Fluid communication with an earth formation through cement

BACKGROUND

0001This disclosure relates generally to equipment utilized and operations performed in conjunction with a subterranean well and, in one example described below, more particularly provides for fluid communication with an earth formation through cement.

0002It is common practice to use cement for securing a casing string in a wellbore, and for providing pressure isolation in an annulus formed between the casing string and the wellbore. In order to produce fluids from an earth formation penetrated by the wellbore into the casing string, or to inject fluids from the casing string into the formation, it is desirable to be able to provide for fluid communication through the cement in the annulus at specific locations. Therefore, it will be readily appreciated that advancements are continually needed in the art of providing fluid communication with an earth formation through cement.

BRIEF DESCRIPTION OF THE DRAWINGS

0003<figref idref="DRAWINGS">FIGS. 1A-C</figref> are representative partially cross-sectional views of an example of a well system and associated method which can embody principles of this disclosure, the well system being depicted after a retarder chemical has been released into a well annulus, after a first zone has been fractured, and after multiple zones have been fractured.

0004<figref idref="DRAWINGS">FIGS. 2A-C</figref> are enlarged scale representative cross-sectional views of an example of a well tool that may be used in the system and method of <figref idref="DRAWINGS">FIGS. 1A-C</figref>, the well tool being depicted in a run-in configuration, after a retarder chemical is discharged from the well tool, and after a valve of the well tool is opened.

0005<figref idref="DRAWINGS">FIGS. 3A-C</figref> are enlarged scale representative cross-sectional views of another example of a well tool that may be used in the system and method of <figref idref="DRAWINGS">FIGS. 1A-C</figref>, the well tool being depicted in a run-in configuration, after a retarder chemical is discharged from the well tool, and after a valve of the well tool is opened.

0006<figref idref="DRAWINGS">FIGS. 4A-C</figref> are representative partially cross-sectional views of another example of a well system and associated method which can embody principles of this disclosure, the well system being depicted after a casing string has been installed in a well, after a first zone has been fractured, and after multiple zones have been fractured.

0007<figref idref="DRAWINGS">FIG. 5</figref> is an enlarged scale representative cross-sectional view of an example of a well tool that may be used in the system and method of <figref idref="DRAWINGS">FIGS. 4A-C</figref>.

0008<figref idref="DRAWINGS">FIG. 6</figref> is an enlarged scale representative cross-sectional view of another example of a well tool that may be used in the system and method of <figref idref="DRAWINGS">FIGS. 4A-C</figref>.

DETAILED DESCRIPTION

0009Representatively illustrated in <figref idref="DRAWINGS">FIGS. 1A-C</figref> is a system <b>10</b> for use with a well, and an associated method, which can embody principles of this disclosure. However, it should be clearly understood that the system <b>10</b> and method are merely one example of an application of the principles of this disclosure in practice, and a wide variety of other examples are possible. Therefore, the scope of this disclosure is not limited at all to the details of the system <b>10</b> and method described herein and/or depicted in the drawings.

0010As depicted in <figref idref="DRAWINGS">FIGS. 1A-C</figref>, a wellbore <b>12</b> has been drilled so that it penetrates an earth formation <b>14</b>. Several specific zones <b>14</b><i>a</i>-<i>d </i>of the formation <b>14</b> are illustrated in <figref idref="DRAWINGS">FIGS. 1A-C</figref>. However, it should be clearly understood that the scope of this disclosure is not limited to situations involving multiple zones of a single formation, or to any particular number of zones. Instead, the principles of this disclosure can be readily applied to situations involving multiple formations or any number of zones (including one).

0011In addition, although the wellbore <b>12</b> as depicted in <figref idref="DRAWINGS">FIGS. 1A-C</figref> is generally vertical, the principles of this disclosure can be readily applied to generally horizontal or inclined wellbores. Thus, it will be appreciated that the scope of this disclosure is not limited to any of the particular details of the wellbore <b>12</b>, formation <b>14</b> and/or zones <b>14</b><i>a</i>-<i>d </i>as described herein or depicted in the drawings.

0012Referring specifically to <figref idref="DRAWINGS">FIG. 1A</figref>, a casing string <b>16</b> has been installed in the wellbore <b>12</b>, and cement <b>18</b> has been flowed into an annulus <b>20</b> formed between the casing string and the wellbore. Eventually, the cement <b>18</b> will harden or “set” to thereby secure the casing string <b>16</b> in the wellbore <b>12</b>, and to seal off the annulus <b>20</b>.

0013To provide for such cementing of the casing string <b>16</b> in the wellbore <b>12</b>, the casing string can include items of equipment known to those skilled in the art as a guide shoe or float shoe <b>22</b> and a float collar <b>24</b>, for example. The use of such equipment to flow cement through casing and out into an annulus external to the casing is well known to those skilled in the art, and so will not be described further herein.

0014As used herein, the term “casing” is used to refer to a protective wellbore lining. Casing can be in the form of tubular products known to those skilled in the art as casing, liner and tubing, for example. Casing can be expanded or otherwise formed downhole, and can be made of a variety of materials (such as, metals and metal alloys, plastics and other polymers, etc.). Thus, the scope of this disclosure is not limited to use of any particular type of casing.

0015As used herein, the term “cement” is used to refer to a cementitious material that hardens downhole to secure a casing and seal off an annulus adjacent the casing. Cement hardens or sets as a result of hydration of the cement. Cement may include Portland cement, as well as a variety of other materials, for example, to vary setting time, to enhance strength, to enhance sealing capability, etc. The scope of this disclosure is not limited to use of any particular type of cement.

0016In the <figref idref="DRAWINGS">FIG. 1A</figref> example, the casing string <b>16</b> includes multiple spaced apart well tools <b>26</b>. The well tools <b>26</b> serve a number of different functions, but in a general aspect, the well tools serve to permit fluid communication between an interior of the casing string <b>16</b> and each of the zones <b>14</b><i>a</i>-<i>d. </i>Thus, in this example, the well tools <b>26</b> are connected in the casing string <b>16</b> at positions corresponding to the respective zones <b>14</b><i>a</i>-<i>d. </i>

0017Note that it is not necessary for a single well tool to be positioned at a corresponding single zone. Instead, for example, multiple well tools could be used for a single zone. As another example, a particular zone (such as a zone that is not presently economically viable for production) may not have a corresponding well tool. Thus, the scope of this disclosure is not limited to any particular arrangement of well tools, or to any particular correspondence between well tools and zones.

