INFLUENCE OF TECHNOLOGICAL REGIMES ON THE DRILLING RATE OF SHALLOW WELLS IN SOFT AND UNCONSOLIDATED ROCKS BY THE ROTARY METHOD AND ON POWER CONSUMPTION

S. S. Sulakshin

The experience of individual Stakhanovite crews that exceed the norms in drilling shallow wells by a factor of 2–3 or more indicates the existence of large reserves for increasing the drilling rates of wells.

Studying the operation of rigs under production conditions, we have come to the definite conclusion that increasing the rate of sinking shallow wells depends not only on the proper, most rational organization of labor, but to a considerable extent also on rationally selected technological drilling regimes, on the rationality of the designs of the equipment used and of the drilling tools.

It must be said that up to now all the results achieved under production conditions have been based mainly on a more precise organization of labor and on the rational selection of the drilling tool. In most cases the technological regime is not controlled. It is determined, as a rule, by the available drilling equipment: rigs with a certain number of revolutions, pumps of a certain capacity, etc. Often this regime cannot be changed for technical reasons. Therefore, in the published literature we do not find properly substantiated recommendations on drilling regimes in soft and unconsolidated rocks.

On the contrary, in some cases even at the present time there are directly opposite judgments on this question. Thus, for example, there is an opinion that the rational number of revolutions when drilling with augers and spoons should be considered no more than 20–30 rpm. Hence even a special term, “slow-rotary drilling,” has become established in the literature, and most researchers try to mechanize manual drilling, copying the regimes inherent to it.

Our investigations show that this is completely irrational. The drilling rate with augers or a spoon, on the contrary, increases sharply as the number of revolutions rises.

The same is true of the pumpless method of drilling. In some cases [1] it is recommended to drill at 60–100 rpm with an axial pressure of not more than 150–200 kg and a number of strokes, depending on the specific weight of the rock and the drilling rate, within the limits of 10 to 18 per minute.

In other cases the authors confine themselves only to general considerations concerning the regime of pumpless drilling. Thus, in a handbook for the shift drilling foreman [2] it is written: “In the pumpless method of drilling the string must rotate at different speeds depending on the useful minerals being penetrated. The pressure on the bottom of the well must be the greater, the larger the diameter of the well. In determining the magnitude of the pressure of the string on the bottom …”

wells, it is necessary to take into account the following factors.” A number of factors limiting the magnitude of the pressure are then listed, but, apart from the fact that the pressure “must not be great,” this memorandum contains no specific instructions. The Stakhanovites of the Ukrgeologiya Trust, when drilling “dry” in coal [3], brought the pressure on the bit up to 500–900 kg, obtaining high rates of penetration.

The number of revolutions in dry drilling in the area of construction of the Stalingrad Hydroelectric Station reached 150 rpm, which also led to a noticeable increase in the drilling rate.

In the investigations carried out in the Altai, on the Volga, and in Zagorsk, we had to work on different rigs, often with limited technical capabilities. Therefore, in determining rational operating conditions, the performance of one and the same drilling bit, operated on different rigs, is sometimes compared. This affects the results obtained in a certain way, but, as it seems to us, it does not play a decisive role in the final conclusions.

In studying drilling regimes by various methods, the following factors were identified as having a substantial influence on the drilling rate of wells in soft and unconsolidated rocks:

1) the number of revolutions of the drilling tool;
2) the amount of fluid supplied to the well (in drilling with flushing), or the frequency of lifting and dropping and the lifting height of the drilling tool (in drilling by the dry method);
3) the magnitude of the axial pressure on the bottomhole;
4) the power of the drilling rig.

