Patent Application
20050247485
This invention relates to drilling tools and methods and is specifically concerned with a casing drilling system in which a casing string is run into the wellbore with the drilling string and expanded while the drilling string is in the wellbore.
The drilling of wells for oil and gas production conventionally employs relatively small diameter drilling pipe joined end to end to form a drill string to which is secured the necessary equipment including a drill bit for creating a wellbore which is of larger diameter than the drilling pipe. After a portion of the wellbore has been drilled, the wellbore is usually lined with a string of tubular casing member joined end to end to define a casing string. This conventional approach requires a cycle of drilling the wellbore, pulling the drill string out of the wellbore to the surface and running casing into the wellbore. The process is time consuming and costly.
The technique of casing drilling has been developed to address the problems of conventional drilling. The casing drilling process involves running a casing string into the wellbore with the drilling string.
Using either of the above techniques, a wellbore may be drilled and then cased to a certain depth, and then the drilling apparatus removed. If the depth of the wellbore is ever later to be extended, it is not possible to reinsert the drilling apparatus into the cased wellbore without resorting to a smaller diameter casing string. As different lower segments of the wellbore are drilled, successively smaller diameter casing strings are required in order to pass through the casing strings above.
To address these and other disadvantages of the prior art, applicant has developed a casing drilling apparatus and method which involves alternating between drilling and casing expansion operations under two different drilling fluid pressure regimes in order to insert and expand casing string into the wellbore while the drill string remains in the wellbore. The present invention therefore allows for formation of a “monobore” well with substantially the same diameter over the total depth. This is made possible by expanding a portion of casing after it is placed in the wellbore and after it passes through the segment of casing before it.
Accordingly, the present invention provides a drilling assembly comprising:
In another aspect, the present invention provides a method of drilling a wellbore comprising the steps of:
The present invention offers increased drilling speed by reducing the time spent expanding the casing and eliminating the need to withdraw the drill string from the wellbore to insert casing. Reduced drilling costs also result due to a reduction in drilling time and elimination of steps and equipment used in the conventional drilling process.
Aspects of the present invention are illustrated, merely by way of example, in the accompanying drawings in which:
In the following description, in referring to the position of components in the drill strings, “above”, “up”, “upper” and the like describe relative positions closer to the ground surface while “below”, “down”, “lower” and the like describe relative positions closer to the bottom of the wellbore.
Referring to
Drilling fluid from fluid source 16 is introduced under pressure into the fluid passage 80 via port 14. Used fluid exits the lower drill string 6 at drill bit 12 and serves to lubricate and cool the bit. The used fluid mixed with material dislodged by drill bit 12 drill flows upwards as indicated by arrows 17 through wellbore 8 in the annular passage external to the drill strings 4 and 6. This annular passage is sealed at surface level to permit collection of the used fluid for filtering and recycling through reservoir 16.
As best shown in
The upper end 22 of lower drill string 6 is formed from a casing string 24 that is telescoped over casing expander unit 20 such that the lower drill string 6 essentially “hangs” on the casing expander unit 20. The lower drill string 6 is maintained in place due to friction plus static pressure between casing string 24 and casing expander unit 20. Alternatively, the lower drill string 6 may be connectable to and supported by the drilling apparatus 13 in similar manner as the upper drill string 4.
The casing expander unit 20 may be comprised of any device, structure or apparatus over which the casing can be moved in order to expand the casing.
In the preferred embodiment, casing expander unit 20 is formed with a generally frusto-conical shoulder 26 that expands outwardly downwardly and forces casing that is moved downwardly past the unit to expand outwardly. Shoulder 26 is shaped and dimensioned to impart an expanding force to a casing that is moved over the shoulder. The expanding force deforms a casing member to a larger internal diameter. In other words, above casing expander unit 20, there is a casing string portion 24a of a first diameter, while below the expander unit, there is an expanded casing string portion 24b of an enlarged diameter. Casing expander unit 20 also preferably includes an annular shoulder 28 spaced apart from frusto-conical shoulder 26 to guide movement of the expanding casing string and to prevent binding of the casing. Shoulder 26 and/or shoulder 28 may also act as an upper seal for expanded casing portion 24b which functions as a section of the drill string fluid passage 80.
