METHODS FOR CUTTINGS FOR A WIRELINE DRILLING TOOL

Abstract

A method of removing cuttings from a workfront of a lateral borehole hole being drilled from a main borehole by a drilling tool is provided. The drilling tool comprising a tool body including a motor, an axial drive mechanism for advancing the tool body in the well, and a drill bit powered by the motor for drilling the underground formation at the workface and producing cuttings as the tool is advanced. The drilling tool is preferably connected to the surface by means of a cable extending through the lateral borehole and main borehole. The method independently comprising transporting the drilled cuttings from the workface to the part of the lateral borehole immediately behind the drilling tool. Transporting the drilled cuttings from immediately behind the drilling tool to the junction of the lateral borehole and the main well. And transporting the cuttings from the junction to a place of disposal.

Description

TECHNICAL FIELD

This invention relates to methods for removing cuttings from a borehole being drilled with a wireline drilling tool. In particular, the invention is applicable to the drilling of small boreholes in oil and gas wells and the like.

BACKGROUND ART

It has been proposed to drill lateral boreholes from a main borehole using a drilling tool that is conveyed and powered via a wireline cable. The aim of such a tool is to create lateral holes, from an already drilled main wellbore. The laterals can have a range of dimensions, for example an internal diameter of between <1 in to 4-6 in, and a length of anything between 2-6 ft microperforations to 1000 ft mini multilaterals. They can be used, for example, to reach and produce bypassed hydrocarbon, to place an injection point to assist the displacement of bypassed hydrocarbon, or to deploy sensors within the reservoir.

Small diameter holes can already be created using coiled tubing drilling, but a wireline deployed system typically involves less equipment at surface (in particular, no rig, or circulation system of any kind may be needed) and hence costs can be reduced.

The rock cuttings generated in the hole-making process must be removed, in order to leave the lateral hole open for production or sensor deployment. The volume of a (2 inch×300 feet) hole is around 0.25 cubic metres or 250 litres, and the associated mass of cuttings (assuming a rock density of 2500 kg/cubic metre) is approximately 600 kg. Drilling rates can be of order 30-60 feet/hour. Hence, cuttings will be generated at a mass rate of 60-120 kg/hour.

Dealing with the rock cuttings created during drilling is a critical issue for success of the wireline conveyed technology. Whereas in conventional drilling there are separate down- and up-going fluid flow paths (within drill pipe, and in the annulus outside between it and the formation) around which drilling mud can be circulated to carry the cuttings, with the wireline drilling tool there is only a single fluid filled region in the hole behind the tool.

The object of the invention to provide methods by which the drilled cuttings can be transported out of the lateral borehole following drilling.

DISCLOSURE OF INVENTION

A first aspect of the invention provides a method of removing cuttings from a workfront of a lateral borehole hole being drilled from a main borehole by a drilling tool comprising a tool body including a motor, an axial drive mechanism for advancing the tool body in the well, and a drill bit powered by the motor for drilling the underground formation at the workface and producing cuttings as the tool is advanced, wherein the drilling tool is connected to the surface by means of a cable extending through the lateral borehole and main borehole, the method comprising:

• • transporting the drilled cuttings from the workface to the part of the lateral borehole immediately behind the drilling tool;
  • transporting the drilled cuttings from immediately behind the drilling tool to the junction of the lateral borehole and the main well; and
  • transporting the cuttings from the junction to a place of disposal;
    wherein the transport around the drilling tool, transport from the drilling tool to the junction and transport from the junction to the place of disposal are all independent of each other.

Preferably, the lateral borehole is filled with a fluid, at least part of which is circulated through the drilling tool during drilling. In this case, transport of the drilled cuttings past the drilling tool can include transport by local fluid circulation.

In another embodiment, the motion of the tool body can be used to move the cuttings. One preferred embodiment of this is to provide the outer surface of the tool body with a thread formation (Archimedian screw) and to rotate the body to move the cuttings by the action of the thread. Other formations or appendages can be provided on the tool body and moved to move the cuttings.

A still further embodiment comprises deformation of the tool body to create a peristaltic wave to move the cuttings.

Transport of the cuttings from behind the tool to the junction with the main borehole can include creating an asymmetric pulsatile flow, preferably with the drilling tool, in the lateral borehole to drive the cuttings to the junction.

In another embodiment, transport to the junction can be performed by drilling the formation underbalanced so as to create a net flow of well fluids back towards the main borehole.

