Mechanical tube wave sources and methods of use for liquid filled boreholes

The current application discloses methods and systems for generating mechanical tube waves in fluid filled boreholes penetrating subterranean formations. In one embodiment, the system of the current application comprises an energy storage chamber; a fast operating valve connected to the energy storage chamber; a pipe connected to the valve and extending to the liquid-filled borehole; wherein the energy storage chamber contains a first pressure that is substantially different from a second pressure in the pipe so that a fast operation of the valve generates a tube wave in the pipe.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. All references discussed herein, including patent and non-patent literatures, are incorporated by reference into the current application.

Tube waves, otherwise known as Stoneley waves, are plane pressure waves that propagate through a tubular medium, or an annulus. In some cases, these waves reflect from changes in the characteristic impedance of the medium. Examples of such changes include: pipe diameter, closed end, free surface, gas bubble, compressibility, density, speed of sound, pipe elastic modulus, pipe supporting material (or lack thereof), holes with flow capacity, etc. With some knowledge of the wellbore geometry and/or the speed of the tube wave, the complex reflection patterns can be interpreted to yield useful information about the wellbore. Some examples of such information include locating the top of cement, identifying the setting of cement, locating which perforations in a well are passing fluid, confirming shifting of control valves, locating coiled tubing relative to downhole features, etc. One particular advantage of using methods based upon tube waves, is information about the bottom of the well can be gleaned using only surface equipment. A particular challenge in applying these techniques is developing a repeatable and reliable means to generate useful tube wave forms. Figures of merit for these sources include rate of pressure change, frequency spectrum, peak power, total energy, repeatability, and reliability.

U.S. Pat. No. 3,254,524 discloses a method and apparatus for testing tubular equipment such as a pipe. A mechanical shock wave is generated by suddenly obstructing a moving fluid, causing a local expansion of the fluid followed by a reversely directed pressure or shock wave that is propagated through the fluid, a phenomenon commonly referred to as “water hammer”. A centrifugal pump is employed to move the fluid in a closed circuit of pipes and to maintain the fluid under a constant pressure. A fast-acting valve is connected to the pipe line downstream from the test specimen. A sudden close of the valve generates a shock wave that propagates reversely through the test specimen and therefore measures the feature of the test specimen.

U.S. Pat. No. 3,979,724 discloses a method and apparatus for determining the position of the bottom end of a long pipe in a deep water-filled borehole. A shock wave is first generated in the water at the surface end of the pipe. The shock wave travels down the pipe to the bottom end of the pipe and passes into the liquid in the borehole, generating an expanding seismic wave in the earth. A plurality of geophones is set out at the surface of the earth to detect the arrival of the seismic wave, based on which the position of the end of the pipe is calculated. In some embodiments, a chamber filled with a combustible mixture is detonated by a spark plug to make the shock wave. In some other embodiments, a chamber containing one or more explosive materials is detonated to produce the shock wave. In some further embodiments, a high pressure liquid is provided through a pipe and a valve to a disc that is scaled across an opening connected to a chamber. The disc is frangible and at a selected pressure of liquid on its surface, will fracture and explosively permit the pressurized liquid in the pipe to expand into the chamber and initiate a shock wave therein.

U.S. Pat. No. 6,401,814 discloses a method for determining the location or displacement of a cementing plug during a cementing operation by transmitting one or more pressure pulses through the fluid in the wellbore. The pressure pluses are reflected off of the plug and received by a pressure sensor. Information regarding the timing of the reflected pressure pulses may be used to determine the location or displacement of the plug. A valve can be opened momentarily to vent pressure from a flowline and, thus, transmit a negative pressure pulse through the fluid in the casing string. Alternatively, an air gun can be used to transmit a positive pressure pulse through the fluid in the casing string. Alternatively, a pump can be operated in a manner to transmit a pressure pulse, such as by varying the pump's motor speed or by momentarily disengaging the motor from the pump, etc.

As disclosed in published U.S. Pat. App. No. 20080239872 A1, achieving accurate, real-time measurements during well completion and stimulation treatments has long been a goal in the oil and gas industry. Accurate measurement of bottom hole pressure during fracture treatments, for example, would allow an operator to observe fracture growth trends in real-time, and change treatment conditions accordingly. Similarly, location of balls seated in perforations would facilitate acid diversion treatments. However, real-time measurements of borehole completion and stimulation treatments are rarely performed with current technology because the borehole environment is hostile to wiring and tends to rapidly attenuate electromagnetic signals. For example, the abrasiveness of the fracturing slurry is destructive to any exposed cable placed in the wellbore for delivering data to the surface.

U.S. Pat. App. No. 20090159272 A1 discloses that tube waves may be used for detection and monitoring of feature state to enhance stimulation operations and remediate failure conditions. For example, proper sealing of perforations may be confirmed based on lack of a reflection of a tube wave by the perforations. Alternatively, at least one of amplitude, frequency, attenuation, dispersion and travel time associated with a tube wave and reflection may be used to determine feature state. If a sealant fails during treatment then the failure condition is indicated by appearance of a tube wave reflection. Consequently, the stimulation operation can be stopped in a timely manner, and remediation by means, for example, of pumping diversion fluid or dropping of balls, can be reinitiated until the difference between the expected responses and responses measured by the instrument along the segment to be stimulated confirm that sealing has taken place and that stimulation of the intended zone can resume. Further, specific remediation steps may be selected based on response of the borehole system to tube waves. The efficacy of the selected remediation steps may also be determined by response of the borehole system to tube waves during or after execution of those steps.

U.S. Pat. App. No. 20080236935 A1 discloses that tube waves may be used to transmit an indication of the depth at which a condition is detected in a well. In particular, the depth is calculated based on the difference in arrival time at the surface of a first tube wave which propagates directly upward in the borehole and a second tube wave which initially travels downward and is then reflected upward. The tube waves may be generated by a canister designed to implode at a certain pressure.

WO2009086279 discloses methods and systems for measuring acoustic signals in an annular region. The system includes a tool housed in a tool housing for deployment downhole in a borehole, and an acoustic transducer mounted on the tool. The acoustic signals can be measured by sensors mounted on a borehole wall or within the downhole tool.

However, there remains a need to further improve the system and method for generating tube waves for use in liquid filled boreholes penetrating subterranean formations.

SUMMARY

According to one aspect, there is provided a system for generating tube waves in a liquid-filled borehole penetrating a subterranean formation. The system comprises an energy storage chamber, a fast operating valve connected to the chamber, a pipe connected to the valve and extending to the liquid-filled borehole, where said energy storage chamber contains a first pressure that is substantially different from a second pressure in the pipe so that a fast operation of the valve generates a tube wave in the pipe. In some embodiments, the system, wherein the first pressure is higher than the second pressure and the generated tube wave is a positive tube wave. In some other embodiments, the first pressure is lower than the second pressure and the generated tube wave is a negative tube wave.

The energy storage chamber may contain a compressible medium, which may be selected from a group consisting of air, nitrogen, alcohol, ethyl ether, water, drilling fluid, cement slurry, oil, and their mixtures. In one example, the compressible medium is compressed nitrogen.

In one illustrated embodiment, the energy storage chamber comprises a plurality of accumulators connected to a common hub, with each accumulator containing compressed nitrogen. Such Nitrogen may be emplaced at a pressure up to 15,000 psi. In one embodiment, such nitrogen was emplaced at a pressure up to 5,000 psi.

The system for generating tube waves in a liquid-filled borehole may optionally include a charger that is connected to the energy storage chamber for pre-charging the energy storage chamber. The charger can be a pump, a compressor, a vent line leading to atmospheric pressure, a plunger that can be moved in or out, or a vacuum, depending on the system setup.

In some embodiments, the generated tube wave is at a pressure that is at least 50 psi above or below the pressure in the pipe. In some other embodiments, the generated tube wave is at a pressure that is at least 200 psi above or below the pressure in the pipe. In some further embodiments, the generated tube wave is at a pressure that is at least 500 psi above or below the pressure in the pipe. In further embodiments where extreme pressure differences are desired, the generated wave may be near the vapor pressure of the fluid or as high as the rated working pressure of the tubulars conveying the pressure wave.

Moreover, the fast operating valve is configured to open or close a flow path of the medium through the valve in less than or equal to approximately 500 milliseconds. In some embodiments, the fast operating valve is configured to open or close a flow path of the medium through the valve in approximately 50 milliseconds. In some other embodiments, the fast operating valve is configured to open or close a flow path of the medium through the valve in approximately 100 milliseconds. In some further embodiments, the fast operating valve is configured to open or close a flow path of the medium through the valve in approximately 200 milliseconds. In one specific embodiment, the fast operating valve was configured to open or close a flow path of the medium through the valve in approximately 120 milliseconds.

