System and Method for Forming Cavities

Abstract

A technique facilitates forming cavities, e.g. perforations, into a geological formation. A jetting tool is moved downhole into a borehole, and an abrasive fluid is pumped down through the jetting tool. The abrasive fluid is discharged under pressure through a plurality of jetting nozzles to form jets of the abrasive fluid which act against a surrounding wall, e.g. a casing or other borehole wall. The jetting nozzles, and thus the jets, are oriented such that a rebound effect of the jets does not detrimentally impact the jetting tool. Consequently, the jets can be used to cut perforations through the surrounding wall and into the formation without eroding or otherwise detrimentally affecting components of the jetting tool.

Description

BACKGROUND

A variety of perforating techniques and fracturing techniques are conducted in wellbores drilled in geological formations. The resulting perforations and/or fractures facilitate flow of desired fluids through the formation and into a wellbore. For example, the production potential of an oil or gas well may be increased by improving the flowability of hydrocarbon-based fluids through the formation and into the wellbore. In some applications, however, difficulties arise in initiating and achieving desirable perforations and fractures to facilitate fluid flow.

SUMMARY

In general, the present disclosure provides a system and method for forming cavities, e.g. perforations, into a geological formation. A jetting tool is moved downhole into a borehole, and an abrasive fluid is pumped down through the jetting tool. The abrasive fluid is discharged under pressure through a plurality of jetting nozzles to form jets of the abrasive fluid which act against a surrounding wall, e.g. a casing or other borehole wall. The jetting nozzles, and thus the jets, are oriented such that a rebound effect of the jets does not detrimentally impact the jetting tool. Consequently, the jets can be used to cut perforations through the surrounding wall and into the formation without eroding or otherwise detrimentally affecting components of the jetting tool.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying figures illustrate various implementations described herein and are not meant to limit the scope of various technologies described herein, and:

FIG. 1 is a schematic illustration of an example of a jetting tool deployed downhole into a borehole via a conveyance, according to an embodiment of the disclosure;

FIG. 2 is a cross-sectional illustration of an example of the jetting tool showing an angling of the jetting nozzles to avoid erosive rebound effects, according to an embodiment of the disclosure;

FIG. 3 is a schematic illustration of the jetting tool illustrated in FIG. 1 as operated during a clean out procedure, according to an embodiment of the disclosure;

FIG. 4 is a schematic illustration of an example of jetting nozzle configuration for forming desired jets of abrasive fluid, according to an embodiment of the disclosure; and

FIG. 5 is a schematic illustration of another example of the jetting tool, according to an embodiment of the disclosure.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to provide an understanding of some illustrative embodiments of the present disclosure. However, it will be understood by those of ordinary skill in the art that the system and/or methodology may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.

The disclosure herein generally relates to a methodology and system for forming cavities, e.g. perforations, into a geological formation. According to an embodiment, a jetting tool is moved downhole into a borehole, such as a wellbore. An abrasive fluid is pumped down through the jetting tool. For example, a surface pumping system for pumping abrasive jetting fluid may be used to deliver the abrasive fluid down through a tubing, e.g. coiled tubing, to an internal flow passage of the jetting tool. From the internal flow passage, the abrasive fluid is discharged under pressure through a plurality of jetting nozzles to form jets of the abrasive fluid. The jets act against a surrounding wall, e.g. a casing or other borehole wall. To avoid erosive effects with respect to the jetting tool, the jetting nozzles, and thus the jets, are oriented such that a rebound effect of the jets does not detrimentally impact the jetting tool. Consequently, the jets can be used to cut perforations through the surrounding wall and into the formation without eroding or otherwise detrimentally affecting components of the jetting tool.

The system and methodology are generally related to well site equipment, such as oil field surface equipment, downhole assemblies, coiled tubing assemblies, and other well related equipment. The jetting tool described herein may be used with many types of well site equipment for a variety of cavity forming operations. However, the jetting tool also may be utilized with various other types of equipment and in other applications, e.g. non-well related applications. In some well applications, the jetting tool is used to direct a stream of abrasive fluid from a tubing interior, such as a coiled tubing interior, through a nozzle or nozzles formed in the jetting tool, and outwardly toward a wellbore casing to create resulting cavities, e.g. perforations.

