RU2464402C2 - Electric pulse well drilling method, and drilling bit - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: drilling is performed at optimum parameters. Specific energy generated on unit length of interelectrode gap is accepted considering specific compression strength of mine rock; movement spacing of drilling bit electrodes during the time period between two high-voltage pulses is selected considering the number of pulses, which is required for electrodes to cover the distance equal to the length of interelectrode gap, and required number of pulses is accepted considering optimum high-voltage pulse energy required for generation of energy in interelectrode gap, which is stored in source of high-voltage pulses, and number of drilling bit electrodes. High-voltage electrodes (1) of drilling bit are installed so that they can move on axis (3) that is electrically connected to high-voltage current lead (5). High-voltage current lead (5) is separated from housing (4) by means of high-voltage insulator (6). Rock-destructing elements (7) with hard-alloy cutters (8) are fixed in the end face part of housing (4). Lengths of interelectrode gaps between high-voltage electrodes (1) and earthed electrodes (2), as well as rock-destructing elements (7) earthed through housing (4) are equal.

EFFECT: application of method using the bit improves the method efficiency.

5 cl, 2 dwg, 1 tbl

Description

The invention relates to the field of destruction of rocks by high-voltage electric discharges developing inside the rock, and additional destruction by carbide cutters of a rotating drill bit. This invention can find application in drilling wells of various diameters without coring: from wells of relatively small diameters required during exploration work, during oil and gas production, to wells with a diameter of 0.5 m or more, which are required in the mining industry and in construction works.

Known electric pulse method of destruction (drilling, cutting) of rocks (patent RU No. 2232271, IPC 7 Е21С 37/18, ЕВВ 7/15, publ. 10.07.2004. Bull. No. 19). The main feature of this method of rock destruction by a moving two-rod electrode device is that the step of moving the device’s electrodes between two electrical pulses is selected from the following condition:

, причем

,

, and

,

where m is the step of moving the electrodes of the device, mm;

W _zap - energy stored by the pulse source, J;

L is the length of the interelectrode gap, mm;

W _opt1 is the optimal fracture energy per pulse for a rock with a Protodyakonov coefficient of 5 J;

n is the number of pulses applied to the two-rod electrode device.

The main disadvantage of this method is that the method is effective only when using a drill bit made in the form of two moving rod electrodes, since when the steps of moving the electrodes for a multi-electrode drill bit are implemented, the destruction process occurs non-uniformly over the entire surface of the face, and individual protruding non-destroyed plots. Moreover, two electrodes (see the drawing in the description of this invention) have practically no mechanical effect on the bottom of the well (or slit). In this regard, the drilling speed of this method by other drilling devices is relatively low, and the application of the method is limited.

Also known is the prototype method of drilling rocks using electric impulse discharges (patent for invention RU 2319009, IPC C2 Е21С 37/18, ЕВВ 7/00 (2006.01), publ. 10.03.2008. Bull. No. 7), according to which the main parameters drilling with a multi-electrode rotating drill bit is selected from the following conditions:

,

,

where f is the frequency of the pulses, imp / s;

υ - peripheral speed of rotation of the drill bit, mm / s;

m is the step of movement of the drill bit between two pulses, mm / imp.

The main disadvantage of the prototype method is the relatively low drilling efficiency, because it does not provide for the determination of the specific energy required to separate per unit length of the interelectrode gap in a particular rock, and there is no possibility of determining the step of movement during rotation of a multi-electrode (number of electrodes k> 3) drill bit. In addition, the comparatively low drilling efficiency is due to the fact that the prototype drilling method does not allow for the effective combined rock destruction: by high-voltage impulse discharges and carbide cutters (cutters in the drill are not provided by this method), and the electrodes are separated from the shell massif only a small part of the pieces of rock that are not torn off by electrical discharges or flushing fluid and are very weakly connected to the massif.

A drill bit is known for an electropulse method of drilling wells with a rotary bit (patent for invention SU No. 730029, IPC 5 E21C 37/18, publ. 10/30/93. Bull. No. 39-40), including a grounded outer crown reinforced with carbide cutters with a protruding in the center there is an electrode inside which high-voltage electrodes are provided with insulation, while the drill bit electrode system is made in the form of an electrode cell, the electrodes of which are arranged so as to form a shape close to the circle sector. When the drill bit rotates around the central axis of the drill, carbide cutters destroy the rock, weakened by high-voltage pulse discharges, but not torn off from the array.

