Drilling system

Abstract: A drilling system comprises a drill string (1) incorporating inbuilt tubular conductors (25), a mud supply passage, and passages for protective or other fluids. The drill string can be advanced by selectively actuable pistons (51,60) exposed to drilling mud flow, by electrically driven traction units (71,74) engaging the drill hole wall or by a linear electric motor element (82) co-operating with a drill hole casing (24), which can be moved thereby relative to the drill string. The drill bit (106) of the drill unit is driven rotatably by an electric motor (111,112) or reciprocably by a linear electric motor (125). The drill unit can be of two relatively slidable parts, with fluid pressure, which may be generated within the unit (189) axially loading the drill bit. Drilling forms can be resisted by clamps (129) clamping the unit and/or the drill string to the drill hole wall. The drilling direction can be adjusted by means of these clamps.

Description: The invention relates to a drilling system, more specifically to a drilling system of the kind in which a drill string extends from topside or stationary equipment to a drill bit for performing a drilling operation. In known systems of this kind, the drill bit may be driven by a motor receiving power by way of the drilling mud supplied to the drilling site, or by an electric motor. Thus US-A-4 436 168 describes an electrically powered system for advancing a rotary boring tool, in which a conduit, which may be flexible to accommodate curved well bores, extends between the surface and an electric motor and is provided internally with electrical conductors. Difficulties are encountered with electric motor drive arrangements because of the length of the necessary cable connection, and the adverse environment in which the electric motor has to operate. Further problems arise in connection with directional or horizontal drilling, because information relating to performance of the drill bit and to its position has to be conveyed along the drill string more or less continuously. Mud pulsing can be employed in the mud drilling systems but the speed of data transmission is low, as is the volume of data that can be transmitted. The present invention is concerned accordingly with the provision of an improved drilling system of the kind described, and of improved components for use in such a drilling system, with particular but not exclusive reference to directional or horizontal drilling operations. The invention accordingly provides a drilling system comprising a drill string extending between topside equipment and a drilling unit, the drill string comprising a drill pipe, a mud pipe within the drill pipe for providing a mud passage for supply of drilling mud from the topside equipment to the drilling unit, characterised by electrical conductor means of tubular configuration and comprising a plurality of electrical conductors within the drill pipe and providing electrical communication between the topside equipment and the drilling unit, the electrical conductor means co-operating with at least one of the drill pipe and the mud pipe to provide at least one fluid passage extending between the topside equipment and the drilling unit. The drill string can be made up of relatively short sections, the conductor means and any protective tubing within each section being then arranged for ready coupling with adjacent sections, with continuity of the electric conductor paths and fluid channels along the drill string. The electric conductor arrangements for a drill string in accordance with the invention can provide mechanical protection for the conductors and can employ simple connection means, for example, screw-threaded or slip-on couplings. The arrangements facilitate the use of an electric motor, which can be either rotary or linear, to drive the drill bit and they moreover provide for prompt transmission of a large volume of data between the fixed or topside control equipment, from which the drill string extends, and sensing and/or control equipment associated with the drill unit. The conditions under which the drill bit is operating, and the direction in which drilling is being carried out, are consequently easily monitored and appropriate control signals readily supplied to the drill unit. Directional control of the drill unit during horizontal or directional drilling is facilitated. The conductor means also facilitate the provision of electrically powered and/or controlled auxiliary equipment at one or more positions along the drill string and also the use of sensor or measurement devices at such positions, as well as the location on the drill string of one or more local power sources of generators, and power and data and control communication between such sources and between them and the top side equipment. The fluid passage or passages provided can be employed for circulation of oil or other protective fluid for one or more of such purposes as cooling, lubrication, insulation, operation of ancillary equipment, and supply of oil or chemicals required for drilling or for connected operations. The fluid can be held static under pressure or can be circulated at a selected pressure either with a special return path or it can be returned mixed with the returning drilling mud, as when the fluid is leaked through labyrinth seals employed for sealing moving parts of the system. Although the drill string is primarily intended for systems in which the drill string is not required to rotate, its use in