Sealed multilateral junction system

#The present invention relates generally to operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a method of forming sealed wellbore junctions.

#Many systems have been developed for connecting intersecting wellbores in a well. Unfortunately, these systems typically involve methods which unduly restrict access to one or both of the intersecting wellbores, restrict the flow of fluids, are very complex or require very sophisticated equipment to perform, are time-consuming in that they require a large number of trips into the well, do not provide secure attachment between casing in the parent wellbore and a liner in the branch wellbore and/or do not provide a high degree of sealing between the intersecting wellbores.

#For example, some wellbore junction systems rely on cement alone to provide a seal between the interior of the wellbore junction and a formation surrounding the junction. In these systems, there is no attachment between the casing in the parent wellbore and the liner in the branch wellbore, other than that provided by the cement. These systems are acceptable in some circumstances, but it would be desirable in other circumstances to be able to provide more secure attachment between the tubulars in the intersecting wellbores, and to provide more effective sealing between the tubulars.

#FIG. 1 is a cross-sectional view of a method of forming a wellbore junction which embodies principles of the present invention and wherein a tubular structure has been cemented within a parent wellbore;

#FIG. 2 is an enlarged cross-sectional view of the method wherein a branch wellbore has been drilled through the tubular structure utilizing a whipstock positioned in the tubular structure;

#FIG. 3 is a cross-sectional view of the method wherein a tubular string is being installed in the branch wellbore;

#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. 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.

#As depicted in FIG. 1, several steps of the method 10 have already been performed. A parent wellbore 12 has been drilled and a tubular structure 14 has been positioned in the parent wellbore. The tubular structure 14 is part of a casing string 16 used to line the parent wellbore 12.

#It should be understood that use of the terms “parent wellbore” and “casing string” herein are not to be taken as limiting the invention to the particular illustrated elements of the method 10. The parent wellbore 12 could be any wellbore, such as a branch of another wellbore, and does not necessarily extend directly to the earth's surface. The casing string 16 could be any type of tubular string, such as a liner string, etc. The terms “casing string” and “liner string” are used herein to indicate tubular strings of any type, such as segmented or unsegmented tubular strings, tubular strings made of any materials, including nonmetal materials, etc. Thus, the reader will appreciate that these and other descriptive terms used herein are merely for convenience in clearly explaining the illustrated embodiments of the invention, and are not used for limiting the scope of the invention.