Patent Application
20080271925
1. Field of the Invention
The present invention generally relates to a coiled tubing bottom hole assembly used to create an acid tunnel in a wellbore formation such that the tunnel is substantially transverse to the wellbore. Acid is pumped at a high pressure down the coiled tubing and out of a nozzle located on the end of a wand located at the end of the bottom hole assembly. The acid exits the nozzle and dissolves the formation creating a tunnel in the formation. The bottom hole assembly positions the nozzle so that the tunnel is substantially transverse to the wellbore. Multiple tunnels may be created in an attempt to increase the hydrocarbon production of the wellbore.
The bottom hole assembly also includes a first knuckle joint and a second knuckle joint to properly position the nozzle against the wellbore. The knuckle joints may be pressure operated and may increase the radius of curvature of the bottom hole assembly while providing a sufficient “attack” angle for the nozzle against the wellbore. The attack angle needs to be sufficient to promote the creation of a tunnel into the formation rather than eroding the exterior of the wellbore. The use of two knuckle joints may ensure a proper attack angle. The use of two knuckle joints may also reduce the chance that the wand will cam lock as it passes through a curved portion of the acid tunnel. The two knuckle joints may be oriented such that the two joints bend within the same plane, which may help the bottom hole assembly to stay within the same plane throughout the formation of the acid tunnel.
The wand may include a telescoping or extending portion to aid in the formation of a tunnel. The nozzle may also be adapted to form an acid tunnel that is oriented to help keep the bottom hole assembly within the same plane as it moves along and creates the entire length of the acid tunnel.
2. Description of the Related Art
It has become common to stimulate a wellbore in an effort to increase the production of hydrocarbons. One method to stimulate an openhole wellbore is to create an acid tunnel that is substantially transverse to the wellbore. Acid tunneling, also referred to as chemically-enhanced drilling, is a process that uses a nozzle attached to a bottom hole assembly that is run into the wellbore with coiled tubing. Once the nozzle is located at the desired location within the wellbore, acid is pumped down the coiled tubing at a high pressure. The high pressure acid exits the nozzle and dissolves the formation adjacent to the nozzle creating a tunnel. The tunnel may be created at a specified location of the wellbore to extend beyond a damaged or non-producing portion of the well.
The bottom hole assembly preferably includes a knuckle joint used to angle the nozzle towards the side of the wellbore. The nozzle is typically located on the end of a wand connected to the knuckle joint. The diameter of the wellbore as well as the geometric configuration of the wand, nozzle, and bottom hole assembly dictate the angle at which the knuckle joint can be bent within the wellbore. The rigidity of the bottom hole assembly causes the bottom hole assembly to have a fixed radius of curvature. The radius of curvature is dictated by the length of the wand, the angle that the knuckle joint bends, and the length of the assembly from the knuckle joint to the coiled tubing connection. These dimensions define a fixed radius through which the bottom hole assembly may travel.
It is generally desired to create an acid tunnel that is substantially transverse to the wellbore so that the tunnel extends beyond a damaged area of the wellbore. It is also important that the tunnel be substantially traverse because it may be desirable to create multiple tunnels within the wellbore. It is important that the attack angle of the nozzle be sufficient to create a tunnel that is substantially transverse to the wellbore. The knuckle of the bottom hole assembly needs to position the nozzle against the wellbore to ensure that the flow of acid out of the nozzle begins to form a tunnel. If the attack angle is too shallow, the high pressure acid may simply widen the bore of the wellbore rather than creating a tunnel transverse to the wellbore. To encourage the creation of a tunnel, the knuckle joint is often configured to have a maximum bend angle of approximately fifteen degrees away from the center of the bottom hole assembly. A fifteen degree bend angle typically allows knuckle to bend causing the nozzle located on the end of the wand to come into contact with the wellbore. Typically, the knuckle will not be bent to its maximum angle until after the tunnel has begun to form. The angle required for the knuckle to contact the wellbore can be decreased by increasing the length of the wand. However, increasing the length of the wand also increases the chance that the wand may become cam locked as it traverse the wellbore and the tunnel entrance.
