CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Application No. 15/001715, filed on January 20, 2016, which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Disclosure

[0001] The disclosure relates generally to drilling of wellbores and particularly to electrical impulse cutting apparatus for drilling such wellbores.

2. Background Art

[0002] Wells or wellbores are formed for the production of hydrocarbons (oil and gas) from subsurface formation zones where such hydrocarbons are trapped. A drill bit at a bottom end of a drill string conveyed from a surface location is rotated to cut through the formation rock to form the wellbores. Commonly used drill bits include mechanical cutters that penetrate the rock due to the weight on the bit to disintegrate the rock into small pieces, referred to as the cuttings or rock cuttings. A drilling fluid is supplied to the drill string that discharges at the bottom of the drill bit, which fluid causes the cuttings to flow through an annulus between the drill sting and wellbore to the surface. Electrical impulse cutting devices have been proposed as an alternative to the conventional mechanical drill bits for forming wellbores. An electrical impulse cutting device utilizes electrodes to impart high voltage pulses into the rock to generate heat and pressure inside the rock to disintegrate the rock into cuttings. Some of the cuttings tend to settle between the electrodes as there is inadequate or no fluid velocity underneath the electrodes to move the cuttings away from the electrodes, inhibiting moving of the cuttings by the drilling fluid to the surface. Therefore, it is desirable to provide electrical impulse cutting devices and system that can effectively move the cuttings away from the electrodes to enable the circulating drilling fluid to move the cuttings to the surface.

[0003] The disclosure herein provides an electrical impulse cutting apparatus configured to move to move cuttings away from the electrodes for effective hole cleaning during drilling of wellbores. SUMMARY

[0004] In one aspect, an electrical pulse cutting device is disclosed that in one non- limiting embodiment includes a pair of electrodes that generate electrical pulses inside an object to disintegrate a section of the object into cuttings, and at least one flow passage in at least one of the electrodes to provide a passage for a fluid under pressure to move the cuttings away from the at least one of the electrodes.

[0005] In another aspect, a method of forming a wellbore is disclosed that in one embodiment includes: conveying a drill string into a wellbore, wherein the drill string includes an electric pulse cutting device at a bottom end of a drilling assembly, wherein the electric pulse cutting device includes a pair of electrodes and wherein at least one electrode includes a fluid flow passage therethrough to allow a fluid under pressure to pass

therethrough to move the cuttings away from the at least one of the electrodes; and disintegrating rock at bottom of the wellbore into cuttings by generating electrical pulses via the pair of electrodes within a selected depth of the rock.

[0006] Examples of the certain features of an apparatus and methods have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features that will be described hereinafter and which will form the subject of the claims.

DRAWINGS

[0007]For a detailed understanding of the apparatus and methods disclosed herein, reference should be made to the accompanying drawings and the detailed description thereof, wherein like elements are generally given same numerals and wherein:

FIG. 1 shows a schematic diagram of an exemplary drilling system that may utilize an embodiment of an electrical pulse drill bit unit or system disclosed herein for drilling wellbores.

FIG. 2 shows an electric pulse drill bit system according to one non-limiting embodiment of the disclosure;

FIG. 3 shows a cutting device or drill bit according to a non-limiting embodiment of the disclosure;

FIG. 4 shows schematic illustration of exemplary electric field lines generated by an electric pulse cutting device inside a rock being disintegrated into cuttings and fluid flow passages through the cutting device to move the cuttings away from the electrodes, according to one non-limiting embodiment of the disclosure; and

FIG. 5 shows a bottom view of an alternative arrangement of electrodes and fluid flow passage that may be utilized in the electric pulse drill bit system of FIG. 2.

DETAILED DESCRIPTION

[0008] FIG. 1 is a schematic diagram of an exemplary drilling system 100 that may utilize an electrical pulse drill bit unit or system 150 disclosed herein for drilling wellbores. FIG. 1 shows a wellbore 110 (also referred to as a "borehole" or "well") being formed in a formation 119 that includes an upper section 111 with a casing 112 installed therein and a lower section 114 being drilled with a drill string 118 that includes an electrical pulse drill bit unit 150. The drill string 118 includes a tubular member 116 that carries a drilling assembly 130 (also referred to as the "bottomhole assembly" or "BHA") at its bottom end. The drilling tubular 116 may be a drill pipe made up by joining pipe sections or it may be coiled-tubing. An electrical drill bit unit 150 having a cutting device 155 at an end thereof forms the bottom section of the BHA 130. The cutting device 155, when activated (as described later) disintegrates the rock formation 119a at the bottom 110a of the wellbore 110 to form the wellbore section 114 of a selected diameter in the formation 119.