0018In the <figref idref="DRAWINGS">FIG. 1A</figref> example, the well tools <b>26</b> each release a cement retarder chemical <b>28</b> into the annulus <b>20</b> after the cement <b>18</b> has been placed in the annulus, but before the cement hardens or sets. The retarder chemical <b>28</b> prevents (or at least substantially retards) hardening or setting of the cement <b>18</b> in the discrete locations in the annulus <b>20</b> external to the individual well tools <b>26</b>. In this manner, fluid communication can be more readily provided between the casing string <b>16</b> and the individual zones <b>14</b><i>a</i>-<i>d </i>at those locations when desired.

0019The retarder chemical <b>28</b> can be any of those that substantially retard or entirely prevent hardening or setting of the cement <b>18</b>. Suitable examples include (but are not limited to) sugar, HR™ or SCR™ series of retarders marketed by Halliburton Energy Services, Inc. of Houston, Tex., USA, lignosulfonates, and X186™ retarder marketed by Schlumberger Limited of Houston, Tex., USA. The scope of this disclosure is not limited to use of any particular retarder chemical.

0020After the retarder chemical <b>28</b> has been released from the well tools <b>26</b>, and after the cement <b>18</b> has set in those sections of the annulus <b>20</b> into which the retarder chemical was not released, fluid communication can be established between the interior of the casing string <b>16</b> and each of the individual zones <b>14</b><i>a</i>-<i>d. </i>For this purpose, each of the well tools <b>26</b> can include a valve (described more fully below).

0021Note that it is not necessary for a well tool that releases a retarder chemical into a wellbore to also include a valve for providing fluid communication between a casing string and a formation zone. For example, the valve could be separate from the well tool that releases the retarder chemical. Thus, it will be appreciated that the scope of this disclosure is not limited to any particular configuration, function or combination of functions of a well tool.

0022Referring additionally now to <figref idref="DRAWINGS">FIG. 1B</figref>, a lowermost (closest to a distal end <b>30</b> of the casing string <b>16</b>) valve of the well tool <b>26</b> is opened. The open valve allows fracturing and other stimulation fluids (such as acid, etc.) to be flowed through the casing string <b>16</b>, out through the un-set cement <b>18</b> external to the valve, and into the zone <b>14</b><i>a </i>to thereby fracture the zone.

0023Because the retarder chemical <b>28</b> prevented (or at least substantially delayed) setting of the cement <b>18</b> external to the well tool <b>26</b>, operation of the valve was not hindered by hardened cement, and the fracturing fluids could readily flow from the well tool to the zone <b>14</b><i>a </i>and thereby exert sufficient fracturing pressure on the zone. If the retarder chemical <b>28</b> does not entirely prevent setting of the cement <b>18</b>, then preferably the retarder chemical at least delays setting of the cement until the valve has been opened and fluid communication has been established between the casing string <b>16</b> and the formation <b>14</b> through the cement.

0024Referring additionally now to <figref idref="DRAWINGS">FIG. 1C</figref>, the valves of each of the other well tools <b>26</b> has been opened in succession. After opening each of the valves, fracturing fluids are flowed through the open valve into the respective one of the zones <b>14</b><i>b</i>-<i>d </i>to thereby fracture the zone, similar to the manner in which the zone <b>14</b><i>a </i>was fractured (see <figref idref="DRAWINGS">FIG. 1B</figref>). Thus, in this example, each of the zones <b>14</b><i>a</i>-<i>d </i>is individually fractured in succession.

0025Note that it is not necessary for each of multiple individual zones to be fractured in succession. For example, two or more zones could be fractured simultaneously, or a single zone could be fractured in multiple locations. Thus, the scope of this disclosure is not limited to any particular sequence of fracturing of zones, or to any number of zones fractured at a time.

0026Referring additionally now to <figref idref="DRAWINGS">FIGS. 2A-C</figref>, an example of a well tool <b>26</b> that may be used in the <figref idref="DRAWINGS">FIGS. 1A-C</figref> system <b>10</b> and method is representatively illustrated. Of course, the well tool <b>26</b> of <figref idref="DRAWINGS">FIGS. 2A-C</figref> may be used in other systems and methods, in keeping with the scope of this disclosure.

0027The well tool <b>26</b> example of <figref idref="DRAWINGS">FIGS. 2A-C</figref> is configured for use as the lowermost well tool closest to the distal end <b>30</b> of the casing string <b>16</b> of <figref idref="DRAWINGS">FIGS. 1A-C</figref>. Another well tool example (such as, that depicted in <figref idref="DRAWINGS">FIGS. 3A-C</figref> and described more fully below) may be used for the well tools that are not lowermost in the casing string <b>16</b>.

0028In <figref idref="DRAWINGS">FIG. 2A</figref>, the well tool <b>26</b> is depicted in a run-in configuration. In this configuration, the well tool <b>26</b> is connected in a casing string (such as, via threaded casing connectors <b>32</b> at opposite ends of the well tool) and deployed into a wellbore. Thus, the well tool <b>26</b> becomes a part of the casing string.

0029The well tool <b>26</b> contains a retarder chemical <b>28</b> in an annular internal chamber <b>34</b>. The internal chamber <b>34</b> is in fluid communication with an exterior of the well tool <b>26</b> (and, thus, in communication with the annulus <b>20</b> in the <figref idref="DRAWINGS">FIGS. 1A-C</figref> example) via one or more discharge openings <b>36</b> formed through a generally tubular outer housing <b>38</b>. In some examples, a membrane, dispersible plug (such as, comprised of grease or wax, etc.) or other type of frangible or removable barrier may be used to prevent leakage of the retarder chemical <b>28</b> from the chamber <b>34</b> to the exterior of the well tool <b>26</b> via the opening <b>36</b>, until it is desired to discharge the retarder chemical from the chamber.

0030In the run-in configuration of <figref idref="DRAWINGS">FIG. 2A</figref>, the chamber <b>34</b> has a certain volume. However, the chamber <b>34</b> volume can be decreased when desired to thereby cause the retarder chemical <b>28</b> to be discharged via the opening <b>36</b>.

0031The well tool <b>26</b> of <figref idref="DRAWINGS">FIGS. 2A-C</figref> also includes a valve <b>40</b>. The valve <b>40</b> is used to prevent, and then selectively permit, fluid communication between the exterior of the well tool <b>26</b> and an internal flow passage <b>42</b> that extends longitudinally through the well tool. When the well tool <b>26</b> is connected in the casing string <b>16</b> and forms a part thereof, the flow passage <b>42</b> becomes part of a flow passage that extends through the casing string.

