of the Venturi is lower than the pressure in annular passage28, due to well known hydrodynamic principles, as taught by Daniel Bernoulli in his bookHydrodynamica(1738). It is this pressure differential that causes the elements of pilot24and piston assembly23(including poppet25) to move and reclose the valve. Without the Venturi effect of the flow restriction in the throat of the poppet seat, the differential pressure available when the pulse valve is open would be too small to reliably move the piston and pilot. The low pressure caused by the Venturi effect is communicated through multiple flow passages32, into annular volume33, and through flow passages34in lower manifold22into volume35. Flow passages36in poppet25communicate the lower pressure into volume37of piston assembly23, and then into central passage38in pilot24. Since central passage38is in fluid communication with an upper volume40, the low pressure is also communicated from upper volume40through radial passages41into annular volume42, which is disposed between an upper annular shoulder of pilot24and an upper internal annular shoulder of piston assembly23. Higher pressure is conveyed through passages46from annular passage28into closed variable volume52. The difference in pressure between variable volumes42and52acts on the pilot to move it upwardly, so that volume52opens, as seen inFIG. 2C.

FIG. 2Cshows the hydraulic pulse valve with the poppet open and with the pilot in its uppermost position within the piston assembly. Since poppet25is open, the differential pressure drop across the pulse valve is low. And, again, there is a much lower pressure created in multiple flow passages32by the Venturi effect of fluid flowing through flow restriction30, and this low pressure is conveyed through annular volume33, flow passages34, volume35, flow passages36, volume37and central passage38. Central passage38conveys this low pressure into upper volume40, but because pilot24has now moved to its uppermost position, annular volume42is closed. The low pressure is also conveyed from central passage38through ports67in the pilot which align with radial ports66in the piston and into piston lower variable volume60. Also, the current position of pilot24communicates the higher pressure in annular passage28through a radial passages46into annular volume47. Annular volume47communicates through radial passages48with annular volume49that is communicating through radial passages61to piston upper variable volume50, which is currently closed. The differential pressure between variable volumes50and60urges the piston assembly to begin moving poppet25downwardly, to the closed position and at least partially block fluid flow through outlet passage31, as illustrated inFIG. 2D.

Turning now toFIG. 2D, the pulse valve is shown with poppet25in its lowest position within the valve body, blocking fluid from flowing from annular passage28through ports29, and with pilot24still in its highest position within the piston assembly. Since the pulse valve is closed, the pressure in outlet passage31is relatively lower than the pressure in annular passage28. The relatively lower pressure in outlet passage31is conveyed through multiple passages32to annular volume33, flow passages34, and into volume35. Again, flow passages36in poppet25communicate the relatively lower pressure into volume37of piston assembly23(as shown inFIG. 2C), and then into central passage38in pilot24. From volume35, the lower pressure is conveyed through a radial passage51and into pilot lower variable annular volume52. Higher pressure within annular passage28is conveyed through radial passage53, into pilot upper variable annular volume42. The differential pressure between variable volumes52and42tends to urge pilot24to move downwardly within piston assembly23, to the position shown inFIG. 2A.

In one exemplary embodiment, radial passage53is restricted in diameter, thereby limiting the fluid flow rate into pilot upper variable volume42and slowing the motion of pilot24. Since poppet25is closed during this time, the flow restriction increases the duration of the pressure pulses that are generated by the pulse valve.

The movement of piston assembly23and pilot24within the valve body then repeats in sequence, as shown inFIGS. 2A-2D, producing a pressure pulse each time that poppet25closes the pulse valve, stopping fluid flow though outlet passage31.

To summarize, from the configuration ofFIG. 2Ain which poppet25is seated within poppet seat13, interrupting fluid flow through the pulse valve and pilot25is disposed at its lowest point within piston assembly, the relatively higher pressure with annular passage28(compared to the lower pressure in inlet passage31) forces the poppet to move upwardly out of poppet seat13, and opens the pulse valve to fluid flow, as shown inFIG. 2B. The Venturi effect produced by fluid flowing through flow restriction30in poppet seat13produces a relatively lower pressure, so that the pressure in annular passage28can be applied to move pilot24upwardly to the top of the valve assembly interior, as shown inFIG. 2C. Then, the pressure in annular passage28, which is greater than the low pressure caused by the Venturi effect of fluid flowing through throat30in poppet seat13, urges poppet25downwardly, at least partially blocking fluid flow through poppet seat13, as shown inFIG. 2D. For each change of position of pilot24and poppet25, it is the differential pressure in the various passages and volumes of the valve assembly that provide the fluid pressure force to move the poppet and pilot components, thereby changing the flow paths through the valve assembly, to repetitively produce pressure pulses.