systems in which rotation is required is not precluded. The drill string can moreover be used as a standard drill string for parts of the drilling process, and can then be equipped with a standard drill bit, the conductor means being used for signalling, for example to control equipment from sensors at the drill unit monitoring the drilling process. The drilling system of the invention can include means for selective movement of the drill string and/or production piping and/or drill hole casings along the drill hole. Such means are of particular significance in the case of deviated, that is, non-vertical, drilling, where placement of production tubing or drill hole linings under gravity cannot be relied upon. The drill string can thus be provided with one or more external piston elements to be acted upon by a flow of drilling mud in the required direction along the space between the drill string and the drill hole wall. The piston elements can be selectively inflatable, as by means of fluid conveyed along the drill string where this has a structure as described above including one or more fluid passages besides the passage for drilling mud. Alternatively, the piston element can be a fixed configuration, with one or more passages containing check valves or selectively operable valves for permitting flow of the drilling mud during normal operation, the valves closing to render the piston element effective when the mud flow direction is reversed in order to advance the drill string. Where production tubing or a casing for lining the drill hole wall is to be brought into position, the drill string can be clamped at its lower end to the drill hole wall, as by clamping means described below with particular reference to certain drill units embodying the invention, and the production tubing or the like can be moved by the action of drilling mud on one or more pistons extending inwardly from the tubing and sliding on the drill string, which can serve as a return path for the mud. After the placement operation has been completed, the drill string is unclamped and withdrawn. The drilling system of the invention can include one or more electrically powered drive means for effecting movement of the drill string and/or production piping and/or drill hole casing along the drill hole. Such drive means can comprise a frame secured externally of the drill string and carrying electrically powered traction elements, for example, wheels, roller or drive belts, engageable with the drill hole wall. The drive means can instead comprise one or more electrical windings secured to the drill string so as to extend around it and to function when energized as an element of a linear electric motor, the other element of which is constituted by a drill hole casing. By suitable energization of the motor windings the drill string casing and the drill string can be relatively moved in either direction or rotationally. This form of drive means in particular can be used also to assist or effect installation of the drill hole casing and/or of production piping after the drilling has been completed, with the leading end of the drill string clamped as described above in connection with the use of drilling mud to effect such placement. Both techniques can of course be used for movement relative to the drill string or other selectively clampable core or guide member in either direction. Power can be supplied to these drive means by way of the conductors extending along a drill string in accordance with the invention as described above. The drilling system of the invention can include a drill unit including a rotational or linear electric motor for applying a rotational and/or reciprocal drive to the drill bit directly or through a mechanical or hydraulic mechanism driven by the motor. In a simple arrangement, the drill unit of the invention comprises a drill bit carried by a drill shaft rotatably driven by an electric motor which may be concentrically arranged around the drill shaft. The motor may be arranged to rotate the drill bit at a predetermined speed or the speed may be adjusted by a frequency control device. The motor can instead be coupled to the drill shaft not directly but by means of a speed/torque converter in the form of a gearbox, hydraulic coupling or hydrostatic transmission device or a combination of these. The drilling system of the invention can include a drill unit having a percusive drill bit reciprocating by a linear electric motor. The linear electric motor can be arranged to drive the drill bit positively in both directions, but alternatively the motor can be arranged to effect movement in one direction only, movement in the other direction being effected by release of a spring which has been stressed during the electrically powered stroke. The drilling system of the invention can include a drill unit in which a linear electric motor advances a plunger in an hydraulic system, the drill bit being reciprocated by the consequential movement of a piston within a hydraulic cylinder of the system. Again, both the operative and return stroke of the drill bit can be positively powered, or a spring loading means can be provided to power one of the strokes, as with the arrangement described above. When the drill string extends generally vertically, its weight applies adequate axial loading to the drill bit, but the drill string cannot be used alone and with sufficient accuracy to apply such loading during horizontal drilling. The drilling system of the invention accordingly can include