Oscillating fluid flow in a wellbore

[0001] This application is related to and claims the benefit of provisional application Ser. No. 60/948,346 entitled “DOWNHOLE COMBUSTION AND STEAM GENERATION,” filed Jul. 6, 2007, which is incorporated herein by reference.

[0002] The present disclosure relates to oscillating fluid flow in a wellbore.

[0003] Heat transfer fluid (e.g., steam and/or others) can be injected into a subterranean formation to facilitate production of fluids from the formation. For example, steam may be used to reduce the viscosity of fluid resources in the formation, so that the resources can more freely flow into a wellbore and to the surface.

[0004] A system for oscillating working fluid in a wellbore includes a fluid supply and a fluid oscillator device. The fluid oscillator device receives the working fluid into an interior volume of the fluid oscillator device and varies over time a flow rate of the compressible working fluid through an outlet of the fluid oscillator device.

[0005] In certain aspects, a system for oscillating compressible working fluid in a wellbore defined in a subterranean formation includes the fluid supply and the fluid oscillator device. The fluid supply communicates compressible working fluid into a conduit disposed within the wellbore. The fluid oscillator device is configured to reside in the wellbore. The fluid oscillator device includes an interior surface that defines an interior volume of the fluid oscillator device, an inlet into the interior volume, and an outlet from the interior volume. The interior surface is static during operation to receive the compressible working fluid into the interior volume through the inlet and to vary over time a flow rate of the compressible working fluid from the interior volume through the outlet.

[0006] In certain aspects, compressible working fluid is directed through at least a portion of the wellbore defined in the subterranean formation and into a fluid oscillator device installed in the wellbore. At least a first portion of the compressible working fluid is directed within the fluid oscillator device to perturb a flow of at least a second portion of the compressible working fluid within the fluid oscillator device. At least a portion of the compressible working fluid is directed out of the fluid oscillator device at a flow rate that varies over time.

[0007] In certain aspects, a working fluid that includes a liquid is directed through at least a portion of the wellbore defined in the subterranean formation and into a fluid oscillator device installed in the wellbore. At least a portion of the liquid is vaporized to form a compressible working fluid. At least a portion of the compressible working fluid is directed out of the fluid oscillator at a flow rate that varies over time.

[0008] Implementations can include one or more of the following features. The compressible working fluid includes heat transfer fluid. The fluid supply includes a heat transfer fluid generator configured to reside in the wellbore. The fluid supply includes a heat transfer fluid generator configured to reside above a ground surface outside of the wellbore. The compressible working fluid includes steam of less than one hundred percent quality. The system includes a conduit in fluid communication with each of the at least one outlets. Each conduit is configured to inject the compressible working fluid into the subterranean formation. The outlet is a first outlet, and the fluid oscillator device further includes a second outlet. The interior surface is configured to alternate a flow of compressible working fluid between the first outlet and the second outlet. A first portion of the interior surface defines a chamber, a third outlet from the chamber into a first feedback channel, and a fourth outlet from the chamber into a second feedback channel. A second portion of the interior surface defines the first feedback channel and the first outlet extending from the first feedback channel. A third portion of the interior surface defines the second feedback channel and the second outlet extending from the second feedback channel. The inlet is configured to direct the compressible working fluid into the chamber. The first and second feedback channels are each configured to direct at least a portion of the compressible working fluid toward a region in the chamber near the inlet. The chamber is a first chamber, and a fourth portion of the interior surface defines a second chamber extending from the first chamber. The second chamber is configured to receive at least a portion of the compressible working fluid from the first chamber and to direct at least a portion of the received compressible working fluid back into the first chamber. The conduit is an outer conduit, and the system further includes an inner conduit disposed within the outer conduit. The fluid oscillator device is configured to receive compressible working fluid from an annulus between the outer conduit and the inner conduit. The fluid supply includes a steam generator. The compressible working fluid includes at least one of air, steam, nitrogen gas, carbon dioxide gas, carbon monoxide gas, natural gas, or another compressible fluid. The interior surface defines a resonant chamber that is static during operation to vary over time a pressure of the compressible working fluid in the interior volume. The fluid oscillator device includes a whistle. The system further includes a hydrocyclone device configured to receive a mixture of compressible working fluid and condensed fluid from the conduit, separate at least a portion of the condensed fluid from a remainder of the mixture, and communicate the remainder of the mixture into the inlet of the whistle. The system further includes a tapered insert defining at least a portion of the interior volume of the whistle and a tapered slot to receive the tapered insert. The received portion of compressible working fluid is injected into the subterranean formation. Injecting the received portion of compressible working fluid into the subterranean formation includes stimulating a flow of resources through the subterranean formation. Injecting the received portion of compressible working fluid into the subterranean formation includes reducing a viscosity of resources in the subterranean formation. The wellbore is a first wellbore and injecting the received portion of compressible working fluid into the subterranean formation includes stimulating a flow of resources through the formation into a second wellbore defined in the subterranean formation. A portion of the compressible working fluid is periodically compressed within the fluid oscillator device. Sound waves are propagated through the subterranean formation. The sound waves are generated by the periodic compression of the compressible working fluid in the fluid oscillator device. The flow rate varies in a periodic manner over time. Directing at least a first portion of the compressible working fluid within the fluid oscillator device to perturb a flow of at least a second portion of the compressible working fluid within the fluid oscillator device includes directing at least the first portion of the compressible working fluid within the fluid oscillator device to perturb a direction of the flow of at least the second portion of the compressible working fluid within the fluid oscillator device. Vaporizing at least a portion of the liquid includes reducing the pressure of the liquid to induce a liquid to gas phase change of the liquid working fluid. The liquid includes condensed water and the compressible working fluid includes steam.