[0009] Still referring to FIG. 1, the drill string 118 is shown conveyed into the wellbore 110 from a rig 180 at the surface 167. The exemplary rig 180 in FIG. 1 is shown as a land rig for ease of explanation. The apparatus and methods disclosed herein may also be utilized with offshore rigs. A rotary table 169 or a top drive 169a coupled to the drill string 118 may be utilized to rotate the drill string 118 and the drilling assembly 130. A control unit (also referred to as a "controller" or "surface controller") 190, which may be a computer- based unit, at the surface 167 may be utilized for receiving and processing data transmitted by various sensors and tools (described later) in the drilling assembly 130 and for controlling selected operations of the various devices and sensors in the drilling assembly 130. The surface controller 190 may include a processor 192, a data storage device (or a computer- readable medium) 194 for storing data and computer programs 196 accessible to the processor 192 for determining various parameters of interest during drilling of the wellbore 110 and for controlling selected operations of the various tools in the BHA and those of drilling of the wellbore. The data storage device 194 may be any suitable device, including, but not limited to, a read-only memory (ROM), a random-access memory (RAM), a flash memory, a magnetic tape, a hard disc and an optical disk. To drill wellbore 110, a drilling fluid 179 is pumped under pressure into the tubular member 116 and the drill bit system 150 is activated. The cutting device 155 disintegrates the rock into cuttings 151. The drilling fluid 179 discharges at the bottom of the cutting device 155 and returns to the surface along with the cuttings 151 via the annular space (also referred as the "annulus") 127 between the drill string 118 and the wellbore 110.

[0010] Still referring to FIG. 1, the drilling assembly 130 may further include one or more downhole sensors (also referred to as the measurement-while-drilling (MWD) sensors and logging-while-drilling (LWD) sensors or tools), collectively designated by numeral 175, and at least one control unit (or controller) 170 for processing data received from the sensors 175. The sensors 175 may include sensors for providing measurements relating to various drilling parameters, including, but not limited to, vibration, whirl, stick-slip, flow rate, pressure, temperature, and weight-on-bit. The drilling assembly further may include sensors or tools, including, but not limited to, resistivity tool, acoustic tool, gamma ray tool, nuclear tool and nuclear magnetic resonance tool. Such sensors and tools are known in the art and are thus not described herein in detail. The drilling assembly 130 also includes a power generation device 186 and a suitable telemetry unit 188, which may utilize any suitable telemetry technique, including, but not limited to, mud pulse telemetry, electromagnetic telemetry, acoustic telemetry and wired pipe. Such telemetry techniques are known in the art and are thus not described herein in detail. Drilling assembly 130 may further include a steering device 160 that enables an operator to steer the cutting device 155 in desired directions to drill deviated wellbores. Stabilizers, such as stabilizers 162 and 164 are provided along the drilling assembly 130 to stabilize the drilling assembly during drilling of the wellbore 110. The controller 170 may include a processor 172, such as a microprocessor, a data storage device 174 and a program 176 for use by the processor to process downhole data and to communicate data with the surface controller 190 via the two-way telemetry unit 188. The data storage device may 172 be any suitable memory device, including, but not limited to, a read-only memory (ROM), random access memory (RAM), flash memory and disk.

[0011] FIG. 2 is a schematic diagram of an exemplary electric pulse drill bit unit or system 200 that may be utilized in any suitable drilling system, including system 100 of FIG. 1. The system 200 includes a cutting device 250 that includes at least a pair of electrodes 252 that come in contact with the rock or the object to be disintegrated. The electrodes 252 include an anode electrode or a cathode electrode 252a and a ground electrode 252b and at least one fluid flow path 254 through at least one or both the electrodes 252, as explained in more detail in reference to FIGS. 3-5. The electrodes 252 are activated by a pulse generation system that includes an electric transformer 210 that supplies power to a rectifier 220 coupled to a high voltage generator 230, which supplies the high voltage energy to the anode or cathode electrode 252a. A pulse generator circuit 240 causes the high voltage generator 230 to provide high voltage pulses to the electrodes 252. The pulse frequency and voltage may be controlled by controllers 170 and or 190 described in reference to FIG. 1. In various aspects, the high voltage generator 230 may include multiple stages and may generate pulses to 600 KV. In one aspect, the pulse frequency may range between 10 Hz and 20 Hz. In general, the pulse frequency may be less than 500Hz. Stabilizers 162 and 164 may be placed on the system 200. Steering unit 160 also may be placed at a suitable location in the system 200.

