Experience in the Use of Periodic Feeding of Borehole Bottoms with Shot in Small Portions at the “Altaitsvetmetrazvedka” Trust

P. I. Stepanov

(Presented by Professor, Doctor A. A. Belitsky)

The productivity of shot drilling, in addition to the rotational speed of the tool and the pressure on the bottom, is greatly influenced by the method of feeding the borehole bottom with shot.

On the basis of the weight of the portion of shot fed to the bottom and the periodicity between feedings (toppings-up), from the practice of drilling exploratory boreholes one may distinguish, in the main, three methods:

1) periodic, subdivided in turn into periodic feeding in small portions and in large portions;
2) run-by-run; and
3) continuous.

With the periodic method of feeding, shot is supplied into the borehole in portions—doses from 50–150 g to 1.0–2.5 kg, with a time interval between successive additions respectively from 5–20 min. to 1.2–2.5 hours. In run-by-run feeding, one portion of shot is poured onto the bottom of the borehole before drilling begins, and this portion ensures the process of deepening the borehole during the run. The continuous method of feeding is characterized by the fact that shot is supplied into the borehole through the rods systematically (continuously). This method may also be called stream feeding, since the shot reaches the bottom through the rods in the form of a continuous stream (rivulet) throughout the entire run.

At present, of the three indicated methods of feeding, the run-by-run and periodic methods are in use, and of these the first is the most widely disseminated. It should be noted, however, that an analysis of the literature summarizing the work experience of leading innovators in drilling exploratory boreholes with shot, as well as our observations of the work of drilling crews in the “Altaitsvetmetrazvedka” trust that use periodic feeding, show that, with all other parameters of the technological drilling regime being equal, the periodic method of feeding the borehole bottom with shot is the most effective, i.e., it gives higher productivity.

Let us consider the advantage of the periodic method of feeding using specific examples.

According to the data of S. I. Zhilkinsky, I. A. Vrubel-Golubkin, and A. P. Gavel (1951), the introduction of the periodic method of feeding in large portions, or, as they call it, the “combined” method, in the Krivoy Rog ԥ

in the geological-exploration trust made it possible sharply to increase drilling productivity per rig-month. Thus, if the productivity per rig-month on average for the trust in 1947 (the use of the run method of feeding) is taken as 100%, then in 1948 (the beginning of the introduction of periodic feeding) productivity per rig-month amounted to 109%; in 1949, 127%; and for 10 months of 1950, 134%.

The sizes of the portions poured into a borehole at the Krivorozhsky Geological-Exploration Trust are characterized by Table 1.

Table 1

It is evident from the table that at the beginning of a run a so-called “initial” portion was fed to the borehole bottom, calculated for drilling for 2.5–3.0 hours of net drilling. Then “hourly portions” were fed to the bottom, calculated for drilling for one hour.

A. M. Magurdumov (1953), describing the advanced experience of a drilling crew headed by senior foreman V. E. Revyakin of the Uzbek Geological Administration, which achieved fulfillment of the plan for 1951 by 113% and for the first half of 1952 by 120.8%, indicates that these results were obtained mainly through the use of periodic feeding of the borehole bottom with shot and the correct flushing regime. The feeding regime was as follows: in accordance with the hardness of the rocks and the borehole diameter, at the beginning of the run a portion weighing 2–8 kg was poured in, for 1.0–1.5 hours of work, and then, after 0.25 linear m of deepening, in an amount equal to 25% of the standard shot consumption per 1 linear m. The addition of shot was carried out through the drill rods with the tool not rotating. Before the initial portion was poured in, the pump was set to maximum capacity; after pouring, the pump was switched to a capacity of 80–100 l/min. After 45 minutes of operation of the tool at the bottom, the supply of flushing fluid was reduced to 40–50 l/min. Before raising the tool, the pump was again set to full capacity.

