US 20090321141 A1
Apparatus for drilling an underground borehole, comprising:
1. Apparatus for drilling an underground borehole, comprising:
a tubular conveyance system including an electric cable and a supply of drilling fluid, the supply of drilling fluid being arranged in use to pump fluid from the surface down the inside of the tubular conveyance so as to return to the surface via the annulus between the outside of the tubular conveyance and the borehole;
a drilling system comprising an electrically powered drilling motor and a pump arranged in use to pump fluid from the borehole outside the drilling system up through the inside of the drilling system;
a connector connecting the drilling system to the tubular conveyance system and to the electric cable, and
a flow diverter at which flow down the inside of the tubular conveyance system is diverted into the annulus, and flow up the inside of the drilling system is diverted into the annulus.
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10. Apparatus as claimed in any preceding claim, wherein the flow diverter is arranged to divert flow from the inside of the drilling system to the annulus above the point at which it diverts flow from the tubular conveyance system into the annulus.
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18. A method of drilling an underground borehole using an apparatus comprising a tubular conveyance system including an electric cable and a supply of drilling fluid; a drilling system comprising an electrically powered pump and a drilling motor; a connector connecting the drilling system to the tubular conveyance system, through which the pump and motor are connected to the electric cable; and a flow diverter; the method comprising:
pumping fluid from the surface down the inside of the tubular conveyance so as to return to the surface via the annulus between the outside of the tubular conveyance and the borehole; and
using the electrically powered pump of the drilling system to pump fluid from the borehole outside the drilling system up through the inside of the drilling system;
diverting fluid flow down the inside of the tubular conveyance system into the annulus, and diverting flow up the inside of the drilling system into the annulus using the flow diverter; and
using the drilling motor to drill the borehole using the drilling system.
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This invention relates to methods and apparatus for drilling boreholes that is particularly applicable to drilling with wireline drilling apparatus carried on coiled tubing.
Current conventional coiled tubing drilling (CTD) employs high hydraulic power delivered from the surface through the coiled tubing (CT) to power a drilling positive displacement motor (PDM) that in turn powers the drill bit. This high drilling power requires a large-diameter CT that demands larger surface installations.
Current methods of changing the trajectory in CTD typically involve a fixed bend on the PDM, and a hydraulic or electric-over-hydraulic means of rotating the bend azimuth. Apart from the larger and heavier surface equipment, this way of drilling on CT is limited in reach by the buckling limit of the CT, and involves a low-efficiency conversion of hydraulic power to drilling footage.
U.S. Pat. No. 2,548,616 describes a method of drilling a well with a conduit to surface through which a fluid is pumped (today's CTD). The option of a cable in the CT with an electric motor at the bottom-hole assembly driving the bit is also described but the conduit still provides the axial thrust for drilling.
EP 0 110 182 describes an apparatus with a hydraulic tractor/crawler (with anchors and a stroker), an umbilical from surface for communications and powering of an electric pump that powers the hydraulic tractor, and methods of steering. The means of rotating the bit are described as purely hydraulic (either from the hydraulic distribution system, or from a hydraulic line from the surface.) CT is also described.
U.S. Pat. No. 6,629,570 describes a high-power electric motor capable of drilling on CT. In use drilling fluid flows through the motor to return to the surface through the bit and annulus (conventional circulation).
WO 2004 011766 describes a wireline powered drilling system in which produced fluid from the borehole is circulated as drilling fluid. A downhole pump is used to perform conventional or reverse circulation through the downhole drilling tool. Flow to the surface is through production tubing around the cable.
Other documents describing wireline drilling systems include WO 2004 072437 and WO 2005 071208.
One object of the invention is to provide a drilling apparatus that does not need large capacity CT due to reduced hydraulic power requirements yet which still provides effective hole cleaning in the drilling region to avoid sticking. The invention achieves this object by providing electric power to the drilling system via a cable and by providing a flow diverter to allow downward drilling fluid flow around the outside of the drilling assembly while using normal annulus flow above the drilling system for good cuttings transport.