Drilling with an Annular Bottomhole and Flushing

This type of drilling was studied mainly under production conditions and, to a small extent, at the instructional drilling test site in Zagorsk. Drilling was carried out with simple core tools in sandy-clayey unconsolidated deposits of categories I and II. In part, drilling was conducted in hard rocks of a sedimentary or igneous complex of categories V–VIII. In drilling, toothed bits and crowns dressed with hard-alloy cutters of octagonal and needle-like shape were used. The flushing fluid was forced in by means of piston pumps of the 100/30, 45/15 type, or gear pumps of the ShGN-3a type. The axial pressure was created by the weight of the tool. Since the wells were shallow, the pressure on the bottomhole varied within insignificant limits.

Influence of the Number of Revolutions

Table 1 presents average data from the results of investigating the influence of the number of revolutions on the rate of deepening when drilling on KA-2M-300, ZIV-75, and BS-16 rigs in sandy-clayey rocks of categories I–II.

The relationship between drilling rate and number of revolutions has a clearly linear character, as can be seen from the graph (Fig. 1). At the same time, the drilling rate increases faster than the rate of rotation increases.

Consequently, in order to increase the drilling rate in soft and unconsolidated rocks, it is first of all necessary to increase the rotational speeds of the drilling tool. However, it must be borne in mind that at high speeds increased wear of the drilling equipment occurs.

Table 1

Fig. 1. Graph of the dependence of drilling rate on the number of revolutions of the core-barrel assembly when drilling with flushing in loose rocks

Influence of the amount of flushing fluid

Table 2 gives the data from the results of the study, from which it is evident that the drilling rate increases significantly with an increase in the amount of fluid injected into the borehole. It should be noted here that the drilling rate was adversely affected by the reduction in the number of revolutions, which occurred in this experiment for technical reasons. Probably, with identical numbers of revolutions, the increase in drilling rate would have been considerably greater. In the present case, however, we have approximately the same drilling rate at 130 rev/min with flushing at 78 l/min and at 180 rev/min, but with flushing averaging 50 l/min. In addition, drilling with an increased amount of flushing fluid was carried out with “BK” type bits, which are poorly suited to these conditions. Consequently, in order to increase the drilling rate in loose rocks, it is necessary to increase the pump capacity.

Table 2

With an increased quantity of flushing fluid pumped into the borehole, the velocity of its movement increases, and with it the kinetic energy of the flow also increases; this energy participates in the destruction of soft rock and carries out

Section 1–1

Section 2–2

View from below

Fig. 2. Diagram of a core barrel for drilling in soft and unconsolidated rocks with flushing

the drilled particles. But, in addition to the bottomhole, the borehole walls and the core are also destroyed. Therefore, the optimum quantity of fluid supplied to the borehole must be established in each specific case in inseparable connection with core recovery.

In order to increase the kinetic energy of the jets of flushing fluid while preserving the core, a drilling tool of the following design may be proposed (Fig. 2). Four strips 3 of small-diameter angle iron (with the flanges toward the pipe) are welded to core barrel 1 and bit 2. In sub 4, which has no through opening, and in the core barrel, channels 5 and openings 6 are drilled, through which the fluid enters the cavities of angles 3, as shown in the figure. Bit 2 carries welded-on thickenings 7, which, like the face of the bit, are set with cutters made of hard alloys. A toothed bit with offset teeth may also be used successfully. In this case the fluid forced by the pump will burst out with great force from the four channels. The entire impact is directed at the bottom of the borehole. The core, however, will be fully protected from the erosive action of the flow.

For the exit of fluid and air from the core barrel when it is filled with core, two check valves 8 are made in the sub.

The pump capacity when drilling under the conditions considered may vary from 30–40 to 130–200 l/min, depending on the stability of the rocks and the design of the drilling tool.

Influence of the Magnitude of Axial Pressure

As investigations have shown, axial pressure when drilling in soft and unconsolidated rocks plays an insignificant role. This is natural, since the resistance of soft rocks to penetration by the cutting tool is small. For this, the weight of the tool alone is usually sufficient.

