Patent Application
20160061002
In the oilfield it has become common practice to drill a well that intersects numerous formations or portions of formations. Sometimes the well may be primarily vertical and sometimes the well may have a significant horizontal section. Once the wellbore has been drilled it is usually necessary to case the well. In the past the casing was typically a number of joints of solid pipe joined together and then run into the wellbore. Once the casing had been located in the wellbore it was then cemented in place by forcing cement through the interior of the pipe, out of the toe of the pipe, and back up around the annular area formed between the casing and the wellbore itself.
With the casing cemented in the well the interior of the pipe casing was effectively sealed from allowing any fluids to flow from the formations to the interior will. The typical practice to access the formations from the interior of the casing has been an operation referred to as plug and perf. In a plug and perf operation a bridge plug with the setting tool top of it and the perforating gun on top of the setting tool are run into the well. Once the bridge plug was located below the lower end of the desired formation zone the bridge plug was set by the setting tool thereby sealing the casing at the bridge plug and preventing any fluid from passing below the bridge plug. The setting tool is then released from the bridge plug in the setting tool and perf gun are raised some distance above the bridge plug. Once the perf gun is located adjacent to the formation to which access is desired to perf gun is fired. The perf gun is a set of shaped charges that when fired are able to pierce the casing and penetrate some distance past the casing into the formation thereby allowing fluid in the formation to flow to the interior of the casing and vice versa. Once the formation is accessed, the perf gun and setting tool are removed from the casing. Fluid is then pumped down the wellbore at high pressure, out through the perforations in the casing and into the formation, which in turn fractures the formation. Once the fracturing operation is complete the pumps at the surface are turned off. A new bridge plug setting tool and perf gun are assembled at the surface and then run into the casing. Once the second bridge plug is located below the second-highest formation, from the toe of the well, the bridge plug is set and the process is repeated until all of the various formations have been fractured. Once all of the formations are fractured, access to the lower formations through the bridge plug is necessary, therefore the usual practice is to run a drill back into the casing and drill out all of the intervening bridge plugs thereby allowing full bore access to all of the formations.
In order to avoid the costs associated with drilling out multiple bridge plugs, a slightly newer practice is to include a number of sliding sleeves in the casing before the casing is run into the well bore and cemented in place. Typically each sliding sleeve has a seat in the sliding sleeve. The seats are arranged so that the smallest diameter sliding sleeve seat is closest to the toe and the largest diameter sliding sleeve seat is closest to the surface. Each sliding sleeve is placed in the casing so that when the casing is run into the wellbore the appropriate sliding sleeve will be adjacent to the formation from which access is desired. When the operator then desires to fracture a particular formation a ball is pumped through the casing. The diameter of the ball is chosen so that it will pass through each of the larger diameter seats in the sliding sleeves closer to the surface but once it gets to the lowest sliding sleeves the ball will seat and allow no further fluid flow to pass the particular sleeve in which it is seated. Fluid pressure on the surface is then increased causing force to be exerted against the ball and its seat thereby opening the attached sliding sleeve. Once the sliding sleeve is open, the formation adjacent the sliding sleeve may then be fractured. After fracturing the formation a slightly larger diameter ball that corresponds to the seat in the next higher sleeve is pumped through the casing where the ball lands in the sleeve and the process is repeated until all of the sliding sleeves have been opened and formations fractured. After the fracturing operations are completed the balls may be allowed to flow out of the well or dissolve to allow access to the formations.
Unfortunately because the diameter of the casing has been restricted by the increasingly smaller diameters of the sleeve towards the toe of the well fracture pressure into the lower formations and production out of the lower formations is inhibited. Another issue that operators run into when they use progressively larger balls from the toe towards the heel is due to the diametric limitations of the number of balls that will fit, and hence a limited ability to be able to treat and access as many zones as possible from a single wellbore. In order to maximize the number of sliding sleeve that may be used in a well the variations from a smaller ball size to next larger ball size is kept as low as possible. Typically a ⅛ inch variation between ball sizes is seen. The limitation on size variation is due to the constraints posed by the material of the sliding sleeves ball seat, the ball itself, and the force applied to the ball and then transferred to the ball seat. For instance a ball seat may be cast-iron whereas the ball may be aluminum, plastic, composite, dissolvable, or other appropriate material. After the ball reaches the sleeve and lands on the seat pressure is applied against the ball and through the ball to the seat in order to overcome any biasing device and shift the sleeve open. However it must be kept in mind will that all of the force applied against the ball is transferred to the seat only through the balls ⅛ inch periphery that is in contact with the seat. Therefore only a limited amount of force may be applied to the ball before either the ball deforms or the periphery of the ball shears thereby allowing the ball to pass through the seat thus causing the failure of the particular sleeve.