[0009] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

[0020] Like reference symbols in the various drawings indicate like elements.

[0021] The present disclosure relates to oscillating fluid flow in a wellbore. In some implementations, the fluid includes compressible working fluid introduced into a subterranean zone through a wellbore. For example, the fluid may be provided (e.g. injected) into a subterranean zone to reduce the viscosity of in-situ resources and increase flow of the resources through the subterranean zone to one or more well bores. In some implementations, the fluid includes heat transfer fluid used in huff and puff, steam assisted gravity drainage (SAGD), steam flood, or other operations. In some implementations, oscillation of compressible working fluid within the wellbore may generate compression waves, for example. Sound waves. In some cases, the compression waves can be used to stimulate production from the subterranean zone. The subterranean zone can include all or a portion of a resource-bearing subterranean formation, multiple resource-bearing subterranean formations, and/or other types of formations.

[0022] Example fluids include heat transfer fluid, compressible fluid, non-compressible fluid, other types of fluids, and mixtures thereof. In some implementations, the fluid includes a mixture of an incompressible fluid and compressible fluid, for example, as a mist, foam, or other mixture. Example compressible fluids include air, carbon monoxide (CO), carbon dioxide (CO₂), molecular nitrogen gas (N₂), natural gas, molecular oxygen (O₂)-enriched or vitiated air, natural gas, steam, and others. In some cases, the compressible working fluid communicated into the wellbore is entirely composed of one of the example compressible fluids listed above. In some cases, the compressible working fluid communicated into the wellbore is substantially entirely (e.g., 98%, 99%, or more) or partially (e.g., 80%) composed of one of the example compressible working fluids above. In some cases, the compressible working fluid communicated into the wellbore is substantially entirely composed of one of the example compressible working fluids above and some contaminates. Heat transfer fluid may take the form of vapor and/or gas, alone or with some condensed liquid, and may include water, carbon monoxide and other combustion byproducts (e.g. from a heated fluid generator and/or other surface and downhole equipment) and/or other fluids. In some cases, heat transfer fluid may include steam, liquid water, diesel oil, gas oil, molten sodium, and/or synthetic heat transfer fluids. Example synthetic heat transfer fluids include THERMINOL 59 heat transfer fluid which is commercially available from Solutia, Inc., MARLOTHERM heat transfer fluid which is commercially available from Condea Vista Co., SYLTHERM and DOWTHERM heat transfer fluids which are commercially available from The Dow Chemical Company, and others. For convenience of reference, the concepts herein are described with reference to steam. However, the concepts herein, including the specific examples and implementations, are applicable to other heat transfer fluids.

[0023] An example implementation includes SAGD, which can be implemented in a well system that includes two or more horizontal wellbores defined in a subterranean formation, wherein an upper wellbore is defined above a lower wellbore. The lower well bore is completed for production (e.g., having a completion string that may include slotted tubulars, sand screens, packers, one or more production strings and/or other completion components) and, in some instances, includes a fluid lift system (e.g., electric submersible pump, progressive cavity pump, rod sucker pump, gas lift system, and/or other fluid lift system) for producing resources of the subterranean formation to the surface. Steam is injected into the subterranean formation through the upper wellbore, and resources are collected from the subterranean formation through the lower wellbore. The steam may stimulate gravity-induced flow of resources into the lower wellbore, and the resources can be produced to the surface. Another example implementation includes steam flood production, which can be implemented in a well system that includes two or more wellbores defined in a subterranean formation. In some cases, both wellbores are substantially vertical wellbores. Steam is injected into the subterranean formation through a first wellbore, and resources are collected from a second wellbore. The second well bore is completed for production and, in some instances, includes a fluid lift system. The injection of steam from the first wellbore creates a pressure gradient across the subterranean formation. For example, the pressure in the formation may be higher in a region proximate the first wellbore than in a region proximate the second wellbore. The pressure gradient may stimulate production of resources from the formation by causing the resources to flow to the lower pressure region and into the second wellbore, and the resources can be produced to the surface. Another example implementation includes huff and puff production, which can be implemented in a well system that includes one or more wellbores defined in a subterranean formation. During a first time period, steam is injected into the subterranean formation through a wellbore, and during a second, subsequent time period, resources are produced from the formation through the same or a different wellbore. The process of injecting steam into the formation and collecting resources from the formation may be repeated in a cyclic manner. The wellbore can be completed for production and, in some instances, include a fluid lift system when the resources are being produced to the surface. In some instances, the wellbore completion can accommodate both production and steam injection.

[0024] FIG. 1A is a diagram illustrating an example well system 100a. The example well system 100a includes a wellbore 102 defined in a subterranean region below a terranean surface 110. The wellbore 102 is cased by a casing 108, which may be cemented in the wellbore 102. In some cases, the wellbore may be an open hole wellbore 102, without the casing 108. The illustrated wellbore 102 is a vertical wellbore. However, in some implementations, a wellbore includes horizontal, curved, and/or slanted sections.