In one specific example, the fast operating valve is a rotary valve that operates on a quarter turn by a pneumatic actuator assisted in opening by a spring. In some other examples, the valve is a regenerative valve, including but not limited to poppet valves, diaphragm valves, flow actuated valves, etc. A regenerative valve is one in which once the motion of the valve has been initiated by an external signal, the motion of the valve is driven by either pressure differences or flow forces internal to the valve such that it will complete its motion even in the event that the external signal is removed. In one embodiment, there is provided a regenerative valve comprising a control chamber, a treating chamber disposed below the control chamber but not in fluid communication with the control chamber, and a poppet that extends from the control chamber to the treating chamber and is capable of reciprocating within the control chamber and the treating chamber. The treating chamber can be connected to the energy storage chamber via an upstream port and the fluid-filled borehole via a downstream port.

In one embodiment, the poppet comprises a control piston disposed inside the control chamber, a treating seat disposed inside the treating chamber, and a stem connecting the control piston and the treating seat. The control piston divides the control chamber into an upper sub-chamber and a lower sub-chamber that are not in fluid communication with each other. The upper sub-chamber is in fluid communication with an outside of the control chamber via an upper port, and the lower sub-chamber is in fluid communication with the outside of the control chamber via an lower port, so that a control fluid can be injected into or depleted from the upper sub-chamber or the lower sub-chamber in order to move the poppet up or down.

In one case, the control piston is a monolithic component of the poppet. In another case, the control piston is a separate component from the poppet, and the control piston is slidingly connected to a narrowed stem of the poppet and is further restricted by a stopper fastened to a top of the poppet.

In an improved version of the poppet valve, a buffering chamber is provided above the control chamber but not in fluid communication with the control chamber. The poppet extends from the buffering chamber through the control chamber to the treating chamber and is capable of reciprocating within the buffering chamber, the control chamber, and the treating chamber. The poppet contains a hollow passage so that the downstream port is in fluid communication with the buffering chamber.

In one embodiment, the treating seat has a cross sectional profile that is larger than that of the stem of the poppet. In another embodiment, the treating seat has a cross sectional profile that is substantially the same as that of the stem of the poppet. In a further embodiment, the treating seat has a cross sectional profile that is smaller than that of the stem of the poppet.

In several illustrated embodiments, the treating seat is configured to engage a structure at the juncture of the downstream port and the treating chamber and seal off a fluid passage from the treating chamber to the downstream port. In one case, the treating seat seals off the fluid passage by a seal disposed in a retaining space formed on a side surface of the treating seat of the poppet. In another case, the treating seat seals off the fluid passage by a seal disposed in a retaining space formed on a bottom surface of the treating seat of the poppet. In a further case, the treating seat seals off the fluid passage by a seal disposed in a retaining space formed on an inner side surface of the downstream port. In an even further case, the treating seat seals off the fluid passage by engaging a disposable component located at an opening of the downstream port to the treating chamber. In yet another case, the treating seat seals off the fluid passage by a disposable component located at a tip of the poppet.

The regenerative valve can also be a regenerative diaphragm valve which may comprise a control chamber, a treating chamber disposed below the control chamber, a diaphragm disposed between the control chamber and the treating chamber, and a poppet disposed at a center of the diaphragm. The treating chamber can be connected to the energy storage chamber via an upstream port and the fluid-filled borehole via a downstream port. The control chamber can be connected to an outside of the valve via a control port. The poppet can be substantially in the shape of a reversed “T” and contain an orifice through a center of the poppet, which enables the control chamber to be in fluid communication with the treating chamber under substantial restrictions.

The regenerative valve can also be a pop-safety relief type valve which comprises an upstream port, a downstream port, a poppet chamber formed between the upstream port and the downstream port, and a poppet disposed in the poppet chamber. Said poppet chamber comprises a section where the poppet is a substantial portion of the cross section of the chamber and the chamber has a larger cross section than the upstream port. A spring can be provided to connect the poppet to the downstream port and push the poppet towards the upstream port. A stopper can be optionally included in the poppet chamber to restrict a movement of the poppet. An orifice can also be provided around a center of the poppet that allows a fluid to pass but with substantial restrictions. Moreover, a trigger can be provided so that when the trigger is engaged, it holds the poppet in a first position, and when the trigger is released, the poppet moves to a second position.

When the regenerative valve is a flow actuated tube wave valve, it may comprise an upstream port, a downstream port, and a swing check disposed between the upstream port and the downstream port. The swing check can be pivotally connected to an inner surface of the valve and is capable of assuming one of two positions: a first position where the swing check is substantially parallel to a longitudinal axis of the valve thereby allowing fluids to pass between the upstream port and the downstream port, and a second position where the swing check is substantially perpendicular to the longitudinal axis of the valve thereby obstructing fluids from passing between the upstream port and the downstream port.

According to another aspect of the application, there is provided a system for generating tube waves in a liquid-filled borehole penetrating a subterranean formation, where the system comprises a weight, an actuator that controls a movement of the weight, a plunger, and a pipe having a top end and a bottom end, where the top end is transverse by the plunger and is not in fluid communication with an outside of the pipe, and the bottom end extends to the liquid-filled borehole for delivering the tube waves generated by the system. The weight is configured to render mechanical impact on the plunger upon an operation of the actuator.

In one embodiment, the system further comprises a spring disposed between the plunger and a top surface of the top end the pipe so that the spring exerts an upward force upon the plunger. In another embodiment, the system may comprise a spring disposed between the plunger and a bottom surface of the top end of the pipe so that the spring exerts a downward force upon the plunger.

According to further aspect of the application, there is provided a system for generating tube waves in a liquid-filled borehole penetrating a subterranean formation, where the system comprises a housing that is connected to a cavity on one end and a downstream port on the other end that is further connected to the liquid-filled borehole; a flyer disposed inside the housing, where said flyer further comprises a hollow space around a center of the flyer; and a piston disposed inside the hollow space of the flyer; where the piston is configured to move up and down inside the hollow space to exert mechanical impacts on the flyer, which in turn moves up and down inside the housing to generate tube waves in the downstream port.

The hollow space of the flyer can be further divided into an upper space and a lower space that are not in fluid communication with each other so that injecting fluids into or depleting fluids out of the upper space or the lower space moves the piston up or down inside the hollow space of the flyer. Optionally, the pressure in the cavity is equalized with the pressure in the downstream port. Optionally, the cavity is made of elastic materials and contains a low bulk modulus fill fluid. Also optionally, a first spring is provided to connect the flyer to the cavity and a second spring is provided to connect the flyer to the downstream port.

According to yet another aspect of the application, there is provided a system for generating tube waves in a liquid-filled borehole penetrating a subterranean formation, where the system comprises a pipe that connects an upstream port on one side and a downstream port on another side; an orifice formed inside the pipe around the juncture of the upstream port and the downstream port; and a deformable object that is configured to assume a first position wherein the deformable object lodges at the orifice and blocks a fluid communication between the upstream port and the downstream port and a second position where the deformable object deforms and passes through the orifice and reopens the fluid communication between the upstream port and the downstream port. In one embodiment, the deformable object is made of degradable material, such as collagen or the plastic poly-lactic acid.

According to an even further aspect of the application, there is provided a system for generating tube waves in a liquid-filled borehole penetrating a subterranean formation, where the system comprises a stinger having a first end and a second end; an actuator connected to the first end of the stinger; a plate formed at the second end of the stinger, said plate having a cross-sectional profile that is larger than that of the stinger; where the actuator is configured to move the stinger up and down in the liquid-filled borehole and the plate generates tube waves in the liquid-filled borehole. This system is particularly useful in the liquid-filled borehole having a free liquid surface under which the second end of the stinger is immersed.

In some cases, the system further comprises a first pressure transducer that is positioned proximate to the second end of the stinger and is connected to a ground surface via a first cable. The first cable can run within an annulus formed between the borehole and the stinger, and is fastened to an external surface of the tube by a clamp. In some other cases, the system further comprises a second pressure transducer that is position at a bottom of the plate and is connected to a ground surface via a second cable. The second cable may run within the stinger. Optionally, a suspension system is provided to afford compliance for the stinger to move up and down.

According to an additional aspect of the application, there is provided an apparatus for generating tube waves in a liquid-filled borehole penetrating a subterranean formation, where the apparatus comprises a canister covered by a microscope slide. In one embodiment, the canister is a glass tube such as a centrifuge tube. The canister may further contain a weighting material.

DETAILED DESCRIPTION OF SOME ILLUSTRATIVE EMBODIMENTS

Embodiments of the current application generally relate to systems and methods for generating tube waves for use in wellbores penetrating subterranean formations. The following detailed description illustrates embodiments of the application by way of example and not by way of limitation. All numbers disclosed herein are approximate values unless stated otherwise, regardless whether the word “about” or “approximately” is used in connection therewith. The numbers may vary by up to 1%, 2%, 5%, or sometimes 10% to 20%. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number falling within the range is specifically and expressly disclosed.

