Patent Application
20120325475
1. Field of the Invention
The present invention is directed toward a cementing tool, a casing string equipped with a cementing tool, and methods of cementing such a casing string. Particularly, the cementing tool is provided with a rupture disc assembly that upon rupture permits cement to flow from the interior of the casing string through the tool sidewall and into the annulus defined by the casing string and downhole formation into which the casing string is run. The cementing tool permits obstructions or voids within the annulus to be bypassed during cementing operations, and allows for multiple-stage cementing operations to be conducted. Further, the cementing tool, if activated during cementing operations, restores the structural integrity of the casing string that might otherwise be lost through the use of other tools or processes.
2. Description of the Prior Art
Surface casing is typically the first casing string run and fully cemented in a well. Surface casing protects fresh water-bearing sands or formations from vertical migration of well fluids that might otherwise contaminate the fresh water carried by these formations. Often too, the well blow out preventer, which is the last line of defense against an uncontrolled well, is secured to the surface casing. Further, surface casing is used to hang off the next string of casing that is run into the well. Given the many functions of surface casing, it is important for the surface casing to be well supported in order to prevent buckling and damage when loaded in this manner.
The purpose of cementing the surface casing is to have a competent sheath of cement to both support and seal around the casing. During cementing operations, cement is introduced into the annulus created between the casing and the formation through which the casing is run. Cement can be introduced into the annulus in a number of ways. One method is “top job” approach wherein cement is directly injected into the annulus from the surface using one or more small diameter pipes pushed down into the annulus. This method may be useful in cementing shallow casing strings, but is not always reliable in that un-cemented pockets can be left in the annulus. Another method involves the circulation of cement down through the center of the casing string and back toward the surface through the annulus. When successfully completed, this method provides a higher degree of confidence that un-cemented pockets have been avoided or minimized. However, the annulus can become obstructed, such as with a collapsed portion of a loose formation which blocks the flow of cement through the annulus. In other instances, cement may be lost from the annulus into the well formation due to the high porosity of the rock or sand that the well bore is drilled through. This loss prevents the cement from reaching the surface and is known as lost circulation or lost returns. In these instances, the casing would need to be perforated above the obstruction or region of lost circulation so that a new flow path for cement into the annulus can be established. This is undesirable as it requires compromising the casing integrity.
Another solution has been proposed involving the use of differential valve (DV) tools. These tools have largely been used as a part of a multistage cementing operation. These tools are typically run where the cementing is planned to be placed in multiple lifts in a single string of pipe. The bottom section of casing is cemented normally. Then the tool is opened and drilling mud is circulated. After the bottom stage of cement has been set sufficiently, the top stage is cemented through the DV tool. These tools are disadvantageous in that the cementing must be performed in stages, rather than in a single pour, thus adding additional operating time to the cementing process. Further, these tools tend to be expensive and most require some kind of actuation operation, and then be drilled out once the cementing stage is completed.
The present invention overcomes a number of the difficulties associated with prior apparatus and methods for cementing a casing string by utilizing a cementing tool that couples adjacent casing sections and comprises an integral rupture disc assembly that can be selectively actuated so as to bypass obstructions in the annulus between the downhole formation and casing string or permit flow of cement into the annulus at a desired elevation.
According to one embodiment of the present invention, there is provided a cementing tool configured for attachment to a casing string. The cementing tool comprises a tubular body including a cylindrical sidewall having an interior surface and an exterior surface. The sidewall interior surface defines a central passage therethrough. At least one channel-forming member is provided that defines a channel located outboard from the central passage. The channel includes at least one open end. At least one port is formed in the sidewall that defines a path for fluid flow between the central passage and the channel. The cementing tool further comprises at least one rupture disc assembly comprising a rupture disc that, in its unruptured state, is disposed in fluid blocking relationship between the central passage and the at least one open end.
According to another embodiment of the present invention, there is provided a casing string that comprises at least one section of casing having a central bore and a cementing tool as described herein attached to one end of the section of casing.