[0025] The well system 100a includes a working string 106 configured to reside in the wellbore 102. The working string 106 includes a tubular conduit configured to transfer materials into and/or out of the wellbore 102. For example, the working string 106 can communicate fluid (e.g., steam, another type of heat transfer fluid, and/or another working fluid) into or through a portion of the wellbore 102. The working string 106 can be in fluid communication with a fluid supply source. The fluid supply source can reside on a terranean surface and/or at another location outside of the well (e.g., on a platform, rig, boat and/or other location) and be at and/or remote from the well site. Alternately, or additionally, the fluid supply source can reside downhole. Example fluid supply sources include a steam generator, a surface and/or downhole compressor, a surface and/or downhole boiler, an internal combustion engine or other surface and/or downhole combustion device, a natural gas or other pipeline, and/or a surface and/or downhole fluid tank (in some instances pressurized). One or more parameters of the fluid flow can be controlled at or downstream from the fluid supply source, for example, by increasing or decreasing compression or combustion rates, adjusting a composition of the fluid, and/or adjusting flow rates (e.g., by use of valves, vents, and/or restriction devices). Example parameters of the fluid flow that may be adjusted include the volumetric flow rate, the mass flow rate, and/or others. As another example, the working string 106 can additionally transfer resources to the surface 110. Example resources include oil, natural gas, coal bed methane, and others types of materials that may be produced from the zone of interest 112 and/or another region. In some implementations, the working string includes jointed tubing, coiled tubing, and/or other types of tubing.

[0026] A number of different tools are provided in and/or attached to the working string 106. In FIG. 1A, a downhole fluid supply system may be provided. The system 100a includes a steam oscillator system 118. The illustrated working string 106 includes a steam generator 116 in fluid communication with the steam oscillator system 118. The steam generator 116 is a downhole fluid supply system which can be installed in the wellbore 102. The example steam generator 116 includes input feeds to receive input fluid from the surface. The example steam generator 116 heats the input fluid to produce steam and/or to heat another type of heat transfer fluid. In some implementations, heat is provided through one or more of a combustion process (e.g., combustion of fuel and oxygen), a non-combustion chemical process, electrical heating, and/or others. Some examples of steam generators (down hole or surface based) that can be used in accordance with the concepts described herein include electric type steam generators (see, e.g., U.S. Pat. Nos. 5,623,576, 4,783,585, and/or others), combustor type steam generators (see, e.g., Downhole Steam Generation Study Volume I, SAND82-7008, and/or others), catalytic type steam generators (see, e.g., U.S. Pat. Nos. 4,687,491, 4,950,454, U.S. Pat. Pub. Nos. 2006/0042794 2005/0239661 and/or others), and/or other types of steam generators (see, e.g. Downhole Steam Generation Study Volume I, SAND82-7008, discloses several different types of steam generators).

[0027] Some implementations include additional or different downhole fluid supply systems. In some cases, a downhole fluid supply system provides an increase in volumetric flow rate at the exit of the downhole fluid supply system as compared to the volumetric flow rate at the entrance of the downhole fluid supply system. For example, the volumetric flow rate may be increase by heating the fluid, inducing a phase change and/or a chemical reaction in the fluid, and/or other techniques. The output volumetric or mass flow rate of the downhole fluid supply system may be controlled, for example in the case of a downhole steam generator, by controlling one or more of the input reactants (e.g., controlling a volumetric flow rate of water, oxidant, and/or fuel), by controlling a reaction process (e.g., a catalytic or other type of reaction), and/or by controlling other parameters (e.g., an electric power generator, a valve, one or more vents, and/or one or more restrictors).

[0028] The steam oscillator system 118 receives heat transfer fluid from the steam generator 116 and emits the received heat transfer fluid into the wellbore 102. The example steam oscillator system 118 can receive steam at a particular flow rate which may be substantially constant or may have some controlled variation over time, as described above. The example steam oscillator system 118 can emit the received steam at a time-varying flow rate relative to the input. For example, the steam oscillator system 118 can emit steam into the wellbore 102 at an oscillating flow rate. In some cases, the steam oscillator system includes a steam whistle, steam horn, and/or another fluid oscillator device that propagates sound waves through the wellbore 102, a well completion, and/or the zone 112.

[0029] The casing 108 includes perforations 114 through which steam can be injected into the zone of interest 112. In some cases, steam is injected into the zone of interest 112 though the perforations 114 at an oscillating flow rate. Additionally, resources (e.g., oil, gas, and/or others) and other materials (e.g., sand, water, and/or others) may be extracted from the zone of interest through the perforations 114.

[0030] The steam oscillator system 118 can include multiple steam oscillator devices at multiple different locations and/or multiple different orientations in the wellbore 102. The steam oscillator system 118 can be installed in a wellbore 102 having a vertical, horizontal, slanted, curved, or another configuration.

[0031] FIG. 1B illustrates an alternate embodiment of an example well system 100b. The example well system 100b includes a steam generator 116 that resides outside of the wellbore, at the terranean surface. The steam generator 116 of system 100b is configured to communicate steam to two different steam oscillator systems 118, which reside in two different wellbores 102. In other implementations, a steam oscillator system 118 is installed in all or fewer than all of three or more wellbores 102 of a single well system.

[0032] In some cases, the steam generator 116 only communicates steam to one of the two wellbores 102. For example, the steam oscillator system 118 of a first wellbore 102 may inject steam into the zone 112, while resources are produced from a second wellbore 102. The steam injected into the zone 112 from the first wellbore 102 may stimulate productivity at the second wellbore 102. For example, the thermal properties of the steam may heat the resources in the zone 112, thereby reducing the viscosity of the resources. In other cases, both steam oscillator systems 118 are used to simultaneously inject steam into the zone 112.