0032The valve <b>40</b> includes a generally tubular sleeve <b>44</b> that can slide longitudinally relative to the outer housing <b>38</b>. In the run-in configuration of <figref idref="DRAWINGS">FIG. 2A</figref>, the sleeve <b>44</b> is retained by one or more shear members <b>46</b> in a position in which ports <b>48</b> formed radially through the sleeve are not aligned with ports <b>50</b> (only one of which is visible in FIG. <b>2</b>A) formed radially through the outer housing <b>38</b>. In this position, fluid communication through the valve <b>40</b> is prevented.

0033In the <figref idref="DRAWINGS">FIGS. 2A-C</figref> example, atmospheric or otherwise low pressure chambers <b>52</b>, <b>54</b> cooperate with various seal surfaces of the valve <b>40</b>, so that the sleeve <b>44</b> is completely or very nearly pressure balanced (that is, external pressures acting on the sleeve are “canceled out” so that the sleeve is not biased to displace by such pressures). In other examples, it may not be necessary for the sleeve <b>44</b> to be pressure balanced (e.g., the shear members <b>46</b> could be designed to resist biasing forces caused by external pressures acting on the sleeve in the run-in configuration).

0034An annular piston <b>56</b> disposed partially between the sleeve <b>44</b> and the outer housing <b>38</b> is not pressure balanced. Instead, external pressures acting on the piston <b>56</b> bias the piston upwardly. One or more shear members <b>58</b> prevent upward displacement of the piston <b>56</b>, until a certain predetermined pressure has been applied to the piston, at which point the shear members shear and permit the piston to displace upward.

0035Note that, when the piston <b>56</b> displaces upward, the volume of the chamber <b>34</b> decreases. Thus, the retarder chemical <b>28</b> will be discharged from the chamber <b>34</b> when the piston <b>56</b> displaces upward.

0036Referring additionally now to <figref idref="DRAWINGS">FIG. 2B</figref>, the well tool <b>26</b> is depicted in another configuration in which the retarder chemical <b>28</b> is discharged to the exterior of the well tool. To achieve this result, a sufficient pressure has been applied to the flow passage <b>42</b> to cause the shear members <b>58</b> to shear and permit the piston <b>56</b> to displace upwardly.

0037The piston <b>56</b> displaces upwardly due to a pressure differential from the flow passage <b>42</b> to the chamber <b>52</b> (see <figref idref="DRAWINGS">FIG. 2A</figref>). This pressure differential biases the piston <b>56</b> upwardly, and displaces the piston upwardly after the shear members <b>58</b> can no longer resist the resulting biasing force.

0038In other examples, other pressure differentials, other ways of displacing the piston <b>56</b>, and/or other means of discharging the retarder chemical <b>28</b> may be used. For example, a pressure differential from the flow passage <b>42</b> to the exterior of the well tool <b>26</b> could be used to bias a piston and discharge the retarder chemical <b>28</b>. Thus, the scope of this disclosure is not limited to any particular configuration of elements of the well tool <b>26</b>, or to any particular way of discharging the retarder chemical <b>28</b>.

0039Note that, in the configuration of <figref idref="DRAWINGS">FIG. 2B</figref>, the sleeve <b>44</b> remains pressure balanced. The chamber <b>52</b> (see <figref idref="DRAWINGS">FIG. 2A</figref>) remains at a relatively low pressure, even though its volume has decreased. Even if the sleeve <b>44</b> is not substantially pressure balanced at this point, the shear members <b>46</b> continue to prevent displacement of the sleeve from its closed position.

0040The sleeve <b>44</b> can be displaced, however, by admitting sufficient pressure to the chamber <b>52</b> to bias the sleeve upwardly with a force great enough to shear the shear members <b>46</b>. For this purpose, a rupture disc <b>60</b> is provided in the sleeve.

0041Referring additionally now to <figref idref="DRAWINGS">FIG. 2C</figref>, the well tool <b>26</b> is depicted in a configuration in which a certain predetermined pressure has been applied to the flow passage <b>42</b>, thereby causing the rupture disc <b>60</b> to rupture and allow fluid communication between the flow passage and the chamber <b>52</b>. This significantly unbalances the sleeve <b>44</b>, so that it has been biased upward with enough force to shear the shear members <b>46</b>, thereby allowing the sleeve to displace upward.

0042Thus, the valve <b>40</b> is in its open configuration. Fluid communication is now permitted between the flow passage <b>42</b> and the exterior of the well tool <b>26</b> via the aligned openings <b>48</b>, <b>50</b>.

0043In operation with the system <b>10</b> and method example of <figref idref="DRAWINGS">FIGS. 1A-C</figref>, the well tool <b>26</b> of <figref idref="DRAWINGS">FIGS. 2A-C</figref> is connected as the lowermost well tool in the casing string <b>16</b>. Cement <b>18</b> is flowed through the casing string <b>16</b> and into the annulus <b>20</b>.

0044In accordance with conventional practice, a wiper plug (such as a five wiper plug, not shown) follows the cement <b>18</b> through the casing string <b>16</b> and eventually lands in the float collar <b>24</b>. Thus, the cement <b>18</b> is placed in the annulus <b>20</b>, and a lower end of the casing string <b>16</b> is sealed off, thereby allowing pressure in the casing string to be increased above hydrostatic.

0045Pressure in the casing string <b>16</b> is increased after the wiper plug lands (for example, in conjunction with pressure testing of the casing string), until a first predetermined pressure at the well tool <b>26</b> is reached. At this first predetermined pressure, the shear members <b>58</b> shear and the piston <b>56</b> displaces upward, thereby discharging the retarder chemical <b>28</b> into the annulus <b>20</b>.

0046The retarder chemical <b>28</b> prevents the cement <b>18</b> external to the well tool <b>26</b> from setting. However, the cement <b>18</b> in portions of the annulus <b>20</b> not exposed to the retarder chemical <b>28</b> is allowed to set.

0047After the cement <b>18</b> has set in portions of the annulus <b>20</b> not exposed to the retarder chemical <b>28</b>, pressure in the casing string <b>16</b> is again increased, until a second predetermined pressure at the lowermost well tool <b>26</b> is reached. The second predetermined pressure is in this example greater than the first predetermined pressure. At the second predetermined pressure, the rupture disc <b>60</b> ruptures, the shear members <b>46</b> shear and the valve <b>40</b> opens. When the valve <b>40</b> is opened, fracturing fluids can flow through the ports <b>48</b>, <b>50</b>, through the unset cement <b>18</b> in the annulus <b>20</b> external to the well tool <b>26</b>, and into the formation zone <b>14</b><i>a </i>to thereby fracture the zone.