The disadvantage of this drill bit is the relatively low efficiency of rock destruction. This is due to the fact that the bulk of carbide cutters are located at a considerable distance from the interelectrode (discharge) gaps, where the zone of rock destruction by high-voltage discharges is located. In the ideal case, when the drill bit is rotated, the cutters should immediately fall into the zone destroyed by the discharges and further destroy the weakened rock in it. In the considered drill bit, only two cutters located at the ends of the rock destruction zone by discharges partially perform this work. All other incisors, before being in this zone, pass, without producing effective destruction, a significant path along the bottom of the well: almost half of the incisors in front of the rock destruction zone by discharges, and the rest behind it.

To increase the efficiency of rock destruction at the bottom of the well by 15% or more allows the electropulse drill bit selected for the prototype (patent for utility model RU No. 69152, IPC E21C 37/18 (2006.01), publ. 10.12.2007. Bull. No. 34), which implements effective combined destruction of rocks: high-voltage pulsed discharges and carbide cutters, and which contains a grounded case and rock-breaking elements reinforced with cutters attached to it, forming elec- tric elements with adjacent insulated high-voltage electrodes native cell, wherein in a near portion of the drill bit in the direction of rotation of each high voltage electrode is placed in front of reinforced cutter rock cutting element in the region of the discharge (an interelectrode) interval, and each rock cutting element located before the high voltage electrode is located away at a distance greater than the discharge gap. In addition, the bit is made in the form of several electrode cells, and each electrode cell is additionally equipped with one or more high-voltage electrodes; the outer ends of the rock-cutting elements reinforced with cutters are connected by conductive arcs reinforced by additional cutters; the bottom-hole part of the high-voltage electrode is made in the form of a plate, and the current-supplying part of one or more high-voltage electrodes is located on the outer surface of the body of the drill bit.

The main disadvantage of this drill bit is the relatively low reliability of its operation due to the complexity of the design. This is due to the fact that high voltage electrodes, incl. additional ones are located evenly throughout the bottom-hole part of the bit, and each high-voltage electrode is equipped with a separate insulation that can withstand a pulsed voltage of hundreds of kilovolts. It is especially difficult to make reliable insulation of each high-voltage electrode with a bottom hole diameter of less than 200 mm. In addition, with relatively large diameters of the drill bit, to increase the reliability of the insulation, it is advisable to place the current-carrying parts of high-voltage electrodes on the outer surface of the drill bit body, but this leads to an additional complication of the drill bit design, which increases the bit cost and makes it difficult to maintain.

The main technical result of the proposed method is to increase the efficiency of drilling with multi-electrode bits when rock is destroyed by high-voltage pulsed discharges and the additional mechanical action of carbide cutters on it due to the determination of the specific energy required to separate the interelectrode gap per unit length, while simultaneously determining the step of movement of the drill bit electrodes during the time between two high-voltage pulses supplied to the bit, and that the depth of breaking rock in one revolution of the bit. In this case, the specific energy value is determined by the known tabular value of the specific mechanical strength for uniaxial compression σ _sr (Lyubimov N.I., Nosenko L.I. Handbook of physical and mechanical parameters of rocks of ore regions. Moscow: Nedra Publishing House, 1978; Erofeev L.Ya., Vakhrameev G.S., Zinchenko VS, Nomokonova G.G. Rock Physics. Tomsk: TPU Publishing House, 2006).

The specified technical result is achieved by the fact that in the electric-pulse method of drilling wells with high-voltage pulsed discharges and mechanical impact on the bottom with the optimal parameters selected for a multi-electrode drill bit, according to the proposed solution, the specific energy released per unit length of the interelectrode gap M _beats is:

M _ud ≥0,23σ _SJ, J / mm

where 0.23 is the coefficient of proportionality;

σ _{compression channel} - specific rock compressive strength, kgf / mm ^2.

