US3908759A

US3908759A - Sidetracking tool

Info

Publication number: US3908759A
Application number: US472316A
Authority: US
Inventors: William S Cagle; Fred H Dillard
Original assignee: Standard Oil Co
Current assignee: BP Corp North America Inc
Priority date: 1974-05-22
Filing date: 1974-05-22
Publication date: 1975-09-30
Anticipated expiration: 1992-09-30

Abstract

A new apparatus and method are described for side-tracking a hole drilled in the earth and lined with casing. A modified bridge plug having a latch-up device on top is set using an electric cable in the casing at a point just below where it is desired to drill through the casing wall. A casing whipstock with a latch-up device to match that on the bridge plug is then run to latch up with the latch-up on the bridge plug. The whipstock is sheared and a window is started with a starting mill of the whipstock. A specially modified diamond side-track bit is then used to finish cutting the casing window and milling the window and starting a side-tracked hole in the formation.

Description

United States Patent 1 Cagle et a1. 7

1 1 Sept. 30, 1975 Filed:

Appl.

lnvcntors:

Assignee:

H. Dillard, Lake Charles, La.

Standard Oil Company, Chicago, 111.

May 22, 1974 US. Cl l66/ll7.6; 166/298 Int. Cl. E21B 7/08 Field of Search 166/1 17.5, 117.6, 297;

References Cited UNITED STATES PATENTS Primary E.\'amilzerDavid H. Brown Attorney, Agent, or Firm.lohn D. Gassett; Paul F. Hawlcy 1 1 ABSTRACT A new apparatus and method are described for sidetracking a hole drilled in the earth and lined with casing. A modified bridge plug having a latch-up device on top is set using an electric cable in the casing at a point just below where it is desired to drill through the casing wall. A casing whipstock with a latch-up device to match that on the bridge plug is then run to latch up with the latch-up on the bridge plug. The whipstock is sheared and a window is started with a starting mill of the whipstock. A specially modified diamond side-track bit is then used to finish cutting the casing window and milling the window and starting a sidetracked hole in the formation.

3 Claims, 6 Drawing Figures US. Patent Sept. 30,1975 Sheet 2 of2 3,908,759

FlGi /4o 'ililllllllllllll llll SIDETRACKING TOOL BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to side-tracking a casing-lined borehole drilled in the earth. The invention relates especially to an apparatus and method for performing side-tracking of a wellbore through a casing.

2. Setting of the Invention Oil and gas are produced from underground formations through wellbores drilled from the surface to the formation. Ordinarily, the wellbores are lined with a steel pipe called a casing. Many times it is desired to change the direction the well is being drilled after casing has been set. Sometimes it is impossible to drill ahead because of unretrievable non-drillable junk in the wellbore. This drilling through the wall of the casing and changing the direction of the borehole is com monly called side-tracking. There has been a large number of apparatus and methods developed for sidetracking operations. A typical and widely used method and apparatus is displayed on page 202, of the Composite Catalog of Oil Field Equipment & Services, Vol. 1, 31st Revision, 1974-75, published by World Oil, a Gulf Publishing Company publication, P. O. Box 2608, Houston, Texas.

Two techniques are commonly used for side-tracking out of existing casings (1) mill a section, or (2) mill a window. In the first technique, i.e., milling a section, the entire section of casing between two levels is completely cut away. There are various ways of obtaining a mill section, but they practically all have certain disadvantages, such as:

l. Tendency of commercially available permanent whipstock which are normally used to rotate;

2. Excess of metal cuttings which become magnetized and cause downhole plugging problems;

3. Difficulty in getting a cement plug across the milled section; and

4. Normally, more round trips of the drill pipe are required than with the present invention. (A round trip is the lowering of drill pipes into the well and adding joints thereto as the pipe is lowered until the bottom part of the drill pipe is at the desired level, and then pulling the casing in a reverse procedure until the bottom of the'drill pipe is out of the hole.)

In some side-tracking operations,- only a window is cut in the casing. As the name implies, cutting a window is really just cutting a hole in the side of the casing. Thus, there are fewer metal cuttings in the hole to cause trouble than when a complete section is milled away. There are still some disadvantages to using a window-milling technique. These include the large amount of time consumed because two or three window mills are required to finish a window, especially in harder steel casing. Each time a new window mill is used, the drill string must be pulledand re-run. Also, an extra trip with the string mill is usually required to clean up the window before drilling ahead with the conventional bit. These disadvantages increase the cost of many sidetracking jobs and could make some completely uneconomical.