0048Referring additionally now to <figref idref="DRAWINGS">FIGS. 3A-C</figref>, another example of the well tool <b>26</b> that may be used in the <figref idref="DRAWINGS">FIGS. 1A-C</figref> example for the well tools not lowermost in the casing string <b>16</b>. Elements of the well tool <b>26</b> of <figref idref="DRAWINGS">FIGS. 3A-C</figref> that are similar to, or perform a function similar to, those of the well tool of <figref idref="DRAWINGS">FIGS. 2A-C</figref> are indicated in <figref idref="DRAWINGS">FIGS. 3A-C</figref> using the same reference numbers.

0049In <figref idref="DRAWINGS">FIG. 3A</figref>, the well tool <b>26</b> is depicted in a run-in configuration, in which the well tool is connected as part of a casing string and installed in a well. In this configuration, the valve <b>40</b> prevents fluid communication between the flow passage <b>42</b> and the exterior of the well tool <b>26</b>. When used in the <figref idref="DRAWINGS">FIGS. 1A-C</figref> example, multiple well tools <b>26</b> would be used, with each well tool positioned adjacent a respective one of the formation zones <b>14</b><i>b</i>-<i>d. </i>

0050Referring specifically to <figref idref="DRAWINGS">FIG. 3A</figref>, the retarder chemical <b>28</b> is contained in the chamber <b>34</b> formed between the outer housing <b>38</b> and a sleeve <b>44</b> on the piston <b>56</b>. When pressure in the flow passage <b>42</b> is increased to a certain predetermined level, a resulting pressure differential (from the flow passage to the exterior of the well tool <b>26</b>) biases the piston <b>56</b> upward with sufficient force to shear the shear members <b>58</b> and allow the piston to displace upward.

0051Referring additionally now to <figref idref="DRAWINGS">FIG. 3B</figref>, the well tool <b>26</b> is representatively illustrated after the shear member <b>58</b> has sheared and the piston <b>56</b> has displaced upward. The upward displacement of the piston <b>56</b> decreases a volume of the chamber <b>34</b>, and thereby causes the retarder chemical <b>28</b> to be discharged via the opening <b>36</b> to the exterior of the well tool <b>26</b>. The valve <b>40</b> remains closed, with the sleeve <b>44</b> blocking fluid communication via the ports <b>50</b> between the flow passage <b>42</b> and the exterior of the well tool <b>26</b>.

0052Referring additionally now to <figref idref="DRAWINGS">FIG. 3C</figref>, the well tool <b>26</b> is representatively illustrated after a plug <b>62</b> has engaged a plug seat <b>64</b>, and a sufficient pressure differential has been applied (e.g., by increasing pressure in the flow passage <b>42</b> above the plug) to shear the shear member <b>46</b> and allow the piston <b>56</b> and sleeve <b>44</b> to displace downward. In this configuration, the valve <b>40</b> is open and permits fluid communication between the flow passage <b>42</b> and the exterior of the well tool <b>26</b>. When the piston <b>56</b> and sleeve <b>44</b> are displaced to their <figref idref="DRAWINGS">FIG. 3C</figref> position, a snap ring <b>68</b> carried on the piston expands radially outward and engages an annular recess <b>70</b> in the outer housing <b>38</b>, thereby preventing subsequent upward displacement of the piston and sleeve.

0053Note that the shear member <b>46</b> was not sheared when the piston <b>56</b> displaced upward (as depicted in <figref idref="DRAWINGS">FIG. 3B</figref>), because the shear member <b>46</b> is received in a slot <b>66</b> formed on the piston <b>56</b>. The slot <b>66</b> allows for upward displacement of the piston <b>56</b> from its <figref idref="DRAWINGS">FIG. 3A</figref> position to its <figref idref="DRAWINGS">FIG. 3B</figref> position, but does not allow the piston to displace downward to its <figref idref="DRAWINGS">FIG. 3C</figref> position until a sufficient pressure differential is applied across the plug <b>62</b>.

0054The plug <b>62</b> may be sealingly engaged with the plug seat <b>64</b> by releasing it into the flow passage <b>42</b> (for example, at the earth's surface) and pumping it through the flow passage to the plug seat. Although the plug <b>62</b> is depicted as being in the form of a ball or sphere, other types of plugs may be used, if desired.

0055In operation with the system <b>10</b> and method example of <figref idref="DRAWINGS">FIGS. 1A-C</figref>, the well tool <b>26</b> of <figref idref="DRAWINGS">FIGS. 3A-C</figref> is used for each of the well tools other than the lowermost well tool in the casing string <b>16</b>. As described above, a wiper plug (such as a five wiper plug, not shown) follows the cement <b>18</b> through the casing string <b>16</b> and eventually lands in the float collar <b>24</b>. Thus, the cement <b>18</b> is placed in the annulus <b>20</b>, and a lower end of the casing string <b>16</b> is sealed off, thereby allowing pressure in the casing string to be increased above hydrostatic.

0056Pressure in the casing string <b>16</b> is increased after the wiper plug lands (for example, in conjunction with pressure testing of the casing string), until a predetermined pressure at the well tool <b>26</b> is reached. At this predetermined pressure, the shear members <b>58</b> shear and the piston <b>56</b> displaces upward, thereby discharging the retarder chemical <b>28</b> into the annulus <b>20</b>. Note that this occurs for all of the well tools <b>26</b> (both for the lowermost well tool, and for the well tools that are not lowermost in the casing string).

0057The retarder chemical <b>28</b> prevents the cement <b>18</b> external to the well tools <b>26</b> from setting. However, the cement <b>18</b> in portions of the annulus <b>20</b> not exposed to the retarder chemical <b>28</b> is allowed to set.

0058After the cement <b>18</b> has set in portions of the annulus <b>20</b> not exposed to the retarder chemical <b>28</b>, pressure in the casing string <b>16</b> is again increased, until a second predetermined pressure at the well tool <b>26</b> is reached. This opens the valve <b>40</b> of the lowermost well tool <b>26</b>, as described above, and the formation zone <b>14</b><i>a </i>is fractured.

