Abstract:
A wellbore junction isolation method and associated apparatus provide convenient isolation of a wellbore junction while permitting certain operations to be performed in a wellbore below the junction. In a described embodiment, a formation intersected by a main wellbore below a wellbore junction is stimulated by fracturing after installing an assembly at the wellbore junction to isolate it from pressures applied during the fracturing operation. In this embodiment, the assembly is installed in a single trip into the main wellbore.

Description:
BACKGROUND 
     The present invention relates generally to operations performed in conjunction with a subterranean well and, in an embodiment described herein, more particularly provides a wellbore junction isolation method and associated apparatus. 
     Wellbore junctions are formed at intersections of wellbores in a well. For example, a main or parent wellbore may have a branch or lateral wellbore drilled extending outwardly from an intersection between the main and branch wellbores. Of course, the main wellbore may extend below the intersection with the branch wellbore, for example, to intersect a formation from which it is desired to produce hydrocarbons into the main wellbore. 
     Unfortunately, however, some wellbore junctions are not able to withstand substantial internal pressure applied thereto. For this reason, pressure within these wellbore junctions is limited to the fracture gradients of the respective formations in which the wellbore junctions are positioned. Thus, if stimulation operations, such as fracturing, must be performed for any formations below the wellbore junctions, expensive, time-consuming and/or complicated procedures must be used to prevent exceeding the fracture gradients of the formations at the wellbore junctions. 
     Therefore it would be quite desirable to provide a method of isolating a wellbore junction which is convenient and easily performed, and which isolates the wellbore junction from pressures applied through the junction. 
     SUMMARY 
     In carrying out the principles of the present invention, in accordance with an embodiment thereof, a method of isolating a wellbore junction is provided in which an isolating assembly is positioned at the wellbore junction and sealingly engaged in a wellbore. The assembly isolates at least one flow passage extending therethrough from the wellbore junction. Pressure may then be applied to the flow passage without that pressure being communicated to the wellbore junction. 
     In one aspect of the invention, the assembly includes two sealing devices which are sealingly engaged between the assembly and one of the wellbores intersecting at the wellbore junction. The sealing devices are sealingly engaged straddling the wellbore junction. In this manner, an annulus formed between the assembly and the wellbore in which the sealing devices are sealingly engaged is divided into three portions, a middle one of which is in fluid communication with the wellbore junction. 
     In another aspect of the invention, the other two annulus portions are in fluid communication with each other via another flow passage formed through the assembly. Thus, a circulation flowpath is formed between the annulus portions above and below the wellbore junction extending through the assembly. 
     In yet another aspect of the invention, the assembly is conveniently installed in a single trip into the well. A particular embodiment described herein includes inner and outer tubular structures, with the sealing devices on the outer structure, and the inner structure sealed to the outer structure above and below the sealing devices. 
     These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of a representative embodiment of the invention hereinbelow and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a method embodying principles of the present invention; and 
     FIG. 2 is an enlarged scale schematic view of the method of FIG. 1, wherein an apparatus embodying principles of the present invention is being utilized in the method. 
    
    
     DETAILED DESCRIPTION 
     Representatively illustrated in FIG. 1 is a method  10  which embodies principles of the present invention. In the following description of the method  10  and other apparatus and methods described herein, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used only for convenience in referring to the accompanying drawings. Specifically, the term “above” is used herein to designate a direction toward the earth&#39;s surface along a wellbore, and the term “below” is used herein to designate a direction away from the earth&#39;s surface along a wellbore, even though the wellbore may not be substantially vertical. Additionally, it is to be understood that the various embodiments of the present invention 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 the present invention. 
     Referring now to FIG. 1, the method  10  is described herein as being performed at a wellbore junction  16  formed by an intersection between a main wellbore  12  and a branch wellbore  14 . The wellbores  12 ,  14  are depicted in FIG. 1 as being cased or lined, but it is to be clearly understood that the principles of the invention may be incorporated into other methods performed in uncased or unlined wellbores. Furthermore, the principles of the invention are not limited to wellbore junctions formed between main and branch wellbores. 
