Patent Application
20120192680
The field of the invention is mills for subterranean use and more particularly mills that have a fabricated body with blade pockets for placement and alignment of inserts.
Mills that are used for making casing exits typically have a cast body with a series of blades. Each blade has an array of polycrystalline diamond inserts commonly referred to as PDC inserts. In some designs the inserts are cylindrically shaped and disposed on each blade in a specific arrangement that uses a nesting feature where inserts in one row are offset from inserts in the row that is above. Because of this arrangement the load during milling is better distributed to prevent body damage and increase mill longevity. In a given row of inserts there is also an optimum center to center spacing of the inserts.
Cast bodies such as those described in U.S. Pat. No. 7,117,960 have been used. These bodies require the blades to be integrated or machined with the bit body. Other designs had welded blades to the bodies using welding techniques that employ high temperatures and can cause stresses in the body at the attachment locations. Some designs use fully cast bodies with pockets in the casting for inserts as illustrated in U.S. Pat. No. 7,178,609. The illustrated design is a dual function mill for making a casing exit and continuing to drill a lateral wellbore. The cast bodies involved a single use mold which made the bits extremely expensive.
Casing exit mills typically have blades that are welded to a machined body using welding techniques that employ high temperatures and can cause stresses in the body at the attachment locations. Additionally for initial assembly there was a logistics problem of stocking separate bit bodies, blades and inserts. Typically the blades were manufactured with flat faces that created placement variability in the insert positioning.
Until recently, machining equipment was not sophisticated enough to machine a mill body with integrated blades. The insert placement on the blades particularly on the lower end of the mill also presented a problem if pockets were to be machined into the blades. Near the bottom center of the mill the spacing was so close as to preclude a milling machine from making the bore that could be the receptacle for an insert. This was because the orientation of the inserts was at that location generally perpendicular to the longitudinal rotation axis creating a clearance too small to allow the machining equipment access to the blade location without interfering with the adjacent receptacle. Apart from all these reasons was that with the level of machining technology available until recently it was not considered economically feasible to machine bodies with integral blades and insert pockets. Often overlooked in such an analysis was the logistical cost of stocking cast bodies apart from blades for specific bodies and inserts for specific blades.
The present invention overcomes the problems with cast bodies described above and offers a machined body with integral blades that have pockets at a desired spacing and further offers the option of a guide for the inserts in the pockets should they have a cutting end that needs positioning in a specific orientation to function properly. Some of the pockets feature a near parallel to the rotational axis orientation to facilitate machining those pockets. Those skilled in the art will fully appreciate the present invention from a review of the detailed description and the associated drawings while understanding that the full scope of the invention is to be determined from the appended claims.
A mill body is machined integrally with blades that have pockets to receive PDC inserts or tungsten carbide. The insert pockets can have an orientation feature to ensure that inserts that require specific rotational orientation are put into the pockets at the right orientation for efficient milling. The orientation of some of the pockets closest to the bottom and center of the bit have their axis reoriented to a near parallel orientation to the bit center axis to allow the bit body and blade fabrication equipment access to drill the insert pocket.
As shown in
The assembly shown in
Those skilled in the art will appreciate that the production technique results in a unitary bit and blade arrangement where the blades have properly spaced pockets of the desired depth and orientation. The inserts are then inserted in the pockets and preferably brazed although other techniques can be used. For inserts that have to be installed in a proper orientation about their longitudinal axes there can be a keyway in a groove in the pocket or the opposite orientation where the key is in the pocket and a matching groove in the insert so that the inserts are in the proper orientation about their longitudinal axes when inserted to be brazed. Some of the pockets can be oriented closer to alignment with the axis of the body 14 to allow access for the machining equipment to make the pocket in what would otherwise be a tight or impossible fit without the reorientation for specific pockets.
Another advantage accrues during the initial assembly in that the inserts are all properly arrayed and at the proper extension from the blade face. Even if the mill is to be redressed after use with fresh inserts, the same advantage still accrues assuming the blades are all in adequate structural condition and the worn inserts carefully removed from their respective pockets.
The unitary structure of the body with the blades takes away a logistical concern of stocking different size blades to go with unique bodies and removes the added body stress from welding the blades to the body in a remote location from the manufacturing facility. While using computer controlled machining techniques to produce the mill with integral blades and pockets is initially more costly, the higher performance that can be obtained at the subterranean location can more than compensate for the initial cost difference over current cast body techniques. The pockets can either be initially machined as the blades are produced or if desired can be omitted to reduce cost of fabrication or to allow alternative insert configurations to be used on any given blade.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below:
