LARGE BORE JAR FOR A DRILL STRING

Abstract

A drill string includes a bit sub mounted to a lower end of a plurality of tubular sections, where at least one tubular section is a jar. The jar and the tubular sections have an inner diameter that is at least 4¼″ and an outer diameter that is 7″ or less. A method of drilling includes the steps of 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.

Description

FIELD

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

Jars are used in downhole tools, most commonly drill strings or fishing tools to help release components that may become stuck.

SUMMARY

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 4¼″ and an outer diameter that is 7″ or less. A coring tool has an outer diameter that is less than 4¼″. The outer diameter may be between 6¾″ and 7″.

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 4¼″ 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 6¾″ and 7″.

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 4¼″ 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.

The method may further comprise the step of activating the jar to free the drill string from an obstruction.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIGS. 1a and 1b 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

A drill string having a large bore jar generally identified by reference numeral 10, will now be described with reference to FIGS. 1a through 3a.

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 FIGS. 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.

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 between 6¾″ and 7″, and an inner diameter that is greater than 4¼″, and preferably 4¼″. 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.

An example will now be described with respect to a retrievable tool used for taking core samples.

Referring to FIGS. 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 FIGS. 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.

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 there be one and only one of the elements.

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.

Claims

1. 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 4¼″ and an outer diameter that is 7″ or less; and

a coring tool having an outer diameter that is less than 4¼″.

2. The drill string of claim 1, wherein the outer diameter is between 6¾″ and 7″.

3. A jar sub for a drill string having a coring bit, comprising:

a jar body having an inner diameter that is at least 4¼″ and an outer diameter that is 7″ or less, the inner diameter being greater than an outer diameter of a core retrieval tool.

4. The jar sub of claim 3, wherein the outer diameter is between 6¾″ and 7″.

5. 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 4¼″ 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.

6. The method of claim 5, further comprising the step of activating the jar to free the drill string from an obstruction.