[0033] FIG. 2 is a diagram illustrating an example steam oscillator system 118. The example steam oscillator system 118 is configured for installation in a wellbore 102. The wellbore 102 includes the casing 108 and the perforations 114. The illustrated steam oscillator system 118 includes an inner working string 106a, an outer working string 106b, packers 202a, 202b, 202c, and multiple steam oscillator devices 204 installed in housings 210. The packers 202 are illustrated as cup-type packers, but could be another type of packer, and operate to isolate axial regions 206 of the wellbore 102. For example, a packer 202 may seal or substantially seal to the casing 108 to isolate an axial section of the wellbore 102. In the illustrated example, an upper region 206a of the wellbore 102 is isolated between a first packer 202a and a second packer 202b. An intermediate region 206b of the wellbore 102 is isolated between the second packer 202b and a third packer 202c. The third packer 202c isolates a lower region 206c of the wellbore.

[0034] The working strings 106 define annular sections in the wellbore 102. In the illustrated system 118, the inner working string 106a defines an inner flow path 208a, for example, through the regions 206a, 206b, and 206c. The inner flow path 208a extends radially from the radial center of the wellbore to the inner diameter of the outer working string 106b. The inner working string 106a and the outer working string 106b define a middle annulus 208b above and within the upper region 206a. The middle annulus 208b extends radially from the outer diameter of the inner working string 106a to the inner diameter of the outer working string 106b. The outer working string 106b and the casino 108 define an outer annulus 208c above and within the upper region 206a. The outer annulus 208c extends radially from the outer diameter of the outer working string 106b to the inner diameter of the casing 108. Below the packer 202b, for example in the intermediate region 206b and the lower region 206c, an annulus 208d is defined between the outer diameter of the outer working string 106b and the inner diameter of the casing 108.

[0035] In the illustrated example, steam oscillator devices 204 are configured to oscillate steam into each of the three regions 206a, 206b, and 206c. A steam oscillator device 204 typically includes one or more inlets for receiving heat transfer fluid, for example, from a steam generator 116. A steam oscillator device 204 typically includes one or more outlets for directing the received heat transfer fluid into an annulus 208 within the wellbore 102, into the zone 112, and/or into another region. During operation, the steam oscillator device 204 communicates heat transfer fluid from the one or more inlets, through all or part of its interior volume, to the one or more outlets. The interior surfaces of the steam oscillator device 204 that cause the flow of heat transfer fluid to oscillate can remain static during operation in varying a flow rate of the heat transfer fluid through the outlet. In certain instances, the steam oscillator device 204 can have no moving parts. In some cases, a steam oscillator device 204 includes a whistle or another device to generate sound waves based on a flow of compressible fluid through the steam oscillator device 204. Some examples of steam oscillator devices 204 that include whistles are illustrated in FIGS. 4A-4L.

[0036] A steam oscillator device 204 may be implemented as an annular steam oscillator device 204, installed in an annulus of the wellbore 102. For example, the steam oscillator device 204 illustrated in FIGS. 3M-Q is a tapered insert designed for installation in an annular housing 210. During operation, the steam oscillator device 204 can experience translational, rotational, vibrational, and/or another type of movement, while maintaining a static internal configuration. The static internal configuration of the steam oscillator device 204 can oscillate a flow of heat transfer fluid through an outlet of the steam oscillator device 204. In some implementations, oscillation of compressible fluid through the outlet can generate longitudinal compression waves (e.g., sound waves). The compression waves can be transmitted to and propagate through a surrounding subterranean zone. In some cases, the compression waves can stimulate production of resources and/or other materials (e.g., sand, water, and/or others) from the zone 112. In some cases, the compression waves can stimulate the wellbore tubulars and/or completion elements to help produce the resources to the surface 110, and/or to prevent or help remediate an undesirable condition. Examples of conditions that may be remediated include build-up or deposit of scale, asphaltines, waxes, sand, hydrates, or another material that can impede production.

[0037] In the upper region 206a, a housing 210a is installed below the packer 202a. The housing 210a carries multiple steam oscillator devices 204 to inject steam into the outer annulus 208c of the upper region 206a at a time-varying flow rate. For example, during operation, heat transfer fluid may be communicated from the steam generator 116 to the housing 210 through the outer annulus 208c above the packer 202a. A sub 306, illustrated in FIGS. 3E-3H, defines a flow path allowing communication of heat transfer fluid from the outer annulus 208c past the packer 202a into the inlets of the steam oscillator devices 204 installed in the housing 210a. The steam may be injected into the zone 112 at an oscillating flow rate from the upper region 206a through the perforations 114.

[0038] In the intermediate region 206b, a housing 210b is installed below the packer 202b. The housing 210b carries steam oscillator devices 204 to inject steam into the annulus 208d of the intermediate region 206b at a time-varying flow rate. For example, during operation, heat transfer fluid may be communicated from the steam generator 116 to the housing 210b through the middle annulus 208b above the packer 202b. A sub 306, illustrated in FIGS. 3A-3D, defines a flow path allowing communication of heat transfer fluid from the upper region 206a past the packer 202b into the inlets of the steam oscillator devices 204 installed in the housing 210b. The steam may be injected into the zone 112 at an oscillating flow rate from the intermediate region 206b through the perforations 114.

[0039] Three steam oscillator devices 204a, 204b, and 204c inject steam into the annulus 208d of the lower region 206c at a time-varying flow rate. For example, during operation, heat transfer fluid may be communicated from the steam generator 116 to the steam oscillator devices 204a, 204b, and 204c through the inner flow path 208a. A sub 306, illustrated in FIGS. 3I-L defines a flow path allowing communication of heat transfer fluid below the packer 202c into the inlets of the steam oscillator devices 204a, 204b, 204c installed in the sub 306. The steam may be injected into the zone 112 at an oscillating flow rate from the lower region 206c through the perforations 114.