Discharging the flow used to move the piston and pilot into flow restriction30rather than overboard, as in a previous design, has a substantial benefit. Specifically, a pressure drop through tools connected below or distal of the pulse valve has no effect on the differential pressure across the pulse valve. The pulse frequency of the pulse valve is thus controlled by the fluid flow rate through the pulse valve rather than by upstream pressure. The fluid flow rate can be controlled by controlling the speed/volume of the pump that supplies pressurized fluid down hole. A higher flow rate produces a higher pulse frequency, so increasing the speed of the pump and/or its volumetric rate can increase the pulse frequency. Furthermore, a range of tools may be attached to the lower adaptor of the pulse valve, depending on the type of work to be done, and the application in which the pulse valve is to be employed.

It should be understood that the flow rate and any bypass fluid flow path (such as the optional bypass grooves discussed below) control the pressure pulse amplitude.

For example,FIG. 6Ais a graph200that shows exemplary upstream pressure pulses202produced each time that the pulse valve closes when there is a relatively low flow rate (i.e., about 22 gpm) of fluid through the pulse valve. In contrast,FIG. 6Bis a graph210that shows pressure pulses212produced when the pulse valve closes, for a higher flow rate (i.e., about 36 gpm) than that ofFIG. 6A. The lower amplitude pulses are artifacts of the experiment, representing reflections of the primary pulse in the test loop. A comparison of the pulses inFIGS. 6A and 6Bclearly shows that increasing the flow rate increases the pulse frequency in a linear predictable fashion.

FIG. 7is a graph220that shows the effect of the Venturi port size on the pulse width. A smaller Venturi port causes a higher pressure differential which results in a shorter pulse width222. A larger Venturi port results in a lower pressure differential and longer pulse width224. The cycle rate remains relatively unchanged.

FIG. 8is a graph230that shows exemplary pressure pulses232generated by a larger pulse valve, with a relatively larger Venturi port. The pulses are a close approximation to an impulse with a cycle period longer than 1 second. This type of pulse is ideal for seismic interpretation, because the travel times of seismic waves in the earth crust for formations of interest, such as oil- and gas production, are on the order of seconds. The long period energy generated by this type of cyclic impulse that is produced by the present exemplary pulse valve also propagates long distances in the earth and is ideal for pore pressure prediction.

FIG. 3shows a cross-sectional view of an exemplary embodiment of poppet seat13.FIG. 4shows a cross-sectional view of an alternative exemplary embodiment of a poppet seat13′, which is modified compared to poppet seat13, to include bypass grooves59. Bypass grooves59prevent poppet25(not shown in this Figure) from completely blocking flow restriction30when the pulse valve is closed, which reduces the pulse amplitude, allowing a higher average fluid flow rate through the pulse valve. It will be noted by those skilled in this art that the bypass function can also be accomplished with ports instead of bypass grooves59, or by preventing poppet25from fully contacting poppet seat13′, thereby creating an annular gap between the two.

FIG. 5is a schematic cross-sectional view100, illustrating a ground surface102on which a well-head104of a well or borehole106is disposed. A conduit108extends from well-head104down into borehole106. On surface102is disposed a pump110that is controlled by a flow rate control112, which can vary the speed of the pump to achieve a desired flow rate of fluid into the conduit through a fluid line114. The fluid circulated under pressure into the conduit is a relatively incompressible liquid, such as drilling mud or water, although other liquids might be used, including a mixture of a liquid and a gas, depending upon the application and its requirements. The conduit may be continuous coiled tubing or jointed tubing. Near the distal end of conduit108is disposed a pulse valve116, which is optionally part of serial string of tools and is configured and functions like the exemplary embodiment described above. Optionally, below (or above) pulse valve116is disposed one or more other tools118and/or120which may be employed. The specific tool(s) and function of pulse valve116depend on the application for which the drill string and pulse valve are being used. Examples of the well-known applications of pulse valves are listed above. Pulse valve116is shown (schematically) discharging into a borehole106that is open to the surface, producing negative pressure pulses122that propagate into the borehole and the surrounding earth, and positive pressure pulses123that propagate inside conduit108, whenever the valve closes Borehole106may also be closed so that all fluid is forced into the formation, in which case, positive pressure pulses are produced in the borehole when the valve opens

