RU78255U1 - CORE DRILLING DRILL WITH INTERNAL LIQUID CIRCULATION - Google Patents

Abstract

The core projectile is designed for drilling wells with bottom-hole circulation of fluid created when the shell is pacing. The projectile includes a core pipe and a ball valve housing rigidly connected to its upper end from a pipe of the same diameter. A steel ball is installed in the valve body, a seat under the ball, and side windows are made for the liquid to exit the core pipe into the well. The ball is made hollow. The outer diameter of the ball and the diameter of the channel of the valve seat are determined by mathematical expressions from the condition that the cross-sectional area of the channel of the seat is equal to the cross-sectional area of the annular gap between the ball and the inner walls of the valve body. The inner diameter of the ball is determined by mathematical expression from the condition of the necessary rate of fall of the ball in the liquid. Using the projectile improves the quality of the core being drilled and the flight length, since the diameter of the channel of the seat and ball of the valve is increased in the projectile and the hydraulic resistance to opening the valve and the circulation of fluid in the projectile during its walking is reduced. 1 s.p. crystals, 3 ill., 1 tab., 1 ave.

Description

The proposed utility model relates to the field of well drilling, namely, to devices that, due to forced mechanical walk of a drill, create reverse internal (bottom-hole) circulation of flushing fluid in its core pipe and well, consisting in the movement of fluid through a closed system in a drill without its exit to the surface and increasing the quality of the core.

Known drill containing a rock cutting bit, a core pipe, a ball valve located inside the upper part of the pipe, a piston with a second ball valve, and a core pipe weighting agent. The piston is connected to the drill pipe string, and the upper part of the core pipe acts as a pump cylinder [2]. Also known is a projectile containing a core pipe and a special pump mounted above it with two ball valves. The pump piston is rigidly connected to the core pipe, and the cylinder to the drill pipe string [3].

The reverse internal (bottom-hole) circulation of the flushing fluid for the removal of the drilled rock particles from under the cutters of the crown is ensured by pacing the pump piston in the core shell [2] and the pump cylinder in the core shell [3]. Walking is carried out periodically using a winch or lever of a drilling rig. In this case, the drill bit of the core projectile does not come off the bottom and the necessary axial load on it is constantly supported by the gravity of the special weighting agent as part of the core projectile.

Core drill [2] and [3] are operational and increase the percentage of core output. However, they are bulky, massive, not easy to maintain, require large material costs for their manufacture and ensure reliable operation, since when working in a slurry environment, their cylinders and pistons quickly wear out. Therefore, core shells [2] and [3] are not used when drilling production wells.

Known drill containing a rock cutting bit, core pipe, an adapter for a drill pipe string and a ball valve, including: a nipple with a channel for the passage of fluid and a seat for a ball, a steel ball, a sludge conduit with side openings for the exit of sludge from the projectile into the well and a limiter the ball moves up [1]. When drilling, the core projectile is continuously rotated while maintaining the required axial load at the bottom and periodically paced (lift the shell above the bottom and dump it on the bottom). The rotation, pacing of the core drill and the transfer of axial load on it is carried out using a drill pipe string. In the process of pacing the core shell inside it and in the well, fluid is circulated.

It is assumed that during the ascent from the bottom of the core projectile [1], the ball valve is always closed, the pressure in the core pipe decreases and fluid moves from the outer annular gap between the walls of the well and the shell along with the slurry. When the projectile is dropped to the bottom, the ball rises up under the pressure of the liquid in the core pipe and the valve opens. In this case, the main part of the liquid with the sludge moves upward and pours into the well through the side openings in the sludge-conducting tube, and the smaller part returns to the bottom through the annular gap between the core and the inner walls of the core pipe.

In practice, a core drill [1] is known as a “pumpless drill”. Its most effective application is for drilling wells that absorb flushing fluid, and for difficulties in delivering fluids to the wells. Required condition

for drilling with a core projectile [1]: in the well there should be a column of liquid with a height slightly higher than the height of the projectile. In most cases, such a liquid is water. If there is no groundwater in the well, then the required amount of water is poured into it during the drilling process. In each voyage, when a projectile is walking around, the water circulating in it is enriched with sludge from the drilled rocks. Therefore, practically drilling is carried out using a natural solution with a density of about ρ = 1150 kg / m ³ .

The simplicity of design, the availability of manufacturing and the economical use of a core projectile [1] are the main reasons for drilling them in the production of wells of any required diameters. Most wells are drilled with a core projectile [1] in loose rocks, using core pipes with diameters from 0.108 / 0.099 to 0.146 / 0.137 m for this.