FIG. 1shows a system100for generating tube waves for use in a borehole10that penetrates a subterranean formation20containing, for example, hydrocarbons. The system100comprises an energy storage chamber50, a fast operating valve40which is connected to the energy storage chamber50, and a pipe30which is connected to the valve40and extends to the wellbore10. The energy storage chamber50may contain a compressible medium, such as air, nitrogen, alcohol, ethyl ether, water, drilling fluids, cement slurries, oil, etc. that can be subject to an elevated pressure that is substantially higher than the pressure in the borehole10. In such an embodiment, a rapid opening of the valve40may generate a tube wave that starts with a positive or increasing pressure in the borehole10as fluid rapidly moves from the energy storage chamber50, through the valve40and into the pipe30to relieve the high pressure down to the wellbore pressure. The resulting tube wave is referred to as a positive tube wave. Alternatively, the energy storage chamber50can be substantially vacuum or under a pressure that is significantly lower than the pressure in the borehole10. In such an event, a fast opening of the valve40may generate a tube wave that starts with a negative or falling pressure in the borehole10as fluid from the wellbore10moves into the pipe30and further through valve40to finally bring the pressure in the energy storage chamber50to substantially the wellbore pressure. The resulting tube wave is referred to as a negative tube wave. In both types of systems the pressure wave generated frequently consists of a complex waveform of which only the beginning part is well described by the “positive” and “negative” language above, but this initial pressure change is what is used to name these waves. Positive is to be interpreted as being positive with respect to or higher than the wellbore pressure with negative being similarly interpreted to be lower than the well bore pressure. A further type of wave consists of an initial peak immediately followed by a peak of opposite sign and similar magnitude. Such a wave is referred to as a doublet.

Optionally, system100may further comprise a charger60that is positioned at the surface of the wellsite and connected to the energy storage chamber50to pre-charge the energy storage chamber50before opening valve40. When a positive pressure tube wave is needed, the charger60can be a pump, an actuated plunger, or compressor that compresses the medium contained in the energy storage chamber50and increases the pressure in the energy storage chamber50. When a negative pressure tube wave is desired, the charger60may be a suction device or a vent that depletes the medium contained in the energy storage chamber50to create a pressure below that in the borehole10.

The energy storage chamber50may comprises one or more sub-chambers (not shown) that are in fluid communication with each other, either in series or in parallel. In one embodiment, the energy storage chamber50comprises a plurality of metal containers (called “accumulators”) that enclose a compressed air, such as nitrogen. The accumulators can be substantially cylindrical in shape, with approximately 80 mm in diameter and 388 mm in length. An internal mechanism is provided to allow a charge of gas or fluid to be retained inside the accumulator at some initial or pre-charge pressure This mechanism allows the external fluid to enter the accumulator and further compress the pre-charged media to a higher pressure. The fluid that has entered may be later allowed to leave, at which point the internal media will resume substantially its pre-charged pressure. In the case of gas as a pre-charge media, the compression and expansion of the gas during this cycle may occur on a time scale short enough that there is little heat exchange with the structures, leading to significant changes in the temperature of the gas and a reduction of the energy delivered while discharging the external fluid. This loss may be mitigated by using internal structures (such as open cell foam, liquids, and open metal forms like mesh and perforated metal) to provide heat during expansion. In the case of a media that is substantially liquid at room temperature this pre-charge pressure is sometimes atmospheric pressure or the vapor pressure of the fluid. Each accumulator may contain an initial pressure up to 15,000 psi in the case where the charging and working pressure of the chamber are 15,000 psi as is common in oilfield treating equipment. The charging pressure may be substantially higher than the working pressure of the pipe30or the wellbore10due to pressure losses in the fast opening valve40. In some cases, the pre-charge for an accumulator used to generate positive tube waves will be pre-charged to approximately ⅓ of the planned charging pressure. In some cases, this pre-charge pressure will be approximately 5,000 psi in the case of a chamber rated for 15,000 charging and working pressure. The accumulators can be charged with external fluid at the wellsite by charger60as shown inFIG. 1of the application. With the appropriate charger60they may also be pre-charged with gas at the well site. Alternatively, the accumulators can be charged offsite at a factory and transported to the wellsite when needed. Due to the small size of the accumulator, it is highly portable and affords great flexibility to oilfield operations.

Typically, for applications in fluid-filled boreholes penetrating subterranean formations, tube waves need to be delivered under relatively high pressure and carry relatively high energy compared with tube waves generated for other uses. This is because the fluid in the borehole is normally under high pressure from the subterranean formation and/or surface equipment such as pumps. Low-energy tube waves may not be able to propagate far enough before it is absorbed by the fluid in the borehole. Also, a low-energy tube wave may not be able to produce a sufficiently high signal-noise ratio for sensors to detect the reflected wave when accompanied by the noise produced during well servicing. Accordingly, in one embodiment of the current application, there is provided a method or system for generating tube waves with a pressure that is equal to or below about 1% of wellbore pressure or equal to below about 50 psi, which are primarily suitable for wellbores not under services, i.e. quiet wellbores. The pressure difference can be either positive or negative. In another embodiment, there is provided a method or system for generating tube waves with a pressure that is between about 2% to about 20% (inclusive) of wellbore pressure or between about 100 psi to 500 psi (inclusive). Again, the pressure difference can be either positive or negative. Tube waves in this range are particularly useful in wellbores under some services but without an extraordinary amount of noises. For wellbores having a substantial amount of background noises (such as wellbores under hydraulic fracturing treatment) or wellbores having changed dimensions and/or structures, tube waves with higher energy are needed. Accordingly, in a further embodiment, there is provided a method or system for generating tube waves with a pressure that is between −30% to −100% of wellbore pressure or +50% to +200% of wellbore pressure.

The valve40can be a plug valve (sometimes referred to as a hammer valve in the oilfield due to the end connections that are assembled using a hammer), a ball valve, or any other type of valves that are capable of opening/closing in a relatively fast speed. In some cases, the valve40is a rotary valve that operates on quarter turns, although other variations can be employed as well. In this patent application, when the terms “fast”, “quick”, and “rapid” are used in connection with the description of the valve40, they generally mean that the valve40is capable of opening or closing the flow path of the medium in a time that is within an order of magnitude of the firing duration of the tube wave, illustrated in for example inFIG. 2Aas time “t”. In one embodiment, the valve40is capable of opening or closing the flow path of the medium in a time that is less than the firing duration of the tube wave. In another embodiment, the valve40is capable of opening or closing the flow path of the medium in a time that is between about 1-3 times (inclusive) the firing duration of the tube wave.

In general, the fast operating valve of the current application is capable of opening or closing the flow path of the medium in less than or equal to approximately 500 milliseconds. In one exemplary embodiment as illustrated inFIG. 2A, the firing duration of the tube wave was approximately 50 milliseconds and the fast-operating valve40was capable of opening or closing the flow path of the medium in approximately 120 milliseconds. In other embodiments, the fast-operating valve40is capable of opening or closing the flow path of the medium in approximately 50 milliseconds, 75 milliseconds, 100 milliseconds, 150 milliseconds, 175 milliseconds, 200 milliseconds, 250 milliseconds, 300 milliseconds, 350 milliseconds, 400 milliseconds, 450 milliseconds, or 500 milliseconds.

The valve40can be pneumatically or hydraulically operated. An actuator (not shown) incorporating a spring (not shown) that acts during the opening or closing cycle of the valve40can be used to increase the opening or closing speed of the valve40. Vane actuators may be selected over piston actuators for this application. In general, the higher the chamber pressure, the more torque is required to open the valve40due to the friction in the seals. However, an increased torque typically means slower opening/closing of the valve40, hence increasing volumes of air or other medium that is passed through the valve40. Therefore, an operator often needs to carefully balance the benefit of operating under higher chamber pressure (hence higher-energized tube waves) and the drawback associated with the increased torque (hence the slower opening/closing of the valve). A proper balance needs to be struck to achieve an overall satisfactory result.

In one specific embodiment of the application, a standard 2×1 size 1502 hammer valve such as the FMC's ULT 150 plug valve part number P516108 was used as the actuator. The specification of the valve can be found at FMC's online catalogue. A spring was used to assist the opening of the valve. This valve has a cylindrical plug with a round cross drill for the fluid passage that is 0.75″ bore. The two ports tapered from the full bore of the end connections (1.75″) down to match the bore of the plug. Two seal sections were disposed, one on each port such that pressure applied to one port pushes the plug into the opposite seal section, effecting a seal. Each seal section had a central hole matching the plug bore. When the plug was rotated such that the plug bore, the two seal section bores, and the two valve port bores are lined up, it was in the open position and provided a path with at least 0.75″ inside diameter through the entire valve. When the plug is rotated 90 degrees this path was closed. When three accumulators were connected to a common wellsite manifold (not shown), an initial pressure of 15,000 psi was achieved upstream of the valve40. The actuator was then activated to rapidly open the valve40, producing a tube wave of approximately 230 psi. The result of one experiment is shown inFIG. 2Aof the current application. The result of another experiment is shown inFIG. 2Bof the current application where the valve was fired into an orifice rather than a well so the outlet pressure signature is simpler comparing to that inFIG. 2Abecause there were no reflections from the borehole.