In order to overcome at least the aforementioned issues an embodiment of the present invention incorporates a dart having at least one spline lengthwise on its periphery to solve both of these problems. The spline is a protrusion outward from the surface of the dart that may be merely a key but typically is set at a slight angle to the direction of movement of the dart. The key may be forward angled or back angled but is usually tapered from a small width on its lower end to a larger width on its upper end.
The dart's tapered key may be referred to as a a tapered spline where the spline will be wider on the upper end of the dart and narrower on the lower end of the dart. The width of the spline corresponds to a particular seat in a particular sleeve or tool downhole and thereby determines which seat the dart will engage and thus which tool will be actuated. The length of the spline determines how much force may be applied against the dart when actuating the tool or when fracking into the formation.
A seat that cooperates with the dart is utilized in the downhole tool. Slightly upstream of the seat is an orienting device. The orienting device interacts with the spline on the dart to rotate the dart, if necessary, such that the spline will slide in place in the cooperative keyway in the seat. As the spline seats in the keyway the angled surface of the spline and its cooperating keyway can be constructed to provide sufficient bearing area to prevent the dart from passing through the seat in the presence of sufficient pressure to fracture the formation.
The dart is able to locate the correct seat as a function of the maximum circumferential width of the spline as compared to the minimum circumferential width of the keyway. Such that as the dart moves downhole if the spline is too slender to engage the keyway then the dart will pass through the sleeve without engaging the seat. In other words the dart passes through other seats on tools closer to the surface than the particular seat for which the dart is sized to land in. Upon reaching the particular seat the spline on the dart first interacts with orienting device. The orienting device turns the dart to align the spline with the keyway then, provided that the spline is wide enough, the spline and keyway will engage allowing the dart to open the sleeve.
The description that follows includes exemplary apparatus, methods, techniques, or instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details.
An additional benefit of having a spline 12 with a first width 24 that increases to a larger width 26 and where that spline 12 seats in the slot 60 that also tapers from a narrower width 68 to a wider width 66 is the large load carrying capability between the spline 12 in the slot 60. The load carrying capability between the spline 12 and the slot 60 is due to the increased bearing area which is a function of the length of the spline and slot interface. In the instance that an increased load carrying capability is required, the load carrying capability of the slot and spline may be increased by lengthening the assemblies.
Usually multiple sliding sleeves 100 are used in a single well. In this event it is necessary to sequentially activate each sliding sleeve 100. Sequential activation begins by opening the sliding sleeve closest to the toe or bottom of the well and then fracturing the formation through the sliding sleeve. Thereafter actuating the next higher sliding sleeve fracturing the adjacent formation through the sliding sleeve and repeating the sequence until all sliding sleeves have been actuated.
In order to actuate a particular sliding sleeve the spline 12 on dart 10 has to cooperate with the orienting sleeve 50 and sliding sleeve 100. However the dart 50 must pass through any sliding sleeves that are in place above the targeted sliding sleeve 100. In order to pass through any sliding sleeves in place above the targeted sliding sleeve, the orienting sleeve utilized in any of the sliding sleeves above the targeted sliding sleeve must have a minimum width that exceeds the maximum width 26 of spline 12. By increasing the width of the spline required to seat in the slot of each higher sliding sleeve a large number of sliding sleeves may be sequentially actuated by a series of darts that each have the same outside diameter but with varying spline widths. For example assuming each spline has a 0.063″ taper and a 0.063″clearance between successive spline widths, Table 1 below illustrates the number of tapered profile slots achievable in an orienting profile with a 4.5″ interior diameter.
In other embodiments of the slot actuated downhole device subassemblies that include the orienting sleeve may be incorporated into the casing string. By including orienting sleeve subassemblies in various predetermined locations in the casing a dart dropped from surface would create a temporary plug in the tubing/casing inner diameter isolating particular zones thereby replacing traditional bridge plugs and allowing operators to merely perforate the casing above the temporary plug allowing a multi-zone fracture stimulation in a manner similar to the more traditional plug and perforate operations.
While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible.
Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.