Lower drill string 6 includes a constriction 31 that connects the expanded portion 24b of casing string 24 with the rest of the lower drill string 6 and communicates the fluid passage 80 through the expanded casing assembly with the fluid passage 80 of the rest of lower drill string 6. The constriction 31 may be comprised of any device, structure or apparatus which is capable of providing a narrowing transition from the casing string to the rest of the lower drill string 6. The functions of the constriction 31 are to convert fluid pressure from within the fluid passage 80 to a downward force acting on the lower drill string 6 and to provide a transition between the casing and the rest of the lower drill string 6.
Referring to
A pup joint may be used to connect constriction 31 with the rest of the lower drill string 6.
As shown in
When the drilling apparatus of the present invention is operated to expand casing, flow restriction device 35 is operated to restrict flow and create an elevated pressure in the fluid passage 80 above the flow restriction device that acts at constriction 31 and at flow restriction device 35 to advance lower drill string 6 past upper drill string 4 while simultaneously expanding the portion of casing string 24 moving past expander unit 20. In contrast, when drilling, the flow restriction device 35 is set to permit substantially unrestricted flow of drilling fluid to drill bit 12. In other words, flow restriction device 35 operates as a bi-pressure subassembly to create two pressure regimes within the drill strings 4 and 6 to switch the drilling assembly between a drilling mode and a casing insertion and expansion mode. The drilling assembly alternates between these two modes to perform its work.
Some development work has been done directed to the notion of simultaneously drilling and expanding the casing by always operating in a high flow, high pressure mode. This technique is not considered workable since the high pressures required for casing expansion are incompatible with lower pressures which are suitable and safe for drilling. Also, the rate of casing expansion is expected to be at least an order of magnitude greater than the drilling penetration mode, depending on conditions, and the forces required for these two modes of operation are likewise incompatible. An important feature of the present invention is the provision of two different pressure regimes in the fluid passage 80 that allow for alternating between the drilling mode and the casing insertion and expansion modes instead of performing these operations simultaneously.
The flow restriction device 35 may be comprised of any structure, device or apparatus which is capable of alternately providing two different pressure regimes in the drill strings 4 and 6. The flow restriction device 35 may be configured to be actuated between the pressure regimes in any manner. For example, the flow restriction device 35 may be actuated by longitudinal or rotational manipulation of the drilling strings 4 and 6 or by pressure or flow variations of drilling fluid in the fluid passage 80.
One device suitable for use as a flow restriction device 35 in the present invention is a bi-pressure subassembly which includes a barrel cam with detents which is movable between positions to control flow of fluid through the unit. The barrel cam is activated by pressure changes in the fluid introduced by cycling the pumps that pump the fluid. One example of equipment that could be adapted to function as a bi-pressure subassembly is the Adjustable Gauge Stabilizer (AGS™) manufactured by Sperry-Sun Drilling Services. The operation of this subassembly is described in the Adjustable Gauge Stabilizer (AGS™) Operations manual which is incorporated herein by reference.
U.S. Pat. No. 6,158,533 to Gillis et al. discloses an Adjustable Gauge Downhole Drilling Assembly (Adjustable Gauge Motor (AGM™))that includes a similar barrel cam apparatus and is also incorporated herein by reference.
As adapted for use in the present invention, the AGS™ and the AGM™ are both able to operate in both an unrestricted fluid flow mode and a restricted fluid flow mode to switch the drilling assembly between drilling mode and casing insertion and expansion mode, respectively.
Depending upon the application of the invention and the design of the bottom hole assembly 10, a flow restriction device 35 which comprises an apparatus similar to that of the AGS™ or the AGM™ may or may not include the function of an adjustable gauge stabilizer. In other words, the structures of the AGS™ and the AGM™ are adapted for use with the invention primarily because of their capability to provide two alternating pressure regimes in the drill strings 4 and 6.
A second device which is potentially suitable to be adapted for use as the flow restriction device 35 is disclosed in U.S. Pat. No. 6,439,321 to Gillis et al for a Piston Actuator Assembly for an Orienting Device. This device comprises a longitudinally movable piston which provides a first partial obstruction and a flow restrictor which provides a second partial obstruction. The first partial obstruction and the second partial obstruction may be selectively aligned or misaligned to provide two different pressure regimes. U.S. Pat. No. 6,439,321 is incorporated herein by reference.
