Wells – Processes – Parallel string or multiple completion well
Reexamination Certificate
1999-11-24
2001-07-03
Dang, Hoang (Department: 3672)
Wells
Processes
Parallel string or multiple completion well
C166S050000, C166S117600, C166S207000, C166S242100, C166S381000
Reexamination Certificate
active
06253852
ABSTRACT:
TECHNICAL FIELD
This invention relates in general to the construction of a lateral branch for a primary well and particularly to a junction member which sealingly connects the main borehole casing and the branch liner casing.
BACKGROUND ART
In recent years, well construction technology has yielded substantial increases in well productivity with the spread of horizontal drilling for the bottom end section of the well. Unfortunately horizontal drilled wells provide limited zonal isolation and do not always permit good completion practices regarding the independent production of different production zones. Research efforts are now concentrating on the possibility of drilling lateral branches either inclined or horizontal from a primary well to enhance further reservoir productivity. Also lateral branches open the potential of tapping several smaller size reservoirs spread around from one single well without the need to sidetrack and redrill the well when moving the production from one production zone to the next. The challenge with multilateral completion is to install a junction apparatus having adequate internal and external pressure capability without relying only on the strength of the local rock formations.
Some prior art junction apparatus designs are based on a low angle side branch casing connected to a window on the main borehole casing. Some prior proposals require in situ milling of a window or a section in the main borehole casing. Milling steel casing downhole is a difficult task. Also, while there are numerous proposals for sealing the branch liner casing to the window, improvements are needed. One design deforms a complete junction assembly to offer a diameter equal or less than the diameter of the main borehole casing and expanding it in situ to the full cylindrical shape. In that design, the junction assembly may be elastomeric or memory metal. The junction assembly is expanded within an enlarged section of the well formed after a section of the casing is milled out.
Due to the side window based connecting link between the main borehole casing and the branch outlet, all these configurations offer poor internal pressure capacity and even more limited collapse capability when the junction is located in unconsolidated or weakly consolidated formations. The poor internal pressure capability and resistance to collapsing exists even when they are fully cemented since cement does not work well in traction. It is therefore highly desirable to have a junction apparatus offering good internal pressure and collapse capability to permit a wide freedom in the location of lateral junction independent from the strength of the cementing job and/or surrounding rock formation.
SUMMARY OF INVENTION
The junction apparatus in this invention has an upper section that connects to an upper string of casing. A pair of branch sections join each other at a junction with each other and with a lower end of the upper section. Each branch connects to a lower string of casing. The apparatus is forced into a collapsed configuration prior to running into the well. While in the well, the apparatus is expanded back to an expanded configuration. While in the collapsed position, a lower portion of the upper section is deformed so that a pair of deep depressions or bights locates on the outer side, the depressions being 180 degrees apart from each other and facing in opposite directions. Also, these depressions extend into an upper portion of the branch sections.
In addition, a support member is joined to the upper section at the junction, the support member having a tail section that extends between the branch sections. The support member has arms that extend upward and join the upper section. The tail section comprises a pair of braces interconnected by a web. The web defines an inner separation wall between the two branch sections and preferably has a portion of substantially constant thickness.
While in the well, internal pressure is applied to force the depressions to disappear.
The upper section will expand in diameter. The branch sections move outward and assume a cylindrical configuration.
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Bracewell & Patterson LLP
Bradley James E.
Dang Hoang
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