According to an embodiment, a jetting tool is run downhole into a wellbore, i.e. run in hole, via coiled tubing or another suitable conveyance. The coiled tubing is used to adjust the depth of the jetting tool to a desired depth at which a first set of perforations is to be formed. An abrasive slurry or similar fluid is then pumped downhole through the coiled tubing, through the jetting tool, and out through the jetting nozzles to perforate a surrounding borehole wall. For example, the jets of abrasive fluid/slurry may be used to perforate a casing and then to further perforate into the surrounding formation a sufficient distance to enable communication of hydraulic pressure into the formation, e.g. into an oil or gas bearing formation.

Once the first set of perforations is formed, the jetting tool may be repositioned at a suitable distance away from the newly formed perforations. The distance from the first set of perforations is selected to ensure the coiled tubing tool string is far enough away from the first set of perforations so that the tool string does not get stuck during a fracturing procedure. A hydraulic fracture slurry is then pumped downhole through an annular space between the coiled tubing and the surrounding casing and out into the perforations. The hydraulic fracture slurry is sufficiently pressurized to fracture the formation which has just been perforated.

Excess hydraulic fracture slurry tends to settle and accumulate above the zone that has just been fractured, and this excess slurry is cleaned out and returned to the surface in a clean out operation. By way of example, the clean out operation may be performed by running the jetting tool back downhole while reverse circulating clean fluid. The clean fluid is reverse circulated from the surface, down through the annulus, in through the jetting nozzles (and/or other suitable passages), and up through an interior of the coiled tubing to a surface collection location. In some embodiments, a reverse circulation check valve, e.g. ball check valve, may be used in cooperation with the jetting nozzles of the abrasive jetting tool to facilitate the clean out operation.

After cleaning out the excess fracture slurry, the jetting tool may be repositioned to another perforation depth or location within the wellbore. At the subsequent perforation depth, another set of cavities, e.g. perforations, may be created through the surrounding casing and into the formation. The perforations are then used for a fracturing operation followed by a reverse circulating clean out operation, as described above. This process of perforating, fracturing, and cleaning out excess fracturing slurry may be repeated a desired number of times to form multiple sets of perforations according to the parameters of a given operation.

During a clean out operation, a consideration for an operator of the abrasive jetting tool is the rate of penetration (ROP) which is defined as penetrated distance of the clean out operation divided by the time of the clean out operation. The ROP is affected by how well the settled slurry may be stirred up and sent flowing back up through the interior of the coiled tubing.

With conventional perforation formation, bottom hole assemblies (BHAs) are not able to direct jets downwardly. Additionally, conventional BHAs suffer from erosion of components, such as erosion of nozzles. With conventional BHAs, the injected abrasive fluid rebounds or reflects back from the surrounding wall and/or from newly formed perforations, thus impacting the bottom hole assembly. The abrasive fluid often contains solid particles which erode material from the BHA, including removal of material from an exterior surface of the tool body. Additionally, the rebound effect can result in the abrasive fluid impacting the nozzles injecting the fluid, thus causing rapid wear of the nozzles and deterioration of the perforating operation.

Referring generally to FIG. 1, an example of a cavity forming or perforating system 20 is illustrated. In this embodiment, perforating system 20 comprises a jetting tool 22 having a tool body 24. The jetting tool 22 may be conveyed into a borehole 26, e.g. a wellbore, by a suitable conveyance 28, such as coiled tubing 30. By way of example, the jetting tool 22 may be directly coupled with coiled tubing 30 via a coiled tubing connector 31. The jetting tool 22 may be connected with coiled tubing connector 31 via threaded engagement or other suitable engagement techniques.

In many applications, the borehole 26 is in the form of a wellbore drilled into a geological formation 32, such as a hydrocarbon fluid bearing formation. In such applications, the jetting tool 22 may be used to facilitate the production of hydrocarbon fluids, e.g. oil and/or gas, from the formation 32. The wellbore 26 may be lined with a suitable casing 34 which provides a surrounding wellbore wall 36 into which the jetting tool 22 is deployed. However, the surrounding wellbore wall 36 may comprise an open borehole or various other materials and/or features lining the borehole 26.

The production of hydrocarbon fluids may be facilitated by forming cavities 38, e.g. perforations, through the casing 34 and into the formation 32. The perforations 38 also may be used to facilitate fracturing operations which effectively fracture the formation 32 to further facilitate the flow of hydrocarbon fluids to the wellbore 26 for production to a suitable collection location.