Present whipstocks can sometimes turn and move up the hole either initially or at a later time. If this happens, the hole is lost and the side-tracking procedure must be repeated all over again. As mentioned suave; casing whipstocks are commercially availaBli: Meet casing whipstocks have a lower portion which has slips which are anchored to the walls of the casing, and an upper part which has a sloping face, and which is really the whipstock part. The upper whipstock part and the lower anchoring portion are run in the well as a unit. It is most difficult to obtain good anchoring with this sytem again either longitudinal or rotational movement in the wellbore.

BRIEF DESCRIPTION OF THE INVENTION This invention includes a novel apparatus for milling a window and a novel method of side-tracking using a novel diamond-type bit. We first modify a downhole packer or bridge plug to have a special latch-up device on top. We then use an electric line and set the bridge plug at the desired depth. We modify a permanent casing whipstock to have a latch-up device at its lower end to match with the latch-up device on top of the bridge plug. We then run and set the casing whipstock latched firmly to the set bridge plug; This prevents the whipstock from turning or moving up the hole. The upper end of the whipstock is held to a starting mill connected to the lower end of a drill string by a shear pin. At this point in the operation, we shear off the shear pin by applying weight to the drill string. We start a window in the side of the casing with the starting mill.

After the starting mill has made its pilot hole through the casing, we pull the drill string and the starting mill and replace the starting mill with a special diamond side-track-bit with which we complete the job of cutting the window. The specially modified diamond bit is different from conventional bits in several respects: (1) its throat is off-center; (2) it has no junk slots on the sides; and (3) the bottom side is substantially flat.

- I BRIEF DESCRIPTION OF THE DRAWINGS Various objectives and a better understanding can be had of the invention from the following description taken in conjunction with the drawings, in which:

FIG. 1 illustrates the overall assembly in full face view set in a casing in cutaway view;

FIG. 2 illustrates, partly in cross section, a downhole assembly, including a modified bridge plug, a whipstock, and latching means to latch the whipstock to the bridge plug means;

FIG. 3 is similar to FIG. 2, except the whipstock is latched into position and the latching means attached to the bridge plug; I

FIG. 4 illustrates a portion of the hollow extension on the bridge plug;

.FIG. 5 is a side view of the diamond bit useful in this invention; and

FIG. 6 is a bottom view of the diamond bit shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION Attention is first directed to FIG. 1 to show the general environment in which the system operates. Shown therein, is a hole 10 lined with a casing 12. It is desired to drill out through the casing 12 at the level 14. Shown inside casing 12, is bridge plug 16, having extension 18. Above extension 18 is a whipstock 20, which has a lower extension 22, which latches with the upper extension 18 of the bridge plug 16. A tubing string 24 is suspended in the wellbore above whipstock 20, and supports a starting mill 26 and pilot 28. The pilot 28 is held if) the upper end of whipstock 20 by a shear pin 30.

Attention is next directed to FIG. 2. Shown therein in the lower portion of casing 12 is bridge plug 16, which may be, for example, a Baker Mercury Model NC wireline casing bridge plug, available from Baker Oil Tools, Inc., P. O. 7400, E. Slauson Ave., Los Angeles, Calif. A hollow extension 34 is connected to the top side of bridge plug 16. The upper edge of extension 34 has annular upwardly facing shoulders 36. Just below shoulders 36, is a latching groove 38 on the internal wall of extension 34. Also provided, are splines 40 (see FIG. 4) on the interior wall of extension 34. Groove 38 is shielded by cup-shaped shield 42, which is held in position by shear pins 44. Whipstock 20 has a modified lower latching means. This includes a stepped cylinder extension which includes a first portion 48 and a smaller reduced portion 50. Extension 50 is sized to be received in cup 42. An annular shoulder 52 is provided between the stepped extension and is designed to fit onto shoulder 75 of cup-shaped shield 42 of the bridge plug 16. Section 48 has latching dogs 54, which are designed to fit into latching groove 38 of extension 34 of the bridge plug 16.

Attention will now be given to the operation of the setting of the device of FIG. 2 to reach the position of FIG. 3. It is important to note that the shear pin 44 has a lower shear point than does shear pin 30. The first thing that is done, after bridge plug 16 has been modified as shown in FIG. 4, is to set the bridge plug by a wireline assembly, not shown but which is well known. The setting tool commonly used is found on page 404, of Composite Catalog, and is connected to the bridge plug 16 by a setting mandrel extending from the setting tool through the hole 77 in the cup-shaped shield 42 to the bridge plug 16. After setting the bridge plug 16, the setting mandrel shears out of the bridge plug 16.

