The invention relates generally to erosion control to protect a downhole structure from erosion resulting from impact by a jet of fluid produced by a flow control device.
A completion system installed in a well typically includes flow control devices (such as in the form of valves) to control fluid flow in the well. The fluid flow can include production flow (to produce hydrocarbons or water from a reservoir) and/or injection flow (to inject fluid into a formation). The flow control function in a downhole valve is usually accomplished by using a flow constriction, such as in the form of a nozzle. The flow rate through the valve is regulated by changing the cross-sectional area available to fluid flow. In most downhole applications, the pressure differential across a valve can be relatively high, which can lead to creation of powerful fluid jets output from the valve.
Many valves control fluid flow in a radial direction of a wellbore. Since the available space in a wellbore is relatively limited, the distance between valves and other structures (e.g., tubing, pipe, casing, etc.) is relatively small. Consequently, a relatively powerful jet produced by a valve that impinges upon a downhole structure can cause substantial erosion of the downhole structure. For example, in the injection context, the fluid jet produced by a valve can impinge upon the casing, which can cause erosion of the casing after some amount of time. Erosion of downhole structures can also occur in the production context, where fluid flows from a wellbore annulus into a tubing or pipe.
Conventional techniques of providing erosion control include providing shrouds around a valve to protect a surrounding structure, such as the casing, from a powerful fluid jet. However, shrouds add to the complexity and expense of a tool string that contains the valve.
In general, according to an embodiment, an apparatus for use in a wellbore comprises a flow control device having a nozzle with an output to provide a jet of fluid. The apparatus further includes a structure proximate the nozzle and positioned a set distance away from the output of the nozzle, where the set distance is greater than a length of the potential core of the jet of fluid.
Other or alternative features will become apparent from the following description, from the drawings, and from the claims.
In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible.
The example tool string depicted in
As depicted in
The fluid jet 110 can impinge upon the casing 102. If the nozzle 106 is placed too close to the casing 102, then the velocity of the fluid jet that impinges upon the casing 102 can be relatively high, which can cause erosion of the casing 102 over time.
However, in accordance with some embodiments, the nozzle 106 is set a distance L away from the wall of the casing 102. Note that
The distance L between a nozzle 106 and the casing wall is set such that the velocity of the fluid jet that impinges upon the casing 102 is reduced to provide erosion control. For a given distance L, the velocity of the fluid jet 110 that impinges upon the casing 102 is reduced depending upon the diameter D of the opening of the nozzle 106. Thus, when designing the completion system, both the nozzle diameter D and the distance L can be selected to achieve a reduction of the fluid velocity of the fluid jet that impinges upon the casing 102. The value of L can be selected to be a smaller value if the diameter D of the nozzle opening is reduced. However, reduction of the nozzle opening diameter leads to reduced flow rate. To compensate for reduced flow rate, a larger number of nozzles of the reduced diameter are provided such that the effective total area available for flow between the module 108 and the wellbore 100 can be increased, such that a target flow rate can be accomplished.
Although reference is made to diameters of nozzle openings, it is noted that nozzle openings can have non-circular shapes, in which case, the largest diameter of the nozzle opening is selected.
Although
The arrangement of the nozzles 106 of
The fluid jet considered is a submerged free jet that spreads through a medium at rest. A submerged fluid jet refers to a fluid jet submerged within the same fluid (e.g., liquid jet submerged in liquid or gas jet submerged in gas). More specifically, some examples include a water jet submerged in water, a hydrocarbon jet submerged in hydrocarbon, a natural gas jet submerged in natural gas, and so forth.
As depicted in
After a distance Xc from the nozzle output end 206, the entire width of the fluid jet 110 is made up of the mixing layer 204. In other words, the potential core 202 extends the distance Xc from the output end 206 of the nozzle 106 (Xc defines the length of the potential core 202 of the fluid jet 110). In the region 216 of the fluid jet 110 that is downstream of the end of distance Xc, the average velocity of the fluid within the fluid jet 110 decreases with increasing distance from the output end 206 of the nozzle 106. Reference is made to “average velocity” of fluid in the mixing layer 204 due to the fact that the actual velocity of fluid in the mixing layer is not constant as a result of turbulent fluid flow.
Generally, the length (Xc) of the potential core 202 varies between four and seven nozzle diameters for incompressible submerged fluid jets. A nozzle diameter is represented by D, where D is the diameter of the inner opening 208 of the nozzle 106. For compressible submerged fluid jets, the length of the potential core 202 increases with increasing Mach number (which represents the velocity of the fluid jet expressed as a Mach number, or the speed of sound).
Generally, the velocity profile of a turbulent free jet is invariant, which means that the length of the potential core in terms of nozzle diameter is substantially the same for all submerged jets.
By setting the distance L properly, a shroud does not have to be provided around the module 108 of the tool string 104 that contains the nozzles 106. A shroud is a protective layer around the outside of the module 108 to protect a downhole structure such as the casing from damage due to erosion by fluid jets. By providing erosion protection without use of a shroud, tool string complexity and costs can be reduced. Note that provision of a shroud around the module 108 effectively reduces the distance L between the shroud and the nozzles 106 of the module 108, which can lead to increased erosion of the shroud. Moreover, bounce-back of fluids from a shroud to the module 108 can cause erosion of the outer wall of the module 108.
Once the diameter D and distance L are set, the tool containing the one or more nozzles is provided (at 408) into the well, such as by running the tool into the well on tubing or on a carrier line such as a wireline or slickline. Once positioned in the well, the nozzles are positioned prescribed one or more distances (L) away from the downhole structure(s) that is (are) the subject of erosion protection according to some embodiments.
While the invention has been disclosed with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover such modifications and variations as fall within the true spirit and scope of the invention.
This claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 60/745,587, entitled “Erosion Control in Flow Control Valves,” filed Apr. 25, 2006.
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Number | Date | Country | |
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Number | Date | Country | |
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60745587 | Apr 2006 | US |