In a still further embodiment, the tool body is provided with a tail pipe extending back along the lateral borehole, the cuttings being transported by pumping them along the tail pipe.

The cuttings can also be transported to the junction by withdrawing the drilling tool from the lateral well so as to push the cuttings back to the junction.

One or more separate transport devices can be provided between the drilling tool and the junction which are shuttled back and forth carrying the cuttings away from the drilling tool.

Flow back to the junction can also be created chemically, for example by igniting propellant charges behind the drilling tool.

Transport away from the junction can include allowing the cuttings to fall into a lower section of the main borehole. In one embodiment, the cuttings can be allowed to fall into a collector which is later removed from the well. In another, the cuttings are later cleaned out via a tubing passed into the well from the surface. In a third, they are simply left in the bottom of the hole.

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

FIG. 1 shows a schematic diagram of a wireline drilling system; and

FIG. 2 shows an embodiment of a shuttle device for cuttings disposal.

MODE(S) FOR CARRYING OUT THE INVENTION

This invention finds a particularly preferred application in wireline drilling systems which have been proposed for drilling lateral boreholes from a main well. FIG. 1 shows a schematic diagram of such a system, comprising a downhole drilling system 10 which is positioned in a lateral well 12 extending from a main well 14. The downhole drilling system 10 is connected to the surface by means of a wireline cable 16 which provides power and control signals during operation. The drilling system 10 comprises a BHA including a tractor system 18 for moving the BHA along the lateral well 12, a power and drive module 20 for converting the electrical power provided by the cable 16 into mechanical drive for rotating a drill bit 22 and applying weight on bit during drilling.

During drilling a lateral hole, rock cuttings are created by the bit 22 at the work front. These are typically a fine dust/powder due to the low ROP and high RPM used in these operations. These are then transported out of the well in three stages:

• 1. From the workfront, past the drilling tool, to just behind the tool;
• 2. From behind the tool along the lateral to the junction with the main hole;
• 3. From the main-lateral junction to some place of ultimate disposal.

There are various ways in which transport from the workfront past the drilling tool might be achieved, including local fluid circulation, motion of the drilling tool body, deformation of the drilling tool body and the use of moveable appendages on the drilling tool body.

For a system based on local fluid circulation, fluid is drawn into the tool from the upper end (i.e. opposite to the drill bit 22), is pumped to and through the drill bit, and returns carrying the cuttings along the annulus between tool and formation. Systems based on motion of the drilling tool body can take a number of forms e.g., the tool body rotates, and a screw thread on the outside forces the cuttings backwards. In another system, the surface of the tool body deforms so as create a peristaltic wave which forces the cuttings backwards. Moveable appendages (scrapers, hairs or cilia, fins or claws) can be provided on the surface of the tool to grasp and push the cuttings backwards or generate a fluid flow that has that effect.

Transport from the junction between the lateral well and the main well can involve simply dumping the cuttings into an extended rat-hole section of the main well, dumping into the rat-hole and cleaning out later with coiled tubing, or dropping them into a junk basket which is later lifted to surface using slickline.

It is beneficial to minimize the volume of cuttings to be transported over large distances. There are a number of possible ways of doing this. When drilling carbonate reservoirs, the drilling fluid can be acidic, so as to dissolve the cuttings. The chemical properties of the drilling fluid can be modified by energy input (e.g. in electrical form) at the drilling tool, so as to ensure that aggressive chemical conditions are only present where they are needed and not throughout the hole where they might cause damage to the drilling tool itself. The wellbore fluid containing the dissolved rock is flowed out of the hole when it is put on production. As an alternative to complete dissolution, the cuttings can be ground to colloidal size, so that they remain in suspension under the action of Brownian motion (the wellbore fluids should be tailored chemically so as to stabilize this suspension against flocculation and aggregation of the suspended solids).

Some fraction of the drilled cuttings can be compacted and plastered into the wellbore wall. While for production holes formation damage and creation of a filter cake is not desirable, for injectors, or holes for sensor placement, the hydraulic sealing that this would create may be necessary. The cuttings can also be compacted, so as to eliminate the volume of the porosity. Other approaches to cuttings disposal creating a fracture in the wellbore wall, and pumping them into that newly created volume; or an initially non-circular and over-gauge hole can be drilled, and some cuttings compacted onto the hole wall so as to created a final circular hole of the required gauge diameter.

There are a number of approaches to providing transport from behind the tool along the lateral to the junction with the main.