0059After the formation zone <b>14</b><i>a </i>is fractured, a plug <b>62</b> is released into the flow passage <b>42</b>, and the plug engages the plug seat of the well tool <b>26</b> corresponding to the formation zone <b>14</b><i>b. </i>Pressure in the flow passage <b>42</b> above the plug <b>62</b> is increased until a sufficient pressure differential is created across the plug to shear the shear member <b>46</b> and displace the piston <b>56</b> and sleeve <b>44</b> downward, thereby opening the valve <b>40</b> of that well tool (see <figref idref="DRAWINGS">FIG. 3C</figref>). Fluid communication is now permitted between the flow passage <b>42</b> and the zone <b>14</b><i>b, </i>and fracturing fluid can be flowed through the ports <b>50</b> to the zone <b>14</b><i>b </i>through the unset cement <b>18</b> exterior to the well tool <b>26</b> with sufficient pressure to fracture the zone. The plug <b>62</b> isolates the previously fractured zone <b>14</b><i>a </i>from pressures applied above the plug (such as, pressure applied to open the valve <b>40</b>, pressure applied to fracture the zone <b>14</b><i>b, </i>etc.).

0060After the formation zone <b>14</b><i>b </i>is fractured, the steps of releasing a plug <b>62</b> into the flow passage <b>42</b>, applying pressure to the flow passage above the plug and fracturing the respective zone can be repeated for each of the well tools <b>26</b> corresponding to the zones <b>14</b><i>c,d. </i>Eventually, all of the zones <b>14</b><i>a</i>-<i>d </i>are fractured as depicted in <figref idref="DRAWINGS">FIG. 1C</figref>.

0061Note that the plug <b>62</b> and plug seat <b>64</b> used to open the valve <b>40</b> of each successive well tool <b>26</b> corresponding to the zones <b>14</b><i>b</i>-<i>d </i>will have an incrementally larger size (e.g., the first plug released will have the smallest size, the next plug released will have an incrementally larger size, etc., and the last plug released will have the largest size). The plugs <b>62</b> and plug seats <b>64</b> can be drilled out after fracturing operations are completed.

0062Note that, in the well tool <b>26</b> examples of <figref idref="DRAWINGS">FIGS. 1A-3C</figref>, the retarder chemical <b>28</b> is discharged from a well tool at a location between the well tool's ports <b>50</b> and the distal end <b>30</b> of the casing string <b>16</b>. This is a preferred (although not necessary) feature of the well tools <b>26</b> that takes into account a tendency of a casing string to elongate when pressure internal to the casing string is decreased. Thus, in the above examples, after the retarder chemical <b>28</b> is discharged from a well tool <b>26</b> and pressure in the casing string <b>16</b> is subsequently decreased, the retarder chemical will be positioned more directly adjacent to the ports <b>50</b>, due to the casing string elongating.

0063Referring additionally now to <figref idref="DRAWINGS">FIGS. 4A-C</figref>, another example of the system <b>10</b> is representatively illustrated. Elements of the system <b>10</b> that are similar to, or perform functions similar to, those described above are indicated in <figref idref="DRAWINGS">FIGS. 4A-C</figref> using the same reference numbers.

0064As depicted in <figref idref="DRAWINGS">FIGS. 4A-C</figref>, the casing string <b>16</b> is installed in the wellbore <b>12</b> and cement <b>18</b> is placed in the annulus <b>20</b>. Multiple well tools <b>26</b> are connected in the casing string <b>16</b> adjacent respective formation zones <b>14</b><i>a</i>-<i>d. </i>

0065Referring specifically to <figref idref="DRAWINGS">FIG. 4A</figref>, it may be seen that each of the well tools <b>26</b> includes an exterior component <b>72</b> exposed to, and contacted by, the cement <b>18</b>. In some examples, the exterior component <b>72</b> can include the retarder chemical <b>28</b>, so that the retarder chemical is released from the exterior component, in order to prevent (or at least retard) setting of the cement <b>18</b> at each of the well tools <b>26</b>.

0066In some examples, the exterior component <b>72</b> can be dissolvable, frangible or otherwise dispersible to thereby provide for a lack of cement <b>18</b> adjacent the ports <b>50</b> of the valve <b>40</b>. This void or lack of cement <b>18</b> can prevent the cement from hindering operation of the valve <b>40</b>, and can provide for enhanced fluid communication in fracturing operations.

0067Referring additionally now to <figref idref="DRAWINGS">FIG. 4B</figref>, the exterior component <b>72</b> corresponding to the lowermost well tool <b>26</b> has dissolved or otherwise dispersed, so that a void <b>74</b> or lack of cement <b>18</b> now exists about the ports <b>50</b>. The valve <b>40</b> of the lowermost well tool <b>26</b> is opened, and the void <b>74</b> provides for enhanced fluid communication between the interior of the casing string <b>16</b> and the zone <b>14</b><i>a. </i>Thus, the zone <b>14</b><i>a </i>can be readily fractured.

0068Note that it is not necessary for the component <b>72</b> to be dispersed prior to opening of the valve <b>40</b> or fracturing of the zone <b>14</b><i>a. </i>In some examples, the component <b>72</b> could remain in place on the well tool <b>26</b> while the valve <b>40</b> is opened, and the component could be dispersed after or when the valve is opened (for example, the component could be frangible so that it is broken when fracturing fluid is pumped outward through the ports <b>50</b>, or the component could be dissolved by flowing a suitable acid, solvent or other dissolving fluid through the open valve <b>40</b>).

0069Referring additionally now to <figref idref="DRAWINGS">FIG. 4C</figref>, the valves <b>40</b> of the well tools <b>26</b> not lowermost in the casing string <b>16</b> have been opened, the exterior components <b>72</b> have been dispersed, and the formation zones <b>14</b><i>b</i>-<i>d </i>have been fractured in succession. A void <b>74</b> or lack of cement <b>18</b> is formed external to each set of valve ports <b>50</b>.

0070Referring additionally now to <figref idref="DRAWINGS">FIG. 5</figref>, an example of a well tool <b>26</b> that may be used for the lowermost well tool in the <figref idref="DRAWINGS">FIGS. 4A-C</figref> example is representatively illustrated. The <figref idref="DRAWINGS">FIG. 5</figref> well tool <b>26</b> is similar in many respects to that of <figref idref="DRAWINGS">FIGS. 2A-C</figref>, and so elements that are similar or perform similar functions are indicated in <figref idref="DRAWINGS">FIG. 5</figref> using the same reference numbers.