Referring to
It will be appreciated by those skilled in the art that not all the components of bottom hole assembly 10 illustrated in
In addition, measurement-while-drilling (MWD) systems can be used with the drilling apparatus of the present invention. Typically, such systems are used to sense and communicate properties such as drilling temperatures, pressures, azimuth and inclination and would be installed in the lower drill string 6 above bottom hole assembly 10 to readily transmit data from the wellbore 8 to the surface.
When used in conjunction with the sliding drilling bottom hole assembly 10 described above and illustrated in
Once a segment of the wellbore 8 has been drilled a desired distance, the bi-pressure subassembly 35 is cycled by a “Pumps Off-Pumps On” sequence of the pumps at the surface supplying the drilling fluid to shift the unit into high backpressure operation in which fluid flow is reduced to the motor, underreamer and bit to such an extent that these components stop functioning. It is contemplated that the flow through the bi-pressure subassembly 35 in this restricted flow position will be extremely small. In other words, the passage through the subassembly will be very small in the restricted flow position. This can be achieved by selecting an appropriate orifice size for the subassembly.
With drilling halted by stopping of the drill bit, the drill strings 4 and 6 are retracted from the surface to retreat drill bit 12 from the bottom 42 of the pilot hole 40. This position of drill strings 4 and 6 is shown in
When using the bottom hole assembly 10 illustrated in
While the illustration of
In most applications, it is preferable that sealed junctions be provided between adjacent segments of casing string 24 In other words, the upper end of a lower segment of casing should preferably be sealingly connected to the lower end of an upper segment of casing. This can be accomplished as a lower segment of casing is expanded, and may involve the use of a rubber cladding on the surfaces of the casing at the ends of the casing. These techniques are already extant in the prior art.
This sealed junction is optional and may not always be required. In fact, in some applications, there may actually be gaps in the borehole between segments of casing.
Fluid flow through the fluid passage 80 is stopped to halt the downward movement of lower drill string 6 and expansion of the casing before drill bit 12 reaches the bottom 42 of pilot hole 40. This may, for example, be achieved by initiating a further “Pumps Off-Pumps On” sequence in order to initiate the drilling of a further segment of wellbore 8. Alternatively, fluid flow may simply be stopped to facilitate an interruption in drilling and casing expansion operations.
There is a potential danger of accidentally “tagging bottom” with the drill bit and underreamer assemblies traveling at full casing insertion and expansion speed. To prevent damage to these components, which would significantly disrupt the entire drilling operation, it is preferable to provide safeguards against this potential danger. Such safeguards may include a device, structure or apparatus for dissipating pressure within the fluid passage 80 in response to an occurrence of tagging bottom or a device, structure or apparatus for absorbing the impact associated with an occurrence of tagging bottom. One or both of these safeguards may be provided and may be provided in one or a plurality of devices, structures or apparatus.
In a preferred embodiment, both safeguards are provided in a single apparatus, which apparatus comprises a shock absorbing unit 60 located above bi-pressure subassembly 35, preferably in the lower drill string 6. Such a unit is shown schematically in
Details of a conventional two-way shock tool or shock absorbing tool which could be adapted for use with the invention can be found in Canadian Patent No. 1,226,274 to Wenzel, which is incorporated herein by reference.
Other mechanisms could be used to accomplish the goal of providing safeguards against damage to the bottom hole assembly 10 due to impact under high fluid pressure. Safeguards directed at dissipating the pressure within the fluid passage 80 should generally be located above the flow restriction device 35 (in either the upper drill string 4 or the lower drill string 6).
Safeguards directed at absorbing the impact of the drill bit 12 at the end of the wellbore 8 may be located at any position in the upper drill string 4 or the lower drill string 6 but are preferably located in the lower drill string 6 in relative close proximity to the bottom hole assembly 10. Where both safeguards are integrated in a single device, structure or apparatus, this device, structure or apparatus should therefore be located above the flow restriction device 35 in either the upper drill string 4 or the lower drill string 6.
