US20100126777A1

Movatterモバイル変換

Info

Publication number: US20100126777A1
Application number: US12/597,666
Authority: US
Inventors: Jørgen Hallundbæk
Original assignee: Welltec AS
Current assignee: Welltec AS
Priority date: 2007-04-26
Filing date: 2008-04-28
Publication date: 2010-05-27
Also published as: MX2009011460A; BRPI0810856A2; EP2140100A2; WO2008131772A2; AU2008243507A1; CN101680281A; WO2008131772A3; CA2684715A1

Abstract

A drilling system for drilling out a sample of a formation, a well, or the like downhole. The drilling system has a drilling head having an at least partly hollow cylindrical body with a circumferential rim. The circumferential rim has at least one cutting edge. Furthermore, the drilling system has a driving unit for rotating the cylindrical body and the cutting edge for cutting a piece out of the formation, and a driving tool such as a downhole tractor for driving the drilling head forward in the well or formation.

Description

TECHNICAL FIELD

The present invention relates to a drilling system for drilling out a sample of a subterranean formation, a well, or the like downhole, comprising a drilling head having an at least partly hollow cylindrical body with a circumferential rim, which has at least one cutting edge, a longitudinal axis going through a centre of the cylindrical body, and a driving unit for rotating the cylindrical body and the cutting edge for cutting a piece out of the formation.

BACKGROUND

Drilling systems are used when drilling a well in a subterranean formation or for taking out a sample of the formation before drilling any further.

Known drilling systems for taking out a sample are constructed from a long line of pipes, the system thus extending from above surface to a destination downhole where the sample is to be taken. The system is mounted by mounting one pipe onto another just before the drilling operation on the drilling rig. The extension of the pipes put together makes the mounting process complicated, and the process is moreover time consuming.

However, the long line of pipes creates a Weight On Bit (WOB) by the force of gravity which is needed for drilling downhole. Such a system creating weight on bit by the force of gravity is not very useful when drilling horizontally, e.g. for taking out a sample, since the force of gravity is substantially decreased when the pipes extend horizontally.

Another known type of drilling system uses coiled tubing, i.e. a long, continuous length of pipe wound on a spool. The pipe is straightened prior to pushing into a wellbore and rewound to coil the pipe back onto the transport and storage spool. Although substantially less time consuming than the system described above, the equipment for coiled tubing drilling still takes a long time to transport to the site. Moreover, coiled tubing drilling still uses the force of gravity to create WOB, and thus does not solve the problem of drilling horizontally.

Therefore, there is a need for a drilling system which is able to take out samples also when drilling horizontally.

Furthermore, in order to prevent a blowout when drilling downhole, the fluid in the well is mixed with a number of chemicals for making a differential pressure downhole. However, due to the differential pressure, the above-mentioned systems sometimes get differentially stuck.

Thus, there is also a need for a drilling system reducing or even eliminating the risk of downhole systems getting differentially stuck.

DESCRIPTION OF THE INVENTION

An aspect of the present invention is, at least partly, to overcome the disadvantages of the drilling systems mentioned above, and to provide an improved drilling system which is able to take out a sample of the formation without getting stuck.

This aspect and the advantages becoming evident from the description below are obtained by a drilling system for drilling out a sample of a formation, a well, or the like downhole, comprising:

a drilling head comprising:

- an at least partly hollow cylindrical body with a circumferential rim and a longitudinal axis going through a centre of the cylindrical body, the circumferential rim having at least one cutting edge,

a driving unit for rotating the cylindrical body and the cutting edge for cutting a piece out of the formation, and

a driving tool such as a downhole tractor for driving the drilling head forward in the well or formation.

By having a driving tool for driving the drilling head forward and provide a weight on bit, the drilling system can drill horizontally into the formation for drilling a branch well or taking out a sample for further investigation.

By combining a downhole tractor and a drilling head, the drilling operation can be performed substantially faster than when using coiled tubing or jointed pipes, since the equipment for using coiled tubing or jointed pipes takes longer time to transport to the operation site and takes longer time to prepare at the operation site. A downhole tractor may easily and quickly be transported to the operation site compared to the equipment necessary for coiled tubing operations, and the preparation time at the operation site is thus substantially decreased, if not eliminated. Moreover, the downhole tractor has proven to be efficient enough to use for drilling operations also, since it can provide a sufficient WOB.

