SYSTEM AND METHOD FOR DRILLING MULTIPLE WELLS

CROSS REFERENCE TO PRIOR APPLICATIONS [0001] This application claims priority from U.S. provisional patent application 61/038,998, filed on March 24, 2008, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION [0002] The present invention relates generally to the drilling and casing of wells. In particular, the invention relates to a method for casing a first well while an adjacent second well is being drilled in a land drilling application.

DESCRIPTION OF THE PRIOR ART [0003] Various drilling methods are known and used in applications such as exploring and/or extracting oil from subterranean deposits. The drilling method is typically conducted on a drill rig, which comprises a drilling platform located above the drilling location. The drilling of the well is often performed in discrete lengths or sections. Upon completion of drilling a section of the well, a cylindrical casing is typically inserted into the borehole to form a liner against the outer surface of the borehole. The casing aids the drilling process in a number of ways. For example, it may seal off high pressure zones from the surface, provide a strong upper foundation to continue drilling deeper, or isolate contaminating fluids from the surrounding earth. A borehole can be drilled to any length using a series of drilling and casing steps. [0004] Current drilling methods generally utilize a single drilling rig that performs both the drilling of the well and the placement of the casing segments. This setup is inefficient because only drilling or only casing can be performed at one time. Each section must first be drilled, and then cased. Some systems attempt to perform simultaneous drilling and casing of a single well. For example, in U.S. 4,544,041 , a design is disclosed that allows for the simultaneous drilling and casing of a single well. However, in this design, a drill string is not used, rather a retractable bit and downhole motor are required and are attached to a string of casing. [0005] In some applications, multiple wells are drilled, generally in a series or an array. When drilling multiple wells, each section of the wells may be drilled and cased sequentially. This approach is referred to as batch drilling, and it results in the multiple wells being drilled in parallel. For example, in a scenario with two wells, the drilling rig would first drill and case

a first length of the first well. The rig would then move to the second well and drill and case a first length of that well. The rig would then return to the first well and drill and case a second length of that well, and so on. This back and forth movement between the two wells would continue until the full length of both wells were drilled and cased. Although batch drilling allows multiple wells to be drilled in parallel, as is the case with drilling a single well, only drilling or only casing can be performed at any one time. In U.S. 7,264,067, a single rig structure is disclosed for drilling and casing multiple wellbores within a single wellhead. However, in this design, only casing or only drilling can be performed at any one time. [0006] It is an object of the present invention to obviate or mitigate at least some of the above disadvantages.

SUMMARY OF THE INVENTION [0007] In one aspect of the invention, there is provided a method of drilling a series of adjacent wells using a drilling rig for drilling and a casing rig for casing, the method comprising: (a) drilling a section of a first well using the drilling rig; (b) moving the drilling rig to an adjacent second well and moving the casing rig to the first well; and (c) drilling a section of the second well using the drilling rig and casing the section of the first well using the casing rig. [0008] In another aspect of the invention, there is provided a method of drilling a series of adjacent wells W ₁ to W _n , where n is an integer greater than 2, the method being performed using a drilling rig for drilling and a casing rig for casing, and the method comprising the steps of: (a) drilling a section of well W ₁ using the drilling rig, where i=1 ; (b) moving the drilling rig to well W ₁₊₁ , and moving the casing rig to well W ₁ ; (c) drilling a section of well W ₁₊₁ using the drilling rig and casing the section of well W ₁ using the casing rig; and incrementing /; (d) repeating steps (b) and (c) until the drilling rig is completed drilling a section of well W _n ; and (e) casing the section of well W _n using the casing rig. [0009] In one embodiment, the casing of the section of the first well occurs concurrently with the drilling of the section of the adjacent second well. [0010] In another embodiment, the casing rig comprises a catwalk and a mast. The mast includes an open section at its lower end, and the catwalk feeds tubular members or stands through the open section to the drilling rig. The catwalk and mast are also used in feeding and inserting casing during the casing operation. [0011] However, it will be appreciated that any rig capable of casing may act as the casing rig. Similarly, any rig capable of drilling may act as the drilling rig.