One aspect of the invention comprises apparatus for drilling an underground borehole, comprising:
The use of the flow diverter makes it possible to provide reverse circulation (circulation of fluid from the annulus into the BHA) where drilling is taking place, so improving hole cleaning in small diameter boreholes and reducing the risk of sticking.
Preferably, the drilling system has separate axial and rotary drive mechanisms. It is particularly preferred that the axial drive mechanism comprises a crawler system. The drilling motor can comprise an electric motor powered through the electric cable. The drilling system typically comprises an electric pump but can comprise a jet pump instead of the electrically powered pump.
Typically the tubular conveyance system comprises coiled tubing. This can be a single coiled tube or can comprise several sections joined end to end. Because the drilling action is handled by the drilling system, it is not necessary that the tubular conveyance system provide the torque for a rotary drilling action nor high axial stiffness to transfer the weight on the bit necessary for drilling.
In a particularly preferred configuration, the flow diverter forms part of the connector. Alternatively, the flow diverter is positioned in the tubular conveyance above the connector.
In use, the flow diverter can direct part of the drilling fluid down around the outside of the drilling system and the remainder of the fluid back to the surface around the outside of the tubular conveyance. Thus the reverse circulation around the drilling system changes to conventional circulation around the tubular conveyance which allows improved cuttings transport in the main part of the borehole. The flow diverter can be arranged to divert flow from the inside of the drilling system to the annulus above the point at which it diverts flow from the tubular conveyance system into the annulus.
One embodiment of the apparatus further comprises a jetting system including one or more flow nozzles arranged to direct jets of fluid inside the borehole to remove accumulated deposits. Preferably, the flow nozzles are adjustable so as to change the direction of flow of fluid therefrom.
In this embodiment, the flow diverter can direct fluid into the flow nozzles for jetting and further comprises a valve adjustable to vary the amount of fluid directed through the flow nozzles and the amount of fluid directed into the annulus.
The apparatus can further comprise a rotatable crown driven by the motor for use in back reaming. A turbine driven by fluid flow from the tubular conveyance system can be connected to drive the crown via a gear train. An electric generator can be connected to the turbine and an electric motor connected to the crown via the gear train, the output of the generator being used to power the electric motor and drive the crown.
Another aspect of the invention comprises a method of drilling an underground borehole using an apparatus comprising a tubular conveyance system including an electric cable and a supply of drilling fluid; a drilling system comprising an electrically powered pump and a drilling motor; a connector connecting the drilling system to the tubular conveyance system, through which the pump and motor are connected to the electric cable; and a flow diverter; the method comprising:
In a preferred embodiment, the method comprises diverting part of the drilling fluid down around the outside of the drilling system and the remainder of the fluid back to the surface around the outside of the tubular conveyance.
Also, it is preferred that the method further comprises the steps of directing jets of fluid from one or more nozzles of a jetting system inside the borehole to remove accumulated deposits. The flow nozzles can be adjusted so as to change the direction of flow of fluid therefrom.
Fluid can be diverted into the flow nozzles for jetting using the flow diverter and adjusting a valve to vary the amounts of fluid directed through the flow nozzles and the amount of fluid directed into the annulus.
The method can further comprise back reaming the borehole using the drilling system. The back reaming can be performed using a rotating crown driven by the drilling motor and/or a hydraulic system.
The drilling operation shown in
The drilling assembly 20 comprises a motor section 22 including an electric motor providing rotary drive to a drill bit 24. Immediately behind the motor section is a crawler unit 26 comprising an open hole tractor for providing axial drive to the drill bit 24. Acting together, the electric motor and the crawler unit 26 provide the drive to the drill bit 24 to allow drilling to proceed. The crawler unit 26 can also be operated in reverse to pull the motor section and bit from the borehole. A pump section 28 is mounted above the crawler unit 26 and has an electric pump mounted therein. A channel extends from the drill bit up through the motor section 22 and crawler section 26 to the pump so that in normal use, the pump can draw fluid and drilled cuttings up through the drill bit 24 and inside the drilling assembly 20.