a drill unit which comprises a first portion carrying the drill bit, a second portion for connection to the drill string, and means for selectively advancing the first portion relative to the second portion. The second portion can be provided with clamping means whereby it can be selectively clamped to the formation being drilled, that is, to the drill hole wall. The two drill unit portions are preferably telescopically related and are arranged to be relatively moved hydraulically. The fluid pressure can be applied by way of the fluid passage with which the drill string is provided, or can be generated locally, within the drill unit, as with fluid pressure used for operating the drill bit. It is frequently of importance that the direction of drilling be controlled and the drilling system of the invention can include a drilling unit having means for orientating the axis of the drill bit at a predetermined angle to the drill hole axis. The drill bit axis can be selectively adjustable relative to the drill unit axis or the drill unit itself can be adjustable relative to the drill hole or its casing, as by clamping means of the kind described above provided with selectively adjustable spacing between the drill unit and the drill hole and casing. The drilling system of the invention can comprise means for clamping the drill string to the drill hole wall or to the drill hole casing at one or more appropriate positions, for example adjacent to the drill unit, so as to transfer the reaction force of the drilling from the drill string. The invention is further described below, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic general view of an entire drilling system embodying the invention; Figure 2 is a partial sectional side view of a drill string which can be incorporated in the system of Figure 1; Figure 3 is a partial cross-sectional view of a first modified form of the drill string of figure 2; Figure 4 is a partial sectional side view of a second modified form of the drill string of Figure 2; Figure 5 is a partial cross-sectional view of a conductor assembly for a third modified form of the drill string of Figure 2; and Figure 6 is a schematic side view of a connector plug for the conductor assembly of Figure 5. The drilling system schematically shown in Figure 1 comprises a drill string 1 extending from topside control and supply equipment located on a platform 2 of a drilling frame or structure 4 resting on the seabed. The drill string 1 extends generally vertically downwardly from the platform 2 within tubing 6 into a drill hole 7 which curves from an upper vertical portion communicating with the tubing to a generally horizontal end portion in which a drill unit 10 at the end of the drill string is operating. The drill string 1 incorporates electric conductors which can perform various functions. They can thus supply power to an electric motor in the drill unit 10 from a power supply unit 12 on the platform 2, the electric motor driving and/or advancing the drill bit either directly or by way of a hydraulic mechanism. Additionally, the conductors can be employed for communication between a system control unit 14 on the platform 2 and condition-sensing equipment and/or a local control unit for the drill unit 10. Multiplexing techniques can be employed to provide a plurality of communication channels on a single conductor, which can additionally supply power along the drill string 1. Drilling mud is circulated between a mud unit 15 on the platform 2 and the drill unit 10 by way of the drill string 1 and the generally annular passage between the drill string and the drill hole wall and pumping units 16 spaced along the drill string within the passage are powered by means of the conductors. Traction units 17 for advancing the drill string 1 along the drill hole are similarly powered and controlled. The drill string 1 can also provide a fluid supply passage or fluid supply and return passages, for fluid communication between equipment 18 on the platform 2 and the drill unit 10 and/or other elements of the system. The fluid can perform a variety of functions, some in place of certain functions of the electrical arrangements described above. The drill string 1 is handled by pipe handling equipment 19 on the platform 2, and the drill string structure can be such that the equipment 19 is conventional. The drill string 1 is suspended from the platform 2 by means of an adapter 20 for effecting the necessary connections between the equipment on the platform 2 and the various supply and communication channels of the drill string 1. In the following more detailed description of various possible forms of certain elements of the system, parts which serve equivalent functions are given the same reference numerals throughout. It will be understood that certain features to be described can be combined in different ways, that is, certain features, for example of one of the drill units can be employed in one or more of the other drill units illustrated. Turning now to the structure of the drill string 1, this is composed of sections of suitable length coupled together. Each section includes rigid electrical conductor means structurally integrated into the drill string section of which various forms are shown in Figures 2-6. As shown in Figure 2, the drill string 1 comprises a drill pipe 21 containing concentrically within it an inner pipe or mud liner 22, the interior of which guides the drilling mud to the drill unit, and conductor tubing 25 received between the mud