Improving the operational efficiency of drilling rock-breaking tools

. Improving the quality and volume of drilling is the main condition for advancing the growth of reserves of raw materials of the national economy and industry. Rock-breaking tools are the main and busiest part of drilling equipment. Most of the operational productivity of drilling equipment depends on the operation of a rock-breaking tool, the improvement of the operational performance of which will reduce the cost of drilling wells and significantly increase drilling efficiency. The issues related to increasing the operational productivity of drilling equipment based on improving the design of rock-breaking tools have not been fully resolved, and their solution is now becoming important. This article presents the results of research devoted to the problems of reducing the efficiency of rock-crushing tools that arose as a result of high temperature at the bottom of the well when cleaning the bottom of the well by blowing air, as well as the sludge regime that occurs during drilling with cleaning with washing liquids prepared on the basis of water. Special attention is paid to improving the efficiency of drilling equipment by creating and implementing a rock-breaking tool design with high performance indicators.


Introduction
During the drilling process, during the destruction of rocks, the teeth of the rock-breaking tool experience temperature stresses as a result of mechanical compression under the action of axial pressure, mechanical bending under the action of tangential forces, heating of the working body and the washing liquid.
The effect of temperature factors on the rock-breaking tool manifests itself in the form of deformation of the matrices, tooth breakage, wear (grinding) of their working surfaces, and reduction of tooth strength and cauterization of tools [1].
Also, when drilling wells with hydraulic cleaning, the appearance of a slurry regime at the bottom of the well creates a process of repeated crushing of the destroyed rock. This leads to a decrease in the mechanical drilling speed, the energy costs of the rock-crushing tool for repeated crushing of the sludge separated from the array (which increases the downhole capacity and reduces drilling efficiency), increases the likelihood of the formation of seals around the rock-crushing tool, accelerates the process of abrasive wear and reduces its durability [2].
Thus, on the basis of the organization of effective flushing of the bottom of the well, it is possible to improve the work of rock-breaking tools, thereby increasing the efficiency of the drilling tool and the drilling process.

Investigation of factors that reduce the effectiveness of a rockbreaking tool
When drilling strong rocks, a high temperature is released, which reduces the microhardness and abrasive properties of the teeth of the rock-breaking tool, as well as increases mechanical deformation. In the process of drilling hard rocks, temperature deformations of the rockbreaking tool prevail, hence the need to normalize temperature regimes taking into account their impact [3].
When drilling wells with hydraulic face cleaning, the presence of a slurry mode under the body of the rock-destroying tool accelerates the wear of its matrix, which leads to tooth breakage, and also causes cavities and scratches on the teeth of the rock-destroying tool, causing their erosion. In addition, the formation of a slurry regime reduces the mechanical drilling speed as a result of repeated crushing of the rock separated from the massif, and leads to an increase in energy consumption for drilling [4].
The design of the drilling rig has been improved. a projectile (Fig.1) containing a vortex tube, which allows normalizing the temperature conditions of the rock-destroying tool when drilling a well with air purification [5]. A drilling shell (Fig.1) containing a vortex tube works as follows. When drilling a well, compressed air is supplied to the cold fraction generator (5) through the outer pipe (3), through the inlet holes (6) of the vortex pipe (7). In the vortex tube, compressed air is divided into cold and hot streams, a cold air stream flowing through the holes of the nut (4) through the adapter (2) is fed to the rock-breaking tool (1), brings the destroyed rocks from the bottom of the well to the surface with simultaneous cooling of the rock-breaking tool. In this device, the cold fraction generator is removable, which allows, if necessary, to change the cooling mode when drilling modes change. Hot air from the vortex tube (5), through a special hole (8), flows out of the pipe (3) to the surface.
After improving the design of the drilling projectile containing a vortex tube, field experimental tests were conducted to study the effect of the purifying air temperature on the durability of the rock-crushing tool and the mechanical drilling speed.
At the last stage of experimental tests, the dependence of the durability of the rockbreaking tool on the rotation frequency of the bit at different temperatures of the purifying air was established.
Thus, the use of the developed drilling projectile containing a vortex tube made it possible to increase the mechanical drilling speed in accordance with drilling modes by 8% and the durability of the bit by 4%.