In a perforating operation, the jetting tool 22 is moved downhole into wellbore 26 to a desired location for forming perforations 38. An abrasive fluid is then pumped down through a flow passage 40 of jetting tool 22 and out through a plurality of jetting nozzles 42. As the pumped, abrasive fluid flows out through jetting nozzles 42 under pressure, jets 44 are formed and act against the surrounding wellbore wall 36, e.g. against casing 34, to form perforations 38 through the casing 34 and into the formation 32. By way of example, the flow passage 40 may extend longitudinally along an interior of tool body 24 and may be aligned with, e.g. concentric with, a longitudinal, central axis 46 of jetting tool 22 (see also FIG. 2).

In some applications, the abrasive fluid is pumped down along an interior 48 of coiled tubing 30, down through the jetting tool 22 via flow passage 40, and out through at least one, e.g. a plurality, of jetting nozzles 42. The outflow through jetting nozzles 42 forms jets 44 of the abrasive fluid which act against the surrounding wellbore wall 36. In this example, the jetting tool 22 may be coupled directly to the coiled tubing 30 such that a fluid may be pumped from the interior 48 of coiled tubing 30 and immediately into the flow passage 40 of jetting tool 22, i.e. without passage through other components. Additionally, the jetting nozzles 42, and thus the jets 44, are oriented at an angle with respect to axis 46 such that a rebound effect of the jets 44 does not detrimentally impact the jetting tool 22.

For example, the jetting nozzles 42 may be oriented such that a rebounded or reflected portion 50 of the abrasive fluid rebounds or reflects in a direction which misses the jetting tool 22, as illustrated in FIG. 1. Thus, the rebound effect of abrasive fluid bouncing off of the surrounding wellbore wall 36 during a perforating operation does not substantially impact the jetting tool 22, and thus does not cause erosion of the jetting nozzles 42 or of other portions of jetting tool 22. This enables the use jets 44 under desired pressures and flow rates to form the desired perforations 38 without detrimentally affecting operation of the jetting tool 22 over time. In a variety of well applications, the jets 44 facilitate formation of perforations 38 far enough into formation 32 to enable communication of hydraulic pressure into the oil or gas bearing formation 32 during, for example, a fracturing procedure.

Referring again to FIG. 2, the desired rebound effect of jets 44 may be achieved by orienting each jetting nozzle 42, and thus each jet 44, at a suitable angle with respect to axis 46. In an embodiment, each jetting nozzle 42 of a plurality of jetting nozzles 42 is oriented to form an acute angle 52 with the axis 46 of between about 55 degrees and about 75 degrees. In some applications, the acute angle 52 between each jetting nozzle 42 and the jetting tool axis 46 may be approximately 65 degrees. The acute angle 52 is measured between axis 46 and a nozzle axis 54 of a corresponding jetting nozzle 42. In some applications, the acute angle 50 may be different for each jetting nozzle 42, but the acute angle 52 also may be the same or similar for each jetting nozzle 42.

In the example illustrated, the acute angle 52 is on the downhole or lead end side of the jetting tool 22. Thus, during a perforating operation, the abrasive fluid forms jets 44 which flow outwardly and downwardly with respect to the jetting tool 22. In this type of arrangement, the reflected or rebounded portion 50 of abrasive fluid is reflected downwardly ahead of the jetting tool 22 such that the abrasive fluid substantially or entirely misses the jetting tool 22. As illustrated, the reflected portion 50 may pass ahead of a lead end 55 of jetting tool 22.

After forming the first set of perforations 38, the jetting tool 22 may be pulled uphole, via coiled tubing 30, a predetermined distance above the previously formed set of perforations 38. A hydraulic fracturing slurry is then pumped down through an annulus 56 between the coiled tubing 30 and the surrounding wellbore wall 36 formed by, for example, casing 34. It should be noted that in some applications, the fracturing slurry may be pumped down along passages other than annulus 56. The hydraulic fracturing slurry is forced outwardly under pressure into perforations 38 to fracture the formation 32. Following the fracturing operation, excess hydraulic fracturing slurry 58 is cleaned out of the wellbore 26 by running the jetting tool 22 back downhole while reverse circulating a clean fluid, as represented by arrow 60 in FIG. 3.

