Completing Horizontal Drain Holes From a Vertical Well

This invention relates to completing one or more horizontal drain holes from a new or existing vertical well.

Horizontally drilled wells have recently become quite popular in attempting to make commercial wells in vertically fractured formations, such as the Austin Chalk or Bakken Shale. Horizontally drilled wells also have many advantages in conventional sandstone reservoirs because of the much improved linear flow characteristics rather than the radial flow characteristics inherent in vertical wells. Horizontal wells typically exhibit greater productivity than vertical wells because more of the formation is exposed to the well bore.

Conventional horizontal completions leave much to be desired in a variety of respects. Because of the way most of the horizontal well bore sections are currently drilled, mechanical pumps are commonly located in the vertical or near vertical portion of the well at a substantial vertical distance above the horizontal well bore. This leads to inefficiencies in pumping liquids from the well. It is much more desirable to position the pump at a location in the well below any producing horizon. In addition, it is desirable in some situations to combine horizontal and vertical completions from the same formation and have them produce into the same vertical well bore. This configuration would enable a formation to be produced to a lower bottomhole pressure than would be possible if the pump were located near the horizontal kickoff point in the vertical portion of the well. It is also desirable in some situations to complete multiple horizontal completions and have them produce into the same vertical well bore. Completing a vertical well in one or more formations in a conventional manner together with horizontal drain hole completions extending from the same vertical well bore is advantageous in many circumstances because it maximizes the efficiency of the downhole and surface equipment associated with the vertical well.

In accordance with this invention, a window is cut in a cased vertical well and a bore hole is sidetracked through the window or a curved well bore is kicked off from a vertical open hole. Angle is built up in a curved well bore until the bore hole is more-or-less horizontal. The horizontal well bore is drilled a substantial distance into a hydrocarbon bearing formation. A production string is run into the well so it extends from adjacent the horizontal well bore, through the curved well bore section and into the vertical cased hole or vertical open hole. The well is cemented so at least the curved portion of the well bore includes an impermeable sheath around the production string isolating the production string from permeable formations above the pay zone and isolating the top of the pay zone. After the cement cures, that portion of the production string extending into the vertical cased hole or vertical open hole is cut off by the use of a conventional full gauge burning shoe/wash pipe assembly, leaving a relatively clean intersection between the curved and vertical well bore sections. Another horizontal well bore section may be drilled and completed off the vertical hole into the same or a different hydrocarbon bearing formation. If a horizontal well bore is drilled from a vertical open hole, the vertical open hole may be cased with a liner after completing the horizontal drilling operation. It will be seen that a pump may be run into the vertical cased well and placed below all of the entries between the horizontal and vertical well bores. In addition, it will be seen that one or all of the hydrocarbon bearing formations may also be perforated in the vertical well to provide both vertical and horizontal completions producing into the same vertical cased well.

One object of this invention is to provide an improved technique for completing horizontal well bores.

A further object of this invention is to provide a technique for completing horizontal well bores in which a mechanical pump may be placed below the entry of the horizontal well bore into the vertical well.

Another object of this invention is to provide a technique for completing hydrocarbon wells so there are both vertical and horizontal completions producing into the same vertical cased well.

These and other objects of this invention will become more fully apparent as this description proceeds, reference being made to the accompanying drawings and appended claims.

FIG. 1 is a schematic cross-sectional view of a vertical cased well extending through a subterranean hydrocarbon bearing formation;

FIG. 2 is a schematic cross-sectional view showing a technique of drilling and completing a horizontal drain hole in accordance with this invention;

FIGS. 3 and 4 are schematic cross-sectional views showing alternate techniques for sidetracking the hole and drilling the curved well bore;

FIG. 5 is a schematic cross-sectional view of a subsequent stage of drilling and completing a horizontal drain hole in accordance with this invention;

FIG. 6 is a schematic cross-sectional view of a second horizontal well bore drilled from a cased vertical well; and

FIG. 7 is a schematic cross-sectional view of a completed well having both horizontal and vertical completions.