However, in the process of drilling when pacing a known core projectile [1], the core entering its core pipe experiences the pressure of the liquid above the core. The values of this pressure can be large and depend on the design of the elements of the ball valve of the projectile and the ratio of their parameters. The pressure of the liquid in the core tube above the core prevents it from entering the pipe, and the selected core does not always satisfy the requirements for it, as it is sealed and has impaired physical and mechanical characteristics.

When a projectile falls on the bottom of a well, an increase in the fluid pressure in the core pipe is caused first by the need to lift the ball, then by high-speed resistance to fluid flow from the core pipe into the sludge-conducting tube through the valve seat channel. To reduce the resistance to fluid exit from the core pipe in the prototype shells, it is recommended to use sludge-conducting tubes with a diameter of 0.033-0.040 m [1, p.290]. The diameter of the ball is 0.026-0.036 m, and the diameter of the channel of the seat (nipple) of the ball valve is 0.022-0.030 m, respectively. Such valve seat channel diameters are 4-5 times smaller than the core diameter of core pipes with diameters from 0.108 / 0.099 to 0.146 / 0.137 m.

The fluid velocity through the valve channel is proportional to the ratio of the square of the core diameter of the core pipe to the diameter of the channel. With small channel diameters, these speeds are large. For example, when a projectile with a core tube with a diameter of 0.146 / 0.137 m falls at a speed of only 1 m / s, the velocity of the fluid flow through the channel with a diameter of 0.026 m reaches 28 m / s. At the same time, the local velocity of the fluid through the valve channel is proportional to the local high-speed resistance.

High-speed local resistance is determined by the Weisbach formula [for example, 4, p.168]

where ζ is the coefficient of local resistance;

V is the fluid velocity through the valve seat channel, m / s;

ρ is the density of the fluid flowing through the channel of the saddle, kg / m ³ ;

v _k is the velocity of the projectile to the face during discharge, m / s;

D _k - the inner diameter of the core pipe, m;

d _c - the diameter of the channel of the seat of the ball valve, m

The value of the coefficient ζ is taken from the tables [for example, 6, Table 4-2] depending on the area ratio: the section of the saddle channel to the cross-section of the core tube and the cross section of the saddle channel to the cross-section of the sludge-conducting tube. When using a projectile with a saddle channel with a diameter of d _c = 0.026 m, an inner diameter of the sludge-conducting tube of 0.04 m and a core tube with diameters of 0.146 / 0.137 m, the coefficient ζ is approximately equal to 1.5. The velocity of the drill when it is dropped to the bottom often reaches 1.5 m / s. Having taken ζ = 1.5; ρ = 1150 kg / m ³ and the velocity of the projectile total V _K = 1 m / s, according to expression (1) calculate

The obtained value of the fluid pressure in the core pipe on the core is quite high. The rocks entering the core pipe during drilling are compacted and their physical and mechanical properties are violated.

When lifting a projectile from the bottom to create a vacuum in the core pipe above the core and suction of fluid from the bottom, it is necessary to accelerate the closing of the valve. For this, it is necessary that the ball instantly overcome the distance of 0.15 m recommended in [1] and block the seat channel. However, when the projectile rises, the liquid enters the core tube primarily through the side windows in the sludge-conducting tube located below the ball, since this does not interfere. This fluid flow and the small annular gap between the ball and the walls of the sludge conduit tube inhibit the fall of the ball of small mass. Therefore, not every projectile lift ensures that liquid enters the core tube from the bottom through the annular gap between its walls and the core and the core in the core tube is rubbed. Because of this, the flight is often stopped, and the projectile is lifted from the well.

It is possible to reduce the pressure of the liquid on the core from high-speed resistance to the exit of liquid from the core pipe through the valve seat channel by increasing the diameter of the channel, respectively, of the ball and sludge discharge pipe. However, as the diameter of the ball increases, the mass of the ball increases in proportion to the diameter in the cube. This is unacceptable, since it increases the pressure of the fluid on the core in the core pipe when the valve is opened.

The essence of the proposed technical solution is to create a core-receiving shell design, which allows to increase the diameters of the channel and the steel ball of the valve while reducing the mass of the ball. This significantly reduces the pressure of the fluid on the core in the core pipe while pacing the shell during drilling.

The main technical result of the proposed utility model is to improve the quality of the core being drilled by reducing the hydraulic resistance of the fluid circulation in the core projectile while pacing it while drilling.