[0040] The steam oscillator system 118 is an example implementation, and other implementations may include the same, fewer, and/or additional features. In some implementations, a different number of annular sections are defined within the wellbore 102. For example, an intermediate working string may be used to define one or more additional annular sections. In some cases, a different number of packers 202 are used to isolate the same or a different number of axial regions 206 in the wellbore 102. In some implementations, more than one housing 210 is installed in one or more of the axial regions 206. All of the example steam oscillator devices 204 are implemented without moving parts, which may allow the steam oscillator devices 204 to perform more consistently and/or to be more durable over long-term operation. However, in other implementations, one or more of the steam oscillator devices 204 includes moving parts.

[0041] FIGS. 3A-D are diagrams illustrating an example sub 306 having the packer 202b and housing 210b of FIG. 2. FIG. 3A is a perspective view of the exterior of the sub 306. The sub 306 includes multiple axial sections that are fabricated separately and assembled before, during, or after installation in the wellbore 102. FIG. 3B is a cross-sectional view of the sub 306. The sub 306 carries the packer 202b around a first axial section of the sub 306. The illustrated packer 202b includes cup seals 302; one oriented to seal or substantially seal against flow in a downhole direction and one oriented to seal or substantially seal against flow in an uphole direction. The seals 302 isolate axial regions of the wellbore 102 from one another. The sub 306 also defines an annulus in fluid communication with the housing 210b. The housing 210b defines three tapered slots distributed circumferentially around the housing 210b. A tapered fluid oscillator device 204 is installed in each of the slots. During operation, heat transfer fluid flows through the middle annulus 208b into each of the steam oscillator devices 204. The steam oscillator devices 204 operate in a static configuration to oscillate the flow of heat transfer fluid into the intermediate region 206b below the housing 210b. FIG. 3C illustrates a cross sectional view of the housing 210b. FIG. 3D illustrates an end view of the sub 306 from the housing end of the sub 306. The end view illustrates the circumferential distribution of the fluid oscillator devices 204 in the housing 210b.

[0042] FIGS. 3E-H are diagrams illustrating an example sub 306 having the packer 202a and the housing 210a of FIG. 2. FIG. 3E is a perspective view of the exterior of the sub 306. The sub 306 includes multiple axial sections that are fabricated separately and assembled before, during, or after installation in the wellbore 102. FIG. 3F is a cross-sectional view of the sub 306. The sub 306 carries the packer 202a around a first axial section of the sub 306. The illustrated packer 202a includes cup seals 302; one oriented to seal or substantially seal against flow in a downhole direction and one oriented to seal or substantially seal against flow in an uphole direction. The sub 306 also defines an annulus in fluid communication with the housing 210a. The housing 210a defines six tapered slots distributed circumferentially around the housing 210a. A tapered fluid oscillator device 204 is installed in each of the slots. During operation, heat transfer fluid flows through the outer annulus 208c into each of the steam oscillator devices 204. The steam oscillator devices 204 operate in a static configuration to oscillate the flow of heat transfer fluid into the upper region 206a below the housing 210a. FIGS. 3F and 3G illustrates a cross-sectional view of the housing 210a. FIG. 3H illustrates an end view of the sub 306 from the housing end of the sub 306. The end view illustrates the circumferential distribution of the fluid oscillator devices 204 within the housing 210a.

[0043] FIGS. 3I-L are diagrams illustrating an example sub 306 having the steam oscillator devices 204a, 204b, and 204c of FIG. 2. FIG. 3I is a perspective view of the exterior of example sub 306. FIG. 3J is a side view of the exterior of the example sub 306. FIG. 3K is a cross-sectional view of the example sub 306, taken along line 3K-3K of FIG. 3J. FIG. 3L is a cross-sectional view of the example sub 306, taken along line 3L-3L of FIG. 3K. Each of the three steam oscillator devices 204a, 204b, and 204c injects heat transfer fluid into the lower region 206c of the wellbore 102 at a different axial position. The steam oscillator devices 204a, 204b, and 204c operate in a static configuration to oscillate the flow of heat transfer fluid into the lower region 206c. Devices 204a and 204b define outlets 314 that direct heat transfer fluid in a radial direction. Device 204c defines outlets 314 that direct heat transfer fluid in a substantially axial direction.

[0044] The volume and flow rate of heat transfer fluid communicated into a particular region 206 of the wellbore 102 may depend on the volume and flow rate of heat transfer fluid communicated into the fluid oscillator devices 204 in addition to the size, number, and configuration of the fluid oscillator devices 204. The fluid oscillator devices 204 installed in the housing 210a are smaller than the fluid oscillator devices 204 installed in the housing 210b, and thus pose more of a restriction than larger fluid oscillator devices 204. Accordingly, more fluid oscillator devices 204 are installed in the housing 210a than are installed in the housing 210b to communicate heat transfer fluid into the two regions 206a and 206b at the same or substantially the same flow rate. In some implementations, the number and size of the fluid oscillator devices 204 in steam oscillator system 118 can be configured to communicate heat transfer fluid into one or more of the regions 206 at different flow rates.

[0045] FIGS. 3M-Q are diagrams illustrating the example fluid oscillator device 204a. The example steam oscillator device 204a includes an interior surface that defines an interior volume of the steam oscillator device 204a. The interior surface defines an inlet 310, two feedback flow paths 312a, 312b, two outlet flow paths 314a, 314b, a primary chamber 316, and a secondary chamber 318. The primary chamber 316 is defined by a portion of the interior surface that includes two diverging side walls. In the illustration, the diverging sidewalls are angled away from the axis AA and toward each of the feedback flow paths 312a, 312b. The feedback flow paths 312 extend from the broad end of the primary chamber 316 to the narrow end of the primary chamber 316, near the inlet 310. The outlet flow paths 314a, 314b extend from the feedback flow paths 312a, 312b, respectively. The secondary chamber 318 extends from the broad end of the primary chamber 316. The secondary chamber 318 is defined by a portion of the interior surface that includes two diverging sidewalls. In the illustration, the diverging sidewalls diverge away from the axis AA.