On the contrary, it is very often necessary to reduce the pressure, especially at a low number of revolutions and with an insufficient amount of flushing fluid, since the bottom of the borehole does not have time to be drilled to the depth of penetration of the cutters. In this case the pressure on the pump pressure gauge increases and rotation of the tool stops. Therefore, the feed of the tool when drilling in soft and unconsolidated rocks must be coordinated in each individual case with the amount of fluid being pumped and the number of revolutions.

In practice, the magnitude of the axial pressure when drilling in soft rocks may be on the order of 250–400 kg on a bit 91–130 mm in diameter.

Power Consumption When Drilling with Flushing of the Annular Bottom

The power consumption for drilling with flushing is comparatively small. It should be noted here that, in drilling in unconsolidated rocks, the state of the borehole, the drilling depth and diameter, and the number of revolutions of the tool strongly affect power consumption. In addition, an increase in the power consumed is usually observed toward the end of a run, and a sharp increase during core wedging, without which, under these conditions, it is impossible to manage.

Table 3 gives some data on power consumption when drilling in loams. Measurements were made by means of two wattmeters, the readings of which were recorded on special sheets.

It should be noted that the power expended for operation of the pump was not taken into account here.

As can be seen from the table presented, the power for drilling with an annular bottom and flushing is very small. But when wedging the core, the power increases by a factor of 2–3.

Table 3

Drilling with an annular bottom-hole by the suctionless method with reverse circulation of the fluid

The study of the drilling processes by this method was carried out chiefly in engineering-geological investigations in the area of construction of the Stalingrad Hydroelectric Power Station.

Drilling was carried out with tools of various designs in rocks of categories II—IV.

Drilling was conducted on KA-2M-300 rigs driven by electric motors, which made it possible to measure power consumption. Despite the narrow range of variation in the drilling regime, it proved possible to reveal a definite dependence of the drilling rate on different regimes.

Influence of the number of revolutions

The number of revolutions varied within the limits from 90 to 150 rpm for tool diameters of 130 and 115 mm.

Table 4 gives averaged comparative data characterizing the drilling rate by the suctionless method as a function of the number of revolutions.

Table 4

As is evident from this table, the drilling rate, which depends strongly on the properties of the rock, increases by a factor of 1.5 to more than 2 with a small increase in the number of revolutions (20–40 rpm).

It is characteristic that for loose, unconsolidated rock (sand) this dependence is manifested only very slightly.

It should be noted that the core obtained in this case fully satisfies the researchers. Obviously, for less critical cases, for example in ordinary geological mapping, the rotational speed of the tool may be increased still further.

For engineering-geological investigations, apparently, special studies must be carried out to determine the dependence of preservation of the core structure on the number of revolutions.

Influence of the frequency of reciprocation and the lifting height of the drilling assembly

From consideration of the essence of this type of drilling it is evident that, owing to the reciprocation of the assembly in the borehole, reverse circulation of the fluid is created. The principal functions of flushing in this case consist in removing particles of broken rock from the bottom hole and cooling the drill bit. Naturally, the more rock is broken per unit time, the more intensively it must be removed, i.e., the more intensive the flow of the flushing fluid must be and the greater the number of reciprocations (strokes per minute) must be.

Since the drilling rate depends first of all on the hardness of the rocks, a general regularity is revealed: the softer the rocks, the more intensive the reciprocation must be. As was established, the drilling rate increases with an increase in the number of revolutions. Consequently, in this case as well, the number of reciprocations of the assembly must increase in order to ensure removal from the bottom of the more intensively forming sludge.

In addition, the rate of removal of particles of drilled rock depends on its specific gravity. Therefore, to increase the efficiency of removing sludge consisting of rock particles with a high specific gravity, it is also necessary to increase the number of reciprocations.

