Abstract:
A wellbore cleaning device comprises a tubular section, a helical scratcher mounted thereon. The helical scratcher contains flexible wires characterized in that the helical scratcher is able to rotate axially to the tubular section when a fluid flows axially to the tubular section. A method for using the device comprises placing the device into the wellbore; allowing the fluid flowing axially to the wellbore wall to rotate the scratcher; removing a deposit at wellbore wall; and leaving a cleaned wellbore wall.

Description:
FIELD OF THE INVENTION 
     The present invention broadly relates to oilfield applications. This invention relates to a movable well bore cleaning device for attachment to a well casing or the like, and more particularly to a movable well bore cleaning device adapted for cleaning the well bore wall before and during cement placement in a subterranean reservoir, such as for instance oil and/or gas reservoir or a water reservoir. 
     DESCRIPTION OF THE PRIOR ART 
     At the completion of every oil and gas drilling operation, whether the operation results in production or a dry hole, it is necessary that some cementing be done in the bore hole. In the case of production, the casing must be cemented in the hole for support thereof and prevention of the flow of fluids between formations. In the case of a dry hole, cement plugs must be set at various depths to seal various formations. 
     When cementing casing, the casing is run into and centered in the hole and then cement is pumped down through the casing to displace the drilling mud from the annulus. When setting a plug, a pipe of relatively small diameter is run into the hole to the depth of the bottom of the plug and cement is pumped through the pipe to displace the mud above the end of the pipe until a plug of sufficient length has been formed at which time the pipe is withdrawn from the hole and the cement is allowed to harden. 
     In all cases, it is necessary that the walls of the bore hole be cleaned of mud cake and the like so that the cement will bond properly with the formation. Failure to remove unreactive solids between the cement sheath and the formation will leave a potential axial flow path for formation fluids, hence compromising hydraulic isolation. 
     Mechanical well bore wall cleaning is accomplished by means of devices known as scratchers. Non-mechanical means of cleaning the well—based for instance on the use of wash fluids flowing in turbulent flow—are being used, but they are felt as being less efficient. The turbulent action of wash fluids can be enhanced by placing passive obstacles in the flow conduit that disturb laminar flow. 
     There are two basic types of scratchers: reciprocating and rotating. Reciprocating scratchers are designed to operate when the casing or pipe to which they are attached is moved axially within the bore hole and they usually include a single collar having a plurality of wire bristles or flat loops of wire extending radially to contact the well bore wall. Another type of reciprocating scratcher includes a pair of collars having a plurality of spiraling wires connecting the collars and a plurality of fingers extending radially outwardly and upwardly from the upper collar, which help cleaning the well bore wall when the casing or pipe is reciprocated. 
     Rotating type scratchers are designed to operate when the casing or pipe to which they are attached is rotated and include an axially extending strip having thereon a plurality of radially outwardly extending loops or bristles or a combination of loops and bristles. There is an additional rotating scratcher which includes a helical strip having thereon a plurality of radially outwardly extending bristles. 
     Reciprocating scratchers clean only when reciprocated; rotating scratchers, with the exception of the helical strip type which cleans to a limited extent while reciprocated, clean only when rotated. 
     In summary, there are a number of existing scratchers that work during casing or pipe reciprocation and/or rotation. Some of them are disclosed in patents U.S. Pat. Nos. 4,750,558; and 3,390,725. However, all existing scratchers require casing movement to work. In other words, if casing or pipe movement is not feasible, which might be a common case due to different reasons, these scratchers are not useful. None of these solutions work when the tubular remain static. 
     There are other devices used for different purposes (casing or pipe centralization), know as centralizers. Some of them (in instance: SpiraGlider) consist of a steel centralizer and two asymmetrically-beveled stop collars. The shape of both centralizer and collars is designed to minimize running resistance. The unique stop collar performs both as a positioning device and provides protection to the leading edge of the centralizer. It is designed specifically for highly inclined or horizontal wells and is ideal for use with liner hangers. This configuration allows the centralizer to rotate and also allows a certain degree of axial movement. These movements have the objective of making easier running the casing or pipe. However, they are not designed to work as scratchers, neither to rotate and/or move axially using the fluids flow to induce such movements. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a movable well bore cleaning device (flow-induced scratcher) that will clean independently of casing movement. It is a further object of the present invention to use the fluids annular flow as the driving force to rotate or move axially mechanical scratchers. 
     In a first aspect, a device for cleaning a wellbore is disclosed, said device comprises a tubular section, a helical scratcher mounted thereof wherein said helical scratcher contains flexible wires characterized in that the helical scratcher is able to rotate axially to tubular section when a fluid flows axially to tubular section. 
     Preferably, the device comprises at least two helical scratchers mounted on the tubular section, wherein the two helical scratchers are connected through a cleaning wire and further comprising a restoring aid connected on one side to tubular section and on the other side on one of the helical scratchers. Alternatively, the device can further comprise, on the helical scratcher, a cone like structure to create a jet with the fluid. 
     In a second aspect, a method to clean a wellbore wall of a well is disclosed, said method comprises the steps of: incorporating a device as previously described into the wellbore; moving the device in the well and allowing the fluid flowing axially to the wellbore wall to rotate the scratcher; removing deposit at wellbore wall; leaving a cleaned wellbore wall. 
     Preferably, the method further comprises the step of selecting a zone of interest and using one scratcher above the zone of interest and a second scratcher below the zone of interest. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further embodiments of the present invention can be understood with the appended drawings. 
         FIG. 1  shows a schematic diagram illustrating the apparatus according to the invention in a first embodiment within the wellbore. 
         FIG. 2  shows a schematic diagram illustrating the apparatus according to the invention in a first embodiment. 
         FIG. 3  shows a schematic diagram illustrating the apparatus according to the invention in a second embodiment within the wellbore. 