The design and operation of pulse valve116so as to use the Venturi effect to develop a lower pressure for operating the pulse valve and to avoid dumping fluid directly into the borehole from the sides of the pulse valve (as has been done in earlier designs described in the above-noted commonly assigned patents) provide several advantages. Since the present novel design does not even include openings in the side of the pulse valve body that can be used to dump pressurized fluid into the borehole, all of the pressurized fluid entering the inlet of pulse valve exits through the outlet and remains available for application to downstream tools. Pulse valve116can also produce a relatively longer duration pressure pulse, which increases the impulse energy and effective range of the pressure pulses. The longer pulse duration is the direct result of reduced differential pressure as discussed above. The use of a flow restriction in flow passage53further increases the pulse width by slowing the flow of the pressurized fluid that moves the pilot. The length of the travel of the pilot and poppet may also be increased to increase the pulse duration; however, this approach leads to increased cost for the pulse valve, since the increased travel length requires longer parts.

A novel aspect of the present pulse valve is its use of the Venturi effect arising from the flow of fluid through the restricted throat of the poppet seat to provide a differential pressure used to operate the pulse valve, i.e., to move the pilot between the upper and lower positions, and to close the pulse valve by moving the poppet into its closed position within the poppet seat. In addition, the cycle rate or pulse frequency of the pulse valve can readily be reduced by reducing the flow rate of the fluid through the pulse valve, to enable seismic interpretation and pore pressure prediction when the tools are used as a seismic source. Further, it is possible to control the impulse amplitude of the pressure impulses produced by the pulse valve by increasing or decreasing the size of the bypass ports, while maintaining pulse duration and cycle rate.

FIG. 9includes three schematic views240that illustrate how an exemplary pulse valve246as described above may be used as an engine to pull a long length of tubing242having components248, such as a motor and mill, jetting nozzle, logging tool, or perforating gun array at its distal end, into a generally horizontal well. When a fluid flow244in tubing242is interrupted by the pulse valve, a tensile load is introduced into the tubing by pulses252, causing it to stretch. In a typical configuration, the pulse duration is on the order of 20 ms, which is the time that the pulse valve is closed, while the period between pulses is about 80 ms, or the interval during which the pulse valve is open. When the tubing stretches, as indicated by reference numeral250, the distal end of the tubing moves forward within the well, e.g., by about one inch, as indicated by a reference number254. When the pulse valve opens again, the hydraulic pulse engine stops moving, but strain pulses252propagate up the tubing, causing the entire tubing string to again move forward a small amount, as indicated by reference numeral256. In a typical application, the motion of the tubing string is on the order of one-inch per pulse, as indicated. The upper end of the tubing is connected to a hoist system in the case of jointed tubing, or to a heavy reel of coiled tubing that constantly feeds the tubing into the well (neither shown). This surface system is massive and absorbs the strain energy pulse, so that it is not reflected back down the well.

FIG. 10includes three schematic illustrations270that show how an exemplary pulse valve280, which is configured and operates as discussed above, may be used to enhance the placement of chemicals, such as an acid278that is flowing through tubing272. The acid is thus forced into a formation276surrounding a wellbore274. In this application of the pulse valve, the upper end of the wellbore is closed so that all of the fluid (e.g., the acid) is forced into the surrounding formation by pressure pulses284. Interrupting the flow of fluid generates an upstream pressure pulse282that stores considerable energy. When the pressure pulse is released, the flow of fluid into the wellbore is substantially greater than the average flow rate of the fluid being pumped, which results in cyclic surging of the flow of the fluid into the formation. The pulse valve thus aids acid placement in the surrounding formation. This same approach can also be used for forcing other types of fluid into the formation around a well.

In the event that the wellbore is open to allow circulation, the surge of fluid introduced into the well causes a surge in the flow velocity in the annulus around the drill string. This flow surge can be used to enhance the transport of sand or other debris out of the horizontal and inclined sections of the wellbore.

Although the concepts disclosed herein have been described in connection with the preferred form of practicing them and modifications thereto, those of ordinary skill in the art will understand that many other modifications can be made thereto within the scope of the claims that follow. Accordingly, it is not intended that the scope of these concepts in any way be limited by the above description, but instead be determined entirely by reference to the claims that follow.