0071One difference between the <figref idref="DRAWINGS">FIG. 5</figref> example and the <figref idref="DRAWINGS">FIGS. 2A-C</figref> example is that the <figref idref="DRAWINGS">FIG. 5</figref> example does not include the chamber <b>34</b> for containing the retarder chemical <b>28</b>, the opening <b>36</b> for discharging the retarder chemical, or the piston <b>56</b> for forcing the retarder chemical from the chamber. However, these elements could be provided in the <figref idref="DRAWINGS">FIG. 5</figref> example, if desired.

0072Similarly, the exterior component <b>72</b> of the <figref idref="DRAWINGS">FIG. 5</figref> example could be provided in the example of <figref idref="DRAWINGS">FIGS. 2A-C</figref>. In the <figref idref="DRAWINGS">FIG. 5</figref> example, the component <b>72</b> is received in an annular recess <b>76</b> formed on an exterior of the outer housing <b>38</b>. In this example, the component <b>72</b> completely overlies the ports <b>50</b>.

0073Operation of the <figref idref="DRAWINGS">FIG. 5</figref> example is similar to that described above for the <figref idref="DRAWINGS">FIGS. 2A-C</figref> example, except that an application of pressure to the flow passage <b>42</b> is not used to discharge the retarder chemical <b>28</b> from the well tool <b>26</b>. Instead, the cement <b>18</b> in the annulus <b>20</b> is allowed to set, and then the valve <b>40</b> is opened by applying pressure to the flow passage <b>42</b> to thereby cause the rupture disc <b>60</b> to rupture. When the rupture disc <b>60</b> ruptures, the shear member <b>46</b> shears and the sleeve <b>44</b> displaces upward, thereby opening the valve <b>40</b>.

0074In one example, the component <b>72</b> can dissolve or otherwise disperse due to contact with the cement <b>18</b>, leaving the void <b>74</b> external to the ports <b>50</b>. In this manner, operation of the valve <b>40</b> is not hindered by presence of the cement <b>18</b>, and fluid communication between the ports <b>50</b> and the formation <b>14</b> through the remaining cement is enhanced.

0075In this example, the component <b>72</b> could comprise a material such as poly-lactic acid (PLA) or poly-glycolic acid (PGA) that dissolves over time as the cement <b>18</b> sets. The component <b>72</b> could comprise a material (such as magnesium) that disperses by galvanic reaction over time as the cement <b>18</b> sets. The scope of this disclosure is not limited to use of any particular material in the component <b>72</b>.

0076In another example, the component <b>72</b> can include the retarder chemical <b>28</b> therein, so that the retarder chemical is released from the component and prevents (or at least retards) setting of the cement <b>18</b> adjacent the well tool <b>26</b>. In this manner, a void would not necessarily be formed external to the ports <b>50</b>, but the unset cement <b>18</b> adjacent the well tool <b>26</b> would not hinder operation of the valve <b>40</b> or prevent fluid communication between the flow passage <b>42</b> and the formation <b>14</b>.

0077The retarder chemical <b>28</b> could leach from the component <b>72</b> over time as the cement <b>18</b> sets in other portions of the annulus <b>20</b>. For example, the component <b>72</b> could comprise an open cell foam material, with the retarder chemical <b>28</b> disposed in pores of the foam material. As another example, the component <b>72</b> could comprise a container for the retarder chemical <b>28</b>, with the container or a barrier associated with the container being made of a material that is dissolvable, frangible or otherwise dispersible to thereby release the retarder chemical from the container.

0078As depicted in <figref idref="DRAWINGS">FIG. 5</figref>, the component <b>72</b> is annular-shaped and is positioned completely external to the ports <b>50</b>. In other examples, the component <b>72</b> could extend into the ports <b>50</b> and/or the component could be otherwise shaped. In examples in which the retarder chemical <b>28</b> is released from the component <b>72</b> prior to release of a pressure applied in the casing string <b>16</b>, it may be beneficial to position the component between the ports <b>50</b> and the distal end <b>30</b> of the casing string (e.g., below the ports <b>50</b> as viewed in <figref idref="DRAWINGS">FIG. 5</figref>), so that when the casing string elongates upon release of the applied pressure, the ports will be positioned adjacent the released retarder chemical.

0079Referring additionally now to <figref idref="DRAWINGS">FIG. 6</figref>, another example of the well tool <b>26</b> that may be used with the <figref idref="DRAWINGS">FIGS. 4A-C</figref> system <b>10</b> and method example is representatively illustrated. The <figref idref="DRAWINGS">FIG. 6</figref> well tool <b>26</b> may be used for the well tools that are not lowermost in the casing string <b>16</b>.

0080The <figref idref="DRAWINGS">FIG. 6</figref> well tool <b>26</b> is similar in many respects to the example of <figref idref="DRAWINGS">FIGS. 3A-C</figref>, and so elements that are similar, or perform similar functions, are indicated in <figref idref="DRAWINGS">FIG. 6</figref> using the same reference numbers. One difference between the <figref idref="DRAWINGS">FIG. 6</figref> and the <figref idref="DRAWINGS">FIGS. 3A-C</figref> examples is that the <figref idref="DRAWINGS">FIG. 6</figref> example does not include the retarder chemical <b>28</b> in the chamber <b>34</b>, the shear member <b>58</b>, the discharge opening <b>36</b> or the piston <b>56</b> for forcing the retarder chemical out of the chamber. However, these elements could be provided in the <figref idref="DRAWINGS">FIG. 6</figref> example, if desired. Similarly, the <figref idref="DRAWINGS">FIGS. 3A-C</figref> well tool example could be provided with the exterior component <b>72</b> of the <figref idref="DRAWINGS">FIG. 6</figref> example.

0081Operation of the <figref idref="DRAWINGS">FIG. 6</figref> example is similar to that described above for the <figref idref="DRAWINGS">FIGS. 3A-C</figref> example, except that an application of pressure to the flow passage <b>42</b> is not used to discharge the retarder chemical <b>28</b> from the well tool <b>26</b>. Instead, the cement <b>18</b> in the annulus <b>20</b> is allowed to set, and then the valve <b>40</b> is opened by releasing the plug <b>62</b> into the flow passage <b>42</b> and applying pressure to the flow passage above the plug, thereby causing the shear member <b>46</b> to shear. When the shear member <b>46</b> shears, the sleeve <b>44</b> displaces downward, thereby opening the valve <b>40</b>.