Referring to FIG. 1, a vertical cased well 10 comprises a well bore 12 drilled into the earth to penetrate a subterranean hydrocarbon bearing formation 14. Typically, the well bore 12 is logged to provide reliable information about the top and bottom, porosity, fluid content and other petrophysical properties of the formations encountered. A relatively large casing string 16, e.g. 7" O.D. or greater, is cemented in the well bore 12 in any suitable manner so an impermeable cement sheath 18 prevents communication between formations in the annulus between the well bore 12 and the casing string 16.

Referring to FIG. 2, a window 20 is cut in the casing string 16 and a curved bore hole 22 is drilled, preferably on a short or medium radius, to intersect the formation 14. In accordance with one technique, the window 20 is cut by using a whipstock 24 set in the vertical cased well 10 where the well is to be sidetracked and the window 20 is conventionally cut with a mill (not shown).

In the alternative, if the vertical cased well 10 is drilled and cased with this in mind, as opposed to reentering an old well or conventionally completing the well 10, the window may be cut in a different manner. As shown in FIG. 3, a well 26 includes a casing string 28 having a drillable joint 30 made of a carbon/glass/epoxy composite material and a plurality of conventional steel joints 32. Because the joint 30 is much easier to drill than the steel joints 32, a cement plug 33 is placed in the well 26 and then dressed down to the kickoff point. A window 34 is then cut in the joint 30 with a conventional bent housing mud motor assembly (not shown). It may be advantageous in some situations to initiate the kickoff with a whipstock/packer assembly (not shown) instead of the cement plug 33.

Referring to FIG. 4, a somewhat different situation is illustrated. A well 15 includes a vertical bore hole 17 having steel casing 19 cemented therein by a cement sheath 21 above a target hydrocarbon bearing formation 23. A vertical open hole 25 is drilled below the casing string 19 to a point below the formation 23. After logging the open hole 25 for formation evaluation purposes, a portion 27 of the vertical open hole 25 is enlarged using conventional underreaming techniques. A cement plug 29 is pumped into the enlarged open hole 27 adjacent the kickoff point and then dressed off after the plug has hardened. A conventional bent housing mud motor assembly (not shown) is then used to drill the curved bore hole 22 in a conventional manner.

In any event, the curved portion of the well bore is begun. Referring back to FIG. 2, a curved bore hole section 22 is drilled toward the hydrocarbon bearing formation 14. Either before or after drilling a horizontal well bore 36 into the formation 14, a pipe string 38 is run through the window 20 at least into the curved bore hole 22 so it extends upwardly into the well 10. The pipe string 38 provides thereon a plurality of centralizers 40 and a plurality of reinforcing members 41. The centralizers 40 support the pipe string 38 off of the bottom of the curved bore hole 22 and the members 41 act to reinforce cement adjacent the window 20 as will be more fully apparent hereinafter. The reinforcing members 41 are positioned on the pipe string 38 so they partially fill the annulus between the curved bore hole 22 and the string 38 in the immediate area of the window 20. The reinforcing members 41 may comprise lengths of the same type wire as used in wire casing scratchers. For reasons more fully apparent hereinafter, the pipe string 38 may wholly or partially comprise joints of drillable material such as a carbon/fiberglass/epoxy composite.

Cement 42 is pumped through the pipe string 38 to surround the pipe string 38, close off the window 20 and extend upwardly into the cased vertical well 10. This prevents formations above the hydrocarbon bearing formation 14 from sloughing off through the window 20 into the vertical well 10, prevents water from formations above the formation 14 from entering the cased vertical well 10 and prevents gas or steam from entering the well 10 from adjacent the top of the formation 14.

The horizontal well bore 36 may be completed in a conventional manner, such as in the open hole or through perforations, or as shown in copending U.S. application Ser. No. 07/920,804, filed Jul. 24, 1992, the disclosure of which is incorporated herein by reference.

After the cement 42 sets up, that portion of the cement 42 and the production string 38 inside the vertical cased well 10 is drilled up. Preferably, the production string 38 is filled with a viscous, low residue, high gel strength water based, temporary blocking agent to minimize the amount of cement and pipe cuttings that enter the curved and horizontal sections of the well.

