Boring or penetrating the earth – Bit or bit element – Casing shoe type
Patent
1998-09-16
2000-05-16
Bagnell, David
Boring or penetrating the earth
Bit or bit element
Casing shoe type
175323, 1662428, E21B 1714
Patent
active
060623268
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to casing shoes of the type used typically in wellbores or boreholes for guiding a casing into the wellbore. The invention relates more particularly to an improved casing shoe adapted both to guide the casing into the wellbore and to perform a degree of drilling and/or reaming of the earth formation. Preferably, the casing shoe will not obstruct the passage of subsequent tools into the well.
It is known, standard practice to use casing shoes for the purpose of guiding a casing string into a wellbore. An example of a typical casing shoe 10 is illustrated in FIG. 1. When running a casing string into a wellbore, the casing string requires a leading edge capable of guiding the string since there may be partial obstructions in the wellbore, such as ledges for example. A standard casing shoe is adequate for this purpose provided that the obstructions encountered are not too severe.
The shoe shown in FIG. 1 comprises a generally cylindrical steel casing 12 having an internally threaded box portion 14 for connection to a complementary pin portion of a casing string, and a central portion 16 of drillable material (such as cement, aluminium, plastics or the like) secured in the interior of the casing 12 forward of the box portion 14 and having a generally rounded nose projecting frontwards beyond the forward end of the casing 12. The central portion 16 has a through-bore 18 to allow the passage of fluids. A shoe of this type may incorporate other, associated equipment, such as a unidirectional ball-valve (not shown) in the bore 18, which inhibits flow of mud from the wellbore into the casing string whilst running the casing, but allows flow of cement from the bore of the casing string into the annulus between the casing string and the wellbore after the full length of the casing string has been run into the wellbore. The present invention may also incorporate such additional, associated equipment.
An important feature of most casing shoes is that the central portion 16 is drillable by standard oilfield drill bits, since it may subsequently be necessary to drill a further section of wellbore beyond the casing shoe. However, there is also a requirement for casing shoes which are not capable of being drilled through.
The advent in recent years of highly deviated or horizontal wells in the oil industry has increased both the frequency and seriousness of difficulties encountered while running wellbore casing strings, to the extent where a conventional casing shoe may be unable to pass a particular obstruction in the wellbore. Obstructions may arise from the bore of the well itself swelling inwardly, as is sometimes the case with hydratable shales for example, or when the wellbore contains ledges caused by drilling through rock formations of differing hardnesses, or due to the accumulation of loose material in the wellbore being ploughed up ahead of the casing shoe until further progress is no longer possible.
This last situation is illustrated in FIG. 2, which shows the casing shoe 10 of FIG. 1 attached to a casing string 20 being run in a near-horizontal wellbore 22 surrounded by competent formation 24. The passage of the casing shoe 10 along the wellbore 22 is obstructed by an unconsolidated formation 26 of loose material.
The consequence of encountering such difficulties are, at best, delays in the schedule of the well programme and, at worst, having to drill all or part of the well again. In any case, significant additional cost is involved.
It is an object of the present invention to provide an improved casing shoe which performs the string-guiding function of standard casing shoes, but which is capable of clearing obstructions which would halt the passage of conventional shoes. In the preferred embodiments of the invention, this involves the ability to ream swelled sub-surface formations and/or to deal with large quantities of unconsolidated solids, whilst (preferably) allowing the subsequent passage of other equipment.
In accordance with the present invention there is provided a casin
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B & W Incorporated Catalogue Extract I (undated).
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Strong Philip
Wardley Michael
Bagnell David
Enterprise Oil plc
Walker Zakiya
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