The coiled tubing is used to push the bottom hole assembly and increase the length of the acid tunnel. The bottom hole assembly is rigid and as discussed above, the geometry of the bottom hole assembly (i.e. the bend angle of the knuckle joint, the length of the wand, and the length from the coiled tubing to the knuckle joint) defines the radius of curvature or “build rate” of the bottom hole assembly. The build rate of the bottom hole assembly determines the “build angle” of the tunnel (i.e. how quickly the tunnel turns so that it is transverse to wellbore). Often it may be desirable to create multiple tunnels in a single wellbore. Thus, it is important to have a build rate in the tunnel that is as high as practically possible, but not so high that it exceeds the yield strength of the coiled tubing that is connected to the tunneling bottom hole assembly. For example, in a 6 inch diameter wellbore, the current bottom hole assembly for acid tunneling typically has a theoretical build rate of 300 degrees per 100 feet of tunnel. This theoretical build rate exceeds the yield radius of curvature of typical coiled tubing. It would thus be beneficial to provide a bottom hole assembly that has a lower build rate, but that also may position the nozzle against the wellbore to ensure a tunnel transverse to the wellbore is created, but with a higher initial starting angle.
Current bottom hole assemblies have been use to create acid tunnels of up to fifty feet or more in length without damaging the coiled tubing. As discussed above, the theoretical build rate of the current bottom hole assembly exceeds the elastic limit of coiled tubing. In theory, if a fifty foot tunnel is created with the maximum build rate of the current acid tunneling bottom hole assembly, then the coiled tubing would exceed yield and the force required to push the tunneling bottom hole assembly along the tunnel would exceed the buckling strength of the unsupported coiled tubing in the borehole. However, there have been instances where a fifty foot tunnel has been created without appreciable damage to the coiled tubing. One explanation for this occurrence is that the bottom hole assembly may have titled or twisted out of its original plane while creating the tunnel while at the same time creating an elongated slot that allows the bottom hole assembly to slide downwards rather than turning a corner. The bottom hole assembly most likely twisted out of plane due to the forces exerted upon the bottom hole assembly as the build rate approaches the coiled tubing's yield radius of curvature. These forces likely cause the bottom hole assembly to twist off its plane affecting the direction and location of the acid tunnel.
The twisting or tilting of the bottom hole assembly out of its original plane may cause the acid tunnel to be formed in an area other than its intended location. For example, the tunnel may not extend through the very damaged or non-producing zone as originally intended. The rotation of the bottom hole assembly may also cause the tunnel to travel substantially parallel with the wellbore rather than substantially transverse limiting the number of tunnels that may be created as well as limiting the beneficial affects from the acid tunnel.
In light of the foregoing, it would be desirable to provide a bottom hole assembly that has a reduced build rate, but still create a tunnel that is substantially transverse to the wellbore. It would further be desirable to provide a bottom hole assembly with two knuckle joints to increase the overall radius of curvature of the bottom hole assembly above the yield radius of curvature of the coiled tubing. It would be desirable to orient the two knuckle joints such that the joints would bend in the same plane. It may also be desirable to provide a bottom hole assembly with an extendable or telescopic wand to aid in the formation of an acid tunnel. It would also be desirable to provide a nozzle adapted to form an acid tunnel that encourages the bottom hole assembly to remain in its original plane as the acid tunnel is created.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.
The object of the present disclosure is to provide a bottom hole assembly having a larger radius of curvature than typical acid tunneling bottom hole assemblies with the bottom hole assembly still capable of creating an acid tunnel transverse to a wellbore. In one embodiment, an apparatus for creating an acid tunnel within a wellbore is disclosed. The apparatus includes a tool assembly having an upper end and a lower end, the tool assembly including an internal fluid passage. A coiled tubing connector connects the upper end of the tool assembly to coiled tubing. The coiled tubing is in fluid communication with the internal passage of the tool assembly.
The apparatus includes a first pressure operated knuckle joint connected to the lower end of the tool assembly. The first pressure operated knuckle joint includes a central bore that is in fluid communication with the internal passage of the tool assembly. The apparatus also includes a second pressure operated knuckle joint. The second pressure operated knuckle joint also includes a central bore that is in fluid communication with the central bore of the first pressure operated knuckle joint. The second pressure operated knuckle joint is located below the first knuckle joint. A member having a central fluid passage may connect the second pressure operated knuckle joint to the first pressure operated knuckle joint.