0082The exterior component <b>72</b> of the <figref idref="DRAWINGS">FIG. 6</figref> example may be the same as or similar to that of the <figref idref="DRAWINGS">FIG. 5</figref> example described above, and may be configured and/or positioned on the <figref idref="DRAWINGS">FIG. 6</figref> example in a similar manner. The <figref idref="DRAWINGS">FIG. 6</figref> component <b>72</b> may be dissolvable, frangible or otherwise dispersible, and/or may include the retarder chemical <b>28</b> therein. The retarder chemical <b>28</b> may leach from the component <b>72</b>, or the retarder chemical may be released by opening of a container of the component (such as, by dissolving or breaking the container or another barrier, etc.).

0083In operation with the system <b>10</b> and method example of <figref idref="DRAWINGS">FIGS. 4A-C</figref>, the well tool <b>26</b> of <figref idref="DRAWINGS">FIG. 6</figref> is used for each of the well tools other than the one closest to the distal end <b>30</b> of the casing string <b>16</b>. As described above, a wiper plug (such as a five wiper plug, not shown) follows the cement <b>18</b> through the casing string <b>16</b> and eventually lands in the float collar <b>24</b>. Thus, the cement <b>18</b> is placed in the annulus <b>20</b>, and a lower end of the casing string <b>16</b> is sealed off, thereby allowing pressure in the casing string to be increased above hydrostatic.

0084If the retarder chemical <b>28</b> is released from the component <b>72</b> of the <figref idref="DRAWINGS">FIGS. 5 &amp; 6</figref> well tools <b>26</b>, the retarder chemical prevents the cement <b>18</b> external to the well tools <b>26</b> from setting (or substantially retards such setting). However, the cement <b>18</b> in portions of the annulus <b>20</b> not exposed to the retarder chemical <b>28</b> is allowed to set.

0085After the cement <b>18</b> has set in portions of the annulus <b>20</b> not exposed to the retarder chemical <b>28</b> (if any), pressure in the casing string <b>16</b> is increased, until a predetermined pressure is reached. This opens the valve <b>40</b> of the lowermost well tool <b>26</b>, as described above, and the formation zone <b>14</b><i>a </i>is fractured. If the component <b>72</b> remains on the lowermost well tool <b>26</b> when the valve <b>40</b> is opened, the fluid(s) flowed through the ports <b>50</b> may cause the component to dissolve, break or otherwise disperse.

0086After the formation zone <b>14</b><i>a </i>is fractured, a plug <b>62</b> is released into the flow passage <b>42</b>, and the plug engages the plug seat of the well tool <b>26</b> corresponding to the formation zone <b>14</b><i>b. </i>Pressure in the flow passage <b>42</b> above the plug <b>62</b> is increased until a sufficient pressure differential is created across the plug to shear the shear member <b>58</b> and displace the sleeve <b>44</b> downward, thereby opening the valve <b>40</b>.

0087Fluid communication is now permitted between the flow passage <b>42</b> and the exterior of the well tool <b>26</b>, and fracturing fluid can be flowed through the ports <b>50</b> to the zone <b>14</b><i>b </i>through the cement <b>18</b> exterior to the well tool <b>26</b> with sufficient pressure to fracture the zone. If the component <b>72</b> remains on the well tool <b>26</b> when the valve <b>40</b> is opened, the fluid(s) flowed through the ports <b>50</b> may cause the component to dissolve, break or otherwise disperse.

0088If the retarder chemical <b>28</b> was released from the component <b>72</b>, unset cement <b>18</b> external to the well tool <b>26</b> provides for direct fluid communication and application of fracturing pressure to the zone <b>14</b><i>b. </i>If the component <b>72</b> is dispersed, then the resulting void <b>74</b> external to the ports <b>50</b> provides for ready communication of fluid pressure to the cement <b>18</b> external to the well tool <b>26</b> and, if the cement is set, the cement can be readily broken down by such pressure to thereby provide direct fluid communication to the zone <b>14</b><i>b. </i>Note that, in some examples, the retarder chemical <b>28</b> may be released from the component <b>72</b>, and the component may be dispersed.

0089After the formation zone <b>14</b><i>b </i>is fractured, the steps of releasing a plug <b>62</b> into the flow passage <b>42</b>, applying pressure to the flow passage above the plug and fracturing the respective zone can be repeated for each of the well tools <b>26</b> corresponding to the zones <b>14</b><i>c,d. </i>Eventually, all of the zones <b>14</b><i>a</i>-<i>d </i>are fractured as depicted in <figref idref="DRAWINGS">FIG. 4C</figref>. Note that the plug <b>62</b> and plug seat <b>64</b> used to open the valve <b>40</b> of each successive well tool <b>26</b> will have an incrementally larger size (e.g., the first plug released will have the smallest size, the next plug released will have an incrementally larger size, etc., and the last plug released will have the largest size). The plugs <b>62</b> and plug seats <b>64</b> can subsequently be drilled out.

0090If the component <b>72</b> in the <figref idref="DRAWINGS">FIGS. 4A-6</figref> examples disperses and the voids <b>74</b> are thereby formed, and if the voids extend completely about the well tools <b>26</b>, then an advantage is obtained in that a plane of minimum principal stress in the formation <b>14</b> will necessarily intersect the voids. Since the voids <b>74</b> provide for enhanced application of fluid pressure to the cement <b>18</b> external to the well tools <b>26</b>, and to the formation zones <b>14</b><i>a</i>-<i>d </i>external to the cement, the voids will also provide for enhanced application of fluid pressure to a plane of minimum principal stress at each zone, thereby reducing a pressure that would otherwise need to be applied in order to produce a fracture in the zone.

0091It may now be fully appreciated that the above disclosure provides significant advancements to the art of providing fluid communication with an earth formation through cement. In some examples described above, a well tool <b>26</b> can include a retarder chemical <b>28</b> that prevents (or at least retards) setting of cement <b>18</b> external to the well tool. In other examples described above, a well tool <b>26</b> can include a component <b>72</b> that releases the retarder chemical <b>28</b> and/or disperses to thereby form a void <b>74</b> and provide for enhanced communication with the formation <b>14</b>.

0092The above disclosure provides to the art a system <b>10</b> for use with a well. In one example, the system <b>10</b> can comprise a well tool <b>26</b> including a retarder chemical <b>28</b>, and casing connectors <b>32</b> at opposite ends of the well tool. The retarder chemical <b>28</b> is released from the well tool <b>26</b> into an annulus <b>20</b> surrounding the well tool and retards setting of a cement <b>18</b> in the annulus.

0093The retarder chemical <b>28</b> may be released from an internal chamber <b>34</b> of the well tool <b>26</b>.