         FIG. 4  shows an alternate schematic diagram illustrating the apparatus according to the invention in a second embodiment within the wellbore. 
         FIG. 5  shows a schematic diagram illustrating the apparatus according to the invention in a third embodiment within the wellbore. 
         FIG. 6  shows an alternate schematic diagram illustrating the apparatus according to the invention in a third embodiment within the wellbore. 
         FIG. 7A  shows a schematic diagram illustrating the apparatus according to the invention in a fourth embodiment.  FIGS. 7B and 7C  show two possible configurations of cones attached to the helical blades. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows the wellbore cleaning device in a well, comprising a formation  10 , a wellbore wall  11  and the rotating scratcher  1  inside. The rotating scratcher comprises at least one helical blade  30  equipped with flexible wires  31  that are long enough to touch the wellbore wall. A fluid  5  circulates in the annulus between a tubular  20  and the wellbore wall. A deposit  2  is situated on the wellbore wall. The action of the rotating scratcher  1  removes the deposit  2 , leaving a cleaned wellbore wall  3 . In a first embodiment, the well bore cleaning device is able to rotate radially only.  FIG. 2  shows the cleaning device in more detail. The cleaning device is made of one of several helical blades  30 , fastened together. These blades can freely rotate around the casing and their axial movement is restricted by means of top and bottom stop collars  21  and  22  fastened to a tubular  20 . The blades are equipped with flexible wires  31  long enough to touch the wellbore wall  11 . These blades can be fitted with wires along their full length or only along part of their length to reduce the drag with the wellbore wall. 
     The flow of fluid  5  circulating axially in the wellbore imparts a rotating movement to the blades that, upon rotation, scratches any fragile deposit on the wellbore wall along the full length of the rotating scratcher. This fragile deposit may be made of filter cake, settled solids (barite or cuttings) or other kind of debris. The removed material is cleaned out of the hole by the flow of the annular fluid and leaves a cleaned wellbore wall  3 . 
     The deposit  2  is this fully replaced by the circulating fluid. If the circulating fluid is a cement slurry, it will bond with the formation upon setting and provide an efficient hydraulic isolation barrier in the annulus. The hydraulic isolation in regions with a cleaned wellbore wall  3  will be much better than in untreated places without scratchers because the presence of a fragile deposit at the cement-formation interface presents an easy leakage path. 
     In a second embodiment, the wellbore cleaning device is equipped with a plurality of rotating scratchers on the tubular, placed at different depths along the tubular to ensure several hydraulic isolation sections along the well ( FIG. 3 ). Rotating cleaning devices can be placed above and below a zone of interest  7 , in order to insure hydraulic isolation from other zones above and below the reservoir. In such a way, cement  300  in direct contact with the wellbore wall  11  provides a section with an efficient hydraulic seal  8 . Similarly, multiple rotating cleaning devices can be used in long sections in order to provide several hydraulic seal sections at any required casing or pipe (i.e., surface casing, intermediate casing, etc), as illustrated in  FIG. 4 . In such a way also, cement in direct contact with the wellbore wall provides a section with an efficient hydraulic seal  8 . 
     In a third embodiment, the wellbore cleaning device is able to rotate radially and also move axially.  FIG. 5  illustrates an example of a rotating and reciprocating cleaning device. The cleaning device is made of multiple “rings”  40  attached together. These rings can freely rotate around the casing and their axial movement is allowed within certain pre-determined length. The rings are equipped with flexible wires  31  long enough to touch the wellbore wall. These rings can be fitted with wires either along their full length or only along part of their length to reduce the drag with the wellbore wall. The rings are also fitted with helical blades  30  designed to make the rings rotate with the fluid circulating axially in the wellbore. In order to improve the cleaning efficiency, cleaning wires  32  can be used as link between two rings. These flexible wires would allow the rings to move axially within a certain length. Moreover, and whenever required, an axial movement restoring aid  41  (i.e., a spring, etc) attached to the stop collar  22 , may be used to aid the movement against the flow (i.e., down towards the bottom of the casing). Axial movement of the rings would depend on fluids. properties and circulating rate. Therefore, depending on the drag force of the fluid applied on the ring, its axial position can change. In other words, changes of fluid type (washes, mud, cement, etc), and rates will lead to changes in the rings&#39; axial position, extending the cleaning effect to a section effectively longer than the length of the ring. 
     As for the rotating cleaning device described before, the flow of the fluid circulating axially in the wellbore imparts a rotating movement to the rings which, upon rotation, will scratch any fragile deposit on the wellbore wall along the full length of the rotating scratcher. This fragile deposit may be made of filter cake, settled solids (barite or cuttings) or other kind of debris. The removed material is cleaned out of the hole by the flow of the annular fluid. 
     The deposit is thus fully replaced by the circulating fluid. If this circulating fluid is a cement slurry, it will bond with the formation upon setting and provide an efficient hydraulic isolation barrier in the annulus. This hydraulic isolation will be much better than in places without scratchers because the presence of a fragile deposit at the cement-formation interface presents an easy leakage path. 
     Preferably, the tubular will be equipped with a plurality of rotating and reciprocating scratchers, placed at different depths along the tubular to ensure several hydraulic isolation sections along the well. 
       FIG. 6  illustrates the wellbore after cementing, where a rotating and reciprocating wellbore cleaning device was used before and during cement placement  300 . In such a way, cement in direct contact with the wellbore wall provides a section with an efficient hydraulic seal  8 . 
     In a fourth embodiment, the wellbore cleaning device comprises one or more cones  700  in the wings or helicoidal part of the cleaning device to allow the circulating fluid to enter a cone and create a jet that can further clean ( FIG. 7A ). The shape of the cone can vary, as shown in  FIGS. 7B and 7C .