The step of moving the electrodes of the drill bit during the time between two high-voltage pulses m is chosen from the condition:

, мм,

mm

where L is the length of the interelectrode gap, mm;

n is the number of pulses required for the electrodes to travel a distance equal to L, imp .:

here W _opt is the optimal energy of a high-voltage pulse necessary for separation in the interelectrode gap, J (for materials on W _opt, see the example of a specific implementation).

In addition, it is advisable to carry out drilling, destroying the rock for one revolution of the drill bit to a depth of:

h = (0.2 ÷ 0.3) L, mm.

This choice of h is due to the fact that during electrical breakdown of rock between two bipolar electrodes, the discharge tears off a piece of rock from the array with the formation of a spall funnel, the depth of which in different rocks is 0.2–0.3 of the length of the interelectrode gap. In this regard, h is chosen no more than 0.3L in order to mechanically act only on that rock, which is located above the bottom of each spall funnel.

The main technical result of the proposed device is to increase the reliability of high-voltage insulation by simplifying the design. The maintenance of the drill bit is also simplified, especially when replacing failed high-voltage insulation, and the cost of the bit is reduced.

The specified technical result is achieved by the fact that in the drill bit containing high-voltage and grounded electrodes, as well as a grounded body to which rock-breaking elements reinforced with carbide cutters are attached, according to the proposed solution, high-voltage electrodes are mounted on one axis and are movable in a vertical plane, and the lengths of interelectrode gaps between each high-voltage electrode and the nearest grounded electrode, as well as between the inner ends of the rock cutting elements and ne high voltage electrode are identical.

It is also advisable to grounded and / or high-voltage electrodes to perform spring-loaded.

In addition, it is advisable to carry out each high-voltage electrode in the form of a tongue.

Examples of specific performance of the proposed method and device.

Figure 1 shows the end view of the proposed drill bit, and figure 2 presents a photograph of the manufactured bit, which conducted experimental work on the implementation of the method and device. The drill bit consists of three high-voltage electrodes 1 and two grounded electrodes 2, i.e. total number of electrodes k = 5. High-voltage electrodes 1 are made in the form of tongues movable in a vertical plane, fixed at one end on axis 3. With a small weight of the electrodes and a higher repetition rate of high-voltage pulse discharges, it is advisable to make these electrodes, as well as grounded 2 or part of the electrodes, spring-loaded. A high-voltage conductor 5, which is electrically connected to the axis 3 and provided with a high-voltage insulator 6, is passed through the body of the drill bit 4, and in the part of the bottom face of the body 4, where there are no high-voltage electrodes 1 and grounded electrodes 2, rock-cutting elements 7 reinforced with carbide cutters 8 are made, made from VK8 alloy. The lengths of the interelectrode gaps between each high-voltage electrode 1 and the nearest grounded electrode 2 are equal to the lengths of the interelectrode gaps between the inner ends of the rock cutting elements 7 and the adjacent high-voltage electrode 1. The diameter of the bit is D = 200 mm, and the length of each interelectrode gap is L = 28 mm.

Consider the work of this bit in the proposed way. The drill bit is mounted on a rock block placed in a flushing fluid (purified water) so that it completely covers all the electrodes. Used sandstone and granite blocks with a specific mechanical compressive strength (σ _SJ) 8.6 and 13.0 kgf / mm ^2, respectively. Flushing fluid is pumped through the internal cavity of the drill bit, the housing 4 is grounded, while the rock cutting elements 7 and the grounded electrodes 2 are grounded, and from a source of high-voltage pulses with an stored energy of 75 J (operating voltage of the pulse source U _p = 215 kV) through the high-voltage conductor 5 to the axis 3 high-voltage electrodes 1 supply high voltage pulses and immediately begin to rotate the drill bit at a speed of 0.177 rpm with an axial force of 150 kgf for sandstone and 375 kgf for granite. During electrical breakdowns of the rock between the high-voltage electrodes 1 and grounded 2, as well as between the inner ends of the rock-cutting elements 7 and the adjacent high-voltage electrode in the rock, electrical discharges occur, tearing off part of the rock with the formation of spalling funnels, which are filled with a flushing liquid acting as an insulating material . Each subsequent discharge automatically occurs in undamaged rock. Near the spalling funnels, the rock from the action of electric discharges is in a weakened, disturbed state, but is not torn off from the massif. Carbide cutters 8 cut the protrusions of rock remaining between the spalling funnels to a depth that is no more than the depth of the spalling funnel.