The apparatus further includes a wand having a first end, a second end, and a central bore. The first end of the wand is connected to the bottom of the second pressure operated knuckle joint. The central bore of the wand is in fluid communication with the central bore of the second pressure operated knuckle joint. A nozzle is connected to the second end of the wand. The nozzle being in fluid communication with the coiled tubing through the tool assembly, first knuckle joint, second knuckle joint, and the wand. Alternatively, a wand having at least one external port may be used in place of the disclosed nozzle and wand configuration as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure. Alternatively, the wand of the bottom hole assembly may be telescopic allowing the end of the wand to extend as the bottom hole assembly creates the acid tunnel.
The first pressure operated knuckle joint and the second pressure operated knuckle joint of the apparatus may be adapted to bend within the same plane. The use of two knuckle joints may provide that the radius of curvature of the apparatus be greater than the yield radius of curvature of coiled tubing. The apparatus of claim 2, wherein the maximum angle that first pressure operated knuckle joint and the second pressure operated knuckle joint may each bend is less than approximately ten degrees.
In another embodiment, a coiled tubing bottom hole assembly for acid tunneling in a wellbore the bottom hole assembly is disclosed. The bottom hole assembly includes a coiled tubing connector that connects the bottom hole assembly to coiled tubing. A nozzle is connected to the lower end of the coiled tubing bottom hole assembly and a first knuckle joint is connected above the nozzle. The first knuckle joint includes a bore that is in fluid communication with the nozzle. The bottom hole assembly includes a second knuckle joint connected to the bottom hole assembly. The second knuckle joint includes a bore and is positioned above the first knuckle joint and below the coiled tubing connector. The nozzle is in fluid communication with the coiled tubing through the bottom hole assembly, the second knuckle joint, and the first knuckle joint.
The knuckle joints may be pressure operated. The knuckle joints may be various non-torque bearing or torque bearing joints and may be actuated by various means as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure. The knuckle joints may be adapted to bend to a specific degree. The knuckle joints may be limited to bending less than approximately ten degrees from center. Preferably, the first and second knuckle joints are configured to bend collectively less than approximately fifteen degrees. The first knuckle joint and the second knuckle joint are preferably oriented to bend within substantially the same plane. This orientation may help to prevent the twisting of the bottom hole assembly off of its original build plane as it forms a tunnel.
The bottom hole assembly may further include a wand having a central bore, a first end, and a second end. The first end of the wand may be collected to the first knuckle with the second end of the wand being connected to the nozzle. The wand may include a telescoping or extending section that aids in the formation of the tunnel. The nozzle of the bottom hole assembly may includes a plurality of ports in an asymmetrical pattern. The asymmetrical pattern may be adapted to form an elliptical hole in a wellbore formation. Alternatively, the nozzle may include a plurality of ports in a symmetrical pattern with a plurality of flow channels in an asymmetrical pattern adapted to form an elliptical hole in the wellbore formation.
One embodiment of the invention is an apparatus used to create a transverse acid tunnel in a wellbore. The apparatus includes a bottom hole assembly that has an upper end and a lower end. The upper end of the assembly is connected to coiled tubing and the assembly further includes a fluid path through the assembly that is in communication with the coiled tubing. The apparatus also includes a means for jetting acid into the wellbore. The means for jetting acid is connected to the lower end of the bottom hole assembly and is in fluid communication with the coiled tubing through the bottom hole assembly. The bottom hole assembly further includes a first means for selectively bending the means for jetting acid towards the wellbore and a second means for selectively bending the means for jetting acid towards the wellbore.
The apparatus may also include means for extending the means for jetting acid away from the bottom hole assembly. Additionally, the first means for selectively bending may be adapted to bend in the same plane as the second means for selectively bending. The radius of curvature of the bottom hole assembly may be greater than the yield radius of curvature of coiled tubing due to the first means for selectively bending and the second means for selectively bending.
One embodiment of the invention is a method of creating an acid tunnel within a Wellbore. The method includes connecting a bottom hole assembly to coiled tubing and Positioning the bottom hole assembly at a desired location within the wellbore. The bottom hole assembly includes a first knuckle joint, a second knuckle joint, and a nozzle with the nozzle being located at the bottom end of the bottom hole assembly. The method further includes actuating the first knuckle joint to move the nozzle towards the wellbore and actuating a second knuckle of the bottom hole assembly so that the nozzle is substantially in contact with the wellbore method also includes pumping acid down coiled tubing and jetting the acid out of the nozzle to create an acid tunnel that is substantially transverse to the wellbore.