In some other embodiments, the valve40can be one of the regenerative valves as discussed in more detail below. Generally speaking, a regenerative valve means a type of valve that opens with an increasing force once an initial stage of opening is assumed. In some cases, the regenerative valve has a moving element disposed therein, said moving element having a first area that is exposed to a first port and a second area that is exposed to a second port, where said first area is different from the second area so that the moving element is held in a closed position upon the second port until an external force is applied to push the moving element away from the second port. At that moment, an increasing force is exerted by one of the first pressure in the first port and the second pressure in the second port functions on one of the first area and the second area, therefore push the moving element to a fully opened state.

An example of a regenerative valve140is shown inFIG. 3, which comprises a control chamber130, a treating chamber120, and a poppet103disposed therein. A set of seals107,108are provided between poppet103and the valve body170, therefore preventing the control chamber130and the treating chamber120from being in fluid communication with each other. For clarity, the seal that is positioned close to the control chamber130side is called the control fluid seal108; the seal that is positioned close to the treating chamber120side is called the treating fluid seal107. Optionally, a port155can be provided between the control fluid seal108and the treating fluid seal107and used for purposes such as lubricating the friction between the poppet103and the valve body170and providing a path for leakage to leave the valve body170and be visible externally.

Within the control chamber130, the poppet103further comprises a control piston135that extends substantially perpendicularly from the longitudinal axis “Y” of the poppet103. A control piston seal109is provided between the control piston135and the side walls of the control chamber130, therefore separating the control chamber130into two sub-chambers131,132that are not in fluid communication with each other inside the control chamber130. An upper port151is provided to open the upper sub-chamber131of the control chamber to the control fluid. A lower port152is provided to open the lower sub-chamber132of the control chamber130to the control fluid. A cushion160can be provided at the top wall of the control chamber130to reduce the mechanical impact of the poppet103on the valve140by providing an orifice that slows the end of the poppet's motion in a gradual fashion rather than by an abrupt impact.

Within the treating chamber120, the poppet103similarly comprises a treating seat137that extends substantially perpendicularly from the longitudinal axis “Y” of the poppet103. Unlike the control piston135in the control chamber130, the treating seat137in the treating chamber120does not extend all the way to the side walls of the treating chamber120. Instead, the peripheral wall of treating seat137may be fully surrounded by the treating fluid during operation and the treating seat137does not divide the treating chamber120into multiple sub-chambers.

As used in this patent application, terms such as “up”, “down”, “upper”, “lower”, “top” and “bottom” and other like terms indicate relative positions of the various embodiments of the system and apparatus of the present application which is vertically oriented as shown in the drawings. However, it should be borne in mind that the system and apparatus of the present application can be oriented vertically, highly deviated from the vertical, or horizontally. Depending on the circumstances, such terms may refer to a left to right, right to left, or other relationship as appropriate.

In one embodiment, the lower portion of the treating seat137tapers downwardly and inwardly, generally indicated as113inFIG. 3of the application. Therefore, the horizontally cross-sectional area of the treating seat137is reduced from a larger top surface area to a smaller bottom surface area. A complimentary but steeper profile can be provided at the bottom wall of the treating chamber120where a downstream port110is connected to the treating chamber120. Therefore, when the poppet103moves downwardly towards the downstream port110, a tight seal can be formed between the treating seat137and the bottom wall of the treating chamber120where the downstream port110joins.

The treating chamber120is further connected to an upstream port115. During operation, a treating fluid can be introduced into the treating chamber120via the upstream port115and, when treating seat137is not engaged with the bottom wall of the treating chamber120, the treating fluid flows through the treating chamber120and discharges through the downstream port110.

For the ease of reference, as used in the current application, the cross-sectional area of the portion of the poppet that engages and seals the downstream port110is called the “seat area” of the poppet, and the cross-sectional area of the main body of the poppet is called the “stem area” of the poppet. Therefore, in the embodiment shown inFIG. 3, the seat area (A2) of poppet103is larger than the stem area (A1) of poppet103. This feature leads to a rapid, regenerative opening of poppet103.

Starting with the situation when the poppet103is in an opened condition, the upstream port115is in fluid communication with the treating chamber120which in turn is in fluid communication with the downstream port110, i.e. P1=P2. To close the valve140, the poppet103needs to be moved downwardly to engage the downstream port110. This can be achieved by introducing the control fluid into the upper sub-chamber131of the control chamber130via the upper port151. The control fluid needs to be supplied at a pressure such that pressure times the area of the control piston135is larger than the P2pressure times the area of the poppet stem at seal170. The increased pressure in the upper sub-chamber131pushes down the control piston135, which in turn brings down the poppet103.

After the poppet103engages with and seals off the downstream port110, the pressure in the treating chamber120is increased by introducing high-pressured treating fluid via the upstream port115. The increased pressure in the treating chamber120acts to push the poppet103down. Eventually, the pressure in the treating chamber120is sufficiently high that it is no longer necessary to maintain a positive pressure in the upper sub-chamber131of the control chamber130because the pressure P2times the annular area between A1and A2exceeds the force due to the pressure P1times the area A2. At this point, the positive pressure in the upper sub-chamber131can be completely removed. In some cases, even a negative pressure can be introduced into the upper sub-chamber131, which may further facilitate the rapid opening of the valve140when it is time for the valve to open. It may also be advantageous to have A1and A2disposed such that some pressure is always required in the upper sub-chamber131to keep the valve closed.

To open the valve140, a positive pressure can be introduced into the lower sub-chamber132of the control chamber130. Alternatively, a negative pressure can be introduced into the upper sub-chamber131. At a certain point, an equilibrium is achieved when the downward force exerted by the pressure P2in the treating chamber120on the upper surface of the treating seat137is exactly the same as the sum of the upward force exerted by the borehole pressure P1on the lower surface of the treating seat137plus the upward force exerted by the positive pressure in the lower sub-chamber132(or the negative pressure in the upper sub-chamber131) of the control chamber130on the treating seat135of the poppet103.

Thereafter, a slight increase in the positive pressure in the lower sub-chamber132(or a slight increase in the negative pressure in the upper sub-chamber131) of the control chamber130will break the equilibrium and the poppet103will begin to move upwards to open the valve140. With the treating seat137departing slightly from the corresponding structure at the bottom wall of the treating chamber120where the downstream port110is connected, a small annulus is formed between the tapered portion of the treating seat137and the bottom wall of the treating chamber120. Accordingly, the treating chamber120starts to become in fluid communication with the downstream port110. The pressure P1in the downstream port110starts to rise and the pressure P2in the treating chamber120starts to decrease. Moreover, with the appearance of the small annulus, the entire seat area (shown as A2inFIG. 3) becomes subject to the increasing pressure P1. As a result, the upward force exerted by the increasing pressure P1on the seat area A2of the treating seat137grows rapidly, exceeding the downward force exerted by the decreasing pressure P2on the upper surface of the treating seat137. The net result is a regenerative, upwardly oriented, force that rapidly pushes the poppet103to a fully opened position.

The control fluid can be any medium that is capable of being injected into a cavity and exerting forces therein, such as air, nitrogen, alcohol, diethyl ether, water, silicone, hydrocarbon oil, their mixtures, etc. Similarly, the treating fluid can be any medium that is capable of being injected into a cavity and exerting forces therein, such as air, nitrogen, alcohol, diethyl ether, water, silicone, hydrocarbon oil, their mixtures, etc.

FIG. 4shows an improved embodiment ofFIG. 3, where an improved regenerative valve240is provided. The improved regenerative valve240does not contain a control piston135that extends all the way to the side walls of the control chamber130, as inFIG. 3. Instead, a disc235is provided between the poppet203and the side walls of the control chamber230, which divides the control chamber230into an upper sub-chamber231and a lower sub-chamber232. A set of seals209,209′ are provided at the side walls of the disc235to ensure that the upper sub-chamber231and the lower sub-chamber232are not in fluid communication with each other in the control chamber230. In one embodiment, the stem of the poppet203is narrowed at the region where the disc235is provided. Therefore, a shoulder237can be formed on the stem of the poppet203so that when disk235moves downwardly, the disc235can make contact with the shoulder237and push down the poppet203. Similarly, a stopper236can be provided at the top of the poppet203so that when disk235moves upwardly, the disc235can make contact with the stopper236and push up the poppet203. In this embodiment, the weight of the poppet203that needs to be moved upwardly or downwardly during an opening or closing motion of the valve is reduced, because the disc235does not form a portion of the poppet203. Accordingly, a faster opening or closing of the valve can be achieved.

In one embodiment, the upper port251is connected to a space260, which in turn is connected to the upper sub-chamber231of the control chamber230. The control fluid contained in space260can function as a shock absorption mechanism for the upwardly moving poppet203. This can be advantageous because a separate cushion (such as cushion160inFIG. 3) can be eliminated.

FIG. 5shows another improved embodiment ofFIG. 3. There, a pressure balanced regenerative valve340is provided. In this embodiment, poppet303contains a passage way304for fluids in the downstream port310to travel upwardly towards a buffering chamber360that is located on top of the control chamber330, as shown by arrows inFIG. 5. The passage way has a first orifice302that opens to the downstream port310and a second orifice302′ that opens to the buffering chamber360. Therefore, the buffering chamber360is in fluid communication with the downstream port310, and the pressure in the buffering chamber360is the same as the pressure in the downstream port310, i.e. P1. Hence, the valve340in the current embodiment is called a “balanced pressure” valve. Because one of the treating pressures is balanced by being applied to both sides of the poppet303, a much smaller actuator can be used to operate the valve. A faster actuation may also be achieved.