From the materials of V. I. Molchanov, who conducted studies in the Kaza Geological-Exploration Expedition of the West Siberian Geological Administration for the purpose of developing optimal parameters of the technological regime of shot drilling, it is also evident that the introduction of periodic feeding in large portions through the borehole collar made it possible in 1953 to achieve fulfillment of production norms for the drilling shop as a whole by 121% and to increase net drilling time to 69.3%, as against 34.8% in 1950. The drilling technology used in this case was as follows:

1) borehole feeding with shot was periodic. Before lowering the tool into the borehole, 5–6 kg of No. 4 shot was poured in, calculated for drilling for two to three hours; then, after two to three hours, without stopping rotation of the tool, an additional 1.5–2.0 kg of No. 3 or No. 2 shot was added through the borehole collar, and after an hour to an hour and a half an additional addition was made in the same amount and also through the borehole collar;

2) flushing, when the charge reached the bottom, amounted to 40–30 l/min; at the beginning of the run it decreased to 27–18 l/min and at the end of the run was 10–11 l/min (for a bit diameter of 91 mm);

3) the pressure on the bottom during drilling at speed I (90 rpm) with a KAM-500 machine was 22–25 kg/cm² of the working area of the bit face; at speed II (150 rpm) it was 18–22 kg/cm².

E. G. Meerson (1949), summarizing the experience of a drilling crew headed by senior drilling foreman M. I. Devyatkin of the Kirovograd Geological Prospecting Party of the Uraltsvetmetrazvedka trust, shows that this crew, having applied periodic feeding through a shot feeder (of M. I. Devyatkin’s design), also achieved high production figures. The annual plan for 1948 was fulfilled by the crew in 9 months at a net drilling time of 60–70%.

In the geological prospecting parties of the Altaitsvetmetrazvedka trust, the periodic method of feeding in small portions has now become widely used. This feeding method has been introduced since 1951–1952 on the initiative of the head of the trust’s physico-technical laboratory, engineer N. A. Gribsky. At first this method of feeding boreholes with shot was introduced for the purpose of combating zenithal deviation of boreholes. To carry out periodic feeding in small portions, N. A. Gribsky, together with M. I. Kazantsev, designed the D-3 shot feeder. During experimental production drilling with the shot feeder, carried out in order to determine the influence of the quantity of shot at the bottom on the degree of borehole deviation, it was observed that, along with a reduction in zenithal deviation, drilling productivity also increased. In addition, a reduction in shot consumption by 40–50% was noted in comparison with the run-by-run method; at the same time it turned out that the amount of sludge in the borehole does not exceed 0.1–0.5 m, and so on.

After these experimental studies, an intensive campaign began for the broad introduction of this feeding method in all geological prospecting parties of the Altaitsvetmetrazvedka trust. Beginning in 1953, the author of this article, in close contact with N. A. Gribsky, carried out work to determine the economic effectiveness, as well as the advantages and disadvantages, of periodic feeding in small portions as compared with run-by-run feeding under the production conditions of the geological parties of the Altaitsvetmetrazvedka trust.

The periodic method of feeding in small portions found especially wide application in the Belousovka and Berezovka geological prospecting parties. In other parties of the trust, owing to the lack of the necessary number of shot feeders, and also to an underestimation of this feeding method on the part of engineering and technical personnel and practical drillers, this feeding method was used only by individual drilling crews.

Using the example of the Belousovka Geological Prospecting Party of the Altaitsvetmetrazvedka trust, it is possible to show what reserves for increasing drilling productivity are inherent in the periodic feeding method (Table 2).

It is evident from Table 2 that, as the periodic method of feeding in small portions is introduced, production-and-economic indicators improve with respect to productivity, net drilling time, and also the reduction of working time spent eliminating various kinds of accidents.

The drilling crew of this party, headed by senior foreman P. A. Vaal and including shift foremen E. A. Zuev, A. P. Simachev, and M. P. Fomin, which systematically applies periodic feeding in small portions, in 1955 had average annual indicators much—

Table 2

which exceed the average figures for the Belousovskaya GRP as a whole (Table 3).

Table 3

It follows from this that the production-and-economic indicators for the Belousovskaya GRP as a whole are by no means the limit. They would have been still better if all shift foremen of this party had applied the proper regime of feeding the bottom with shot and the flushing regime. Individual shift foremen continue to drill with run-by-run charging, or they maintain an incorrect regime of periodic feeding and flushing (either too much whole shot is fed to the bottom, or too little flushing fluid).