0094The retarder chemical <b>28</b> may be released from an exterior of the well tool <b>26</b>.

0095The retarder chemical <b>28</b> may be released from an exterior component <b>72</b> of the well tool <b>26</b>, the exterior component being exposed to the cement <b>18</b>. The exterior component <b>72</b> may dissolve in response to exposure to the cement <b>18</b>.

0096The exterior component <b>72</b> may be annular-shaped. The retarder chemical <b>28</b> may leach from the exterior component <b>72</b>.

0097The retarder chemical <b>28</b> may be released in response to application of pressure to an interior of the well tool <b>26</b>.

0098The well tool <b>26</b> can include a valve <b>40</b> that selectively prevents and permits fluid communication between the annulus <b>20</b> and an interior flow passage <b>42</b> that extends longitudinally through the well tool <b>26</b>. The retarder chemical <b>28</b> may be released in response to application of a first pressure to the interior flow passage <b>42</b>, and the valve <b>40</b> may be opened in response to application of a second pressure to the interior flow passage <b>42</b>, with the second pressure being greater than the first pressure.

0099The retarder chemical <b>28</b> may be released in response to application of a predetermined pressure to the interior flow passage <b>42</b>. The valve <b>40</b> may be opened in response to placement of a plug <b>62</b> in the interior flow passage <b>42</b> and application of a predetermined pressure differential across the plug.

0100A method of retarding setting of a cement <b>18</b> at one or more discrete locations in a well annulus <b>20</b> is also provided to the art by the above disclosure. In one example, the method comprises releasing a retarder chemical <b>28</b> from at least one well tool <b>26</b> connected in a casing string <b>16</b>. The releasing step is performed after the cement <b>18</b> is placed in the annulus <b>20</b>.

0101The releasing step can include releasing the retarder chemical <b>28</b> into the annulus <b>20</b> only proximate the at least one well tool <b>26</b>.

0102The releasing step can include releasing the retarder chemical <b>28</b> from an internal chamber <b>34</b> of the well tool <b>26</b>.

0103The releasing step can include releasing the retarder chemical <b>28</b> in response to application of pressure to the well tool <b>26</b>.

0104The releasing step can include releasing the retarder chemical <b>28</b> from an exterior component <b>72</b> of the well tool <b>26</b>. The releasing step can include the retarder chemical <b>28</b> leaching from the exterior component <b>72</b>. The releasing step can include the exterior component <b>72</b> dissolving.

0105The releasing step can be performed after flowing of the cement <b>18</b> into the annulus <b>20</b> is ceased.

0106The method can also include opening a valve <b>40</b>, thereby permitting fluid communication between the annulus <b>20</b> and an interior flow passage <b>42</b> extending through the well tool <b>42</b>. The opening step can be performed after the releasing step.

0107The releasing step can include releasing the retarder chemical <b>28</b> into the annulus <b>20</b> at a position between a distal end <b>30</b> of the casing string <b>16</b> and a port <b>50</b> of the valve <b>40</b>.

0108A well tool <b>26</b> is also described above. In one example, the well tool <b>26</b> can comprise a valve <b>40</b> that selectively prevents and permits fluid communication via a port <b>50</b> between an exterior of the well tool <b>26</b> and an interior flow passage <b>42</b> extending longitudinally through the well tool, an annular recess <b>76</b>, and an annular dispersible exterior component <b>72</b> received in the annular recess <b>76</b>.

0109The exterior component <b>72</b> may be dissolvable in response to contact with a fluid (such as the cement <b>18</b>). The exterior component <b>72</b> may be positioned external to the port <b>50</b>.

0110The exterior component <b>72</b> may include a retarder chemical <b>28</b>. The retarder chemical <b>28</b> may leach from the exterior component <b>72</b>.

0111The valve <b>40</b> may open in response to application of a predetermined pressure to the interior flow passage <b>42</b>.

0112The valve <b>40</b> may open in response to application of a predetermined pressure differential across a plug <b>62</b> placed in the interior flow passage <b>42</b>.

0113Also described above is another well tool <b>26</b> example that can include a valve <b>40</b> that selectively prevents and permits fluid communication between an exterior of the well tool <b>26</b> and an interior flow passage <b>42</b> extending longitudinally through the well tool, an internal chamber <b>34</b>, and a retarder chemical <b>28</b> disposed in the internal chamber <b>34</b>.

0114The well tool <b>26</b> can also include a discharge opening <b>36</b>. The retarder chemical <b>28</b> may be discharged to an exterior of the well tool <b>26</b> via the discharge opening <b>36</b>.

0115The retarder chemical <b>28</b> may be discharged from the well tool <b>26</b> in response to a first predetermined pressure applied to the interior flow passage <b>42</b>. The valve <b>40</b> may be opened in response to a second predetermined pressure applied to the interior flow passage <b>42</b>, the second pressure being greater than the first pressure.

0116The valve <b>40</b> may be opened in response to a predetermined pressure differential applied across a plug <b>62</b> placed in the interior flow passage <b>42</b>.

0117Although various examples have been described above, with each example having certain features, it should be understood that it is not necessary for a particular feature of one example to be used exclusively with that example. Instead, any of the features described above and/or depicted in the drawings can be combined with any of the examples, in addition to or in substitution for any of the other features of those examples. One example's features are not mutually exclusive to another example's features. Instead, the scope of this disclosure encompasses any combination of any of the features.

0118Although each example described above includes a certain combination of features, it should be understood that it is not necessary for all features of an example to be used. Instead, any of the features described above can be used, without any other particular feature or features also being used.

0119It should be understood that the various embodiments described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of this disclosure. The embodiments are described merely as examples of useful applications of the principles of the disclosure, which is not limited to any specific details of these embodiments.

0120In the above description of the representative examples, directional terms (such as “above,” “below,” “upper,” “lower,” etc.) are used for convenience in referring to the accompanying drawings. However, it should be clearly understood that the scope of this disclosure is not limited to any particular directions described herein.

0121The terms “including,” “includes,” “comprising,” “comprises,” and similar terms are used in a non-limiting sense in this specification. For example, if a system, method, apparatus, device, etc., is described as “including” a certain feature or element, the system, method, apparatus, device, etc., can include that feature or element, and can also include other features or elements. Similarly, the term “comprises” is considered to mean “comprises, but is not limited to.”

0122Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the disclosure, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of this disclosure. For example, structures disclosed as being separately formed can, in other examples, be integrally formed and vice versa. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the invention being limited solely by the appended claims and their equivalents.