The buffering chamber360is separated from the control chamber330by a set of seals311,312and a port313disposed therebetween. Therefore, the buffering chamber360is not in fluid communication with the control chamber330. Likewise, the control chamber330is separate from the treating chamber320by a set of seals307,308and a port305disposed therebetween. Therefore, the control chamber330and the treating chamber320are not in fluid communication with each other. Optionally, a bearing314can be provided to facilitate the alignment of the poppet303in the middle of the valve340, and to reduce the impact of the pressure pulse on the seals, such as seal307by providing a throttling orifice. Also optionally, the treating chamber320can be equipped with more than one port315,315′ to improve the characteristics of the valve and reduce the side loads on the poppet303.

In this embodiment, the stem area may be selected independently depending on the purpose one intends to achieve. If the seat area is larger than the stem area, the poppet303will latch closed when the pressure in the treating chamber320is higher than the pressure in the downstream port, i.e. (P2>P1). Conversely, if the seat area is smaller than the stem area, the poppet303will latch closed when the pressure in the treating chamber320is lower than the pressure in the downstream port, i.e. (P1>P2). In one embodiment, the seat area is approximately zero.

To reduce the mechanical impact caused by rapidly opening the poppet303on the body of the valve340, a space337can be created in the upper sub-chamber331of the control chamber330, which as inFIG. 3, is separated from the lower sub-chamber332of the control chamber by a seal309disposed on the side wall of a control piston335. An upper port351is in fluid communication with the space337, which in turn is in fluid communication with the upper sub-chamber331of the control chamber330. A lower port352is in fluid communication with the lower sub-chamber332of the control chamber330. Space337is configured to closely fit a shoulder336formed at the corner of the poppet303and the control piston335. Therefore, when poppet303moves upwardly, the shoulder336engages with the space337creating an annular orifice. The control fluid in the space337is compressed to produce a resistant force against the movement of the poppet303. Therefore, the impact of the poppet303on the valve340is reduced. In one embodiment, the shoulder336may be made as a separate ring with some clearance on the poppet stem such that it can self align with space337and reduce the requirement for precision machining of these parts.

FIG. 6illustrates several different types of sealing mechanisms that may be applicable to the embodiments of the current application. They are provided as examples, not limitations, to the current application. Other variations are possible and should be considered within the scope of the current application. In general, sealing mechanisms in the current application are susceptible to wear and tear due to the high pressure in the chambers, fast motion of the poppet, and/or the pulsation of the fluids. In some cases, positive seal retaining mechanisms are employed; in some other cases, bonded seals are used. In some cases, high yield stress plastic (such as PEEK) or other elastic materials are used in the seal; in some other cases, metal to meal seal is employed. In some cases, one or more components of the sealing mechanism are modular so that they can be dissembled and replaced after wear and tear.

Referring now toFIG. 6, various different types of sealing mechanisms are depicted in the context of sealing the poppet403and the downstream port410, although it should be noted that such sealing mechanisms may be applicable to other locations of the valves as well. InFIG. 6A, a retaining space412is provided on the poppet403to accommodate the seal411, so as to prevent seal411from being extruded or dislocated from its original position due to pulsations of the fluids, frictions from the wall414of the downstream port410, etc. Alternatively, inFIG. 6C, the seal431and the retaining space432can be provided in the inner surface of wall414of the downstream port410.

To reduce the frictional force caused by the inner surface of the wall414of the downstream port410, inFIG. 6B, the seal421and the retaining space422can be provided at the bottom surface of the poppet403. Therefore, the seal is created between the bottom surface of the poppet403and the top surface of the wall414of the downstream port410. In all of these sealing systems the flexible sealing member may be advantageously bonded to the either the poppet403or to a replaceable part attached to the poppet.

InFIG. 6D, a replaceable component443is provided between the poppet403and the wall414of the downstream port410. In the illustrated embodiment, the displaceable component443is in the shape of a circular disc; however, other shapes can be applicable as well. Also, in the illustrated embodiment, the disc443is disposed upon a shoulder416created around the opening of the downstream port410. A seal441within a retaining space442can be optionally included between the disc and the wall414. A retaining ring444can be employed to keep the disc443in place. In the illustrated embodiment, the retaining ring444is lodged inside a retaining space445located in the vertical surface of the shoulder416at a location that is above the seal441. Protrusion446helps steer the high speed flow from a radial direction to an axial direction.

FIG. 6Eshows an improved version ofFIG. 6D. There, two shoulders416,417are created in the wall414of the downstream port410. The first shoulder416accommodates the replaceable disc453. A seal451is provided within a retaining space452, both located in the vertical surface of the first shoulder416. Alternatively, the seal may be located on the replaceable disc453. The second shoulder417is wider and higher comparing to the first shoulder416, and it accommodates the stopper454. Unlike the stopper444inFIG. 6Dwhich is lodged inside a retaining space445, inFIG. 6E, the stopper454is lodged in position by threads. That is, the outer surface of the stopper454comprises a series of threads which can engage with a series of complimentary threads located on the vertical wall of the second shoulder417. Optionally, a slanted surface458is created between the poppet403and the replaceable disc453to improve the overall seal of the assembly. Further, the angle of the poppet nose may sometimes be slightly steeper than the angle of the replaceable seat453in order to produce a line contact where the two come together. In this case, one or both of the elements may be expected to deform slightly to produce a contact strip such that the contact pressure is equal to the yield stress of the softer of the two materials.

FIG. 6Fshows a further improved version of the seal mechanism that can be used in the current application. Here, a replaceable component463is provided as a portion of the poppet403instead of the downstream port410. Specifically, in the illustrated embodiment, a tip466is created at the bottom of the poppet403. A replaceable disc463can be slid or screwed on the tip466and retained by a stopper464. In the illustrated embodiment, the stopper engages the tip466by threads, although other means of engagement can be utilized as well. Optionally, a seal461located within a retaining space462can be provided between the tip and the replaceable disc463. In one embodiment, a slanted surface468is created between the replaceable disc463and the wall414of the downstream port410to improve the overall seal of the assembly. In all of these sealing systems it may be advantageous to minimize the width of the sealing contact between the poppet and the seat to ensure that the sealing area of the poppet is close to the intended area, facilitating the desired regenerative action of the valve.

FIG. 7shows a regenerative diaphragm valve540. The left portion ofFIG. 7illustrates the cross-sectional view of the valve540in the closed state; the right portion ofFIG. 7illustrates the cross-sectional view of the valve540in the open state. Specifically, in the depicted embodiment, a diaphragm550is provided between a control chamber530and a treating chamber520. The control chamber530is equipped with a control port507; the treating chamber520is equipped with a port515. In the illustrated embodiment the diaphragm550is connected by a screw551to the body of the chambers on one side, and by a disc555and a stopper558to a poppet503on another side. A seal552within a retaining space553can be optionally provided between the disc555and the diaphragm550. While the drawing shows a relatively thick elastomer diaphragm, a metal diaphragm (typically corrugated) is also suitable for this service.

In the illustrated embodiment, poppet503has a cross-sectional profile that is substantially in the shape of a reversed “T”. The large base provides a large seat area that can engage and seal the downstream port510, which is optionally equipped with a port509; the slender stem comprises threads on the outer surface which can engage the stopper558and/or the retaining disc555of the diaphragm550. Optionally, an orifice is provided through the center of the poppet503, which enables the control chamber503to be in fluid communication with the treating chamber520, albeit with substantial restrictions.

In operation, the valve540can be regeneratively opened to produce fast onset of tube waves. Starting from the condition when the poppet503is in the open state, i.e. right half ofFIG. 7, the treating chamber520is in fluid communication with the downstream port510. The control port507is then opened to allow fluids being pumped into the control chamber530. When the pressure in the control chamber530is sufficiently high, the diaphragm550and the poppet503are pushed down to engage with and seal off the downstream port510. Once a seal is achieved, the pressure in the treating chamber520raises, partially or completely due to fluids passed through the orifice506in the poppet503. To fire the valve540, control port507can be opened either to the atmosphere or to the port509of the downstream port510. When the pressure in the control chamber530falls enough to pull the poppet503off its seat, the valve540regeneratively opens.

A pressure relief valve (not shown) to limit the maximum differential pressure across the diaphragm550can be optionally included, especially for use in high pressure services, which would further expedite the opening of the valve. Moreover, a gas chamber (not shown) can be optionally connected to the control chamber530, which would further expedite the opening of the valve by providing the ability to compress the contents of the control chamber530during opening.