Table 4 gives the indicators for actual productivity per rig-month, net drilling time, and accident rate obtained by the Zyryanskaya GRP from 1940 through 1955.

Table 4

In this GRP, shot feeders began to be introduced in 1952–1953; however, they have not found broad introduction and application up to the present ...

time. Thus, in 1955 only 15 shot crushers were in operation, whereas the average annual number of rigs operating monthly was 44.5. However, even the use of periodic feeding through a shot crusher on one-third of the rig fleet had a significant effect on increasing productivity for the expedition as a whole—from 77 linear m in 1940 and 1950 to 98.8 linear m in 1955.

For comparison it should be noted that in those geological exploration expeditions of the Altaitsvetmetrazvedka trust where only the round-by-round method of feeding is used, no increase in drilling productivity is observed. At the same time, shot consumption and accident rate increase from year to year. As an illustration, Table 5 gives the production and economic indicators of the Leninogorsk GRE.

Table 5

A study of the work experience of the leading drilling crews of the Altaitsvetmetrazvedka trust, carried out by means of photographic time-motion observations, showed that these crews achieve high production indicators not only through the use of periodic feeding in small portions, but also through a properly established flushing regime. The flushing regime is maintained almost constant throughout the run and decreases slightly only toward the end because of the reduction in the magazine slot. In this case, the amount of flushing fluid per unit time is almost twice as great as that recommended for the round-by-round method of feeding.

The regime of periodic feeding of borehole bottoms with shot in small portions and the flushing regime used by the leading drilling crews of the Altaitsvetmetrazvedka trust when drilling in slightly fractured rocks are presented in Table 6.

Table 6

By applying this regime, drilling crews achieve not only an increase in drilling productivity by 40–50 percent or more and a saving of shot amounting to 40–50% of the norm, but also improve the quality of the work; in particular, the percentage of core recovery increases, the accident rate decreases, boreholes deviate less, etc.

The criterion for monitoring the correctness of the regime used for feeding the borehole with shot is the uniformity of core treatment. If the core is treated unevenly, this serves as a signal that the feeding regime has been set incorrectly. In such a case, either the weight of the portion of shot supplied to the bottom is increased, or the interval between additions is reduced.

Let us consider why the periodic method of feeding borehole bottoms with shot makes it possible to increase drilling productivity in comparison with the trip method. This is achieved mainly by increasing the time of actual drilling and increasing the rate of advance per unit time. In comparison with the trip method, the time of actual drilling with periodic feeding increases owing to an increase in the duration of the run, a reduction in the time spent reaching the bottom and flushing the borehole at the beginning and end of the run, and a reduction in accidents caused by the tool becoming stuck in the borehole and by breaks in the drill-rod string.

With trip feeding, the duration of the run depends mainly on the working capacity of the portion of shot charged into the borehole. As the shot wears and the drilling rate decreases, new portions are not added, since this leads to the tool becoming stuck in the borehole; therefore at the end of the run the tool is usually pulled. With periodic feeding, a definite condition of workable shot is maintained at the bottom throughout the entire run by adding ever-new portions of whole shot to the bottom. The run continues either until the core barrel is completely filled with core, or until advance is stopped owing to wear of the slot of the magazine of the shot bit.

The time of actual drilling with periodic feeding increases owing to a reduction in the expenditure of working time on flushing the borehole after the tool has been lowered into the borehole and before the core is wedged, and also on reaching the bottom at the beginning of the following run. Photochronometric observations show that, with periodic feeding, these auxiliary operations require 2–3 or more times less working time than with trip charging. If, for example, with periodic feeding in small portions 5–10 minutes are spent on this, then with trip feeding 15–25 minutes are spent, and in some cases even more. Here the saving of working time is achieved because, with periodic feeding, the borehole, being treated uniformly throughout the entire run, does not require additional dressing of the walls at the beginning of the following run, whereas with trip feeding the borehole is usually treated into a cone. In addition, the uniform dressing of the borehole walls makes it possible to maintain a comparatively high flushing rate throughout the entire run, as a result of which much sludge does not accumulate at the bottom. The amount of the latter, with periodic feeding in small portions and with correctly established and maintained flushing, does not exceed 0.1–0.5 m.