[0046] The interior surface of the steam oscillator device 204a that causes the flow of heat transfer fluid to oscillate is substantially static during operation. As illustrated, the steam oscillator device 204a has no moving parts. That is to say that in producing an oscillatory fluid flow, the illustrated example device 204a does not rely on linkages or bearing surfaces creating or supporting gross relative movement between mechanical components of the device 204a.

[0047] In one aspect of operation, heat transfer fluid flows into the steam oscillator device 204a through the inlet 310. At a given time, the heat transfer fluid flows along only one of the sidewalls of the primary chamber 316. For example, due to the Coanda effect, the flow of heat transfer fluid may be biased toward one sidewall of the primary chamber 316, creating an imbalanced flow through the chamber 306. As a result, at a given time there may be a faster flow rate into one of the two feedback flow paths 312a or 312b. The feedback flow paths 312 are configured to direct a portion of the heat transfer fluid back into the primary chamber 316 proximate the inlet 310 so as to perturb the existing flow of heat transfer fluid through the primary chamber 316. For example, the perturbation can cause the flow bias to shift from one sidewall to the other sidewall. In this manner, the flow of heat transfer fluid through the steam oscillator device 204a oscillates between the feedback flow paths 312a and 312b. Accordingly, the flow of heat transfer fluid through each of the outlets 314a and 314b oscillates over time. For example, the steam oscillator device 204a may produce a pulsating flow through each of the outlets 314a, 314b.

[0048] In one aspect of operation, liquid working fluid is directed into the steam oscillator device 204a, and the liquid working fluid is vaporized to form a compressible working fluid in the steam oscillator device 204a. The compressible working fluid can then flow out of the fluid oscillator device 204a at a time-varying flow rate. For example, high pressure liquid water (e.g. water comprising a pressure higher than the pressure of fluids in the surrounding subterranean formation) is communicated into the steam oscillator device 204a. The pressure of the liquid water drops when the liquid water enters the steam oscillator device 204a. The temperature of the liquid water is sufficient to overcome the heat of vaporization of water, and a phase change is induced, causing the liquid water to vaporize to steam in the steam oscillator device. Depending on thermodynamic conditions, in some implementations, the liquid working fluid can vaporize in any portion of the interior volume of the steam oscillator device 204a (e.g., the inlet 310, the primary chamber 316, the feedback flow paths 312, and/or the outlets 314), just before entering the steam oscillator device 204a, and/or just after exiting the steam oscillator device.

[0049] In one aspect of operation, heat transfer fluid enters the primary chamber from the inlet 310 and flows primarily along a first sidewall toward the feedback flow path 312a, and a portion of the heat transfer fluid enters the feedback flow path 312a. Some of the heat transfer fluid flows from the feedback flow path 312a through the outlet 314a, while some of the heat transfer fluid flows from the feedback flow path 312a back into the primary chamber 316 proximate the inlet 310. The heat transfer fluid enters the primary chamber 316 proximate the inlet 310 and perturbs the flow of heat transfer fluid through the primary chamber 316 from the inlet 310. The perturbation causes the heat transfer fluid to flow through the primary chamber 316 along the second sidewall (i.e., toward the feedback flow path 312b), rather than the first sidewall. A portion of the heat transfer fluid enters the feedback flow path 312b. Some of the heat transfer fluid flows from the feedback flow path 312b through the outlet 314b, while some of the heat transfer fluid flows from the feedback flow path 312b back into the primary chamber 316 proximate the inlet 310. The heat transfer fluid enters the primary chamber 316 proximate the inlet 310, and perturbs the flow of heat transfer fluid through the primary chamber 316 from the inlet 310. The perturbation causes the heat transfer fluid to flow through the primary chamber 316 along the first sidewall (i.e., toward the feedback flow path 312a), rather than the second sidewall.

[0050] The secondary chamber 318 may enhance the frequency and/or amplitude of fluid oscillations through the outlets 314. In the illustrated example, the portion of the interior surface that defines the secondary chamber 318 includes two diverging sidewalls that meet a curved sidewall. In other implementations, the sidewalls are all straight, to form a trapezoidal secondary chamber 318. The secondary chamber 318 can receive a flow of heat transfer fluid and return a feedback flow of heat transfer fluid into the primary chamber 316 to perturb the flow of fluid in the primary chamber 316.

[0051] FIGS. 4A-L are diagrams illustrating example steam oscillator systems 118 and steam oscillator system components. The example steam oscillator systems 118 and components in FIGS. 4A-L each include one or more steam oscillator devices 204 that generate oscillatory compression waves in a compressible fluid medium. For example, a steam whistle 204d is an example of a steam oscillator device that generates sound waves based on an oscillatory flow of steam and/or other heat transfer fluids. In some cases, the steam whistle 204d generates sound waves having frequencies in the range of 100 to 1000 Hz. In other cases, the steam whistle 204d generates sound waves having lower or higher frequencies.