According to yet another embodiment of the present invention, there is provided a method of cementing a casing string in a well. The method comprises positioning a casing string comprising a central bore and at least one cementing tool as described herein in a downhole formation. Next, cement is injected downhole through the casing string central bore and cement is caused to flow into an annulus located between the casing string and the formation.
a is a cross-sectional view of the cementing tool of
b is a cross-sectional view of an alternate embodiment of a cementing tool being equipped with male and female threaded connector structure;
The present invention provides apparatus and methods that are particularly suited for the running in and cementing of a casing string into a well bore. As illustrated in
Turning next to
Sidewall 24 also comprises at least one port 34, and in the embodiments illustrated two ports, formed therein that extend between interior surface 26 and exterior surface 30. Thus, port 34 defines a fluid flow path between the interior and exterior of tool 20 that is substantially perpendicular to the flow path through tool 20 defined by passageway 28.
In each port 34, a respective rupture disc assembly 36 is received and secured to sidewall 24. In the embodiment illustrated in
Both rupture disc assembly embodiments 36, 52 comprise a rupture disc 62. In the embodiment illustrated in
Cementing tool 20 also comprises at least one channel-forming member 64 secured to the sidewall exterior surface 30. Member 64 cooperates with sidewall exterior surface 30 to define a channel 66 that, upon rupture of rupture disc 62, is in fluid communication with the interior of tubular body 22. As shown, channel 66 is longitudinal with respect to tool 20, however, it is within the scope of the present invention for channel 66 to be oriented about different axes. As shown in
As noted above, cementing tool 20 is configured to be attached to at least one casing section 18. Tool 20 includes connecting structure 90 to facilitate this attachment. In the embodiment illustrated in
The use of cementing tool 20 in the cementing of casing string 10 is illustrated in
After casing string 10 has been run into downhole formation 16, cement is placed in annulus 14. In certain embodiments this is accomplished by injecting cement through casing central bore 32 toward its lowermost downhole margin 102 at which point the cement is directed into annulus 14 and flows upwardly toward the surface. In an ideal situation, cement continues to flow until the entirety of annulus 14 is filled with cement. However, it can arise that certain portions of downhole formation 16 do not possess sufficient integrity and can collapse around casing string 10 after it is run in, or alternatively a region of lost circulation may be encountered that can present a limitless void. When this occurs, an obstruction 104, or void (not shown), to the flow of cement 100 in annulus 14 is created. It is understood that the effect of either an obstruction 104 or void is substantially the same in that the flow of cement upwardly through annulus 14 is impeded. Therefore, even though the following discussion is made in terms of encountering an obstruction 104, a void due to a region of lost circulation may be substituted therefor.
Should such an obstruction (or void) be detected, the present invention advantageously permits the obstruction (or void) to be bypassed and the introduction of cement 100 into annulus 14 to continue without significant interruptions to the cementing operation, such as the need to pull or run tools downhole. If an obstruction 104 is encountered, the fluid pressure of the cement being pumped downhole may increase. In particular embodiments, the increase in cement pressure is detected by an operator, however, this does not always need to be so. At this point, a rupture disc 62 carried by rupture disc assembly 36, 52 may be ruptured by increasing the pressure of the cement within casing string central bore 32 proximate rupture disc 62 so that the disc opens and cement may flow through port 34, 56 and into the annulus thereby bypassing obstruction 104. If cement returns to the surface are not achieved as expected, the operator may determine that a region of lost circulation has been encountered and the cement is being directed into a porous formation. The operator can then increase the pressure of the cement being flowed down through casing string central bore 32 to open rupture disc 62. In certain embodiments, rupture disc 62 is configured to rupture at a pressure of up to 90% of the rated casing strength. This ensures that disc 62 does not rupture due to normal operating conditions experienced in the well, but rather only in response to encountering an annular obstruction or void during cementing operations. Further, if no obstruction is encountered during cementing operations, rupture disc 62 provides sufficient strength so as not to compromise the overall integrity of casing string 10. As shown in
Generally, cementing tool 20 should be located within casing string 10 at a higher elevation than obstruction 104. Knowledge of the formations through which the well is being drilled can assist the operator in positioning a cementing tool 20 within casing string 10 in a location that is likely to be at a higher elevation than where an obstruction 104 or void is likely to form. In certain operations, though, it may be difficult to forecast this information. In those situations, a plurality of cementing tools 20 can be periodically installed between casing sections 18 along the length of casing string 10. The frequency of placement of cementing tools 20 can vary depending upon the conditions expected to be encountered in the well, however, in certain embodiments cementing tools can be located within casing string 10 at a spacing of approximately at least every 100 feet, at least every 250 feet, at least every 500 feet, or at least every 1000 ft. Use of a plurality of cementing tools 20 increases the likelihood that at least one cementing tool 20 will be located at a higher elevation than the obstruction, so that the obstruction can be bypassed.