liner and the drill pipe. The conductor tubing 25 comprises a plurality of concentric metal tubes, for example three such tubes for a 3-phase power supply, with sleeves of solid insulation material between them. A concentric tubular conductor assembly of this kind is described in EP-A-0 063 444 to which reference may be made. The conductor tubing 25 is spaced from both the drill pipe 21 and the mud liner 22 to define inner and outer annular passages 26,27 which can be employed as supply and return paths for fluid. The fluid has insulating properties where the conductor tube assembly is internally and externally free of insulation. Suitable spacing means are provided to maintain the concentric relationship of the mud liner 22 the conductor assembly 25 and the drill pipe 2. For example, as shown in the lower part of Figure 2, the conductor assembly 25 can be provided with externally projecting hangers 29 arranged to rest with suitable insulation, on an internal shoulder of the drill pipe. Connection is made between the ends of adjacent sections of the drill pipe 21 in any suitable way, the lower end of the upper section being shown as provided with a downwardly and inwardly tapered end portion engageable with a mating tapered portion at the upper end of the lower section. The ends of the tubular conductors of the upper conductor tubing 25 are stepped back one from the other, and the conductors of the tubing in the lower section are stepped back in the contrary manner to provide for continuity of electrical connection and insulation between the two sections, in a way described in more detail in EP-A-0 063 444. The upper end of the mud liner 22 in the lower section has a stepped end portion for reception in the lower end of the liner of the upper section, with sealing rings operative between the two mud liner sections. In the modified drillstring structure of Figure 3, the conductor tubing is constituted as an assembly of separate arcuate portions or segments 30 of a tube, with insulation between them. The conductor segments 30 are held in position by an inner pipe 31 spaced outwardly of the mud liner 22 and provided with radially outwardly extending spacers 32 which engage the drill pipe 21. Insulation 34 is provided between each segment 30 and the inner pipe 31, and the insulation may extend also to the outer surface of the segment. Each segment 30 is spaced from the drill pipe to provide one of the supply and return passages 26,27 for a protective fluid, of which the other is formed between the inner pipe and the mud liner. In the alternative conductor tubing arrangement shown in Figure 4, the mud supply is by way of an annular passage between the drill pipe 21 and a protective pipe or mud liner 22 concentrically received therein and surrounding a tubular conductor 25 which corresponds generally to the tubular structure assembly of Figure 2, but is of course of smaller diameter. The supply and return passages 26,27 for the protective fluid are in this arrangement within the conductor tubing 25 and between it and the mud liner 22 respectively. As shown, connection arrangements at the ends of adjacent drill pipe sections are similar to those provided for in the arrangement of Figure 2. Suitable spacers 40 and hangers 41 extend between the mud liner 22 and the drill pipe 21 to maintain the mud liner and conductor tubing in correct concentric relationship within the drill pipe. In accordance with Figure 5, the conductor tubing arrangement of Figure 4 can be modified to include segmental conductors 30 similar to those of Figure 3. Thus for example three segmental conductors 30, with insulation 34, surround an inner pipe 31 from which radial spacers 32 extend to the mud liner 22. The conductor segments 30 are spaced from the mud liner to define the outer passage 27 for protective fluid, and the interior of the inner pipe defines the inner such passage 26. Where segmental conductors are employed, as shown in Figures 3 and 5, and the drillstring sections are connected together by screw-threaded connections at their ends, so that the relative angular location is not predetermined, electrical continuity between respective segments 30 can be achieved by the coupling arrangement shown in Figure 6. Here, each of the conductor segments at the end of a drillstring section is in electrical connection with a respective end contact ring 42. The end rings 42 are of successively larger diameter contact downwardly from the free end of the section to form a male coupling assembly. the co-operating female assembly (not shown) is formed as a socket with internal steps matching in diameter and axial spacing the external steps of the male assembly illustrated. At these steps, respective conductor segment ends are exposed, so that they can engage the contact rings of the male coupling assembly. In any of the arrangements of Figures 2-6, one of the protective fluid passages can be omitted where the fluid is to be leaked into the drilling mud at the drill unit so that no return path is required. For example, as shown on the lefthand side of Figure 3, the mud liner 22 can simply be omitted, so that its function is performed by the inner pipe 31. Although the invention has been described with reference to fixed offshore platform it will be evident that it can be employed also with floating drilling rigs or vessels and onshore drilling installations. It will evident that the drilling system and the various components can be modified substantially within the proper scope of the invention.