Improving the efficiency of hydraulic cleaning of the bottom of the well from sludge
The uniform distribution of the sludge formed at the bottom of the well under the rockbreaking tool along the axis increases the efficiency of cleaning the bottom of the well from the sludge. This distribution of sludge excludes its repeated crushing.
It is advisable to consider the scheme of movement of the sludge separated at the bottom of the well, which ensures optimal movement of the separated sludge in the bottom of the well, and thereby develop a design of a rock-breaking tool that allows effectively cleaning the bottom of the sludge. The paw of the three-ball chisel is bent 50 radially, a carbide blade with a height of 2 mm and a thickness of 4 mm is installed on top of the paw at an angle of 40.
An improved design of a three-ball chisel with a diameter of 76 mm is shown in Fig. 2. a b In order to determine the effectiveness of an improved rock-breaking tool reducing and preventing the formation of a slurry regime at the bottom of the well, experimental tests were conducted.
Experimental tests were carried out in the following order: conventional and advanced three-pin bits were operated under the same geological conditions, with different drilling modes, until the bit was completely worn out. The axial load force (Ros) applied to the bit was 7.5 kN, 10 kN, 12.5 kN and 15 kN, and the rotational speed (n) for each value of the axial load force of the same bit was 80, 100, 120 and 140 min -1 , respectively. Based on the results of experimental tests, the dependence of the mechanical drilling speed of a conventional and improved bit on the axial load and the number of revolutions was established [6,7].

Discussion
From the graphs presented in Figs.3 and 4, it was found that the use of an improved chisel contributes to an increase in mechanical speed by an average of 6%.
In the course of experimental tests, the dependence of the wear resistance of conventional and advanced three-pin bits on drilling modes was investigated. Figures 3 and 4 below show graphs of the dependence of the wear resistance of conventional and advanced three-pin bits on the axial load and rotational speed [8,9,10].
When using a perfect bit (Fig.3), with the parameters of the drilling mode parameters Рос = 7.5 kN, n = 80 min -1 , G=6.8 l/s, the durability of the bit was 135 meters, with an increase in the number of revolutions to 100 min -1 , the durability was 130 meters. It is established that when the number of revolutions increases to 120 and 140 min -1 , the durability of the chisel increases to 8-10 m. It follows from this that the efficiency of the improved bit is achieved in the case of a rotation speed of more than 120 min -1 .  A comparative graph of the durability of a conventional and improved chisel at a rotation speed (n) of 140 min -1 is shown in Fig.5. Based on the analysis of the above experimental test results, it can be noted that the improved three-ball drill bit increases the mechanical speed (Vm) of drilling and the durability of the bit by reducing the formation of a slurry regime in the bottom of the well. Also, as a result of experimental tests, it was found that at rotation frequencies (n) 120-140 min -1 , axial force 10-12.5 kN, high efficiency of the proposed bit is achieved.
Thus, the use of an improved design of a three-ball chisel with a 50 bend in the radial direction and a carbide blade mounted on the surface of the chisel at an angle of =40 allowed to increase the durability of the chisel by 8%.

Conclusion
Based on the conducted research, the following conclusions are made, which have theoretical and practical significance: -the condition of the casing and teeth of the rock-destroying tool have a significant impact on the drilling process, and the condition of the rock-destroying tool itself depends on the movement of sludge particles under its casing; -in the process of drilling wells with air purification, the determination of rational values of drilling modes to normalize the temperature and temperature modes of operation of the rock-destroying tool is carried out using the developed mathematical model; -in the process of drilling a well in rocks of the 5th -8th category by strength to normalize the temperature conditions of the face at an initial air temperature of -20 ℃, the number of revolutions of the bit (n) should be in the range of 100-120 min -1 with an axial load (Pос) of 10 kN and the number of revolutions of the bit (n) should be in the range of 80-100 min -1 at axial load (Pос) 12.5 kN; -by directing the flow of sludge particles directly into the flushing channel of the rockdestroying tool, the conditions for cleaning the bottom of the well from sludge are improved, while the maximum removal of sludge is achieved at an angle of movement of its particles 45; -the improved design of the three-roller bit increases the mechanical speed (Vм) of drilling and the durability of the bit by reducing the formation of a slurry regime in the bottom of the well. Also, as a result of the conducted experimental tests, it was found that the high efficiency of the proposed bit is provided at 120-140 min -1 revolutions (n) and 10-12.5 kN of axial load; -it was found that the use of an improved design of a three-ball bit with a bend of 50° in the radial direction and a carbide blade mounted on the surface of the bit at an angle of =40 relative to a conventional design under certain drilling conditions increased the mechanical drilling speed by 6% and the durability of the bit up to 8%.