One approach is to use an asymmetric pulsatile flow. This involves, for example, sucking wellbore fluids slowly into a reservoir within the drilling tool, then expelling them quickly so as to blow the cuttings back along hole. This is a hydraulic transport mechanism, which exploits the non-linear rate dependence of most hydrodynamic processes to generate a mean solids flow backward along the hole. In order to ensure good transport, it may be necessary to combine with a large amplitude zero mean pulsatile flow (or acoustic field) to prevent the cuttings from becoming packed in a bed on the low side of the hole. The properties of the fluid filling the hole are also important, and should be chosen so as to avoid stickiness and/or aggregation of the cuttings. It may also be beneficial here, or elsewhere, to pre-process the cuttings into a shape and size that is optimal for transport.

Drilling underbalanced is another way to convey the cuttings to the junction with the main well. In productive zones, drilling underbalanced will cause fluids to flow into the lateral. The resulting axial flow will transport the cuttings along the hole, and the radial inflow will contribute to lifting and fluidizing the cuttings bed. Controlled underbalance can be generated using a gas lift valve deployed at a shallow depth. Other benefits of drilling underbalanced are well-known, and include reduced risk of sticking and formation damage, and increased rate of penetration. The underbalance can be applied continuously, or in pulses so as to create a short period of intense flow (again, the non-linearity of most hydraulic transport processes means that short periods of high velocity will be more effective that continuous low rate flow, for the same time-mean rate). In designing the specific process to be allied, a balance must be achieved between volume of cuttings to be moved and the ability of the formation to supply fluid.

The cuttings can be pumped back along the lateral in a tail pipe. The drilling tool trails alight weight tail pipe, along which cuttings are pumped. Fluid and cuttings are drawn in, at the drill bit, and are then pumped backwards through the tool and into the tail pipe. The interior profile of the tail pipe can be tailored so as to enhance transport, e.g. a helical “swirl pipe” profile, or periodic baffles or constrictions, all of which can assist conveyance at low fluid velocities, and may induce turbulent flow, which will enhance (fine) cuttings carrying capabilities.

The drilling tool itself can be used to move the cuttings. In this case, cuttings are allowed to build up behind the working drilling tool. Periodically drilling is stopped and the tool is pulled back along the lateral, so that the accumulated cuttings are pushed along in front of the tool (in this case pushed by the upper end of the tool).

A number of techniques are based on the idea of shuttles. The basic idea is to move the cuttings by carrying or pushing them using a separate vehicle that shuttles back and forth between the drilling tool and the lateral-main junction. Many realizations are possible. The vehicle can, for example, pull itself along the wireline, or move using wheels, tracks, or feet contacting the hole wall. It can carry its own power supply (recharged at the drilling tool, or at a mother tool in the main hole), or gather power inductively from the wireline cable, or it can be passive and moved by winching from the drilling tool and/or a tool at the junction. Single or multiple vehicles can be used. Examples include:

• • a robot shuttle “bulldozer”, pushing cuttings before it;
  • compacting cuttings into spheres and rolling them back, using the bulldozer, in line along the lateral;
  • compacting or encapsulating the cuttings into large well defined “beads”, and pushing them back along the wireline cable as if on a necklace, removing them at surface on pulling out of hole or dropping them into the junk basket or rat hole;
  • a robot shuttle “dumper truck”, carrying cuttings; and
  • a “jawed” shuttle that runs in along hole, drives jaws into cuttings pile behind tool, closes jaws so as to pick up a volume of cuttings and reverses back along lateral to drop cuttings at junction.

There are various possibilities for implementation of an autonomous vehicle to carry out these tasks. FIG. 2 shows an embodiment of the ‘jawed’ shuttle which comprises a shuttle body 30 which is attached to the wireline cable 16 connected to the drilling tool 10. The shuttle body includes a tractor device 32 which can be operated to move the shuttle back and forth along the cable 16. A pair of jaws 34 are provided at the end of the body 30 and can be moved between open positions in which the interior of the shuttle communicates with the borehole, and a closed position in which it is obscured. In FIG. 2, the jaws 34 are shown in the open position. In use, the shuttle can start at one end of the lateral well, for example close to the junction with the main well (not shown). The jaws 34 can then be opened and the tractor device 32 activated to draw the shuttle along the cable 16. The jaws 34 dig into the cuttings bed 36 (typically on the lower side of the lateral) and the motion of the shuttle scoops the cuttings into the shuttle body 30. When the body is full, the tractor device can be operated to withdraw the shuttle to another location where the stored cuttings can be disposed of. This process can be repeated while drilling proceeds.