Claims: A drilling system comprising a drill string extending between topside equipment and a drilling unit, the drill string comprising a drill pipe (21), a mud pipe (22) within the drill pipe for providing a mud passage for supply of drilling mud from the topside equipment to the drilling unit, characterised by electrical conductor means (25;30) of tubular configuration and comprising a plurality of electrical conductors within the drill pipe and providing electrical communication between the topside equipment and the drilling unit, the electrical conductor means cooperating with at least one of the drill pipe and the mud pipe to provide at least one fluid passage (26,27) extending between the topside equipment and the drilling unit. A drilling system as claimed in claim 1 wherein the electric conductor means (25;30) is located between the drill pipe (21) and the mud pipe (22), a first and a second of the fluid passages being between the conductor means and the drill pipe and between the conductor means and the mud pipe respectively. A drilling system as claimed in claim 1 wherein the electric conductor means (25;30) is within the mud pipe (22), and a first and a second of the fluid passages being between the conductor means and the mud pipe and within the conductor means respectively. A drilling system as claimed in claim 1, 2 or 3 wherein the plurality of electrical conductors comprises concentric tubular conductors having sleeves of solid electric insulation therebetween. A drilling system as claimed in claim 1, 2 or 3 wherein the plurality of electrical conductors comprises angularly spaced arcuate conductors (30) engaged by a support pipe (31) having radially extending spacer portions between the conductors. A drilling system as claimed in claim 5 wherein the support pipe (31)is within the plurality of conductors. A drilling system as claimed in claim 5 wherein the spacer portions (32) extend to the drill pipe or to the mud pipe and define therewith a plurality of the fluid passages. A drilling system as claimed in claim 5, 6 or 7 wherein insulating material (34) surrounds each of the arcuate conductors (30). A drilling system as claimed in any one of claims 1 to 7 having means at said topside equipment supplying electrically insulating fluid along the at least one fluid passage, the fluid providing insulation for the electrical conductor means. A drilling system as claimed in claim 9 having two of the fluid passages (26,27) along which the fluid is circulated from and back to the topside equipment. A drilling system as claimed in any preceding claim wherein the passage or passages communicate with the drilling unit. A drilling system as claimed in claim 11 wherein operation of the drilling unit is effected by fluid conveyed by the at least one fluid passage. A drilling system as claimed in any preceding claim having at least one drive unit carried externally by the drill pipe (21) and selectively operable to move the drill pipe along a drill hole. A drilling system as claimed in any one of claims 1 to 12 wherein the drill pipe externally carries at least one piston element selectively inflatable by fluid conveyed by the at least one fluid passage for effecting movement of the drill pipe along a drill hole in response to fluid movement therealong. A drilling system as claimed in any preceding claim having at least one remotely controllable power generating unit in the drilling unit and/or the drill pipe (21) for effecting local control and/or sensor operations.

Inventors: MOHN FRANK, MOHN, FRANK
Applicants: FRAMO DEV LTD, FRAMO DEVELOPMENTS (U.K.) LIMITED
Application year: 1987
Main classification: E21B17
IPC codes: E21B7, E21B17, E21B4, E21B47