Title of invention: A Single-Trip Whipstock Wellbore Sidetracking Unit

Technical Field to which invention relates: the present invention relates to methods and tools for forming a window through the wall of a well casing at a certain depth and azimuth so that a new borehole can be drilled outside the cased borehole, and particularly to new and improved methods and tools of the type described.

Indication of the Background Art:

An opening or a window is formed in a casing, in a wellbore with a milling apparatus, that has metal cutting structures on portions of its surface. Typically, the tool is attached by a threaded connection at the top to a section of drill pipe or components comprising a bottom hole assembly and is run down a well to cut a window through the side of a piece of casing.

In simplest methods, the only force that urges the mill sideways into the casing is the inherent stiffness of the milling tool and associated drill pipe transversing a curve in the casing. In many cases, this force is not sufficient to initiate and maintain cutting action.

In some cases, in order to enhance the sideway action of the milling apparatus, a device known as a whipstock is used. A whipstock mainly consists of a wedge shaped object, anchored in the casing wellbore which props the milling apparatus and forcibly directs it outward through the side of the casing, thereby facilitating formation of the window.

The usual process of sidetracking using a whipstock starts by running a string and setting an anchored whipstock. After the whipstock has been set, a second drill string running takes place and milling apparatus is run to mill and drill a rat-hole that deviates over to one side of the casing. The window can be formed by various number of trips from one to four. During milling operation, drilling fluid also known as mud is fed to the well.

Technical Problem to be solved:

The present inventors have recognized problems associated with milling in a wellbore in a hard, tough, abrasive earth formation. Rather than being deflected into such a formation by the taper of a whipstock, the formation itself may deflect the mill against the whipstock resulting in damage to the whipstock and ineffective or incomplete milling of casing. There has long been a need for an efficient and effective milling guide and method of its use. Specifically, technical problems to be solved by this invention include: Multiple number of trips needed to finish a sidetracking job which requires excessive amount of time and manpower; short full gauge window which causes high dog leg severity that prevents tools from going down the sidetracked borehole; excessive torque which damages the mill and whipface and causes failure.

Therefore, an objective of this invention is to provide new and improved method and tool combination for a hydraulically anchored whipstock in a well casing to robustly cut a sidetracking window in a single trip of a running string into and out of the casing.

Disclosure of Invention:

This invention is designed as a single-trip whipstock unit for sidetracking operations in wellbores, with reduced risk and cost. The present sidetracking unit comprise of three main parts: milling apparatus, whipstock and anchor apparatus that are connected together from top to button, respectively.

The milling apparatus comprises of a tubular body with two milling structures on it, hence is called a bimill. The lower milling structure cuts the casing first therefore is called lead mill. The window is further enhanced by the upper milling structure which is accordingly called follow mill.

The shapes of lead mill and follow mill are optimized for effective and efficient window forming. Lead mill is pear-shaped i.e. it has a smaller part followed by a larger part. The smaller part is called pilot mill and is the advancing part of the lead mill, which eases the cutting by forming a smaller window first. The larger part of the lead mill is the full gauge section which mills a window with desired full gauge width. The follow mill is melon shaped i.e. it has a full gauge section with tapered cutting structures at both sides.

The surfaces of lead mill and follow mill comprise of at least three metal cutting blades. Blades are spiral longitudinal strips of crushed carbide and cutting diamonds. The spiral shape enhances a smooth cutting operation. The tip of the lead mill is covered with a bulk of crushed carbide to improve milling at core point.

The milling body is a stepped hollow shaft with a longitudinal core hole. This hole is used to transfer hydraulic fluid and drilling fluid. The lead mill, further has a hole that is attached to a hydraulic pressure line, several holes to release drilling fluid during milling and a threaded hole to be attached to the whipface by a shearable connection.

The whipface is a hardened steel ramp along which a mill turns as it cuts a hole in the side of the casing to start a sidetrack or lateral wellbore. The whipface is roughly a tubular wedge shape which is thinner at the upper end. There is a transverse hole at the upper end to be attached to the milling apparatus by the shearable connection. There is another hole blow that hole through which the hydraulic pressure line passes. This pressure line goes through a slit behind the whipface and connects the core hole of the milling apparatus to the inside of the anchor apparatus. On the whipface, on the opposite side of the slit, these is a deflection surface which comprises of at least two inclined surfaces with different inclination angles.

The deflection surface forms the wedge shape of the whip face that pushes the mill sideways into the casing. The deflection surface is concave to envelop the curvature of the milling structures.