Data revealing the dependence of the drilling rate on the number of reciprocations of the assembly when drilling in rocks with a specific gravity of about 2.7 under approximately identical conditions are given in Tables 5, 6, 7, 8, and 9. From these it is seen that:

a) when drilling in loose, unconsolidated rocks (sands), reciprocation must be practically continuous—up to 50 strokes per minute;

b) when drilling in rocks of the sandy-silty type with weak cement, the number of reciprocations must also be increased—up to 30 strokes per minute;

c) in siltstones the maximum drilling rate is achieved with a number of strokes of 14–19 per minute;

d) when drilling in sandstones, the intensity of reciprocation will depend on the hardness of the rock; the weaker the sandstone, the greater the reciprocation should be, and, conversely, the stronger the rock, the less frequently the tool may be raised.

Table 5

Change in penetration rate as a function of the number of reciprocations of the tool when drilling in sand

Table 6

Change in the rate of penetration as a function of the number of swings of the tool when drilling in sandy–silty rocks

Table 7

Change in the rate of penetration as a function of the number of swings of the tool when drilling in aleurolites

Table 8

Change in the rate of penetration as a function of the number of swings of the tool when drilling in argillites

Table 9

Change in the rate of penetration as a function of the number of swings of the tool when drilling in sandstones

The average number of strokes may be taken as within the range of 14–18 per minute;

d) when drilling in ore minerals that yield heavy sludge, the instructions for core recovery [1] recommend a number of strokes per minute from 12 to 17.

When drilling in argillites, within the observed limits, the dependence of the drilling rate on the number of strokes is manifested less clearly (Table 8). This, however, may be explained by the insufficient number of observations, all the more so because the average values are derived from work with different tools and bits. Therefore the latter figures should not be regarded as a quantitative characteristic of the dependence under consideration, but only as a qualitative one and, to some extent, a preliminary one. It should be noted here that non-pump drilling in clayey rocks generally proceeds abnormally and is of low efficiency.

The dependence of the drilling rate on the number of strokes of the tool is clearly illustrated by the graphs (Figs. 3 and 4).

Fig. 3. Graph of the dependence of the drilling rate in sand on the number of strokes of the core-barrel tool in non-pump drilling

Taking into account that an increase in the number of strokes of the tool often leads to a more rapid rise of the core to the sub, and consequently to cessation of the circulation of the fluid, excessive intensity of reciprocation of the tool should be avoided.

As the investigations have shown, drilling by the non-pump method in clayey rocks, and especially in clays, is very inefficient, since the fluid circulating at an insufficient velocity thickens very rapidly; the clayey mass begins to envelop the core barrel, especially from the inside; a “gland” is formed, and the circulation of the fluid essentially ceases; consequently, deepening proceeds at a slow rate.

The same phenomenon is observed even when drilling with flushing, if the quantity of fluid supplied to the borehole is insufficient. Therefore, when it is necessary to drill clayey rocks by the non-pump method,

it follows, if this is permitted, that clean water should be added to the borehole more often, or the borehole should be cleaned of fine sludge, which increases the viscosity of the fluid.

Drilling in clayey rocks must be carried out with more intensive reciprocation. For example, a noticeable increase in the drilling rate in argillites was obtained with a number of strokes within the range of 18–32 per minute.

Fig. 4. Graphs of the dependence of drilling rate on the number of strokes of the tool string in pump-free drilling:

a — for sandy-aleuritic rocks; b — for aleurolites;
c — for argillites; d — for sandstones

When drilling shallow wells and when there is a sufficient inflow of fluid, drilling with reverse circulation may be recommended, with discharge of the fluid to the surface through the drill-rod string, stuffing box, and hose. In this case no holes are made in the rods.

The height to which the tool string is raised in the process of pump-free drilling practically varies within the interval from 2–3 to 8–10 cm and depends mainly on the condition of the mud in the borehole. The cleaner the mud, the smaller the lifting height may be.

The principal shortcoming of pump-free drilling is the small amount of advance per run because of silting of the clearances between the core and the core barrel and especially of the ball valve, which leads to cessation of circulation of the flushing fluid.