BRIEF DESCRIPTION OF THE DRAWINGS [0012] An exemplary embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which: [0013] Figure 1 is a side view of a drilling and casing system in a first position; [0014] Figure 2 is a side view of the drilling and casing system in a second position; [0015] Figure 3 illustrates a method of drilling three holes; and [0016] Figures 4(a)-(l) illustrate, by way of example, a method of drilling three holes using the drilling and casing system of Figures 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION [0017] In general terms, there is provided a method for drilling a second well while casing an adjacent first well. It has been recognized that current batch drilling techniques only service one well at any given time and that only drilling or casing can be performed at one time. This inefficiency can be eliminated by having a first rig for drilling and a second rig for casing, which trails the first rig. In such arrangement, the two rigs are referred to herein as working in "tandem", thereby allowing two wells to be serviced separately and preferably concurrently if possible. On a site with multiple wells to drill and case, the two-rig system can move along a series of wells performing the drilling and casing of adjacent wells. [0018] As used herein, a "drilling rig" refers to a rig that is primarily used to perform drilling operations. Likewise, a "casing rig" refers to a rig that is primarily used to perform casing operations. This includes existing rigs operating for that purpose or a specially designed arrangement. A well may be drilled and cased in discrete lengths, which will be referred to as "sections." By way of example only, the well could be drilled in three sections. In this case, the first section will be referred to as the "surface hole section," the second section will be referred to as the "intermediate hole section," and the third section will be referred to as the "final hole section." However, it will be appreciated that the well could be drilled in any number of sections, including a single section. [0019] Figures 1 and 2 show an embodiment of a drilling and casing system 1 situated at a well pad requiring three wells. The drilling and casing system 1 comprises a drilling rig 2 working in tandem with a casing rig 3. The drilling rig 2 is an existing rig commonly used in existing drilling operations. The casing rig 3 works in combination with the drilling rig 2 to case a first well while a second adjacent well is being drilled. The casing rig 3 comprises, in one embodiment, a power catwalk 4 and a mast 8, both of which are standard in the art. The catwalk 4 is used to feed tubular members, or "tubulars," to the drilling rig 2. Each tubular 5

is connected to another tubular 5 on the drilling rig 2 to form a stand. The stands are stored as a group 6, such that the group 6 is easily accessible when a stand is required to be attached to the drill string. Alternatively, one may instead use an integrated power catwalk, which connects two tubulars into a stand and feeds the stand to the drill rig 2. An example of such a catwalk is described in detail in the applicant's U.S. Application Publication No. 2007/0221385, the entire contents of which are incorporated herein by reference. The catwalk 4 and mast 8 are also used to assist in inserting the casing into the drilled hole section. Hoisting equipment in the mast 8 picks up the casing and delivers it vertically into the well. [0020] In a further embodiment, the casing rig 3 may include an open section 9 at the lower end of the casing mast 8, thereby allowing a tubular 5 to be delivered through the mast 8 to the drilling rig 2. [0021] The drilling and casing system 1 is sufficiently mobile to move between adjacent wells without difficulty. In one embodiment, the system 1 is mounted on a skidding system 7. Alternatively, a rail system with wheels on a track could be employed, or any other alternative apparatus that allows the system 1 to be mobile may be used. [0022] With further reference to Figure 3, an embodiment of a method of the invention will now be described in the context of a well pad that requires the drilling of three wells in three sections. It will be appreciated though that the method is applicable to well pads that require the drilling of any number of wells greater than one. In fact, the larger the number of wells to be drilled, the more efficient the method will be since concurrent drilling and casing will be possible in more steps. It will also be appreciated that the method is applicable to the drilling and casing of wells in any number of sections. For convenience, the method will be described with respect to the above mentioned system, but it will be appreciated that any system that performs the described method may be used. [0023] Turning therefore to Figure 3, at step 100, the drilling rig 2 is situated over the first well W1 , and the casing rig 3 trails the drilling rig 2. This is the position illustrated in Figure 1. The drilling rig 2 receives each tubular 5 from the catwalk 4, connects a single, double, or triple combination of tubulars into stands, and adds each stand to the drill string as drilling of the surface hole section of well W1 proceeds. Once the surface hole section is drilled, at step 102 the drilling rig 2 moves to the second well W2 , and the casing rig 3 moves to well W1. This is the position illustrated in Figure 2. The drilling rig 2 then drills the surface hole section of well W2 while the casing rig 3 is free to perform a casing operation on the surface hole section of well W1. In a situation where the casing operation is completed before the drilling step, the casing rig 3 can prepare for the casing for well W2.