Drilling of the cement 42 and production string 38 is accomplished by use of a conventional full bore burning shoe/washpipe assembly. Although any suitable burning shoe may be used, a typical choice would be a Type D Rotary Shoe from Tri-State Oil Tools which cuts on the bottom of the shoe and on the inside. Basically, the burning shoe cuts away the periphery of the cement 42 and production string 38, leaving a core shaped remnant which is caught by an internal catch device (not shown) located above the washpipe or with a conventional fishing tool run after the burning shoe/wash pipe assembly is retrieved. If a cement plug is used to initiate the curved bore hole section 22 as in FIGS. 3 and 4, then the vertical cased well or the vertical open hole 25 is configured to drill another horizontal drain hole using similar techniques or a production liner is run.

If a whipstock is used to initiate the curved bore hole section 22 as in FIG. 2, the preferred whipstock 24 is a modified version of that shown in U.S. Pat. No. 5,113,938. In this type whipstock, a lower assembly 44 includes a packer 46 for anchoring the whipstock 24 at a desired location. A wedge shaped upper end 48 is pivoted by a pair of short pins 50 to the lower assembly 44. An axial passage 52 extends through the upper end 48 past the pivot pins 50 to receive a setting tool (not shown). The setting tool (not shown) holds the upper end 48 in alignment with the lower assembly 44 as the whipstock 24 is run into the well 10. When the packer 46 is set and the setting tool (not shown) removed, the upper end 48 pivots about the pin 50 into engagement with the casing 16.

The whipstock 24 has been modified in two respects. First, a drillable shoulder 54 has been provided to position the upper end 48 away from the casing 16. Second, a locator ring 56 of a drillable metal is incorporated in the lower assembly 44. As the cement 42 and production string 38 are being cut away by the burning shoe (not shown), the drillable shoulder 54 allows the burning shoe to get behind the wedge shaped upper end 48 to cut the cement 42 and production string 38 below the top of the wedge shaped upper end 48. The locator ring 56 provides an indication to the driller that the burning shoe is past the window 20 and the location of the bottom of the burning shoe is immediately above the packoff elements of the packer 46. When the burning shoe completes drilling of the production string 38, only cement will be drilled for a somewhat variable distance, e.g. two-three feet, between the bottom of the production string 38 and the locator ring 56. Because the locator ring 56 is a drillable metal, the driller will realize that metal is being cut again by the burning shoe. The thickness of the locator ring 56 is known, so the driller can recognize when it has been drilled through. It will be seen that the reinforcing elements 41 act, much as rebar in poured concrete, to reinforce the cement 42 adjacent the window 20. In addition, fibrous material, such as Halliburton's TUF cement additive disclosed in U.S. Pat. No. 3,774,683, may be added to the cement to make the hardened cement less brittle with more resiliency to shock and vibration loading.

After the locator ring 56 is drilled up, the hole is circulated to remove all cement and pipe cuttings and the burning shoe/wash pipe assembly and its captive cement-pipe remnant is removed from the well leaving the situation as shown in FIG. 5. The whipstock 24 is then removed from the vertical cased well 10 using any suitable fishing tool such as a taper tap 58. The axial passage 52 is partially cleaned out by advancing and rotating the taper tap 58 into the passage 52 and pumping therethrough. The taper tap 58 is lowered into the passage 52 until it torques up and catches or anchors in the whipstock 24. Picking up on the taper tap 58 unseats the packer 46. If the packer 46 is an inflatable packer, as is preferred, picking up on the taper tap 58 shears the packer deflation pin thereby allowing the packer 46 to deflate. The whipstock 24 is thereby released from securement to the casing 16 and is removed from the cased vertical well 10.

As shown in FIG. 6, another horizontal completion 60 may be provided to produce into the vertical cased well 10, using the same techniques as previously discussed.

As shown in FIG. 7, the well 10 may then be completed by running a downhole pump 62 on the end of a tubing string 64 below the entry of the production string 38 into the vertical well 10. If desired, perforations 66 may be shot through the casing 16 to complete the formation into the vertical cased well 10 as a vertical completion as well as the horizontal completion through the production string 38.

Although this invention has been disclosed and described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms is only by way of example and that numerous changes in the details of construction and operation and in the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.