In order to eliminate the indicated shortcomings, we proposed and tested a tool for pump-free drilling that differs somewhat from the known ones.

structures. This instrument consists of the following main parts: a core barrel \(4^{1}/_{2}\) m long, a bit, an adapter, an open sludge tube, a rod connected to the adapter, a nipple, and a short rod with holes and with a ball. A distinctive feature of the instrument is the completely different arrangement of the holes in the tube in which the ball valve is placed (Fig. 5).

Fig. 5. Operating diagram of Sulakshin’s non-pump drilling instrument:

1—core barrel; 2—adapter; 3—rod; 4—ball;
5—window; 6—short rod; 7—holes; 8—sludge tube

As can be seen from the drawing, directly above the ball 4 an oval window 5, measuring \(10 \times 20\) mm, is cut. In the upper end of tube 6, another 2–3 holes 7 are drilled, the diameter of which is 6–8 mm. This arrangement of the holes ensures clear and, in most cases, trouble-free operation of the valve.

Removal of the sludge from the sludge tube is easily carried out with the aid of an ordinary flushing syringe.

The extraction of the core is also much simpler in this instrument. For this purpose it is sufficient to disconnect tube 6 with ball 4 and attach a rod with a packing gland and a hose from the pump. All this can easily be done even

one worker. Switching on the pump and forcing out the core takes one minute. In this case the frequently practiced shaking out of the core is also carried out much more simply, since the ball, bouncing when the tool is shaken, opens access for air through the window located directly above the ball. Owing to this, the vacuum that forms when the core leaves the core barrel is quickly compensated by air.

When working with this tool, clogging of the valve almost completely ceased, the core was sucked into the adapter much less often, and the entire drilling process was sharply improved. This was noted by all drilling foremen who worked with this tool in the Stalingrad expedition.

All the improvements listed, in our opinion, were obtained owing to the use of a valve device of the proposed system, which provided favorable conditions for the operation of the ball. Indeed, when the tool moves downward (Fig. 5a), the liquid displaced from core barrel 1 rushes upward through the through opening in adapter 2 and along rod 3, lifting ball valve 4. The flushing fluid, saturated with sludge, begins to pour out through window 5 in rod 6. Part of the liquid, overtaking the ball, exits through additional openings 7. Through these same openings also pours out the liquid that the moving ball drives ahead of itself. In the string of rods the water level, even if it rises, does so only very slightly. At the next moment the ball will close the upper opening in rod 6 (Fig. 5b), and all the flushing fluid together with sludge will begin to pour out only from window 5 and openings 7, entering sludge tube 8.

As soon as the tool comes to rest on the bottom, the ball will fall downward (Fig. 5c). Liquid from the string of rods, if its level was somewhat higher than in the borehole, will pour out through the same openings. Subsequently, as the tool moves upward (Fig. 5d), the liquid, continuing to pour out from window 5, will wash ball 4 from above, preventing sludge from settling on it. Thus, reverse flows of liquid in the rods are utilized. All sludge coming from the core barrel and located in the column of liquid above the tool settles into sludge tube 8, which does not occur in tools with a closed sludge tube.

In the event that large fragments of rock are sucked into tube 6, they easily pass through window 7 when ball 4 is in its uppermost position. During the entire operation of the tool only one case was noted when a piece of rock of elongated shape, measuring \(48 \times 22 \times 15\) mm, became stuck in window 7.

Thus, the merits of the described tool design include:

a) reliable operation of the ball valve, which is associated with more effective operation of the tool in the borehole and an increase in penetration per run;

b) simplicity of assembly and disassembly of the tool and ease of cleaning the sludge tube and valve;

c) ease of extracting the core from the core barrel with a small number of operations connected with this.

The improvements made in the tool for pumpless drilling increased the productivity of this drilling method, as is evident from the comparative data presented on the operation of tools of different designs (Table 10).

Influence of Axial Pressure

Axial pressure, as in all other methods, has a substantial effect on the drilling rate only in hard rocks. In the present case, the impacts of the bit on the bottom, obtained at the moment the tool is dropped during its walking action, are of great importance. Therefore, when drilling in more

in hard rocks the axial pressure should be applied according to the general rules for core drilling.