In one embodiment, the downhole tractor may be connected to and powered through a wireline.

In addition, the drilling system may further comprise at least one tightening means for providing a closing of the well above the drilling head for preventing a blowout.

By having a tightening means, the well or hole in the formation can be divided into an upper part in relation to the bottom of the well or hole and a lower part comprising the drilling system or at least most of it. In this way, a blowout can be prevented without use of chemicals creating a differential pressure, and thus without risking that the system gets differentially stuck.

In one embodiment, the tightening means may be expandable.

Moreover, the cylindrical body may have a closed end opposite the cutting edge.

In another embodiment, the circumferential rim may have a plurality of cutting edges.

In addition, the circumferential wall may have at least one slot.

In yet another embodiment, the hollow body may have a length up to 10 metres.

Moreover, the drilling system may further comprise a gas cartridge or a pump for inflation of the tightening means with gas or fluid from the well.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail below with reference to the drawings, in which

FIG. 1 shows a drilling system according to the invention, and

FIG. 2 shows another embodiment of the drilling system according to the invention.

The drawings are merely schematic and shown for an illustrative purpose.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a drilling system1 according to the present invention comprising abarrel drilling head2, adriving unit6 for rotating thebarrel drilling head2, and adriving tool8 such as a downhole tractor. The drilling system1 is submerged into the well orsubterranean formation10 by thedriving tool8 which is powered through awireline11 by a power means above surface.

Thedrilling head2 is rotationally driven by thedriving unit6 at a certain speed, and the weight on bit (WOB) is controlled by thedriving unit6 so that the longitudinal displacement of thecutting edge5 towards e.g. theformation10 is held constant during the drilling process.

Due to the fact that the weight on bit (WOB) is created by thedriving unit6 and not just by the force of gravity, the drilling system1 can also drill horizontally, e.g. for taking outsamples7 horizontally.

Thedrilling head2 has a partly hollowcylindrical body3 that is closed at oneend13 and has acircumferential rim4 at the other end. Thecircumferential rim4 has at least onecutting edge5 which, when rotated by thedriving unit6, cuts out apiece7 orsample7 of theformation10. In this way, the drilling system1 can be used for both for drilling a well downhole and for taking outsamples7 for further investigation.

Due to the fact that thedrilling head2 has a hollowcylindrical body3, thedrilling head2 is able to receive thesample7 that is being cut out and bring it up with the rest of the system1. In this embodiment, the inside of thehollow body3 is 6 metres in depth, and the drilling system1 is therefore able to cut out asample7 of almost 6 metres. In another embodiment, thehollow body3 may be as long as 10 metres.

As shown inFIG. 1, the drilling system1 further comprises a tightening means9 positioned around thewireline11 for closing a lower part of the well in order to prevent a blowout without using chemicals.

In this embodiment, the tightening means9 is expandable. The expandable tightening means9 is in the form of an expandable ring blown up by gas positioned in agas chamber12 or agas cartridge12 within the drilling system1. In another embodiment, the fluid surrounding the drilling system1 is used to expand thetightening means9 by use of apump14 and a filter for filtrating the fluid before it is pumped into thetightening means9. Preferably, thepump14 and the filter are positioned in the part of the drilling system1 between the connection to thewireline11 and thedownhole tractor8.

The tightening means9 may also be positioned around thedownhole tractor8 as shown inFIG. 2. Hereby, the tightening means9 need not be expanded as much as when positioned around the wireline, and the tightening means9 can also be non-expandable, e.g. a rubber ring. Thus, the expansion of the tightening means9 is quicker and easier since the volume of the tightening means9 need not be as large as if positioned around thewireline11, and thegas chamber12,gas cartridge12, orpump14 can be positioned in the side of thedownhole tractor8 providing a quick inflation of the tightening means9.

Thedriving unit6 is an electrical motor which drives thedrilling head2. Themotor6 has a shaft for driving thedrilling head2. The shaft may be connected to thedrilling head2 through a gear connection. In this way, onedrilling head2 may be replaced by anotherdrilling head2.

For providing a differential pressure below the expandable means9, the drilling system1 comprises apump14 which may be any kind of suitable pump. In this embodiment, thepump14 is a one-step centrifugal pump, but in another embodiment thepump14 may be a multi-step centrifugal pump, a jet pump, or a piston pump.