Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02763234 2011-12-23
TITLE
[0001] Large bore jar for a drill string
FIELD
[0002] This relates to a large bore jar, a drill string that incorporates a
large bore jar, and
a method of using the same, such as a drill string that may be used for
coring, where the large
bore jar allows retrievable tools to travel along the drill string.
BACKGROUND
[0003] Jars are used in downhole tools, most commonly drill strings or fishing
tools to
help release components that may become stuck.
SUMMARY
[0004] According to an aspect, there is provided a drill string, comprising a
bit sub
mounted to a lower end of a plurality of tubular sections. At least one
tubular section
comprises a jar, the jar and the tubular sections having an inner diameter
that is at least 4 '/4"
and an outer diameter that is 7" or less. A coring tool has an outer diameter
that is less than 4
1/4". The outer diameter may be between 6 3/4" and 7".
[0005] According to an aspect, there is provided a jar sub for a drill string
having a coring
bit, comprising a jar body having an inner diameter that is at least 4'/4" and
an outer diameter
that is 7" or less, the inner diameter being greater than an outer diameter of
a core retrieval
tool. The outer diameter may be between 6 3/4" and 7".
[0006] According to an aspect, there is provided a method of coring,
comprising the step
of. providing a drill string comprising a bit sub mounted to a lower end of a
plurality of
tubular sections, at least one tubular section comprising a jar, the jar and
the tubular sections
having an inner diameter that is at least 4 '/4" and an outer diameter that is
7" or less; inserting
the drill string into a downhole formation; causing the bit sub to drill a
core sample that is
received within a tubular section; and inserting a core retrieval tool through
the drill string to
retrieve the core sample.
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[0007] The method may further comprise the step of activating the jar to free
the drill
string from an obstruction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] These and other features will become more apparent from the following
description in which reference is made to the appended drawings, the drawings
are for the
purpose of illustration only and are not intended to be in any way limiting,
wherein:
FIG. la and lb are detailed side elevation views in section of a jar.
FIG. 2 is a side elevation view in section of a drill string with a jar
FIG. 2a is a detailed side elevation view of the drill bit in a drilling
configuration.
FIG. 3 is a side elevation view in section of a drill string with a jar and a
drill bit
in a coring configuration.
FIG. 3a is a detailed side elevation view of the drill bit in a drilling
configuration.
DETAILED DESCRIPTION
[0009] A drill string having a large bore jar generally identified by
reference numeral 10,
will now be described with reference to FIG. 1a through 3a.
[0010] Referring to FIG. 2, drill string 10 is designed with an inner bore 11
that allows
retrievable tools to be inserted. This type of drill string may be used when
coring samples are
required. Referring to FIG. 2 and 3, starting from the bottom, drill string 10
has a bit sub 12
and a number of tubular sections, including core barrels 14, drill pipe
sections 16 and a jar 16.
Jar 16 may be included at any desired distance above bit sub 12. The position
of jar 18 will
depend on where it is anticipated that drill string may become stuck. If jar
18 is too far above
or below this location, its effectiveness will be reduced. These
considerations are understood
by those skilled in the art in relation to other downhole tools that
incorporate jars.
[0011] Referring to FIG. 1, jar 18 has a large bore that allows retrievable
tools to pass
through. Jar 18 has a generally thinner sidewall than most other jars, and is
large enough to
be incorporated into a drill string 10 that is designed to obtain a core
sample. For example,
drill string 10 and jar 18 may each have an outer diameter that is less than
7", and preferably
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between 6 3/4" and 7", and an inner diameter that is greater than 4 '/4", and
preferably 4 '/4".
This inner diameter is a common size that many retrievable tools are designed
to be used
with, particularly in relation to coring drill strings. The actual design of
jar 18 may vary
depending on the preferences of the user. However, jar 18 may be a mechanical
jar or a
hydraulic jar. As the operation of mechanical and hydraulic jars generally is
well known in
the art, only a brief description of a hydraulic jar will be given here. The
depicted hydraulic
jar is be activated by applying vertical pressure on the outer tubular 20 of
jar 18. Whether the
pressure is upward or downward will depend on the design of the jar and/or the
preferred
direction of the jarring force. After a predetermined delay, outer tubular 20
is released to
move axially and strikes inner tubular 22, applying a jarring force to free
drill string 10 when
it is obstructed or otherwise stuck. It will be understood that a jar may be
designed in many
ways.
[0012] An example will now be described with respect to a retrievable tool
used for
taking core samples.
[0013] Referring to FIG. 2 and 2a, during a drilling operation, bit sub 12
includes a
removable central bit portion 22 that drills a full bore. When a core sample
is to be taken,
central bit portion 22 is removed as shown in FIG. 3 and 3a. This is done by
removing
central bit portion 22 through drill string 10. The presently described drill
string 10 with jar
18 allows such coring tools to pass through drill string 10, while giving
drill string 10 the
ability to "jar" string 10 loose in the event that it becomes stuck. Once
central bit portion 22
is removed, a core sample 24 may then be drilled from the downhole formation
into which
drill string 10 has been inserted. Core sample 24 is then received in a core
barrel 14. The
core sample 24 is then retrieved using core retrieval tool 26. If drill string
10 becomes stuck
or otherwise obstructed downhole, jar 18 is activated to free drill string 10.
[0014] In this patent document, the word "comprising" is used in its non-
limiting sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires that
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there be one and only one of the elements.
[0015] The following claims are to be understood to include what is
specifically
illustrated and described above, what is conceptually equivalent, and what can
be obviously
substituted. Those skilled in the art will appreciate that various adaptations
and modifications
of the described embodiments can be configured without departing from the
scope of the
claims. The illustrated embodiments have been set forth only as examples and
should not be
taken as limiting the invention. It is to be understood that, within the scope
of the following
claims, the invention may be practiced other than as specifically illustrated
and described.