[0052] FIGS. 4A-D illustrate an example steam whistle assembly 418 that includes a single steam whistle 204d. FIG. 4A is a perspective view showing a partial cross-section of the steam whistle assembly 418. The steam whistle assembly 418 includes a housing 414 that defines two axial steam inflow paths 412 and a cavity for the steam whistle 204d. FIG. 4B is a side view of the steam whistle assembly 418. FIG. 4C is a cross-sectional side view of the steam whistle assembly 418 taken along axis 4C-4C of FIG. 4B. FIG. 4D is an end view of the steam whistle assembly 418.

[0053] As shown in FIG. 4C, the steam whistle 204d includes in inner surface that defines an inlet 404, an outlet 408, and a chamber 406. The steam whistle 204d can be implemented with no moving parts. The steam whistle 204d has a substantially static configuration to produce an oscillatory flow of heat transfer fluid through the outlet 408. For example, during operation the flow rate of steam through the outlet 408 (e.g., volume of steam per unit time) can oscillate over time. The oscillatory flow of heat transfer fluid may be generated by pressure oscillations in the chamber 406. The pressure oscillations may produce compression waves (e.g., sound waves) in a compressible heat transfer fluid. In some instances, the volume of the chamber 406 can be adjusted, for example, with a adjustable piston in the chamber 406 (not shown), to allow adjustment of the frequency of the oscillations. The compression waves can be transmitted from the wellbore 102 into the zone 112. For example, the compression waves can propagate through and interact with a subterranean formation and the resources therein. Of note, the compression waves need not necessarily propagate solely via the heat transfer fluid and through the perforations in the casing. As will be appreciated, the compression waves will propagate from the whistle through the various solid, compressible and incompressible elements of the wellbore, subterranean formation, and related fluids the casing into the formation.

[0054] During operation, steam flows into the steam whistle 204d through the inlet 404. The incoming steam strikes the edge 410, and the steam is split with a substantial portion flowing into the chamber 406. As steam flows into the chamber 406, the pressure of the steam in the chamber 406 increases. Due to the pressure increase in the chamber 406, steam inside the chamber 406 begins to flow Out of the steam whistle 204d through the outlet 408. The flow of steam from the chamber 406 through the outlet 408 perturbs the flow of steam from the inlet 404, and at least a portion of the steam flowing from the inlet 404 begins to flow directly through the outlet 408 rather than into the chamber 406. As a result, the pressure of the steam in the chamber 406 decreases. Due to the pressure decrease in the chamber 406, the flow of steam from the inlet 404 shifts again and begins to flow into the chamber 406. The cyclic increase and subsequent decrease of the pressure of steam in the chamber 406 continues. In this manner, the pressure of the steam in the chamber 406 oscillates over time, and accordingly, the flow of steam through the outlet 408 oscillates over time.

[0055] FIGS. 4E-H are diagrams illustrating an example steam oscillator system 118. The illustrated example steam oscillator system 118 includes a hydrocyclone device that can improve the quality of steam, for example, by separating condensed water out of a mixture of steam and condensed water. In some implementations of a well system 100, the steam that is delivered to the steam oscillation system 118 is not pure steam. For example, the steam may include some condensed water, and the hydrocyclone may reduce or eliminate an amount of condensed water that reaches a steam oscillator device 204. In some cases, condensed water inside of a steam oscillator device 204 can alter the performance of the steam oscillator device 204. For example, liquid water inside the chamber 406 of a steam whistle 204d may alter the amplitude and/or frequency of compression waves generated by the steam whistle 204d. Therefore, the hydrocyclone device may improve performance of the steam oscillator system 118 by reducing an amount of condensed fluid that reaches a steam oscillator device 204. In certain instances, the hydrocyclone device may be provided apart from a steam oscillator device 204, and used generally to separate particulates and/or condensed liquid from the steam to be injected. In certain instances, a coalescing membrane and/or other type of separator can be used in addition to or as an alternative to the hydrocyclone separator.

[0056] FIG. 4E is a side cross-sectional view of the example steam oscillator system 118. The example steam oscillator system 118 includes a whistle assembly 418 and a hydrocyclone assembly 416. The whistle assembly 418 includes two steam whistles 204d. In other implementations, the whistle assembly 418 can include the same or a different number of steam whistles 204d in the same or a different configuration. For example, the steam whistle assembly 418 of FIG. 4A and/or FIG. 4I can be implemented in the example steam oscillator system 118 of FIG. 4E. The steam whistle assembly 418 of FIG. 4E is in fluid communication with the hydrocyclone assembly 416. The hydrocyclone assembly 416 includes three components that are illustrated in FIGS. 4F, 4G, and 4H respectively. The three illustrated components of the hydrocyclone assembly 416 include a hydrocyclone unit 432, a sleeve 430, and an insert 434.

[0057] In one aspect of operation, steam flows toward the hydrocyclone assembly 416 along an axial flow path (not illustrated) through the whistle assembly 418. For example, the whistle assembly 418 may define one or more steam inflow paths 412, as in the whistle assembly 418 of FIGS. 4A-D. From the axial flow paths in the whistle assembly 418, steam flows into the hydrocyclone assembly 416. The steam that flows into the hydrocyclone assembly 416 may include some condensed water. The hydrocyclone assembly 416 converts the axial flow of steam to a rotary flow of steam in order to separate at least a portion of the condensed water from the steam and to improve the quality of the steam.