Pop-safety relief type valves can also be used to produce tube waves. An example is shown inFIG. 8A. The valve540comprises an upstream port515, a downstream port510, and a poppet chamber520formed between the two ports. A poppet503is disposed inside the poppet chamber520. The poppet is connected to a spring504on one side, which in turn rests upon a seat512that is formed where the downstream port510connects to the chamber520. The spring504exerts forces on the poppet503, pushing the poppet503towards the upstream port510.

Starting with the “closed” condition as shown in the left half ofFIG. 8A, the poppet503rests upon a seat512formed around the opening of the upstream port515to the poppet chamber520and seals the upstream port515from the poppet chamber520. Thereafter, the pressure in the upstream port515is increased and/or the pressure in the poppet chamber520is decreased. When the pressure difference between the upstream port510and the poppet chamber520is sufficiently high to overcome the downward force exerted by the spring504, the poppet503is started to be lifted off the seat512. When this happens, more area of the poppet503is exposed to the high pressure coming from the upstream port510due to its close proximity to the walls of the poppet chamber520, which further compresses the spring504. The regenerative force rapidly pushes the poppet503to an “open” position, as shown in the right half ofFIG. 8A.

Optionally, a stopper505is provided inside the poppet chamber520to restrict the motion of the poppet503and avoid fully compressing the spring504. In the illustrated embodiment, the stopper505is in the form of one or more extrusions located on the inner wall of the poppet chamber520. However, other forms of stoppers can be used as well. With the stopper505in place, the valve540can produce positive pulses followed by sudden steps at the downstream port510and negative pulses followed by sudden steps at the upstream port515. The sudden impact of the poppet on the stops will tend to form a tube wave with a doublet character in the event that the stored energy is exhausted in a time comparable to the transit time of the poppet503between the seat512and the stopper505. If the stored energy is expended in a time significantly longer than this transit time, port510will generally experience a positive tube wave.

FIG. 8Bshows a variation to the embodiment inFIG. 8Athat acts on a flowing fluid stream rather than opening a connection between two areas of differing pressures. There, valve540′ comprises an upstream port515′, a downstream port510′, and a poppet chamber520′ formed between the two ports. A poppet503′ is disposed inside the poppet chamber520′. The poppet is connected to a spring504′ on one side, which in turn rests upon an opening where the downstream port510′ connects to the poppet chamber520′. The spring504′ exerts forces on the poppet503′, pushing the poppet503′ away from the downstream port510′.

Starting with the “open” condition as shown in the right half ofFIG. 8B, the poppet503′ is held in position between one or more stoppers505′ formed on the inner surface of the poppet chamber520′ and a trigger507′ that transverse the wall of the poppet chamber520′. The fluid flows from the upstream port515′, into the poppet chamber520′, through an orifice506′ formed in the center of the poppet503′ and around the outside of poppet503′ towards the downstream port510′, shown by arrows inFIG. 8B. Due to the small size of the orifice506′, the fluid flows with significant restrictions across the orifice506′. A pressure drop is created between the poppet chamber520′ and the downstream port510′.

When it is time to fire the valve, the trigger507′ is pulled to release the poppet503′. The force of the spring504′ is overcome by the pressure drop between the two sides of the poppet503′ and the poppet503′ is quickly pushed towards the downstream port510′. The poppet503′ finally comes into contact with a seat512′ formed around the opening of the downstream port510′ to the poppet chamber520′ and seals the downstream port510′ from the poppet chamber520′, producing a negative tube wave in the downstream port510′ and a positive tube wave in the upstream port515′. The orifice506′ still allows a small quantity of fluids to pass from the poppet chamber520′ to the downstream port510′, however the flow path is significantly restricted due to the small size of the orifice506′.

FIG. 8Cshows a further variation to the embodiments inFIGS. 8A and 8B. There, the trigger507′ is removed. The valve540″ operates essentially on the fluids flowing from the upstream port515″ to the downstream port510″. Starting from left half ofFIG. 8Cwhere the valve540″ is in a closed position, the fluid flows from the upstream port515′, into the poppet chamber520′, through an506′ formed in the center of the poppet503′ towards the downstream port510′, shown by arrows inFIG. 8C. Due to the small size of the orifice506″, the fluid flows with significant restrictions across the orifice506″ in addition to the restriction between the outside diameter of the poppet503″ and the housing520″. A pressure drop is created between the poppet chamber520″ and the downstream port510″. At a certain point, the pressure drop is sufficiently high so that the downward force caused by the pressure difference exceeds the upward force caused by the spring504″. As the poppet503″ approaches the seat512″, the pressure drop across the poppet rapidly increases, causing the poppet to be driven toward the seat faster. The poppet503″ is pushed down to rest upon the seat512″ of the downstream port510″ abruptly. At this time the flow speed at the upstream port515″ is suddenly reduced or stopped, generating a negative pulse in the downstream port510″ and a positive pulse in the upstream port515″. One or more stoppers505″ can be provided on the inner surface of the poppet chamber520″ to provide sudden stops to the poppet503″ and produce a more repeatable switching behavior with flow.

FIG. 9shows a flow actuated tube wave valve640. A conduit670comprises a downstream port610, an upstream port615, and a swing check603disposed between the two ports. The swing check603is pivotally connected to the inner wall of the conduit670around a point604which is located about the juncture of the downstream port610and the upstream port615. The swing check603can pivot between an “open” position where the swing check603is substantially parallel to the longitudinal axis of the conduit670, as shown in the right half ofFIG. 9, and a “closed” position where the swing check603rests upon a seat612formed on an opposite inner wall of the conduit670so that the swing check603can be substantially perpendicular to the longitudinal axis of the conduit670when it is in the closed position, as shown in the left half ofFIG. 9.

In operation, the swing check603is first held at the open position by an actuator (not shown) to allow the downstream port610to be in fluid communication with the upstream port615. The actuator is then released. The fluid flow will carry the swing check603downwardly into the closed position. This produces a negative pulse at the downstream port610and a positive step change at the upstream port615. The swing check603can then be restored to its open position either by mechanical means or by reversing the fluid flow path in the conduit670.

FIG. 10discloses one type of hammer source that can also be used to produce tube waves. In this system, i.e. hammer source700, kinetic energy from weight760driven by actuator770is transferred to plunger703by impact, which in turn produces tube waves in port710. Specifically, in the illustrated embodiment, a plunger703is provided across a top wall711of the port710. A seal707is provided between the plunger703and the top wall711to prevent the port710from being in fluid communication from the outside. A bearing714can be optionally included to improve the stability of the plunger703in the top wall711and to reduce pressure pulsations seen by seal707. A spring704is provided to push the plunger in a resting position where the bottom of the plunger is substantially adjacent to the top wall711of the port710. Optionally, a vented washer705is provided between the bottom of the plunger703and the top wall711to eliminate the suction created by the bottom of the plunger703on the top wall711when the plunger703moves during firing.

In operation, the actuator770causes the weight760to move rapidly towards the top of the plunger703. Upon impact, the kinetic energy from the weight760is transferred to the plunger703, causing the plunger703to move downwardly inside the port710. The bottom of the plunger703pushes the fluids inside the port710and generates a positive pulse at the port710. This is the firing position of the plunger703. Thereafter, the weight760is pulled back by the actuator770and the spring704(as well as the pressure in the port710) pushes the plunger back to its resting position. The plunger703is now ready for firing again.

It should be noted that although in the illustrated embodiment inFIG. 10the spring704is provided outside the port710, it can also be provided inside the port710, for example, at a location currently occupied by the vented washer705. In such a case, the spring will exert a downward force on the plunger703, which is in turn balanced by the upward force exerted by the pressure in the port710. Therefore, with a suitable strong spring, when the plunger703is at the resting station, there is zero or a minimal amount of upward forces on the plunger. A relatively smaller amount of impact by the weight760can produce an effective dislocation of the plunger703.

FIG. 11shows a pulse generated by a hammer source comprising an approximately 60 psi tube wave on top of an approximately 540 psi baseline pressure.

FIG. 12discloses a hammer source that is pressure balanced. The hammer source800comprises a tubular housing805that is connected to a cavity820on one end and to a port810on the other end. In one embodiment, the pressure in cavity820is equalized with the pressure in the port810. In one embodiment, the cavity820is made of elastic materials and/or contains a low bulk modulus fill fluid such as ethyl alcohol, diethyl ether, silicone oil, or similar.

A flyer803is provided within the housing805, between the cavity820and the port810. A set of springs870,871are provided to keep the flyer803generally centered within the housing805. In the illustrated embodiment, the flyer803is substantially hollow in the center of its body, where a piston804is located. In the illustrated embodiment, the piston804is substantially in the shape of a cylindrical rod, although other shapes can be used as well. Approximately around the middle of the longitudinal axis of the piston804, a circular extension is formed that divides the hollow space inside the flyer803into an upper chamber830and a lower chamber840. A seal860is provided between the circular extension and the inner surface of the hollow space inside the flyer803to ensure that the upper chamber830is not in fluid communication with the lower chamber840.

An upper flyer port832is formed on the side wall of the flyer803to connect the upper chamber830to the small space located between the housing805and the flyer803. An upper housing port831is formed on the side wall of the housing805to connect the small space located between the housing805and the flyer803to the outside of the housing805. Accordingly, the upper chamber830of the flyer803is in fluid communication with the outside of the housing805via the upper flyer port832, the small space located between the housing805and the flyer803, and then the upper housing port831.