Table 10

At present it is customary to assume that, with an increase in axial pressure, the natural structure of the core is disturbed. Therefore, when drilling engineering-geological wells, the magnitude of the axial pressure is recommended within the limits of 150–200 kg.

No one has yet experimentally established the dependence between axial pressure and preservation of the core structure. It is possible that, at a low number of revolutions, increased axial pressure will have an adverse effect. But it seems to us that increasing the axial pressure to 300–400 kg will not affect the core structure. And this pressure, when drilling in soft rocks, even in wells of large diameters, is quite sufficient.

Power Consumption

The power consumption in pumpless drilling was measured from the readings of two wattmeters every 5 minutes of net drilling. Power measurements were made in various rocks. As can be seen from the data thus obtained, within the investigated limits the drilling depth has almost no effect on power consumption. The character of the rocks, which determine the condition of the well, the type of bit, and the number of revolutions of the tool have a greater effect.

Table 11 gives average data characterizing the power expended on various processes. As can be seen from the table, the greatest power is expended on rubbing down the core—on average 8.0 kW. The maximum values in this case reach 10 kW and more. A large amount of power is required for hoisting the tool. On average it reaches 5.5 kW at a well depth of 26–46 m. The maximum values sometimes exceed 10 kW.

In drilling, a comparatively small amount of power is usually expended, 2.8–3.4 kW. Moreover, these figures include the power consumed for idle rotation of the drilling tool and for rotation of the rig itself, which takes up to 1.3 kW. Consequently, on average 1.5–2 kW is expended on breaking the bottom-hole rock and on friction of the working tool against the bottom hole, and often even less.

It should be noted here that sometimes a 10 kW electric motor could not cope with the maximum load and stopped. This gives grounds to believe that in some cases power greater than 10 kW is actually required. Drilling by the pumpless method with a tool of 8″ diameter was successfully provided by a 19 kW motor.

Table 11

Drilling with a solid bottomhole, without flushing (dry), using spoon and spiral augers

This type of drilling was studied during work in Altai and in Zagorsk. Drilling was carried out with spoons and spiral augers of various diameters in loose deposits: loams and clays of categories I–II, on KA-2M-300 and BS-16 rigs driven either by gasoline engines or by electric motors. In the latter case, measurements of power consumption were taken.

On the basis of the data obtained, the dependence of drilling rate on the number of revolutions, axial pressure, well depth, and the character of the rocks was established.

Influence of the number of revolutions

When drilling with a spoon, this factor has less effect than, for example, axial pressure. Table 12 gives averaged data on the dependence of the drilling rate with a spoon in loams on the number of revolutions of the tool.

Table 12

It is evident from this that when the number of revolutions of the tool is doubled, the drilling rate with a spoon increases almost threefold (294.0%). This can be represented more clearly graphically (Fig. 6).

When drilling with a spiral auger in loams and clays, a somewhat different picture is observed, as is evident from the data given (Table 13).

Table 13

When the number of revolutions is increased threefold, the drilling rate increases by a factor of 6, and increasing the number of revolutions by a factor of 5.5 leads to an increase in the drilling rate of more than 10 times. This is clearly illustrated by the following graph (Fig. 7).

Fig. 6. Graph of the dependence of the drilling rate with a spoon bit on the number of revolutions

Fig. 7. Graph of the dependence of the drilling rate with an auger on the number of revolutions

Fig. 8. Graph of the dependence of the drilling rate with a spoon bit on axial pressure.

Average run drilling rate at 118–134 rpm and an axial pressure of 40–75 kg. Average run drilling rate at 115–134 rpm and an axial pressure of 120–150 kg.

Influence of Axial Pressure

Axial pressure in drilling with a bucket has the same essential significance as the number of revolutions in drilling with spiral augers, as is evident from the figures given (Table 14). When drilling with a bucket in loams, doubling the pressure increases the drilling rate by more than four times. For drilling in loose rocks with spiral augers, axial pressure is not of essential importance.