[0012] FIG. 3 shows an electric pulse cutting device 300 (also referred herein as the "cutting device" or "drill bit") made according to a non-limiting embodiment of the disclosure. The cutting device 300 is shown to include a hollow body 310 that carries an electrode system 320 at its bottom. The electrode system 320 is shown to include a ground electrode 330 that includes an outer circular member 332 and radial members 332a, 330b and 330c extending inward from the circular member 332. An anode or a cathode electrode 340 is shown to include members 340a, 340b and 340c extending outward from the center 350. In the particular configuration of FIG. 3, the electrode members 340a, 340b and 340c are inside the circular electrode member 330 and wherein electrode member 340a is between electrode members 332a and 332b, electrode member 340b is between electrode members 332b and 332c, while electrode member 340c is between electrode members 330c and 330a. A cutting device according to this disclosure may include any number of fluid flow passages in any suitable configurations through the electrodes to move the cuttings away from one or more electrode members when fluid (for example, fluid 179, FIG. 1) flows under pressure through such passages during drilling of a wellbore to aid the cuttings to flow to the surface with the fluid. In the particular configuration of the electrode system 320, the ground electrode 330 is shown to include a number of flow through passages 345 (such as integrated nozzles). Each such passage receives fluid 179 from fluid flow passages 355 in the body 310. The fluid 179 discharges at the bottom of the electrode system 320 and moves the cuttings away from one or more electrode members, which process aids the fluid 179 to carry the cuttings to the surface.

[0013] FIG. 4 shows a schematic diagram 400 of electric field lines generated by an exemplary electric pulse cutting device made according to this disclosure inside an object, such as a rock, to be disintegrated into cuttings 445 and fluid flow passages through the cutting device that move the cuttings away from one or more electrodes or electrode members. FIG. 4 shows a pair of electrodes 420 and 430 in contact with an object 410 immersed in a fluid, such as a drilling fluid 179 (FIG. 1). Electrode 420 includes a fluid passage 422 that receives the fluid 179 under pressure from a passage 460 in the body of the cutting device and discharges the fluid 179 onto the rock 410 in contact with the electrode 420. Similarly, the electrode 430 includes a fluid passage 432 having an inlet 432a that receives the fluid 179 from a passage 465 in the body and discharges the received fluid onto the rock 410. The electrodes 420 and 430 when excited produce electric field lines 460a in the fluid 179 and lines 460b inside the rock 410. The depth of the field lines 460b in the rock 410 depends upon the voltage and the spacing between the electrodes. Electric discharge along field line 460b produce high temperature plasma resulting pressure waves inside the rock 410 that disintegrate the rock into cuttings 445. The number of electrode members, their relative positions, the voltage and the frequency of pulses is selected for optimal wellbore formation and rate of penetration of the drill bit (150, FIG. 1) into the formation. It should be noted that any suitable configuration of the electrodes and flow passages may be utilized for electrical pulse cutting systems made according to this disclosure.

[0014] FIG. 5 shows a bottom view of an alternative arrangement of electrodes 552 of an electric pulse cutting device 500 according to another non-limiting embodiment of the disclosure. The cutting device 500 is shown to include ground electrodes 520a, 520b and 520c placed spaced apart along a circle. Anode electrodes or cathode electrodes 530a, 530b and 530c are also placed spaced apart along the circle, wherein electrode 530a is between electrode 520a and 520b, electrode 530b is between electrode 520b and 520c while electrode 530c is between electrode 520c and 520a. Electrodes 520a, 520b and 520c are shown to include fluid passages 524a, 524b and 524c respectively, while electrodes 530a, 530b and 530c are shown to include fluid passages 534a, 534b and 534c respectively. Additionally, electrodes 530a, 530b and 530c are shown to include insulations 532a, 532b and 532c respectively.

[0015] The foregoing disclosure is directed to the certain exemplary non-limiting embodiments. Various modifications will be apparent to those skilled in the art. It is intended that all such modifications within the scope of the appended claims be embraced by the foregoing disclosure. The words "comprising" and "comprises" as used in the claims are to be interpreted to mean "including but not limited to". Also, the abstract is not to be used to limit the scope of the claims.