     As illustrated in FIG. 1, the main wellbore  12  extends below the wellbore junction  16  to intersect a formation or zone  18 . It is desired to perform a stimulation operation, such as fracturing, on the formation  18  to thereby increase production of hydrocarbons therefrom. However, it is also desired not to apply excessive internal pressure to the wellbore junction  16 . Of course, the principles of the invention may be incorporated into other methods in which it is not desired to produce hydrocarbons from a formation, or in which it is not desired to perform stimulation operations. 
     Referring additionally now to FIG. 2, a somewhat enlarged view of the wellbores  12 ,  14  and the junction  16  therebetween is representatively illustrated. Further steps of the method  10  have been performed in which a wellbore isolation assembly  20  is installed in the main wellbore  12  in a single trip. The assembly  20  is installed by conveying it into the wellbore  12  suspended from a work string  22 . 
     The assembly  20  includes an outer tubular structure  24  and an inner tubular structure  26 . For example, the outer structure  24  may include one or more lengths of liner and the inner structure  26  may include one or more lengths of tubing. A flow passage  28  is formed through the inner structure  26  and another flow passage  30  extends in the space between the inner and outer structures  24 ,  26 . 
     The inner structure  26  is connected and sealed to the outer structure  24  at to a three-way tubular connector  32 . The connector  32  is also the point at which the work string  22  is attached to the assembly  20 . The inner structure  26  is also sealed to the outer structure at a seal  34 . Preferably, the seal  34  is an o-ring seal or packing received in a polished bore formed in the outer structure  24 , but other types of seals may be used without departing from the principles of the invention. 
     The outer structure  24  further includes two ported subs  36 ,  38  and two sealing devices  40 ,  42 . An upper one of the ported subs  36  is positioned between an upper one of the sealing devices  40  and the connector  32 . A lower one of the ported subs  38  is positioned between a lower one of the sealing devices  42  and the seal  34 . When the sealing devices  40 ,  42  are sealingly engaged in the main wellbore  12  as depicted in FIG. 2, the upper ported sub  36  provides fluid communication between the flow passage  30  and an annulus  44  formed between the assembly  20  and the wellbore  12  above the upper sealing device  40  via one or more ports in a sidewall of the upper ported sub, and the lower ported sub  38  provides fluid communication between the flow passage  30  and the annulus  44  below the lower sealing device  42  via one or more ports in a sidewall of the lower ported sub. 
     Preferably, the sealing devices  40 ,  42  are of the type well known to those skilled in the art as cup packers. However, other types of sealing devices may be utilized in keeping with the principles of the invention. In the method  10 , the packers  40 ,  42  are positioned so that they straddle the wellbore junction  16  and thereby seal between the assembly  20  and the wellbore  12  above and below its intersection with the wellbore  14 . In this manner, the annulus  44  is divided into three portions, a middle one of which is in fluid communication with the wellbore junction  16  external to the assembly  20 . The upper and lower annulus  44  portions are in fluid communication with the flow passage  30  via the ported subs  36 ,  38 . 
     To perform a fracturing operation, a slurry (indicated by arrows  46 ) including fluid and proppant is pumped down the work string  22 , through the flow passage  28  and into the formation or zone  18 . Return circulation of fluid (indicated by arrows  48 ) is directed from the annulus  44  below the lower packer  42  to the flow passage  30  through the lower ported sub  38 , and then from the flow passage  30  to the annulus  44  above the upper packer  40  through the upper ported sub  36 . 
     Note that the method  10  permits two flow passages  28 ,  30  to be positioned across the wellbore junction  16 , the flow passages being isolated from each other and from the junction in the assembly  20 , and permits the annulus  44  above and below the assembly to be isolated from the junction  16 . This result is accomplished in only one trip into the well. 
     Of course, a person skilled in the art would, upon a careful consideration of the above description of a representative embodiment of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to this specific embodiment, and such changes are contemplated by the principles of the present invention. 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 present invention being limited solely by the appended claims.