Another approach is to use techniques based on a distributed actuation concept. In this case, the basic idea is to distribute the motive forces along the entire length of the lateral, for example by using cilia on the wireline, a peristaltic sheath surrounding wireline, an Archimedes screw surrounding wireline, an Archimedes screw in a tail pipe, driven from tool. In other cases, the techniques mimic leaf-cutter ants through a swarm of tiny carrying devices each of which carries a small load, or a chain of people passing fire buckets along the line.

Chemical techniques can be used to create extra flow. The drilling tool can contain a number of charges of propellant, that are ignited periodically. A large volume of gas is generated, which causes a flow along the lateral, which in turn carries the cuttings.

It is also possible to tailor the hole trajectory to assist transport. This can involve drilling the hole slightly uphill, and allowing the cuttings to fall downhill under gravity, optionally with shaking, or pulse flow, to assist transport, or use continuous direction/azimuth and inclination measurements to ensure that the borehole has minimal tortuosity to minimize potential cleaning hazards, e.g., sumps, etc.

Other changes within the scope of the patent will be apparent.

Claims

1. A method of removing cuttings from a workfront of a lateral borehole hole being drilled from a main borehole by a drilling tool comprising a tool body including a motor, an axial drive mechanism for advancing the tool body in the well, and a drill bit powered by the motor for drilling the underground formation at the workface and producing cuttings as the tool is advanced, wherein the drilling tool is connected to the surface and powered by means of a cable extending through the lateral borehole and main borehole, the method comprising: wherein the steps of transporting around the drilling tool, transporting from the drilling tool to the junction and transporting from the junction to the place of disposal are all independent of each other.

transporting the drilled cuttings from the workface to the part of the lateral borehole immediately behind the drilling tool;

transporting the drilled cuttings from immediately behind the drilling tool to the junction of the lateral borehole and the main well; and

transporting the cuttings from the junction to a place of disposal;

2. A method as claimed in claim 1, wherein the lateral borehole is filled with a fluid, at least part of which is circulated through the drilling tool during drilling.

3. A method as claimed in claim 2, wherein transport of the drilled cuttings past or through the drilling tool includes transport by local fluid circulation.

4. A method as claimed in claim 1, wherein the motion of the tool body is used to move the cuttings.

5. A method as claimed in claim 4, comprising providing the outer surface of the tool body with a thread formation and rotating the body to move the cuttings by the action of the thread.

6. A method as claimed in claim 4, wherein other formations or appendages are provided on the tool body and moved to move the cuttings.

7. A method as claimed in claim 4, comprising deforming the tool body to create a peristaltic wave to move the cuttings.

8. A method as claimed in claim 1, wherein transport of the cuttings from behind the tool to the junction with the main borehole includes creating an asymmetric pulsatile flow in the lateral borehole to drive the cuttings to the junction.

9. A method as claimed in claim 8, wherein the pulsatile flow is created using the drilling tool.

10. A method as claimed in claim 1, wherein transport to the junction is performed by drilling the formation underbalanced so as to create a net flow of well fluids back towards the main borehole.

11. A method as claimed in claim 10, wherein the underbalance is created by a periodic burst of gas that allows the overall rockface pressure to be maintained at over or near balance, but helps increase transport velocities in the borehole.

12. A method as claimed in claim 1, wherein the tool body is provided with a tail pipe extending back along the lateral borehole, the cuttings being transported by pumping them along the tail pipe.

13. A method as claimed in claim 1, wherein cuttings are transported to the, junction by withdrawing the drilling tool from the lateral well so as to push the cuttings back to the junction.

14. A method as claimed in claim 1, wherein one or more separate transport devices are provided between the drilling tool and the junction which are shuttled back and forth carrying the cuttings away from the drilling tool.

15. A method as claimed in claim 1, wherein flow back to the junction is created chemically

16. A method as claimed in claim 15, wherein flow is created by igniting propellant charges behind the drilling tool.

17. A method as claimed in claim 1, wherein transport away from the junction includes allowing the cuttings to fall into a lower section of the main borehole.

18. A method as claimed in claim 17, wherein the cuttings are allowed to fall into a collector which is later removed from the well.

19. A method as claimed in claim 17, wherein the cuttings are later cleaned out via a secondary or plurality of tubing(s) passed into the well from the surface.