The technical result is achieved as follows. The proposed core drill for drilling with internal circulation of the fluid contains a core pipe with a drill bit, an adapter for

a drill pipe string and a ball valve including a metal body, a saddle with a central through channel for fluid passage, a stainless steel ball to block the channel, a sludge conduit with holes in its side walls to allow fluid and cuttings from the drilled rocks to enter the well.

The distinctive features of the proposed core projectile are that the ball is hollow, the holes for the exit of fluid and sludge into the well are made in the side walls of the valve body, the inner diameter of the valve body is taken to be the inner diameter of the core tube, the diameter of the valve seat channel and the outer diameter of the ball are selected possible by the reliability of the channel overlapping by the ball and the ball moving up and down in the valve body from the condition that the saddle channel cross-sectional area and the annular gap between the ball and the inner walls of the valve body.

A distinctive feature of the proposed core projectile is also that the inner diameter of the ball is determined by the expression obtained from the condition of the necessary rate of fall of the ball in the liquid

where d and D are the inner and outer diameters of the ball, respectively, m

Figure 1 shows a General view of the proposed core projectile during the climb up when pacing; figure 2 is the same during the movement of the projectile to the bottom and during drilling; figure 3 - diagram of the forces acting on the ball valve shell at the initial moment of dumping it to the bottom. Arrows with dashed lines in FIGS. 1 and 2 conventionally show a scheme of fluid circulation when a shell is walking around.

The proposed core drill for drilling with internal fluid circulation consists of a rock cutting rock drill bit 1, core tube 2, valve body 3, valve seat 4 with a central through passage for fluid passage through it, steel hollow

ball 5, side holes 6 in the walls of the valve body to exit through them sludge from the projectile into the well, an adapter 7 under the drill pipe string 8.

Drilling the proposed shell is carried out according to the pump-free drilling scheme. A core projectile with a ball valve is lowered into the well on a drill pipe string, rotated and periodically paced. In connection with the design features of the proposed core projectile, the conditions for circulating fluid in it when it is paced differ from the conditions for circulating fluid in the apparatus [1] and can improve the quality of core obtained during drilling, i.e. increase drilling efficiency.

During the lifting on the string of drill pipes 8 of the core drill from the bottom of the well (Fig. 1), ball 5 closes the channel of the valve seat 4. In this case, the fluid pressure decreases inside the core pipe 2 above the core and from the outer annular gap between the borehole walls and the projectile, the fluid moves (is sucked) into the core pipe 2, which involves drilling rock particles from the bottom, washes and cools the drill bit 1. During dropping the projectile to the bottom of the well (figure 2), the ball 5 rises up under the pressure of the liquid located in the core pipe 2 and the valve opens.

The differences in the conditions of fluid circulation during drilling with the proposed core drill are as follows. When dropping a projectile to the bottom at the first moment after opening the channel of the valve seat 4, the ball 5 rises no higher than the side holes 6 in the walls of the housing 3 and does not reach the adapter 7, which can at the same time perform the functions of the ball limiter up. The difference is also in the fact that after the discharge of the projectile to the bottom, already at the beginning of the drill bit 1 at the bottom, the ball 5 is lowered and held by the flow of liquid exiting the core pipe 2 at a small distance from the valve seat 4. The next time the projectile rises from the bottom, the ball 5 from this position instantly lowers into the seat 4 and closes the valve channel. Instantly lower the ball 5 into the saddle 4 when lifting the core projectile from the bottom contribute to: a small distance

between the ball and the seat, the pressure on the ball of fluid flow from the well through the side windows 6 of the valve body located above it into the core pipe and the velocity of the ball falling in the liquid is greater than that of the prototype.

These differences are due to the fact that in the proposed projectile significantly increased: a) the diameter of the channel of the saddle 4; b) the area of the annular section between the ball 5 and the inner walls of the valve body 3; c) the outer diameter and the rate of incidence of the ball in the liquid while maintaining the necessary mass of the ball by making it hollow.

Increasing the diameter of the channel of the seat 4 and the annular gap between the ball 5 and the valve body 3 reduces the speed resistance to movement of the main part of the liquid with slurry from the core pipe 2 through the channel 4 of the seat, the annular gap between the ball 5 and the inner walls of the valve body 3 and then through the side holes 6 in the valve body 3 into the well. This significantly reduces the pressure of the liquid on the core 9 in the core pipe 2 and improves the quality of the obtained core.