At the bottom of the whipface there is a pin hole that connects the whipface to the anchor which fixes the bottom of the whipface while the top of the whipface rests against the casing wall.

The anchor apparatus is a hydraulic set. At the top of it there is a slot and a pin hole which is attached to the whipface forming a hinge joint. Inside the slot there is another hole connected to the hydraulic pressure line that feeds the anchor with hydraulic pressure. Around a section of anchor there are several moveable anti-slip surfaces that have a rough spiky surface.

These surfaces are pushed out and pressed against the casing by means of hydraulic pressure.

In another embodiment, anchor is also a packer that seals the wellbore. In this embodiment, on another section of the anchor, there is a tubular deformable body made from rubber called clamping rubber. This body is pressed hydraulically and bulges outward toward the casing, thereby sealing the wellbore below it.

The Shearable connection between milling apparatus and whipface consists of a shear bolt that goes through the hole at top of whipface and screws in the hole on the side of lead mill.

A sidetracking operation begins by connecting this whipstock sidetracking unit to a bottom hole assembly or a drilling string. Then the sidetracking unit is run down the well to the desired depth and is rotated to the desired azimuth. The anchor is activated and set by increasing hydraulic pressure which pushes out the anti-slip surfaces, and in another embodiment clamping rubber as well. Then, the shearable connection is detached by applying an upward force. Afterwards, rotation and weight is applied on milling apparatus which push it down on the deflection surface and therefore sideways into the casing while drilling fluid is fed through the mill body. After forming a window, the milling apparatus is pulled up and removed from the well.

This hydraulically set, one-trip system helps to avoid the costly time and fees associated with mechanical bottom-hole designs and multiple-trip operations.

Brief Description of Drawings:

FIG. 1 is the isometric view of the general assembly of sidetracking unit.

FIG. 2 is the side view of the milling apparatus.

FIG. 3 is the isometric view of the whipface.

FIG. 4 is the isometric view of the hydraulic anchor apparatus.

FIG. 5 is the section view of mill.

FIG. 6 is the section view of whipface.

FIG. 7 is the front view of the lead mill.

Description of at least one way of carrying out the invention:

Referring to FIG. 1 , the single-trip whipstock wellbore sidetracking unit consists of three main parts: the milling apparatus 1 which is a bimill, a whipface 2 and an anchor apparatus 3.

Referring to FIG. 2, the milling apparatus 1 consists of a tubular mill body 5 with an API connector 4, follow mill 6 and lead mill 7.

Referring to FIG. 3, the whipface 2 has a hole 8 that makes a shearable connection with milling apparatus by using a shear bolt 9. A hydraulic pressure line passes through the hole 10. The inclined concave deflection surface 11 pushes the lead mill and follow mill into the casing. The whipface is Connected to the anchor by pin hole 12.

Referring to FIG. 4, anchor apparatus 3 connects to the whipface by a pin 12 and has a hole 13 connected to the hydraulic pressure line which feed hydraulic fluid inside the anchor. Antislip surfaces 14 and 24 move radially outward by aforementioned hydraulic pressure. These surfaces are pushed against the casing wall and prevent longitudinal and rotational slipping, respectively; thereby fixing the anchor and whipstock. In another embodiment, the tubular rubber body 15, i.e. clamping rubber, is also pressed by hydraulic pressure and expands radially outward to seal the wellbore.

Referring to FIG. 5, the mill body 5 has a core hole 6 which carries hydraulic fluid and delivers it in the hydraulic pressure line through a hole 17. Subsequent to anchor setting, the core hole 16 delivers drilling fluid and injects in through holes 18 while milling, there are three holes 18 at equal distance around the lead mill, the milling apparatus further comprises a threaded hole 19 that connects to shear bolt 9. Furthermore, the milling tip 20 is a bulk of crushed carbide.

Referring to FIG. 6, there is a slit 21 on the backside of the whipface 2 (opposite the deflection surface 11) through which the hydraulic pressure line passes.

Referring to FIG. 7, lead mill 7 has a section with smaller diameter called the pilot 22. The pilot mills a small window prior to milling a full gauge window, therefore reducing the maximum load. The lead mill surface is covered by spiral longitudinal blades 23. Number of blades can be three or higher. Each blade consists of strips of cutting diamonds and crushed carbides. Blades on the follow mill 6 are similar to lead mill 7.

Explicit Indication of Industrial Application:

One industrial application of this invention is to to drill around obstructions or to reposition the bottom of the wellbore for geological reasons. Oriented sidetrack is required if a certain azimuth direction is essential in locating a targeted producing formation.