Basic experimental data obtained for a study of optimum parameters of the method are given in the table, where the energy released per unit length of the interelectrode gap M _ud ≥0,23σ _SJ, J / mm, characterizes the energy input per unit length of the electrode gap L, mm, depending from the rock fortress, at which its destruction by a high-voltage discharge is still possible with the formation of a spall funnel; Q, cm ³ / imp. - the productivity of the destruction of the rock in one pulse; w is the energy spent on the destruction of 1 cm ³ rock.

Table 1 Granite M _beats , J / mm Q, cm ³ / imp. w, J / cm ³ Destruction effect 3.96 0.13 445 Funnel 2.97 0.10 530 Funnel 2,37 0.08 1018 No split 1.98 0.058 1188 No split Sandstone 2.83 0.38 118 Funnel 1.96 0.19 158 Funnel 1,64 0,078 309 No split 1.44 0.05 491 No split

The table shows that when M _ud = 0,23σ _{compression channel} (for granite 2.97 J / mm for sandstone 1.96 J / mm) and M _beats> 0,23σ _{compression channel} (for granite 3.96 J / mm , for sandstone 2.83 J / mm) rock destruction occurs. When M _ud <0,23σ _{compression channel} (for granite 2.37 and 1.98 J / mm for sandstone 1.64 and 1.44 J / mm) no formation of spall funnel, despite the fact that the discharge passage is introduced into the interior rock massif. Table for M _ud <0,23σ given volume _{compression channel} well at inlet and outlet from the sample discharge channel without formation of spall funnel.

For experimental verification of the step of moving the electrode system

при

используют буровое долото с общим числом электродов k=5. Значение W_опт для песчаника 510 Дж и для гранита 527 Дж взяты из табл.2 на с.8 описания известного изобретения (аналога): патент RU №2232271, МПК 7 Е21С 37/18, Е21В 7/15, опубл. 10.07.2004. Бюл. №19.

at

using a drill bit with a total number of electrodes k = 5. The value of W _opt for sandstone 510 J and for granite 527 J are taken from table 2 on p. 8 of the description of the known invention (analogue): patent RU No. 2232271, IPC 7 Е21С 37/18, Е21В 7/15, publ. 07/10/2004. Bull. No. 19.

In our proposed invention, W _app = M _beats · L. The energy stored by the pulse source used by us is W _zap = 75 J, which corresponds to:

а шаг перемещения составляет m=L/n=28/27=1,04 мм.Based on the table, this is more than the value of M _beats necessary for sandstone. Therefore, the number of pulses

and the displacement step is m = L / n = 28/27 = 1.04 mm.

For one revolution of the drill bit (340 s), 560 pulses were supplied, which at L = 28 mm corresponds to n = 25 pulses, i.e. there is good agreement between the experimental results and the calculation according to the proposed formula for n.

As a result, during one revolution, the proposed method drilled a well with a depth of 5.5 mm at t = 1.04 mm. Without applying high voltage impulses to the drill bit, i.e. only carbide cutters, 1 mm drilled per revolution, i.e. several times less.

Reducing the step of moving the electrode system to m = 0.7 mm, i.e. 1.48 times compared with m = 1.04 mm, led to an increase in the number of pulses that must be applied along the interelectrode distance to n = L / m = 28 / 0.7 = 40 pulses. When, at a constant pulse repetition rate from the source of high-voltage pulses, the rotational speed of the bit was reduced by 1.48 times, this, accordingly, led to a decrease in the drilling speed, because one revolution of the bit took more time. At the same time, the drilling depth at the same time with discharges and cutters for one revolution of the bit did not increase and amounted to 5.5 mm, because it is determined by the depth of penetration of the discharge channel into the rock h = (0.2 ÷ 0.3) L. The excess energy released in the interelectrode gap for 40 pulses was spent on regrinding of the rock cut off from the bottom - sludge, i.e. with a decrease in the step of moving the electrode system under unchanged other conditions, the energy consumption for the destruction of a unit volume of rock increases and the speed of combined drilling decreases.