Similarly, a lower flyer port842is formed on the side wall of the flyer803to connect the lower chamber840to the small space located between the housing805and the flyer803. A lower housing port841is formed on the side wall of the housing805to connect the small space located between the housing805and the flyer803to the outside of the housing805. Accordingly, the lower chamber840of the flyer803is in fluid communication with the outside of the housing805via the lower flyer port832, the small space located between the housing805and the flyer803, and then the lower housing port831.

A seal890is provided between the inner surface of the housing805and the outer surface of the flyer803, at a longitudinal location that is between (1) the upper flyer port832/the upper housing port831, and (2) the lower flyer port842/the lower housing port841. Therefore, the flow path to the upper chamber830of the flyer803is completely separated from the flow path to the lower chamber840of the flyer803.

A set of upper seals837,838is provided between the inner surface of the housing805and the outer surface of the flyer803, at a longitudinal location that is above the upper housing port831to ensure that the fluid injected from the upper housing port831flows towards the upper flyer port832and enters the upper chamber830, instead of leaking off to towards the cavity820. An orifice833can be optionally included between the upper seals837,838for lubricating purposes and the like.

Similarly, a set of lower seals847,848is provided between the inner surface of the housing805and the outer surface of the flyer803, at a longitudinal location that is below the lower housing port831to ensure that the fluid injected from the lower housing port831flows towards the lower flyer port832and enters the lower chamber830, instead of leaking off to towards the port810. An orifice843can be optionally included between the lower seals847,848for lubricating purposes and the like.

In operation, the piston804can be moved up and down within the hollow space of the flyer803by injecting or depleting fluids in the upper chamber830or the lower chamber840of the flyer803. The moving piston then impacts the upper inner surface835or the lower inner surface845of the flyer803, causing the flyer803to move up and down to generate tube waves at the port810. Motions of the flyer803that do not result in impacts can also generate tube waves if they are rapid enough.

FIG. 13discloses a method of generating tube waves by pumping objects through an orifice. In the embodiment illustrated, an orifice940is provided on an inner surface of a tube905. A ball903is introduced into the upstream port920of the tube905towards the orifice940, as shown inFIG. 13A. At this moment, the upstream port920is in fluid communication with the downstream port910, although with some restrictions caused by the orifice940. Thereafter, the ball903reaches the orifice940and obstructs the flow path of the fluid from the upstream port920to the downstream port910, as depicted inFIG. 13B.

The pressure in the upstream port920then increases, forcing the ball903to deform and partially pass through the orifice940, as shown inFIG. 13C. Then, with a slightly further increase of the pressure in the upstream port920, the ball903is popped free into the downstream port910, creating a positive tube wave at the downstream port910, as illustrated inFIG. 13D. An exemplary pulse was recorded and shown inFIG. 14, where a tube wave of approximately 1000 psi was generated on top of a 3000 psi baseline at the end of 12,000 feet of tubing. The bottom two traces show the tube wave generated while the top trace shows pumping pressure. The first spike on the bottom two traces indicated the ball landing in the orifice. The second spike in the bottom two traces indicated the ball popping through the orifice. InFIG. 14, HS1indicated a piezoelectric high speed pressure transducer that only responds to changing pressures; it does not measure continuous pressure. HS1was illustrated as the bottom trace that was always close to zero. HS1was located at the outlet of the well, as was the conventional pressure transducer V1(middle trace). Conventional pressure transducer V3(top trace) was located at the inlet to the coiled tubing reel; it observed pump strokes and was around 11,774 feet from the orifice. The first small peak in HS1and V1indicated the ball landing in the orifice. When the wave front from the flow stopping reaches the inlet to the coiled tubing, the pressure started to rise (the big hump). The next sharp negative spikes on the bottom two traces were the ball popping through. It took a while for the other end of the coiled tubing to observe the release of pressure.

It should be noted that the orifice may be located at the surface, downhole, or both. Multiple orifices may be used in parallel to allow higher flows before landing balls. Although ball shaped objects are illustrated inFIG. 13, objects of other shapes may be used as well. Moreover, crushable and/or hollow objects may be used to increase the pulse generated and/or avoid leaving objects in the well. In one embodiment, degradable balls such as the collagen “bioballs” used as sealers in fracturing operations are used, and the balls are fed into the tube by a traditional fracturing ball dropper. The tube wave creation can be conducted at the surface, at the end of a coiled tubing, or at the end of a drill pipe. Other variations are also possible and should be considered within the scope of the current application.

FIG. 15discloses a stinger1003that is specially suited for providing tube waves when a free surface1015is available. In the illustrated embodiment, the stinger1003comprises a string of tubes (such as PVC pipes) that is connected to a piece of surface equipment (such as an actuator) on one end and hangs freely inside a wellbore on the other end. In the illustrated embodiment, an actuator1080is configured to move the stinger1003up and down, and the stinger end1004has an enlarged cross-sectional area compared to the remaining portion of the stinger1003. Therefore, when the stinger1003moves up and down in a wellbore1001containing fluids1002, tube waves can be produced in the wellbore1001. Producing tube waves near free surfaces is particularly difficult because of the limit on negative pressure set by the hydrostatic pressure between the free surface and the tube wave generator. In general, the deeper the tube wave generator can be placed, the larger the amplitude of wave that can be produced.

Optionally, a first pressure transducer1009is provided at the stinger end1004, is connected to the surface by a first cable1011located inside the hollow center of the stinger1003. Also, a second pressure transducer1012can be optionally provided at the external surface of the stinger, towards the distal end of the stinger1003but upstream from the stinger end1004. The second pressure transducer1012is connected to the surface by a second cable1014, which may be fastened to the stinger1003by clamps1013.

Suspension systems1086,1087can be optionally included to provide compliance for the stinger1003to move up and down. In one embodiment, the suspension systems1086,1087are springs. In another embodiment, the suspension systems1086,1087are air bags. In a further embodiment, the suspension systems1086,1087are inner tubes.

FIG. 16discloses a method of coupling a tube wave source1103through a free surface1115into a fluid filled wellbore1114. In general, the coupling device comprises a string of tubes1102that has two ends: the first end is connected to the wave source1103located on the surface of a wellsite; the second end is hanging freely in the fluid of the wellbore1114. In one embodiment, the second end of the tube1102comprises an expandable bag1105, which can expand or contract depending on the pressure inside the bag1105. In one embodiment, the tube1102is filled with fluid that is introduced by a pump1108through a valve1107from a reservoir1106, all located on the surface of a wellsite. A valve1009can be optionally included to release air or excessive pressure in the tube1102. A vacuum pump (not shown) can also be optionally included to facilitate the process of filing the tube1102. The compliance of the bag1105allows the pressure at the surface of the tube wave source1103to be higher than it would be if the tube were open ended. In the event of a free surface115that is much lower than the height of the tube wave source1103, the negative pressure that could be generated at the surface of the tube wave source1103would be severely limited by cavitation of the working fluid. In the case of water as a fill fluid in the tube, the free surface1115must be much less than 32 feet below the tube wave source1103for it to produce useful tube waves without the presence of the bag1105.

In one embodiment, the fluid in the tube1102is the same as the fluid in the downhole1110. In another embodiment, the fluid in the tube1102is slightly lower in density compared with the fluid in the downhole1110. When the tube wave source1003is fired, a tube wave propagates down tube1102and causes bag1105to expand and contract, therefore coupling the tube wave source to the wellbore1114. Optionally, a partial or complete seal (not shown) between the wellbore and the tubes1102may be provided above bag1105. Optionally, a pressure transducer1111may be attached to tube1102with cable1113optionally attached to tube1102by device1112.

FIG. 17shows the effect of using a long, tubular chamber whose tube wave transit time is comparable to the physical length of the pressure pulse. This is directly analogous to electrical transmission lines. In general, it is not desirable to have the pulse length and the chamber length to be comparable, as optimized storage chambers are generally larger in diameter than the conduit connected to them and tend to have a chamber length less than 20 to 30 times their bore. Such a structure would be used to produce tube waves of a particular shape. If this is desired, an optimized storage chamber may be placed at one or more locations along a length of normal pipe suited to this service. Appropriately placed changes in impedance of the outlet pipe may also be used to perform this sort of wave shaping.FIG. 17Ashows the physical location of the pressure transducers1,2,3, and4. A fast valve is disposed between transducers1and2. The length of pipe leading to transducer3is shorter than that leading to transducer4. The closed pipework containing pressure transducers2,3, and4is pressurized to P0. The outlet pipe is pressurized to pressure P1. The graph shows the four pressure traces vs. time. The fast valve is opened at time T1and is assumed to open in a period much less than the time between T1and T2. When it opens, there is an immediate rise in pressure at transducer1, to level P2and a corresponding drop in transducer2down to level P2. The pressure wave travels toward transducers3and4as the fluid expands, indicated schematically by the arrows. At time T2, the pressure wave reaches transducer3and its pressure drops to level P2. A reflected wave returns from transducer3toward transducer2. Similarly, the initial wave reaches transducer4at time T3. When this happens, the pressure falls to P2and a reflected wave returns. When the reflected wave from transducer3reaches transducer2the pressure falls to P3, which is still above P1due to continued fluid flow. This produces another reflected wave into the pipe to transducer4. When the first reflected wave from transducer4reaches transducer2at time T5, the pressure drops to P4(which will be equal to P1if the outlet pipe system is much larger than the storage volume), as the flow out of the system has stopped temporarily. The first reflection from transducer3into the line to transducer4produces the short pulse seen between T7and T9on transducer2. Other, smaller reflections may be present but are not shown. Diagrams similar to these are familiar to those skilled in the art of modeling electrical transmission lines. The methods of modeling transmission lines may be directly applied to tube wave lines once this analogy is understood.