The execution of the ball 5 hollow allows you to increase its outer diameter to the size necessary to overlap the increased diameter of the channel of the seat 4. The mass of the hollow ball 5 with an increase in its outer diameter is increased to a limit that provides the necessary and somewhat greater than the prototype, the speed of the ball in the liquid. Moreover, the inner diameter of the ball is chosen such that the specific gravity of the ball (per unit area of the channel of the saddle 4) is less than that of the projectile [1]. Accordingly, there is less fluid pressure on the core in the core pipe when the valve is opened and the core being drilled get better quality.

The ability to perform the proposed core projectile using the above distinctive features and achieve the claimed technical result are confirmed theoretically.

When the core projectile is dropped to the bottom of the well in the core pipe 2 above the core, an excess fluid pressure p occurs, which is necessary to open the ball valve and exit the fluid

core pipe (figure 3). The pressure p creates the pressure force F of the liquid in the core pipe 2 on the ball 5 through the channel with a diameter d _c of the valve seat 4

To raise the ball, the conditions must be met

where M is the mass of the ball, kg;

F ₁ - pressure force of a liquid column in the well above the ball, pressing it to the valve seat, N;

F ₂ - pressure force of the liquid column in the well under the ball above the valve seat, pushing the ball out of the seat, N.

The mass of a solid (solid) ball of diameter D is

where ρ _m is the density of the material of the ball, kg / m ³ .

Pressure forces on a ball of a liquid column with a height N in a well

where ρ is the density of the liquid column, kg / m ³ .

Substituting (3), (5), (6) and (7) into (4) and solving it with respect to p, we obtain

A decrease in ρ by expression (8) is practically possible only by changing the values of ρ _m , D and d _c . Fundamentally, a ball can be made of metals of various densities and polymers. In a slurry environment, a stainless steel ball works best. The surface of balls made of lighter metals and plastics is scratched when working in a slurry environment, and they quickly fail.

From the expression (8) it follows that the pressure p decreases in proportion to the increase in the diameter d _{c of} the valve seat channel squared. This is good, as it corresponds to one of the distinguishing features

proposed utility model. However, with an increase in the diameter of the seat channel, the diameter of the ball increases accordingly (moreover, D is greater than d _c ). A, since in the expression (8) the diameter of the ball is in the cube, and the diameter of the saddle channel is squared, it turns out that with increasing d _{c the} value of p increases. But this is true when using a solid ball. One of the distinguishing features of the proposed technical solution is that the ball is made hollow. The mass of the hollow ball is

Substituting (3), (6), (7) and (9) into (4) and solving it with respect to p, we obtain

In the proposed core projectile, when the valve is closed, the ball plunges into the saddle to half its diameter. This ensures a stable position of the ball in the saddle during the extraction of the core projectile from the well. So that the particles of sludge in the liquid do not settle on the surface of the seat and do not interfere with reliable closure of the valve with a ball, the seat is made with a large slope of its spherical surface. For this, the outer diameter D of the ball exceeds the diameter of the channel d _{c of} the valve seat by approximately 0.006 m

The dimensions of all the elements of the core shell in (11) and everywhere in the text in meters.

The diameter of the channel d _c perform the maximum allowable and different depending on the internal diameter D _k of the valve body and core pipe, respectively. At the same time, the speed and resistance to fluid movement through the seat channel are minimal. The rational diameter of the channel d _{c of} the valve seat is determined from the condition that the cross-sectional area of the channel of the seat and the annular gap between the ball and the inner walls of the valve body are equal or differ very slightly. In this case, the fluid velocity in the annular gap will not be higher than

the speed of its exit from the channel of the seat, the ball during drilling will fall close to the seat and take a position below the side windows in the valve body (figure 2). When the projectile rises from the bottom, the ball instantly lowers into the saddle due to the small distance between them, as well as under the pressure of the fluid rushing from the well into the core pipe through the side windows in the valve body located above the ball.

From the condition of equality of the cross-sectional areas of the channel of the seat and the annular gap between the ball and the walls of the valve body, and also taking into account relation (11), the diameter of the channel of the valve seat is determined from the expression

After calculating the value of d _{c from} (12) and adding to it 0.006 m according to (11), the value of the outer diameter D of the ball is obtained. A similar value of D is calculated from the expression obtained after substituting (12) in (11)

With the already known outer diameter D of the ball, the value of the inner diameter d of it affects the strength, mass, and, accordingly, the rate of fall of the ball in the liquid, and its pressure in the core tube during the fall of the projectile to the bottom and the lifting of the ball when the valve is opened.