The drilling assembly 20 is connected to the end of the CT by means of a connection unit 30. The connection unit 30 provides a mechanical connection between the CT and the drilling assembly 20 and an electrical connection between the electric cable and the electrical components of the drilling assembly 20.
In the embodiment of
The connector shown in
Once the drilling operation has been performed, the task of pulling the drilling assembly 20 out of hole (POOH) can potentially encounter problems depending on the condition of the drilled hole. Solutions depend on the POOH condition. The drilling assembly 20 can include sensors to assess the condition of the borehole for the risk of solids build-up that can potentially impede the movement of the BHA and/or CT in the well. The sensors included in the tool to detect such conditions include calliper, azimuthal density neutron, and internal and annular pressure sensors.
As the drilling assembly 20 is pulled back, it can drag with it cuttings left in the borehole and these can eventually accumulate sufficiently to create a barrier through which it cannot be pulled by use of the CT alone. One solution for such a case is to jet fluid backwards in the annulus while POOH to mobilize cuttings and transport them in the annulus, so that they do not accumulate to cause a potential sticking problem. The fluid jetting can be provided by nozzles, preferably in or near the connector 30 but potentially in other parts of the drilling assembly 20 or elsewhere in the CT. One preferred form of jetting arrangement is shown in
The jetting arrangement can include a mechanism using hydraulic or electric signals such that allows the direction of the flow from the nozzle to be adjusted in the vicinity of the cuttings, to further mobilize the cuttings, or to give some directional jetting focus as necessary. Dictation of the outward and rear jetting flow ratio will give further control on the cleaning efficiency for the specific conditions. As previously mentioned, measurements incorporated in the tool (e.g. internal and annular pressures) can be used to determine the condition, optimum jetting configuration, and to confirm the effectiveness of the cleaning operation (e.g. by a decreased equivalent circulating density ECD).
Hydraulic signalling can include methods such as flow rate changes and modulation from the surface unit pump, and ball drops. Electric signals can include solenoid activation, or use of bi-stable valves (to decrease the need for high power consumption during extended periods of time as is the case with traditional solenoids). Such bi-stable valves are described by EP113578.
A pure jetting of a ledge as the tool is being pulled (or is tractoring) back out, might not be enough to overcome the ‘step’ it encounters. Swelling formations such as shales, coal sloughing, or other such formations can cause large steps to form. In such a case, mechanical means of smoothing out the ledge or drilling some of the swelled formation (to a dimension larger than the diameter of the tool) might be required. Various solutions are described above in relation to
One solution to this problem is to use an electric motor driving a rotating crown. However, since the hydraulic power of the CT flow is available, other methods are possible for creating the reaming action without consuming power from the wireline cable.
One such approach involves using the CT flow to power a turbine whose axis turns the reamer crown via a gear train. Another involves using the CT flow to power a turbine connected to an alternator to create electrical power that can then run an electric motor that turns the reamer crown through a gear train.
It can be particularly advantageous to use both techniques, back reaming with a rotating crown and jetting, for difficult conditions where one method alone might prove slow or less effective.
In the simplest configuration, as shown in
In another embodiment, a downhole valve can also be included to dictate the proportion of flow split between exit ports 36 and jetting nozzles 46. Apart from being able to change between jetting and simply circulating, this valve can also produce pressure pulses to remove harder ledges in a similar manner to that described in U.S. Pat. No. 5,944,123 and U.S. Pat. No. 6,062,311. The valve can either be electrically activated using surface commands, or hydraulically commanded using flow variation schemes (e.g. switches to jetting above a specific flow rate and pressure drop.)
An additional advantage of power available in the fluid in the CT is the ability to power a jet pump in the pump section 28. This jet pump can replace the electric motor driving the pump. The use of a jet pump will create a small increase in surface power needs but has the advantage that the tool length can be substantially reduced (pump, transmission, gear box, motor, oil compensation, motor control and drive electronics), while increasing the reliability.
Furthermore, a dual pump system can be employed to circulate around the drilling assembly 20 and in the lateral borehole 16, and to act as a booster in the well 14 to circulate cuttings to the surface.
Other changes can be made while staying within the scope of the invention.