[0024] Once the above drilling and casing is complete, in step 104 the drilling rig 2 moves to the third well W3, and the casing rig 3 moves to well W2. The drilling rig 2 then drills the surface hole section of well W3 while the casing rig 3 is free to perform a casing operation on the surface hole section of well W2. Once drilling and casing is complete, in step 106 the drilling rig 2 moves past well W3 to allow the casing rig 3 to move over well W3 and case its surface hole section. During the casing of well W3, the drilling rig 2 is not being used. This conveniently provides an opportunity to perform any small maintenance tasks that may be necessary or desired to prepare the drilling rig 2 for drilling the next section of the wells. [0025] Once the casing of the surface hole section of W3 is complete, at step 108 the drilling and casing system 1 returns to its beginning position such that the drilling rig 2 is back aligned over well W1 with the casing rig 3 trailing (as in Figure 1). The process (steps 100 to 108) then repeats for the drilling and casing of the intermediate hole sections and then the final hole sections of wells W1 to W3. [0026] Figures 4(a)-(l) further illustrate each step of the method illustrated in Figure 3 using, by way of example only, the drilling and method system 1 of Figures 1 and 2 to drill three holes in three sections. In Figure 4(a), the drilling rig 2 is situated over the first well W1 , and the casing rig 3 trails the drilling rig 2. The drilling rig 2 receives each tubular 5 from the catwalk 4, connects a single, double, or triple combination of tubulars into stands, and adds each stand to the drill string as drilling of the surface hole section of well W1 proceeds. Figure 4(a) corresponds to step 100 in Figure 3. [0027] In Figure 4(b), the drilling rig 2 has moved to the second well W2, and the casing rig 3 has moved to well Wl This corresponds to step 102 in Figure 3. The drilling rig 2 drills the surface hole section of well W2 while the casing rig 3 is free to perform a casing operation on the surface hole section of well W1. [0028] In Figure 4(c), the drilling rig 2 has moved to the third well W3, and the casing rig 3 has moved to well W2. This corresponds to step 104 in Figure 3. The drilling rig 2 drills the surface hole section of well W3 while the casing rig 3 is free to perform a casing operation on the surface hole section of well W2. [0029] In Figure 4(d), the drilling rig 2 has moved past well W3 and the casing rig 3 has moved over well W3. This corresponds to step 106 in Figure 3. The casing rig 3 cases the surface hole section of W3. [0030] In Figure 4(e), the casing and drilling system 1 has returned to its initial position (step 108 in Figure 3). The process (steps 100 to 108 in Figure 3) is then repeated for the

drilling and casing of the intermediate hole section of each of the three wells, as illustrated in Figures 4(e)-(h). Upon completion of the drilling and casing of the intermediate hole sections, the process is once again repeated for the drilling and casing of the final hole section of each of the three wells, as illustrated in Figures 4(i)-(l). [0031] It will be appreciated that it is typically necessary to install a blowout preventor (BOP) into each section of the well after the section has been cased. The BOP may be installed, or "nippled up", any time after the surface casing section of a well is complete, but before the next section of that well is drilled. As an example, in Figure 4(e), the BOP is installed in the surface hole section of well W2 while the intermediate hole section of well W1 is being drilled. However, the BOP could instead be installed in well W1 immediately after the casing operation is complete (e.g. at the step illustrated in Figure 4(d)). [0032] The above described method of drilling and casing multiple wells eliminates at least some of the inefficiencies of current batch drilling techniques by allowing a first well to be cased while an adjacent second well is being drilled. This is a departure from the practice of using a single rig to drill and then case a section hole of a first well prior to moving to a second well. In the single rig case, one can only ever drill or case, and it is not possible to case a first hole while drilling a second hole. [0033] It will be appreciated that alternative embodiments of the preferred drilling and casing system 1 described in Figures 1 and 2 may be substituted without departing from the spirit or scope of the invention. For example, although in the embodiments described above the drilling rig 2 and casing rig 3 be physically detached, they may alternatively be attached and arranged as one unit. Mobility may be provided by a skidding system 7, or by wheels on a rail or any other apparatus achieving the same means. Moreover, the drilling rig 2 comprises any rig able to perform the drilling operation, and the casing rig 3 comprises any rig able to perform the casing operation. This includes existing rigs operating for that purpose or a specially designed arrangement. The drilling and casing system 1 encompasses any system comprising a rig structure for drilling a second hole and casing an adjacent first hole. [0034] Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.