A particular advantage of the drilling apparatus and method of the present invention is that it permits the resumption and extension of a wellbore 8 that has already been cased to a certain depth without introducing progressively reduced diameter sections. Using conventional drilling techniques, it is not possible to reinsert the drilling apparatus into the cased wellbore 8 without resorting to a smaller diameter casing string. As different lower segments of the wellbore 8 are drilled, successively smaller diameter casing strings are required in order to pass through the casing strings above. With the apparatus and method of the present invention, it is possible to install subsequent casing strings in each new section as the casing strings are movable through the existing pre-expanded wellbore 8 for expansion after they are positioned in the newly drilled portion of the wellbore 8. When the drilling assembly of the present invention is used in this manner to extend an existing cased well, upper drill string 4 is extended into the well to a point adjacent the end of the installed casing to position the casing expansion unit 20 to begin expansion of the new casing string at a location that preferably results in some overlap of the casing strings.
In practice, it is sometimes necessary to retrieve the bottom hole assembly 10 from the end of the drilling strings if a component breaks or if drilling is completed. If constriction 31 is formed from latch coupling 71, the latch coupling 71 provides a convenient point of retrieval for the bottom hole assembly to facilitate removal. One alternative retrieval mechanism that can be incorporated in the bottom hole assembly of the present invention is described in U.S. Pat. No. 5,197,553 (Leturno) or U.S. Pat. No. 5,271,472 (Leturno) which are incorporated herein by reference. A second alternative retrieval mechanism is also discussed in U.S. Pat. No. 5,472,057 (Winfree) which is also incorporated herein by reference. Other retrieval mechanisms for the bottom hole assembly or portions thereof may also be used with the invention.
The foregoing description primarily details a drilling system according to the present invention that relies on a sliding drilling arrangement using a downhole drilling motor 50 as shown in
In the rotary drilling arrangement, downhole motor 50 may not be required. Instead, the drill bit 12 may be driven by rotation of either or both of the drill strings 4 and 6.
If both the upper drill string 4 and the lower drill string 6 are to be rotated, then consideration must be given to ensuring that the drill strings 4 and 6 rotate together. The frictional forces between the upper drill string 4 and the lower drill string 6 at the location of the casing expander unit 20 may or may not be sufficient to transmit torque from the upper drill string 4 to the lower drill string 6. It may therefore be necessary either to rotate both of the drill strings 4 and 6 simultaneously from the surface or to provide a more positive mechanism for ensuring that torque can be transmitted from the upper drill string 4 to the lower drill string 6. Such a mechanism may comprise a latch mechanism or splines, ridges or grooves in engaging surfaces of the upper drill string 4 and the lower drill string 6.
Alternatively, if only the lower drill string 6 is to be rotated during rotary drilling, a bearing assembly (not shown) at casing expander unit 20 would be required to accommodate rotation of the casing string relative to the casing expander unit 20 when in drilling mode.
The invention may also be utilized with a combination of rotary drilling and sliding drilling techniques by combining the features of both the sliding drilling embodiments and the rotary drilling embodiments as described above and by incorporating a downhole motor 50 in the bottom hole assembly 10 even where rotary drilling is contemplated.
While a downhole motor 50 in the bottom hole assembly 10 may be unnecessary in a rotary drilling arrangement, a drilling fluid restriction device 35 is still required to provide lubricating drilling fluid to the drill bit during drilling mode and to develop the necessary high pressure in the fluid passage 80 to permit expansion of the casing during casing expansion mode.
It may, however, be possible for some applications of the invention to eliminate the constriction 31 if sufficient force can be developed at the flow restriction device 35 to permit expansion of the casing during casing expansion mode. This possibility depends upon the extent to which the flow restriction device 35 restricts flow in the fluid passage 80 when the flow restriction device 35 is in casing expansion mode. This possibility also depends upon the ability to provide a transition between the casing and the rest of the lower drill string 6 without the constriction 31.
Alternatively, it may be possible to combine the functions of the constriction 31 and the flow restriction device 35 at a single location in the lower drill string 6 instead of at longitudinally spaced locations. An integrated constriction 31 and flow restriction device 35 could for example provide a transition between the casing and the rest of the lower drill string 6, convert fluid pressure within the fluid passage 80 to a downward force acting on the lower drill string 6, and provide for two different pressure regimes.
Although the present invention has been described in some detail by way of example for purposes of clarity and understanding, it will be apparent that certain changes and modifications may be practised within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2,401,813 | Sep 2002 | CA | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CA03/01362 | 9/5/2003 | WO | 6/28/2005 |
