Wells – Processes – Parallel string or multiple completion well
Reexamination Certificate
2001-11-06
2004-06-22
Bagnell, David (Department: 3672)
Wells
Processes
Parallel string or multiple completion well
C166S050000, C166S117600
Reexamination Certificate
active
06752211
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method and apparatus for the completion of multilateral wells, that is, when one or more lateral wells are drilled from a primary well bore, and more particularly to a new and improved method and apparatus for a junction between the primary well bore and a lateral well bore.
2. Background of the Invention
Multiple lateral bores are typically drilled and extended from a primary or main well bore. The main well bore can be vertical, deviated, or horizontal. Multilateral technology can be applied to both new and existing wells, and provides operators several benefits and economic advantages over drilling entirely new wells from the surface. For example, multilateral technology can allow isolated pockets of hydrocarbons, which might otherwise be left in the ground, to be tapped. In addition, multilateral technology allows the improvement of reservoir production, increases the volume of recoverable reserves, and enhances the economics of marginal pay zones. By using multilateral technology, multiple reservoirs can be produced simultaneously, thus facilitating heavy oil production. Thin production intervals that might be uneconomical to produce alone become economical when produced together with multilateral technology. Consequently, it has become a common practice to drill deviated, and sometimes horizontal, lateral boreholes from a primary wellbore in order to increase production from a well.
In addition to production cost savings, development costs also decrease through the use of existing infrastructure, such as surface equipment and the well bore. Multilateral technology expands platform capabilities where space is limited, and allows more well bores to be added to produce a reservoir without requiring additional drilling and production space on the platform. In addition, by sidetracking depleted formations or completions, the life of existing wells can be extended. Finally, multilateral completions accommodate more wells with fewer footprints, making them ideal for environmentally sensitive or challenging areas.
The primary wellbore may be sidetracked to produce the lateral borehole into another production zone. Further, a lateral wellbore may be sidetracked into a common production zone. In sidetracking, a whipstock and mill assembly is used to create a window in the wall of the casing of a wellbore. The lateral wellbore is then drilled through this window out into the formation where new or additional production can be obtained.
One of the objectives of a multilateral well is containment of the surrounding formation. Production from a lateral borehole can be difficult if the lateral borehole is drilled through a loose or unconsolidated formation. If the lateral borehole is drilled through an unstable or unconsolidated formation, the formation will tend to cave into the borehole. The formation can also slough off, causing deleterious debris to mix with the production fluids. Thus, it is preferred to contain the formation to prevent cave-ins and slough-offs.
Formations that contain a significant amount of shale can be a particular problem. If the bore surfaces at and near the junction are not covered with a liner, chips and aggregate in this area tend to be drawn into the produced fluids and foul the production. Unfortunately, lining the bore surfaces near the junction can be complex and time consuming. Various devices have been proposed to provide a junction at the interface of the primary and lateral wellbores.
There have been attempts to use a perforated insert through the window to allow production from both the primary bore and lateral bore while reducing contamination from chips and aggregate. The perforations are aligned with the primary bore and fluid from the primary bore passes through the perforations. Unfortunately, the perforations tend to become clogged by the chips and aggregate and allow the chips and aggregate to contaminate the product, thereby reducing the effectiveness of this type of insert. Also, the use of a perforated insert hinders the ability to reenter the main bore below the junction.
The junction of the lateral borehole with the primary wellbore is usually ragged and rough as a result of the milling of the window through the casing to drill the lateral borehole. It is particularly difficult to seal around the window which is of a peculiar shape and has a jagged edge around its periphery.
A large area is exposed to the formations when the window is cut in the casing. A tie-back assembly may be disposed adjacent the junction of the lateral borehole and primary wellbore. See for example U.S. Pat. No. 5,680,901. The tieback assembly and liner limit the exposure of the formation through the window cut in the casing.
U.S. Pat. No. 5,875,847 discloses a multilateral sealing device comprising a casing tool having a lateral root premachined and plugged with cement. A profile receives a whipstock for the drilling of the lateral bore hole through the lateral root and cement plug. A lateral liner is then inserted and sealed within the lateral root.
TAML (Technology Advancement Multi-Lateral) defines six levels for a multi-lateral junction for a lateral borehole. For example, level three merely includes a junction with the main casing and a liner extending into the lateral borehole without cementing or sealing the junction. If the liner is merely cemented at the junction, it is a level four since cement is not acceptable as a seal. Level four simply includes cement around the junction. Level five requires pressure integrity at the junction.
Prior art multilateral wells are sealed with cement using a method well-known to those with skill in the art and described hereinafter.
Level five includes seals used to achieve pressure integrity around the junction. For example, in level five, separate tubulars extend through the main borehole and through the lateral borehole. A packer is placed around the upper ends of these tubulars to pack off with the casing of the cased main borehole. The lower end of the tubular extending through the main tubular includes a packer for sealing with the main tubular below the junction, and the lower end of the other tubular extending through the lateral borehole seals with an outer tubular in the lateral borehole below the junction. The lateral borehole preferably has been previously cased so that a seal can be set with that tubular extending into the lateral borehole. Since there are separate tubulars and both bores are now packed off, there can be independent production from each bore without commingling. The pair of tubulars above the junction may extend all the way to the surface, or one well may be produced through a production pipe extending to the surface and the other well may be produced through the annulus formed by the casing and the production pipe extending to the surface.
Where the formation pressure is substantially the same in the pay zones being produced by the main and lateral boreholes, the hydrocarbons from the main and lateral boreholes may be commingled. However, it is sometimes desirable to separate production so that each well can be independently controlled, such as where the pay zone pressures are different. In that case, separate tubulars are used to produce the individual wells, as previously described in a level five junction, or one well may be plugged off if necessary. Whether production is commingled or independent has no bearing on how a multilateral well is classified.
If the formation is a solid formation, the lateral borehole, for example, need not even include a casing or liner and may be produced open hole. If the lateral borehole is unconsolidated or unstable and would tend to cave in, the lateral borehole would be cased off or include a liner to contain the formation. For example, it is common in the prior art to run and set a liner in the lateral borehole with the liner extending from the flowbore of the casing and down into the lateral borehole. Cement is then pumped down through the cased main b
Allison Glenn L.
Desai Praful C.
Dewey Charles H.
McGarian Bruce H.
Bagnell David
Conley & Rose, P.C.
Smith Matthew J
Smith International Inc.
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