The strength of a steel ball of any diameter during non-pumping drilling is provided with a wall thickness of more than 0.003 m. The speed of a ball falling in a fluid depends on the density of the fluid, the mass and size of the ball. The mass of a hollow ball depends on its outer and inner diameters. The greater the mass of the ball, the greater the speed of its fall and valve closure.

The falling velocity of spherical bodies in liquids and solutions is determined by the well-known Rittinger formula [4, p. 5, p.248]

where c is the coefficient of resistance to the movement of the ball in the liquid;

K = 5.11 - coefficient [5, p. 248], m ^0.5 / s;

ρ _W - the average density of the hollow ball, kg / m ³ ;

ρ is the density of the liquid, kg / m ³ .

The average density of a hollow ball is

where ρ _m is the density of the ball material, kg / m ³ (steel density ρ _m = 7850 kg / m ³ ).

In a core projectile [1], the rate of fall of all-metal balls with diameters from 0.026 to 0.036 m is considered sufficient. But the greater the speed of the ball falling, the better, since the valve closes faster. Therefore, in the proposed core projectile, the rate of fall of a hollow ball in a liquid is limited by the rate of fall of an all-metal ball with a diameter of 0.04 m, for which

Substituting (15) into (14) and equating that obtained with (16) (because of the necessity of equal falling velocities of an all-metal ball with a diameter of 0.04 m and a hollow one), we find that at a fluid density ρ = 1150 kg / m ³ corresponding to or very close its actual value in the well,

Based on the justified and above mathematical expressions, the parameters of the ball valve elements of the proposed projectile are calculated using a core pipe of any diameter required for drilling with internal bottom-hole fluid circulation.

EXAMPLE. Determine the basic parameters of the ball valve elements of the proposed projectile and compare it with the prototype by the magnitude of the fluid pressure on the core, which can occur in core pipes with diameters of 0.108 / 0.099 m of shells during their walk. The main parameters of the elements of the prototype: the diameter of the channel of the valve seat 0,028 m; the diameter of the steel all-metal ball is 0.036 m.

The DECISION is given with reference to the obtained mathematical expressions.

1. For a projectile with equal internal diameters d _k = 0,099 m of the core pipe and valve body, the diameter of the seat channel is calculated by the formula (12)

2. By the expression (11) or (13) determine the required outer diameter of the ball

3. Check the equality of the area of the channel of the seat and the gap between the walls of the valve body and the ball .

4. By the expression (17) calculate the required inner diameter of the ball

5. To compare the shells of the proposed and the prototype by the quality of the core, the fluid pressure on the core in the core tubes of these shells is determined by the first terms on the right of expressions (10) and (8), respectively, since the parameters of the ball valve affect the values of only this member. Denoting the fluid pressure by the first terms of expressions (8) and (10) through p ₁ , calculate the pressure on the core in the core pipes:

a) the prototype of the first term on the right of the expression (8)

b) the proposed projectile for the first term on the right of the expression (10)

The calculated values of the pressures p ₁ show that when using the proposed core projectile, the pressure of the liquid in the core pipes on the core that occurs when the ball valve is opened is less than when using the prototype projectile. This is positive. However, the main advantage of the proposed core projectile is that with an increase in the diameter of the channel of the valve seat, the local local resistance to fluid movement through the channel of the seat decreases significantly.

The value of the velocity resistance to the outflow of fluid through the channel of the valve seat of the prototype, previously calculated by the expression (1), is more than a hundred times greater than the resistance calculated by the expression (8) that occurs when the prototype ball rises. The proposed core projectile in comparison with the prototype allows tens and hundreds of times to reduce local high-speed resistance to fluid flow through the channel of the ball valve seat. This is confirmed by the data table.

Compared Indicators Inner diameter of sludge outlet tube * and valve body - D _K , 10 ^-3 m 40 * [1] 99 118 137 Diameter, 10 ^-3 m: d _c - saddle channel thirty 67 80 94 D - ball (outer) 36 73 86 one hundred d - ball (inner) 0 53 66 80 Ball wall thickness, 10 ^-3 m solid 10 10 10 The average density of the ball ρ _W , kg / m ³ 7850 4846 4302 3831 Ball mass, kg 0.19 0.98 1.43 2.00 Area, 10 ^-5 m ² : saddle channel 70.7 352.4 502.4 693.6 clearance between valve body and ball 23.9 351.1 512.5 688.4 Ball fall rate, m / s 2,34 2.48 2.48 2.47 Resistance p ₁ to valve opening, kPa 3.06 2.75 2.80 2.83 The frequency reduction rate of resistance (in comparison with the prototype * [1]) one 24.88 50.57 96.39

The table shows the design parameters of the main elements of the prototype ball valve (marked with *) and the proposed core projectile and important technological parameters that arise during the drilling process.