Finally, it should be noted that the time of actual drilling with periodic feeding increases owing to a sharp reduction in accidents caused by the tool becoming stuck at the bottom by shot or sludge, and to a reduction in the time spent eliminating other types of accidents, in particular breaks in the drill-rod string. With trip feeding, when there is a large amount of sludge in the borehole, breaks, as a rule, become more complicated.

with a sludge grab, and much working time is spent on eliminating them.

Data on the reduction of working-time expenditures for eliminating accidents at the Belousovskaya and Berezovskaya GRP of the “Altaitsvetmetrazvedka” trust are given in Table 7.

Table 7

As can be seen from Table 7, in these GRP, as periodic feeding in small portions is introduced, the accident rate decreases. An analysis of the reports drawn up for accidents in the indicated GRP shows that, when the run-by-run method of filling shot into the bottom was used, the main share of seizures occurred because the tool became wedged by shot when it reached the bottom, and also as a result of the tool being jammed by sludge when rotation was stopped. As the periodic method of feeding in small portions is introduced, accidents for these reasons become fewer and fewer. Although seizures still occur in these GRP, they now arise chiefly either as a result of collapse of the borehole walls, or owing to the column pipe being “filled” with shot when the rod string breaks at great depth during drilling in hard rocks. The reduction in the accident rate when the periodic feeding method is used is explained by the nature of the enlargement of the borehole. Laboratory, as well as production, investigations have established that the development of the clearances between the core and the bit, and between the bit and the borehole wall, depends chiefly on the size of the shot particles and, to a lesser degree, on their quantity in the borehole. In this case the clearance between the bit and the borehole wall is 1.3–1.5 times greater than the clearance between the bit and the core. Hence, knowing the size of the core, one can always determine the true diameter of the borehole at the bottom.

Table 8 presents data on the character of core treatment and borehole enlargement under periodic and run-by-run feeding.

In this table the core diameter is shown according to data from numerous measurements under production conditions. In this connection it is observed that, with

¹) The increase in working-time expenditures for eliminating breaks at the Berezovskaya GRP in 1954, compared with previous years, was caused by complex geological conditions.

Table 8

¹ The clearances between the core and the bit, and between the bit and the borehole wall, are shown as dimensions on one side.

With periodic feeding in small portions, the processing of the core over almost the entire run is uniform, and only at the end of the run, over an interval usually equal to the length of the bit, does the core increase in diameter, since at this moment no shot is being fed and the drilling process is carried out by the shot remaining from the preceding additions. With run-by-run feeding, as the initially charged portion of shot is split and reduced in size, the diameter of the core increases, while the diameter of the borehole, on the contrary, decreases. At the beginning of the run, both with run-by-run and with periodic feeding, the processing of the core is the same. Table 8 shows that with periodic feeding the clearance between the bit and the borehole walls is equal to 2–2.5 diameters of whole shot grains throughout the entire run and only at the end of the run—and then only over a short interval—decreases to 1–1.5 diameters. With run-by-run feeding this is already observed in the middle of the run, and at the end the clearance between the bit and the borehole wall becomes equal to almost half the diameter of the shot grain. Consequently, with run-by-run feeding, when the core jams, and also at the beginning of the next run when approaching the bottom, the bit may be caught by split shot of the same diameter as that used for drilling, i.e., in our case shot of 3 mm diameter (No. 3), not to mention shot grains of larger size. With periodic feeding, however, in order for the bit to become wedged at the bottom at the end of the run, shot grains one or two numbers larger than those with which drilling is being carried out are needed.