An increase in the displacement step m> 1.04 mm leads to an increase in the speed of rotation of the bit and to a decrease in the number of impulses supplied per revolution at a constant pulse repetition rate. This, in turn, leads to a decrease in the volume of destruction by high-voltage discharges up to the appearance of indestructible zones, which reduces drilling productivity and increases energy consumption during combined drilling.

We performed sandstone drilling at a step of moving the electrode system m = 3 mm at the above drilling parameters. The number of pulses along the length of the interelectrode gap L = 28 mm was n = 9 pulses, which is less than 27 pulses. 3 times with a step m = 1.04 mm. For one revolution of the drill bit, the proposed method drilled a well 2 mm deep, which is 2 times more than the mechanical method (see above), but 2.75 times less than the proposed method with a step m = 1.04 mm.

With repeated exposure of the discharge channel to the rock, the maximum penetration depth of the channel and, consequently, the depth of destruction by the electric pulse method is up to 0.3L, depending on the length of the interelectrode gap and the properties of the rocks. At the same time, protrusions remain on the bottom of the well. Therefore, the penetration depth of the well with an electric pulse drill bit, not reinforced with cutters, per one revolution of the bit is less than 0.3L. The rotation of the electric pulse drill bit with carbide cutters can significantly increase the depth of drilling, cutting off the protrusions of the rock at the bottom of the well. In this case, the axial pressure on the drill bit is selected from the drilling condition to a depth of (0.2 ÷ 0.3) L.

In our experience, when drilling sandstone with high-voltage electric discharges only, the maximum fracture depth from the introduction of the discharge channel into the sandstone was 5.6 mm, and the depth of penetration by the drill bit was 2.5 mm, which is 2.24 times less than the maximum fracture depth, since the drill bit was located on the undestroyed ledges of the rock. When drilling by the proposed method with an axial pressure on the drill bit of 150 kgf, the penetration depth of the drill bit per revolution in sandstone was 5.5 mm, i.e. almost equal to the maximum depth of the spalling funnels.

The experiments also showed high reliability of high-voltage insulation, which has never failed. This is due to the simplification of the design of the drill bit. In the proposed design of the drill bit, the high-voltage insulation is made in the form of one insulator 6 of the high-voltage current lead 5, and in the prototype bit, each high-voltage electrode is equipped with its own high-voltage insulation, and grounded elements are placed between these electrodes. As a result of this, the thickness of the high-voltage insulator 6 bits of the proposed design is several times greater than the insulation thickness of each high-voltage electrode of the prototype bit, therefore, its electric strength is several times higher than in the prototype.

Claims (5)

1. Electropulse method of drilling wells with high-voltage pulsed discharges and mechanical impact on the bottom, according to which a multi-electrode drill bit is drilled at selected optimal parameters, characterized in that the specific energy released per unit length of the interelectrode gap, M _beats
M _ud ≥0,23σ _SJ, J / mm
where 0.23 is the coefficient of proportionality;
σ _{compression channel} - specific rock compressive strength, kgf / mm ^2,
the step of moving the electrodes of the drill bit during the time between two high-voltage pulses m is chosen from the condition

where L is the length of the interelectrode gap, mm;
n is the number of pulses required for the electrodes to travel a distance equal to L, imp .:

where W _opt is the optimal energy of a high-voltage pulse, necessary for separation in the interelectrode gap, J;
W _zap - energy stored by a source of high voltage pulses, J;
k is the number of electrodes of the drill bit, pcs. 2. The electric pulse method according to claim 1, characterized in that the drilling is carried out, destroying the rock for one revolution of the drill bit to a depth
h = (0.2 ÷ 0.3) L, mm. 3. A drill bit containing high-voltage and grounded electrodes, as well as a grounded housing, to which rock-breaking elements reinforced with carbide cutters are attached, characterized in that the high-voltage electrodes are mounted on the same axis and are movable in the vertical plane, and the lengths of the interelectrode gaps between each high-voltage electrode and the nearest grounded electrode, as well as between the inner ends of the rock cutting elements and the adjacent high-voltage electrode are the same. 4. The drill bit according to claim 3, characterized in that the grounded and / or high-voltage electrodes are spring-loaded. 5. The drill bit according to claim 3, characterized in that each high-voltage electrode is made in the form of a tongue.

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