All the parameters of the ball valve elements of the proposed projectile and the technological parameters arising from drilling are calculated using the given mathematical expressions, which are obtained taking into account the design distinctive features of the proposed projectile.

Slight discrepancies in the values of the seat channel area and the annular gap area between the inner walls of the valve body and the ball given in the table are due to the rounding of the values of the valve element parameters during their calculations to the nearest hundredth, tenths and even whole units. However, these discrepancies are not significant and do not affect the performance of the proposed core projectile with the calculated parameters. For example, the proposed core projectile reduces the flow resistance to the outflow of liquid from the core pipe with diameters of 0.146 / 0.137 m through the valve seat channel by 96.36 times compared with the prototype equipped with a core pipe of the same diameters. This despite the fact that given in Table valve seat area of the channel of the proposed core shell with core barrel diameters of 0.146 / 0.137 m 0.000052 m ² greater than the area of the annular gap between the inner walls of the valve housing and ball.

As can be seen from the table, increasing the diameter of the channel of the valve seat and ball, increasing the area of the annular gap between the inner walls of the valve body and the ball to a value equal to or close to the area of the channel of the seat, making the ball hollow with an internal diameter calculated by the proposed mathematical expression, allows you to: resistance to the opening of the valve and to reduce by ten times the local high-speed resistance to fluid movement through the channel of the ball valve seat; increase ball falling speed and valve closing speed.

The use of the proposed core projectile with internal fluid circulation compared with the known core projectile adopted as a prototype, when drilling increases:

a) the quality of the obtained core, as it reduces the pressure on it of the liquid in the core tube of the projectile;

b) the speed of opening and closing the ball valve due to the reduction of hydraulic resistance to lifting the ball and finding it at a close distance from the valve seat when the drill bit is working on the bottom of the well;

c) the reliability of the fluid circulation in the core projectile, including between the inner walls of the core pipe and the core, due to an increase in the speed of opening and closing of the ball valve;

g) the length of the flight in connection with the improvement of fluid circulation and a decrease in the reasons for spontaneous grouting of the core in the core tube.

INFORMATION SOURCES

1. Volkov S.A., Sulakshin S.S., Andreev A.A. Drilling business. - M .: Nedra, 1965, p. 287-296, Fig. 219 (prototype).

2. Volkov A.S., Volokitenkov A.A. Drilling of wells with reverse circulation of flushing fluid. - M .: Nedra, 1970, pp. 104-106, Fig. 41 (analogue).

3. Sholokhov L.G., Bazhutin A.N. Deep pump. A.S. No. 185794, publ. BI No. 18, 1966 (analogue).

4. Macovei N. Hydraulics of drilling. Per. with the room. - M .: Nedra, 1986.

5. Vozdvizhensky B.I. Drilling mechanics. - M.: Gosgeolizdat, 1949.

6. Chugaev P.P. Hydraulics. - L .: Energy, 1970.

Claims (2)

1. A core drill for drilling with internal fluid circulation, comprising a core tube with a drill bit, an adapter for a drill pipe string and a ball valve including a metal housing, a seat with a central through channel for fluid passage, a stainless steel ball to block the channel, a slurry conduit with holes in its side walls for the exit of fluid and sludge from the drilled rocks into the well through them, characterized in that the ball is hollow, the holes for the exit of fluid and sludge into the well are s in the side walls of the valve body, the inner diameter of the valve body is taken to be equal to the inner diameter of the core pipe, the diameter of the valve seat channel and the outer diameter of the ball are selected as high as possible from the condition of minimizing the resistance to liquid outlet from the core pipe and the outer diameter of the ball is determined from the condition of equal section area of the saddle channel and the cross-sectional area of the annular gap between the ball and the inner walls of the valve body according to the expression

where D is the outer diameter of the ball, m; D _k - the inner diameter of the valve body and core pipe, m 2. A core drill for drilling with internal fluid circulation according to claim 1, characterized in that the inner diameter of the ball is determined by the expression obtained from the condition for the required rate of fall of the ball in the fluid

where d and D are the inner and outer diameters of the ball, respectively, m