Table 14

In Figure 8 this dependence is clearly expressed graphically. Consequently, in order to obtain high drilling rates with spiral augers, it is necessary to go over to higher numbers of revolutions, while for drilling buckets it is necessary to increase both the number of revolutions and the axial pressure.

Investigation of these factors makes it possible to recommend, for mechanical drilling, screw augers and buckets \(1.5\text{–}2.0\ m\) long, which will considerably increase the advance per run and, consequently, labor productivity by 2–3 times and more. In addition, when drilling in sandy soils and even in clays that are not strongly moistened, auger drilling at high revolutions may be used.

The use of augers can also be carried out when penetrating quicksands according to the following scheme: a string of casing pipes, built up with pipes of small length (\(1.5\text{–}2.0\ m\)), is sunk with the aid of a vibrator [4], while removal of the rock from the pipes is carried out with a string of augers rotated by the rotor. This will eliminate the need to use manual labor for casing the pipes and will replace the low-productivity process of bailing.

Power Consumption

Measurements of power consumption were made after every \(0.25\ m\) of advance. Table 15 gives the average values of power consumption when drilling with buckets of two diameters in loams.

When the number of revolutions is increased by approximately 2.1 times, power consumption increases by 1.88 times. In addition, the power expended increases by 1.6 times when the diameter of the drilling bit is increased (\(145\text{–}185\ mm\)).

When drilling with screw augers in loams, this picture is essentially repeated, as is evident from Table 16.

Here, when the number of revolutions is increased by 2.1 times, the power also increased by 1.88 times.

Table 15

Obviously, such a regularity will also appear with further changes in the main indicators.

From the data presented it is evident that drilling with an auger requires greater power than drilling with a spoon.

Table 16

Conclusions

On the basis of the experimental studies, the results of which are presented in this article, important practical conclusions may be drawn.

1. When drilling in soft and unconsolidated rocks with core barrels and augers, the rate of advance, and consequently the productivity, are determined mainly by the number of revolutions of the drilling tool. Moreover, the drilling rate increases twice as fast as the number of revolutions of the tool (the number of revolutions increases 2.5 times and the drilling rate 5 times; the number of revolutions 5 times and the drilling rate 10 times, etc., as is evident from the data given in Tables 1 and 13).

2. When drilling with flushing, the rate of advance increases substantially with an increase in the amount of fluid pumped into the borehole (Table 2).

3. When drilling by the pumpless method (with local circulation of the fluid), the rate of advance depends on the number of reciprocations (oscillations) of the tool per unit time. Moreover, for different rocks there are optimum values of the number of oscillations.

1. When drilling with spoon bits, the rate of penetration depends almost in direct proportion both on the axial pressure and on the number of revolutions.

2. The maximum values of the power expended in drilling shallow wells in soft and unconsolidated rocks reach 8–10 kW and only in isolated cases are greater by a factor of 2–2.5.

3. The hoisting power at the given depths almost does not exceed the power expended on drilling; their values are fairly close.

4. An engine power of 15–20 kW fully ensures the drilling of wells with an initial diameter of up to 8″ and a final diameter of about 3–4½″ to a depth of up to 100 m under forced drilling conditions by any method.

REFERENCES

1. Ministry of Geology. Temporary instruction for taking core in core drilling. Gosgeolizdat, 1950.

2. Rosinus P. L. and Stepanov G. I. Pump-free drilling. Handbook for the shift drilling foreman. Gosgeolizdat, 1951.

3. Work experience of Stakhanovite geological-service workers. Work of Stakhanovite drilling crews. Ukruglegeologiya Trust. Gosgeolizdat, 1949.

4. Palyanov P. F. Casing wells with pipes by means of a vibrator. Journal Razvedka nedr, No. 5, Gosgeolizdat, 1952.