The whipstock 20 with its extension, as shown in FIG. 2, is next connected to a drill string, similarly in a manner to that shown in FIG. 1. The Whipstock is then lowered by lowering the drill string until extension 50 fits into cup 42. This point can be detected by a reduced weight on the drill string. At this time, we orient the Whipstock to the desired direction, if that is required. We next set down weight on the drill string and shear shear pin 44. This causes cup 42 to be shoved down to where the Whipstock will be in its lower position with respect to the bridge plug and its extension, and shoulders 76 of the Whipstock extension will rest on shoulders 36 of extension 34 of the bridge plug. At this time, dogs 54 are firmly latched into grooves 38 of the bridge plug extension. The Whipstock is prevented from rotating by the splines 49 of its extension mating with the splines 40 of the bridge plug extension. The Whipstock is prevented from vertical movement by dogs 54, which are latched firmly into latching groove 38 of the bridge plug extension.

We next set down sufficient weight on the drill pipe to shear shear pin 30 and then begin rotating the drilling assembly. The pilot 28 follows along the plane of the Whipstock 20 until the starting mill 26 cuts into the casing. After the pilot hole has been cut in the wall of the casing by the starting mill and the pilot extends about 2 feet below the top of the Whipstock, the drill string is pulled to the surface. At this time, we remove the starting mill 26 and pilot 28 and replace it with a modified diamond bit, shown in FIGS. and 6. This modified bit is used to complete the cutting of the window in the wall of the casing and can be used to drill several feet into the formation. At this point, we again pull the drill string and replace the modified diamond bit with a conventional bit most suited for drilling the formation at this particular interval.

Following the above procedure can reduce the cost of prior side-tracking methods by as much as $20,000 (for an operation costing $3,500 per day) by eliminating as many as four round trips.

Attention is next directed to FIGS. 5 and 6 which show the modified diamond drill bit. FIG. 5 is a side view and there are no junk grooves or slots along the side 70. The bottom of the bit has been modified considerably from normal bits. It has a center 72; however, the throat is not at the center of the bit. The throat or fluid courses 74 are off center. The reason for this is that, when the throat is in the center of the bit, the casing cuttings tend to clog it, but, when it is not in the center, clogging does not occur. We have found that the most suitable size diamonds for cutting casing is in the range of about 8 l2 stones/carat. In all other repsects, the diamond bit can be made along conventional manufacturing procedures.

While the above description has been made in detail, various modifications can be made thereto without departing from the spirit or scope of the invention.

We claim:

1. A downhole device for setting in a cased wellbore, from which it is desired to drill a side-tracked well, which comprises:

an anchor means for anchoring in said cased borehole;

an anchor means extension extending upwardly from said anchor means, and including latching means having:

a hollow cylindrical member having an internal latching groove near its upper end;

internal spline means on the internal surface of the said cylindrical member;

a cup-like member set in said cylindrical member;

a first shear pin holding said cup-like member to said cylindrical member;

a Whipstock;

a Whipstock extension including a lower cylindrical member for fitting into said cup-like member and an intermediate cylindrical portion above said lower portion and having external splines thereon, said external splines matching the internal splines of said cylindrical member of said anchor means extension when inserted therein;

latching dogs on said intermediate member of said Whipstock extension for latching into said latching grooves of said anchor means cylindrical member.

2. Apparatus, as defined in claim 1, including a second shear pin in the upper portion of said Whipstock and extending horizontally beyond the face of said Whipstock, said second shear pin having a highershear strength than said first shear pin.

3. Apparatus, as defined in claim 2, including a drill string suspended in said cased borehole, a starting mill with pilot connected to the lower end of said drill string, the lower end of said pilot being connected to said second shear pin.

Claims

1. A downhole device for setting in a cased wellbore, from which it is desired to drill a side-tracked well, which comprises: an anchor means for anchoring in said cased borehole; an anchor means extension extending upwardly from said anchor means, and including latching means having: a hollow cylindrical member having an internal latching groove near its upper end; internal spline means on the internal surface of the said cylindrical member; a cup-like member set in said cylindrical member; a first shear pin holding said cup-like member to said cylindrical member; a whipstock; a whipstock extension including a lower cylindrical member for fitting into said cup-like member and an intermediate cylindrical portion above said lower portion and having external splines thereon, said external splines matching the internal splines of said cylindrical member of said anchor means extension when inserted therein; latching dogs on said intermediate member of said whipstock extension for latching into said latching grooves of said anchor means'' cylindrical member.

2. Apparatus, as defined in claim 1, including a second shear pin in the upper portion of said whipstock and extending horizontally beyond the face of said whipstock, said second shear pin having a higher shear strength than said first shear pin.