The method may also include extending the nozzle towards the acid tunnel. The nozzle may be extended by a telescopic section of a wand. The method may also include orienting the first knuckle joint and the second knuckle joint so that both knuckle joints bend within substantially the same plane. The method may include limiting the collective bend angle for both knuckle joints to less than approximately fifteen degrees. Alternatively, the method may include limiting the bend angle of the first knuckle joint to less than approximately ten degrees and limiting the bend angle of the second knuckle joint to less than approximately ten degrees.
The method may include the steps of pushing the coiled tubing to create a longer acid tunnel and pulling up the coiled tubing once the acid tunnel is a desired length. After the coiled tubing has been pulled up the method may include locating the nozzle at a different location within the wellbore. After being positioned at a different location, the method may include pumping acid down the coiled tubing and jetting acid out of the nozzle to create a second acid tunnel that is substantially transverse to the wellbore.
The method may include using a rotary indexing device in the top portion of the acid tunneling BHA to position the nozzle in a direction away from the previously formed tunnel to ensure that tunnels are spaced more effectively around the circumference of the wellbore.
While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Illustrative embodiments of the invention are described below as they might be employed in a bottom hole assembly having a radius of curvature that is greater than the yield radius of curvature of coiled tubing and that may be used to produce an acid tunnel transverse to a wellbore. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
Further aspects and advantages of the various embodiments of the invention will become apparent from consideration of the following description and drawings.
Acid is pumped at a high pressure down the coiled tubing and through the bottom hole assembly 100 until the acid exits the nozzle 170. The back pressure from the nozzle causes the pressure elbow 150 to be actuated positioning the nozzle 170 against the wellbore. At this position, the acid exiting the nozzle begins to dissolve the formation 20 creating a tunnel 30 as shown in
With the configuration shown in
l sin θ>D−d/2
The above formula illustrates that in order to have the nozzle 170 touch the side of the wellbore 10 the length I of the wand multiplied the sine of the angle θ must be greater than the diameter D of the wellbore minus ½ of the diameter d of the bottom hole assembly. Thus, increasing the wand length decreases the angle θ necessary to touch the wellbore. As discussed above, increasing the length of the wand 160 increases the chance that the bottom hole assembly 100 may become cam locked within the tunnel 30. However, increasing the initial kickover angle θ also decreases the radius of curvature such that the radius of curvature of the bottom hole assembly 100 may be smaller than the yield radius of the coiled tubing 5.
Once the tunnel is begun, the pressure elbow 150 is bent to its maximum kickover angle θ to increase the build angle of the tunnel as shown in
Acid may be pumped at a high pressure down the coiled tubing and through the bottom hole assembly 100 until the acid exits the nozzle 170. With the nozzle 170 positioned against the wellbore 10, the acid exiting the nozzle 170 begins to dissolve the formation 20 and create a tunnel 30 as shown in
The use of two knuckles 155, 156 increases the lateral displacement of the nozzle 170 with a smaller initial kickover angle θ1, θ2 for each knuckle. Assuming that the length 1 of the wand 160 is equal to the length between the first knuckle 155 and the second knuckle 156 and that the initial kickover angle θ1 for the first knuckle 155 is equal to the kickover angle θ2 for the second knuckle 156, the following equation may be used to determine the minimum kickover angle θ required for the nozzle 170 to touch the wall of the wellbore 10.
l(sin θ+sin 2θ)>D−d/2
The above formula illustrates that a smaller initial kickover angle is required to touch the nozzle 170 to the wall of the wellbore 10 when the bottom hole assembly 100 includes two knuckle joints 155, 156. The use of two knuckle joints provides that a smaller maximum kickover angle may be used for each knuckle joint without sacrificing a quick build angle for the tunnel. The use of two knuckle joints also permits a smaller maximum kickover angle may be used to create a tunnel substantially transverse to the wellbore. The use of smaller maximum kickover angles may be used to increase the radius of curvature of the bottom hole assembly above the yield radius of curvature of coiled tubing while still providing a sufficient attack angle and build angle.
Although various embodiments have been shown and described, the invention is not so limited and will be understood to include all such modifications and variations as would be apparent to one skilled in the art.
