Whipstock with curved ramp

Abstract

The whipstock face below the mounting lug is initially curved with a fairly long radius to protect the whipstock body initially. After moving down the minimally sloping curved face a transition to a greater angle is presented to increase the lateral forces on the window mill and to force the mill laterally to exit the tubular through the window. The transition after the curved portion is preferably to a flat inclined surface to the ramp bottom.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is section view of a prior art design with the ramp longer than the intended window and the formation of a pocket as a result;

FIG. 2 is a section view of a prior art design that shows milling the whipstock and the anchor instead of licking out when needed to make the window bottom;

FIG. 3 is an illustration of the whipstock ramp having a curved upper face and a lower ramp section that is preferably flat and inclined.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 3 shows a whipstock 10 with an overall ramp 12 that has an arcuate upper section 14, a transition point 16 and a lower ramped section 18. The curved section preferably extends for 33% or less of the total length of ramp 12. The ramp 12, for purposes of the percentage allocation, begins below a lug (not shown) that holds a window mill (not shown) to the whipstock 10 for running into the wellbore. While the radius of the curved section can vary with the size of the whipstock 10, the initial portions of the curved section are at a fairly minimal slope so as to exert a fairly moderate lateral force on the window mill as the milling starts. However, unlike totally curved whipstocks of the past, the present invention recognizes that the lateral force must be increased to get the window mill through the window and to properly kick off the lateral. For that reason a transition occurs at 16 to what is preferably a flat surface at a greater incline than the terminal incline at the lower end of the curved section 14.

While the curved section 14 can be a single radius, it can also be a composite surface of radii that vary to progressively smaller radii in the downhole direction. The initial inclination of a tangent line to the curved section near its top is preferably between 0.5 and 1 degrees. The flat section can have an inclination of about 3 degrees or more depending on the end inclination of the curved section. In any event, the flat section will represent an increase over the terminal inclination of the curved section 14.

Those skilled in the art will appreciate that with the small initial angles of the upper reaches of the curved section 14 the stress in the connection between the window mill and the next mill above it is also minimized as the bending of that component is reduced until some part of the window has been made. On the other hand, at some point of making the window the lateral forces on the window mill need to increase to assure a proper exit for the new lateral and the segment 18 helps to do that. There is less material that needs to be removed to produce the whipstock using the curved upper section 14.

While the lower section 18 is described as flat those skilled in the art will appreciate that it can be a single or multiple slopes.

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:

Claims

1. A whipstock for downhole use, comprising: a body having a ramp with a lower and an upper end where a portion of said ramp is curved and a portion of the ramp is at least one flat disposed on at least one slope.

2. The whipstock of claim 1, wherein: said curved portion extends up to 33% of the length of said ramp.

3. The whipstock of claim 2, wherein: said curved portion is at a constant radius.

4. The whipstock of claim 2, wherein: said curved portion has more than one radius.

5. The whipstock of claim 1, wherein: said at least one flat comprises a single flat surface to said lower end of said ramp.

6. The whipstock of claim 1, wherein: said at least one flat comprises a plurality of flat surfaces to said lower end of said ramp.

7. The whipstock of claim 6, wherein: said flat surfaces have progressively greater slopes in a direction toward said lower end of said ramp.

8. The whipstock of claim 5, wherein: said single flat portion has a greater slope than said curved portion at the location where said portions meet.

9. The whipstock of claim 1, wherein: a tangent line to said curved portion near the upper end is inclined up to 1 degree.

10. The whipstock of claim 9, wherein: the slope along some portion of said flat portion exceeds 3 degrees.

11. The whipstock of claim 6, wherein: the slope along some portion of said flat portion exceeds 3 degrees.

12. The whipstock of claim 1, wherein: said body comprises a mounting lug for a window mill disposed above said upper end of said ramp.

13. The whipstock of claim 3, wherein: said at least one flat comprises a single flat surface to said lower end of said ramp.

14. The whipstock of claim 13, wherein: said single flat portion has a greater slope than said curved portion at the location where said portions meet.

15. The whipstock of claim 14, wherein: a tangent line to said curved portion near the upper end is inclined up to 1 degree.

16. The whipstock of claim 15, wherein: the slope along said flat portion exceeds 3 degrees.