In the embodiment illustrated, the clean fluid 60 is pumped from a surface location, down through the annulus 56, into the jetting tool 22 through the plurality of jetting nozzles 42, up through flow passage 40, and up along the interior 48 of coiled tubing 30. The clean fluid 60 carries the excess hydraulic fracturing slurry 58 to a collection location at the surface where the hydraulic fracturing slurry 58 may be separated from the clean fluid 60. The jetting tool 22 may then be moved to another desired location along wellbore 26 so as to form another set of perforations 38 at a different well zone. The process of deploying jetting tool 22, forming a set of perforations 38, fracturing formation 32 via the set of perforations 38, cleaning out the excess fracturing slurry, and moving the jetting tool 22 to a subsequent perforation forming location can be repeated a desired number of times for a desired number of well zones.

Depending on the application, the jetting tool 22 may comprise a single jetting nozzle 42 or a plurality of jetting nozzles 42. If a plurality of jetting nozzles 42 is employed for a given application, the jetting nozzles 42 may vary in number and arrangement. In some applications, the jetting nozzles 42 are spaced equidistant about a circumference of the jetting tool 22, although the jetting nozzles 42 can be staggered or arranged with different circumferential distances and/or longitudinal distances between sequential jetting nozzles 42. In FIG. 4, a specific example is illustrated in which the jetting tool 22 comprises three jetting nozzles 42 arranged generally equidistant around the circumference of jetting tool 22 with approximately 120 degrees between sequential jetting nozzles 42. However, greater or lesser numbers of jetting nozzles 42 may be constructed in a variety of arrangements and patterns with the desired acute angle 52 is selected to reduce or eliminate the rebound impact of abrasive fluid flowed outwardly through jetting nozzles 42 under pressure.

Referring generally to FIG. 5, another embodiment of jetting tool 22 is illustrated. In this embodiment, the jetting tool 22 comprises a passage 62 extending through the tool body 24. In some embodiments, the passage 62 may be located at the lead end 55 of jetting tool 22, e.g. aligned with the central axis 46 of jetting tool 22. By way of example, the passage 62 may cooperate with a check valve 64 which acts against a corresponding seat 66 to allow upward flow of fluid, e.g. clean fluid, as represented by arrows 68. However, the check valve 64 blocks outward flow of fluid from internal flow passage 40 to the surrounding wellbore 26. In the embodiment illustrated, the check valve 64 comprises a ball 70 sized to seal against seat 66 during, for example, an injection operation in which fluid flows outwardly through the plurality of jetting nozzles 42.

Without passage 62, the entire flow of returned clean fluid flows through jetting nozzles 42 in a reverse circulation direction during a clean out operation. This action ensures a relatively high flow rate of cleaning fluid through the jetting nozzles 42 and a rigorous removal of excess fracturing slurry 58. Effectively, the rate of penetration can be substantially improved during the reverse clean out operation by enabling a better pick up of solids from the wellbore 26. However, some applications may benefit from the added volume of flow facilitated by the addition of passage 62 and check valve 64. With the addition of passage 62 and check valve 64, clean fluid can be reversed circulated through both passage 62 and jetting nozzles 42 during a clean out operation. With either embodiment, the jetting tool 22 may be constructed in a substantially shorter and simpler configuration as compared to conventional jetting tools.

In addition to reducing or eliminating the rebound effect, the angled jetting nozzles 42 also may be used to break up consolidated solids. For example, the excess fracturing slurry 58 may comprise sand (and/or other solids) which tends to consolidate in the wellbore 26. However, the downhole angle of jetting nozzles 42 enables use of the jetting nozzles 42 for directing jets of fluid against the consolidated solids to effectively chop up the settled sand and/or other solids.

The system and methodology described herein may be employed in non-well related applications which utilize jets for cutting perforations or other types of cavities. Additionally, the overall perforations system may comprise a variety of other and/or additional components. The jetting tool may be conveyed on coiled tubing or another type of suitable conveyance. The flow of injection fluid, e.g. flow of an abrasive jetting fluid and/or flow of hydraulic fracturing slurry, may be directed along an interior of the conveyance or along other suitable flow paths routed downhole along the wellbore. Additionally, various numbers, arrangements, and angular orientations of the jetting nozzles may be employed depending on the parameters of a given application. The jetting nozzles 42 also may comprise a variety of inserts, hardened inserts, coatings, or other features to facilitate creation and control of jets 44.

As described above, the jetting tool 22 provides a simplified construction which enables improvement of the rate of penetration during clean out while providing down jetting capability for improved clean out functionality. The jetting tool 22 also reduces tool erosion otherwise resulting from the rebound effect, thus providing an increased tool life and increased jetting time. The simplified construction and erosion control features of the jetting tool also facilitate performance of jetting operations with a reduced number of additional tool string components and spare parts. The construction of at least some embodiments further facilitates reverse circulation and clean out operations due to a reduced number of orifices for reverse fluid flow. This effectively reduces the potential for detrimental issues arising while employing desired rates of penetration during reverse sand/proppant clean out.