FIG. 18discloses a number of arrangements that can be used to fine tune the generation, delivery, and/or propagation of tube waves, based on the underlying similarity between tube waves and electromagnetic waves in transmission lines. These relationships are not generally known and more importantly, the physical configurations of the tube wave analogues to electrical transmission lines are not previously known as such.FIG. 18Adiscloses the tube wave equivalent of a transmission line terminated with a capacitor at its upper end. The tube wave system that has this behavior is a compliant chamber at the end of a pipe. Compliance may be provided by a cavity filled with the tubing fluid (as shown on the left) or an accumulator (as shown on the right).FIG. 18Bshows the tube wave equivalent of a transmission line terminated with a shorted end; a closed end pipe.FIG. 18Cshows a slug of material1330with a density that is higher than the fluid hardware and transmission lines. The slug1330is configured to be able to move up and down inside the tube1301with the pulsation of the tube waves. In one embodiment, the slug1330is used to produce a lumped equivalent of an inductance placed between two transmission line segments, in a tube wave system.

FIG. 18Dshows a tube1301having a free surface1340near the top of the tube1301. The free surface1340functions equivalently to an open circuited end on a transmission line. By way of example, a positive tube wave impinging on this boundary will rebound as a negative tube wave. In the case of a transmission line, a positive pulse impinging on an open-circuited transmission line end will reflect as a negative pulse.FIG. 18Eshows a tube1301having a reduced diameter towards a section1350further downstream from the surface, therefore creating a shoulder1351which may function as a reflector and as an attenuator. Tube waves coming from side1301will be strongly reflected off of the step in diameter1351and only part of the wave amplitude will pass into the smaller section1350. The transmission line analogy is a junction between two transmission lines of different characteristic impedance, such as a 75 Ohm line connected directly to a 50 ohm line. Just as in the transmission line world, the larger the step or change in characteristic impedance, the better the reflection and the less signal passes through.FIG. 18Fshows a different version ofFIG. 18Ewhere the transition from the tube1301to the downstream section1360is by way of a slanted surface1361instead of a shoulder1360. This structure is equivalent to two transmission lines of different impedance (as above), but coupled together by a matching transformer. With an appropriate transformer, the wave may be made to transition across the change in impedance without reflection and without energy loss. There will be a concurrent shift between pressure and velocity due to the different impedances, in the same manner that the transmission line matching transformer trades between voltage and current to keep the same power level on both ends. The efficiency of this section increases as the length of the transition increases, with little transformer action seen for transitions less than ¼ wave length.

FIG. 18Gshows a porous material1370inside the tube1301. The porous material1370provides a lousy reflector, in a manner similar to two transmission lines connected together with a resistor.FIG. 18Hshows a tube1301having a perforation1381formed on the side wall of the tubing1301. In the illustrated embodiment, the perforation1381is connected to an enlarged area of enclosure1380, which resembles a subterranean formation under hydraulic fracturing, for example. This provides a lousy reflector in a slightly different configuration and is equivalent to two transmission lines joined together with a load resistor placed across the transmission line terminalsFIG. 18Ishows a side branch1391connected to a pipe1301through a full-bore port1391. This is electrically equivalent to two transmission lines joining with a third stub line. In this case the stub line would be open circuited. Such structures can be used to provide impedance matching at specific frequencies and or to provide a frequency selective reflector. They are also referred to as stub filters.

FIG. 19discloses a number of exemplary terminators that can be used to attenuate tube waves after use or reduce their reflections. Embodiments discloses herein may be applicable in attenuating pulsations in hydraulic fracturing operations where excessive pulsations in the fracturing fluids may be damaging to the pump system. Such terminators are equivalent to the terminating resistors or terminating systems commonly employed in transmission line systems to avoid end reflections.

Specifically,FIG. 19Ashows a tube1401having a closed end1414. Two types of particles are mixed together and packed into the space created by the closed end1414and the side walls of the tube1401. The first type of the particles is dense particles1412. The second type of the particle is compressible particles1411. The dense particles1412can rub against each other and the inner wall of the tube1401. The compressible particles1411allow the pack to move back and forth within the tube1401and absorb the pulse energy. In one embodiment, the compressible particles1411are spheres of low bulk modulus. In another embodiment, the compressible particles1411are encapsulated alcohol or rubber balls. In a third embodiment, the packing density of one or more particles is caused to vary from very densly packed at the closed end1414to low density at the opposite end. Such a structure would minimize reflections even in the instance that the characteristic resistance of the pack is not equal to the characteristic impedance of the tube wave conduit. Other variations can also be used, and should be considered within the scope of the current disclosure. The key characteristics being the ability to absorb energy and having porosity.

InFIG. 19B, a tube1401terminates upon a cavity1424. The cavity1424as illustrated inFIG. 19Bis in a spherical shape, although other shaped cavity can be used in the current application as well. A complaint fluid can be used to fill up the cavity1424, such as air, alcohol, etc. A porous plug1421is provided inside the tube1401, at a location proximate to the cavity1424. The porous plug1421can be made of a porous material commonly known in the art. The porous plug1421together with the compliance material in the cavity1424can function as an effective terminator of tube waves. In a further embodiment, the compliant cavity can comprise an accumulator to reduce the required volume of the system. Such a system is equivalent to a transmission line terminated with a series combination of a resistor and a capacitor. Such a terminator has a frequency response characteristic that is attenuates high frequencies and does not attenuate low frequencies. With a large capacitor (or equivalently a large compliant volume), this system will not attenuate constant pressures but will strongly attenuate varying pressures.

FIG. 19Cshows another tube wave structure. There, an orifice1431is created inside the tube1401, which only allows a portion of the fluid to pass from an upstream chamber1432to the downstream chamber1433. When the fluid flows sufficiently fast, and/or when the orifice1431is of a give size, cavitation1435is created behind the orifice1431. This cavitation1435is effective in blocking tube waves traveling from the downstream chamber1433towards the upstream chamber1432, but not tube waves traveling in the reverse direction. By varying the flow rate and/or the orifice size, this structure may be made to either allow passage or block passage of tube waves in one direction while always passing tube waves in the other direction. Electrically, this structure is similar to either two transmission lines coupled by a diode in series, or a directional coupler

FIG. 20illustrates another source of tube waves that involves an imploding device such as a canister1500. In the depicted embodiment, a simple canister1500in the cross-sectional view includes a hollow body1502which defines an inner chamber1504. The chamber1504may be a vacuum, or be filled with gas at zero to low pressure. The canister body1502can be made from any crushable and/or drillable material, such as frangible glass, tempered glass, or ordinary glass. In one embodiment, the canister body1502is a glass centrifugal tube. Although inFIG. 20a tubular body is depicted, spherical and other shapes may be utilized. In particular, canister shape may be selected for ease of movement within the well, and also for producing particular acoustic characteristics.

The illustrated canister body has an opening1507adapted to receive a pressure rupture disk1508. The opening may be threaded such that a pressure rupture disk with a threaded holder can be mated in the field to yield a canister of selected implosion value. Alternatively, the disk1508is securely fastened to the opening1507of the canister1500by a layer of glue1506, cement, solder, or other attachment methods familiar to those skilled in the art. Weighing materials1505such as bauxite or lead beads can be packed in the canister chamber1504to increase the weight of the canister1500so it may descend in the wellbore fluid without making the assembly difficult to drill with ordinary well drilling tools.

Several different types of rupture disks1508were tested. In some cases, the rupture disks1508were microscope cover slips. In some other cases, the rupture disks1508were plastic lids. In some additional cases, the rupture disks1508were ceramic disks. In some further cases, the rupture disks1508were glass disks or heavy glass disks. Among all the disks tested, microscope cover slips performed exceptionally well because of their precise thickness and consistently high quality.

FIG. 21shows an example of data gathered by using a centrifuge tube covered by a microscope slide. The yellow trace was recorded by a surface hydrophone; the black trace is recorded by a DVS sensor.

The preceding description has been presented with reference to some illustrative embodiments of the Inventors' concept. Persons skilled in the art and technology to which this application pertains will appreciate that alterations and changes in the described structures and methods of operation can be practiced without meaningfully departing from the principle, and scope of this application. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.