The reduction in borehole deviation with periodic feeding as compared with run-by-run feeding, especially in inclined holes, is also explained by the nature of borehole development. Indeed, with run-by-run feeding there is always a large quantity of shot in the borehole, both because large portions are charged and because of the remnants of crushed shot from preceding runs. Therefore the borehole is developed during the run not only by the bit at the bottom, but also by the walls of the rotating core barrel. This additional working of the borehole by the walls of the core barrel becomes greater the farther it is from the bottom. As a result, the core barrel in the borehole, especially its upper end, bearing against the low side of the hole, will deviate farther and farther from its axis, i.e., will descend, while the lower end, on the contrary, will rise. Consequently, the low wall of the borehole, acting as a kind of guide for the core barrel and the bit, as it is worked out along the generatrix of the wedge will continuously promote deviation of the upper part of the core barrel from the borehole axis, and the latter will gradually but systematically curve toward the flattening. With periodic feeding a somewhat different situation is observed. In this case the alignment of the tool string is not disturbed because the additional working of the borehole is absent altogether or is many times less than with run-by-run feeding, since the minimally necessary quantity of shot is maintained at the bottom at all times.

It should be noted that the periodic method of feeding boreholes with shot in small portions is not new. Before 1935–1936, when boreholes were drilled with cast-iron shot, this method was used mainly. To illustrate the feeding regime used at that time, we present Table 9, taken from the Prospector’s Handbook (1935).

The portions indicated in the table were recommended to be charged after 10–15 minutes of net drilling. In this case the amount of flushing fluid was supplied to the bottom at the rate of 0.8–1.0 l/min per 1 linear cm of bit diameter. In the period from 1935 to 1937, the periodic method of feeding in large portions began to gain wide use; later it was replaced by the run-by-run method.

Table 9

The reason why the more productive periodic feeding displaced run-by-run feeding lies, above all, in the fact that at that time in the practice of shot drilling there were no shot feeders that met the requirements imposed on them, namely: simplicity of design, reliability and durability in operation, convenience and simplicity in servicing, the possibility of maneuvering in the delivery of portions of any weight to the bottom without stopping drilling and at any time intervals, small overall dimensions, etc. Therefore the charging was carried out through the rods with the tool not rotating, which took up to 10–15% of the working time during a shift. In addition, as a result of stopping the circulation of the flushing fluid when charging the next portion of shot, accidents were often observed because the tool was seized at the bottom by sludge.

The run-by-run method of feeding also displaced the periodic method because in those days an incorrect feeding and flushing regime was used. Portions that were too small were recommended, with their charging after relatively long intervals of time, as is evident from a comparison of Tables 6 and 9. As a result, the core was processed unevenly, which led to its frequent wedging in the bit when the next portion was charged. In this case, working time was also lost in making an unscheduled lowering and hoisting. The run-by-run method eliminated these shortcomings, and despite the fact that the rate of penetration per unit time was thereby obtained lower than with periodic feeding, the total run-by-run penetration was greater owing to the increase in net drilling time.

Furthermore, at that time it was believed that the most effective rate of penetration was achieved only by chipped particles of shot. In reality, the maximum possible rate of penetration in a run occurs when there is both whole and chipped shot at the bottom. Our investigations showed that this ratio can be maintained only through the use of periodic feeding.

Conclusions

1. The periodic method of feeding borehole bottoms with shot is more productive than the run-by-run method. When periodic feeding is used, drilling productivity increases by 40–50 percent or more.

2. Along with the increase in productivity, with the periodic feeding method the consumption of shot per 1 linear meter of penetration is 40–50% less than with the run-by-run method.

3. With periodic feeding, as compared with run-by-run feeding, the accident rate is reduced, owing to fewer seizures of the tool in the borehole by shot and fewer breaks of the rod string; zenithal deviation of the boreholes is reduced, etc.

1. The periodic method of feeding with the aid of shot feeders should become widely used, since it is an additional reserve for increasing the productivity of drilling boreholes by the shot method with existing production capacities.

REFERENCES

1. Zhilkinskii S. I., Vrubel-Golubkin I. A., Gavelia A. P. — A method of combined feeding of the bottom of boreholes with shot. Razvedka nedr, No. 2, 1951.

2. Magurdumov A. M. — The crew of senior drilling foreman V. E. Revyakin. Uzbek Geological Administration, Gosgeolizdat, 1953.

3. Meerson E. G. — Methods of shot drilling of the crew of senior drilling foreman M. I. Devyatkin. Gosgeolizdat, 1949.

4. Prospector’s Handbook. Part 1. Exploration drilling. ONTI NKTP USSR, 1935.