In embodiments which comprise a plurality of cementing tools 20 located within casing string 10, it may be possible for an operator to detect the presence of an obstruction 104 and determine its approximate elevation within annulus 14. Thus, by controlling the pressure within the casing central bore 32, the operator may be able to selectively actuate the rupture disc(s) 62 carried by a particular cementing tool 20, while leaving the other rupture disc(s) of other cementing tools intact. In other embodiments, the pressure of the cement within casing central bore 32 can be adjusted to cause the rupture of all rupture discs 62 within casing string 10, or only those located at elevations above the obstruction 104. In certain embodiments, in order to facilitate this selective rupturing of rupture discs 62, rupture discs of differing burst characteristics may be employed throughout casing string 10.
In other embodiments of the present invention, the bursting pressure of rupture discs 62 may be selected to automatically rupture upon encountering elevated pressures within central bore 32 that attributable to the encountering of an obstruction 104 to prevent damage to the casing. In these embodiments, actual detection and identification of the location of an obstruction is obviated and cementing operations may continue without any meaningful interruption in the flow of cement into annulus 14.
In still other embodiments, a plurality of cementing tools 20 may be employed so as to carry out multistage cementing operations. In certain instances it may be desirable to selectively cement only certain elevations of the casing string 10. For example, wells with low formation pressures may not be able to sustain the hydrostatic forces of a full column of cement. In other applications, it may be desirable to isolate certain sections of the wellbore or use different blends of cement in the wellbore. Still, in cementing deep, hot holes, cement pump times can be limited so as to prevent full-bore cementing of the casing string during a single stage. In these examples and other situations, it may be desirable to cement casing string 10 in two or more stages.
Typically the stage cementing operation begins as described above in that cement 100 is run cement through casing central bore 32 toward its lowermost downhole margin 102 at which point the cement is directed into annulus 14 and flows upwardly toward the surface. Even though an obstruction or void may not be encountered, once the cement has reached a desired height in annulus 14, the flow of cement is stopped. At this point, it may no longer be possible to resume the flow of cement in annulus 14 by flowing cement down to the lowermost margin 102 and back toward the surface. Instead, the operator can actuate rupture discs 62 at a desired elevation so that the flow of cement into annulus 14 can resume, thus beginning a second stage of cementing. This process can be repeated as necessary or desired.
Once cementing operations have been completed, drilling within the well can be continued by merely drilling out the cement within casing string central bore 32. There are no tools that need to be drilled out along with the cement. Alternatively, once cementing or a cementing stage is completed, any cement remaining within central bore 32 can be pumped or circulated out prior to fully curing so that the step of drilling through cement can be avoided.
A rupture disc assembly 118 is positioned within channel 112 in normally fluid blocking relationship between port 114 and a channel outlet 120. Rupture disc assembly 118 includes a rupture disc 122 and may be configured similarly to rupture disc assemblies 36, 52 discussed above. In one embodiment, rupture disc assembly 118 is threadably received and secured into a corresponding threaded portion 124 of channel 112. When in its unruptured state, rupture disc 122 prevents fluid or cement being flowed through tool passage 116 from passing through channel out let 120 and into the downhole annulus. An optional check valve 126 may be installed toward outlet 120 to prevent fluid being circulated within the annulus or other material from entering channel 112 and interfering with the operation of rupture disc assembly 118.
In one embodiment, port 114 is formed by machining a bore 128 through channel-forming member 108 and sidewall 110 until central passage 106 is reached. Likewise, channel 120 may be formed by machining a bore through channel-forming member 108 that is perpendicular to bore 128. The orifice 130 in channel forming member 108 can later be plugged.
The installation and operation of cement tool 106 is similar to that described above with respect to cement tool 20.
The following description sets for exemplary embodiments according to the present invention. It is to be understood, however, that these examples are provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention.