Although a few embodiments of the system and methodology have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.

Claims

1. A system for forming perforations in a well, comprising: a coiled tubing; anda jetting tool coupled to the coiled tubing by a coiled tubing connector, the jetting tool having a flow passage therein which extends along a longitudinal axis of the jetting tool to a plurality of jetting nozzles, thus forming a flow path through the flow passage and the plurality of jetting nozzles, the plurality of jetting nozzles being oriented such that a rebounded portion of fluid flowing out of the plurality of jetting nozzles and against a surrounding wall is directed to miss the jetting tool.

2. The system as recited in claim 1, wherein each jetting nozzle of the plurality of jetting nozzles is oriented to form an acute angle with the longitudinal axis, the acute angle being between about 55 degrees and about 75 degrees.

3. The system as recited in claim 1, wherein each jetting nozzle of the plurality of jetting nozzles is oriented to form an acute angle with the longitudinal axis, the acute angle being approximately 65 degrees.

4. The system as recited in claim 1, wherein the jetting tool is coupled directly to the coiled tubing such that a fluid may be pumped from an interior of the coiled tubing and immediately into the flow passage of the jetting tool.

5. The system as recited in claim 1, wherein the jetting tool further comprises a seat and a check valve received in the seat.

6. The system as recited in claim 5, wherein the check valve comprises a ball which seals against the seat during an injection operation in which fluid flows outwardly through the plurality of jetting nozzles.

7. The system as recited in claim 5, wherein the seat and the check valve are located along the axis of the jetting tool.

8. A method, comprising: moving a jetting tool downhole in a wellbore drilled into a formation;pumping an abrasive fluid down through the jetting tool and out through a plurality of jetting nozzles to form jets of the abrasive fluid which act against a surrounding wall;orienting the jets such that a rebound effect of the jets does not detrimentally impact the jetting tool; andusing the jets to cut perforations through the surrounding wall.

9. The method as recited in claim 8, wherein moving comprises moving the jetting tool downhole via coiled tubing.

10. The method as recited in claim 8, wherein pumping comprises pumping the abrasive fluid down through a flow passage oriented along a longitudinal axis of the jetting tool and out through the plurality of nozzles.

11. The method as recited in claim 10, wherein orienting the jets comprises orienting the plurality of jetting nozzles at an acute angle of between about 55 degrees and about 75 degrees with respect to the longitudinal axis.

12. The method as recited in claim 10, wherein orienting the jets comprises orienting the plurality of jetting nozzles at an acute angle of approximately 65 degrees with respect to the longitudinal axis.

13. The method as recited in claim 9, further comprising pulling the jetting tool uphole a predetermined distance from the perforations.

14. The method as recited in claim 13, further comprising pumping a hydraulic fracture slurry down through an annulus between the coiled tubing and a surrounding casing and then into the perforations to fracture the formation.

15. The method as recited in claim 14, further comprising cleaning out excess hydraulic fracture slurry by running the jetting tool back downhole while reverse circulating a clean fluid from a surface location down through the annulus, into the jetting tool through the plurality of jetting nozzles, and up through an interior of the coiled tubing.

16. The method as recited in claim 15, wherein cleaning out further comprises returning a portion of the clean fluid through a check valve located downhole from the plurality of nozzles.

17. The method as recited in claim 15, wherein cleaning out further comprises returning the clean fluid in its entirety through the plurality of jetting nozzles.

18. A method, comprising: forming a jetting tool with a central axis, a flow passage extending along the central axis, and a plurality of jetting nozzles in communication with the flow passage;orienting the plurality of nozzles at an angle with respect to the central axis; andselecting the angle such that jets of fluid flowing outwardly through the plurality of nozzles are directed outwardly and toward a lead end of the jetting tool.

19. The method as recited in claim 18, further comprising moving the jetting tool downhole into a wellbore lined with casing; and pumping and abrasive fluid down through the flow passage and out through the plurality of jetting nozzles to cut cavities in a surrounding wall.

20. The method as recited in claim 19, wherein selecting comprises selecting the angle such that a rebound effect of abrasive fluid rebounding off the surrounding wall does not erode the jetting tool.