[0058] When a steam and condensed water mixture enters the hydrocyclone assembly 416, the mixture flows into a circumferential flow path 422 defined by helical threads 429 of the insert 434. As the steam flows along the circumferential flow path 422, the steam acquires angular momentum as it flows into a hydrocyclone inlet annulus 424. From the annulus 424, the steam flows into the hydrocyclone chamber 426. In the hydrocyclone chamber 426, at least a portion of the condensed water and other heavier elements (e.g. particulate) are separated from the pure steam. The condensed water flows in a rotary manner toward the narrow end of the hydrocyclone chamber 426 and through an outlet 440. At least a portion of the steam is separated from the condensed water and flows into the axial flow path 420 defined by a tubular section 428 of the insert 434 and by a tubular surface in the whistle assembly 418. The purified steam flows along the axial flow path 420 into the whistle assembly 418. The surface that defines the axial flow path 420 also defines apertures 442 which allow the steam to flow into the whistle inlets 404. After flowing into the whistles 204d, the steam is oscillated through the outlets 408 as described above.

[0059] FIGS. 4I-L are diagrams illustrating an example whistle assembly 418. FIG. 4I is a cross-sectional view of the example whistle assembly 418. The illustrated example whistle assembly 118 includes four steam whistles 204d in the whistle assembly 418 and a steam oscillator housing 438 to receive a flow of fluid from the outlet 440 of the hydrocyclone assembly 416. For example, the hydrocyclone assembly 416 may separate condensed water from a mixture of condensed water and steam. The separated condensed water may flow through the outlet 440 into an inlet of a steam oscillator device 204 carried in the housing 438. The illustrated example housing 438 defines a tapered slot to carry the tapered steam oscillator device 204. For example, the housing 438 may carry the steam oscillator device 204a illustrated in FIG. 3M. FIG. 4J is a cross-sectional view of the steam oscillator system 118 taken along line 4I-4J of FIG. 4I. FIG. 4K is a cross-sectional view of the steam oscillator system taken along line 4K-4K of FIG. 4I. FIG. 4L is a cross-sectional view of the steam oscillator system 118 taken along line 4L-4L of FIG. 4I.

[0060] Although a number of different examples of devices for oscillating a compressible flow have been described, it should be appreciated that other types of devices exist. In one example, the oscillator device can include a reed type device where one or more thin strips of stiff material (polymer, metal and/or other material) vibrate to produce oscillations when a compressible flow streams over them similar to the operation of a reeded woodwind instrument. The reeded oscillator device can have a single reed that produces oscillations, two reeds that are independent and/or that cooperate to produce oscillations, or more reeds that are independent and/or that cooperate to produce oscillations.

[0061] FIG. 5 is a flow chart illustrating an example process for oscillating fluid in a wellbore defined in a subterranean formation. For example, the process 500 may be used to inject heat transfer fluid, such as steam, into a subterranean formation through a wellbore defined in the subterranean formation, in order to stimulate production of resources from the formation. Additionally or alternatively, the process 500 may be used to propagate compression waves (e.g., sound waves) into the subterranean formation. In some cases, the heat transfer fluid is generated by a heat transfer fluid generator, such as a steam generator. The steam generator may be installed within the wellbore, or the steam generator may be installed above a ground surface. The steam generator may be in fluid communication with a tubular conduit to communicate the heat transfer fluid to a fluid oscillator device.

[0062] At 502, heat transfer fluid is directed into a fluid oscillator device. The heat transfer fluid may be directed into the fluid oscillator at a flow rate that is substantially constant over time. In some implementations, the flow of heat transfer fluid into the fluid oscillator varies over time. The heat transfer fluid flows through an interior volume of the fluid oscillator device.

[0063] At 504, a first portion of the heat transfer fluid within the fluid oscillator device is used to perturb a flow of at least a second portion of the heat transfer fluid through the fluid oscillator device. For example, the first portion of heat transfer fluid may be communicated along a feedback flow path toward an inlet into the fluid oscillator device in order to perturb the flow of fluid from the inlet into the interior volume of the device. As another example, the first portion of heat transfer fluid may be communicated into a primary chamber of the fluid oscillator device from a secondary chamber of the fluid oscillator device. The flow of fluid from the secondary chamber my function as a feedback to perturb the flow of fluid through the primary chamber. As another example, the fluid oscillator device may define a resonant chamber. The fluid oscillator device may be configured to cyclically increase and decrease the pressure of compressible heat transfer fluid within the resonant chamber. The periodic pressure variations in the resonant chamber may generate longitudinal compression waves (e.g., sound waves) that propagate through the subterranean formation.

[0064] In some cases the perturbation of flow within the fluid oscillator device is repeated in a periodic manner. The periodic perturbation may cause a flow of heat transfer fluid to alternate between two different regions of the fluid oscillator device. For example, the flow of fluid through the fluid oscillator device may periodically oscillate between two flow directions within the device.

[0065] At 506, at least a portion of the heat transfer fluid is received from the fluid oscillator at a flow rate that varies in time. The received portion of heat transfer fluid may flow through a flow outlet extending from an interior volume of the fluid oscillator device.

[0066] At 508, the heat transfer fluid is injected into the subterranean formation. The heat transfer fluid may enter the subterranean formation from the wellbore, for example, through perforations in a wellbore casing. The heat transfer fluid may transfer heat energy to resources in the formation and reduce viscosity of the resources. The reduced viscosity of the resources may stimulate production of the resources. For example, a flow of resources into a wellbore may be increased as a result of injecting heat transfer fluid into the formation. In some cases, the heat transfer fluid is not injected into the subterranean formation. For example, a steam whistle fluid oscillator device may be used to propagate compression waves into the subterranean formation, and the heat transfer fluid that flows through the steam whistle may remain in the wellbore and/or flow to the surface.

[0067] In some implementations of the process 500, a parameter of the fluid flow into the fluid oscillator device is varied among two or more levels over two or more time intervals. Example parameters of input fluid flow that may be varied include volumetric flow rate, mass flow rate, velocity, and others.

[0068] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.