SOME ISSUES IN ORGANIZING WORK WHEN DRILLING SHALLOW WELLS IN SOFT AND LOOSE ROCKS

S. S. Sulakshin

The actual drilling of shallow wells in soft and loose rocks, as a rule, takes little time. A large share of success, as studies have shown, depends here on the organization of the work and on saving working time. The time spent on auxiliary and similar operations often has too large a relative weight, which considerably reduces the productivity of shallow drilling.

Work connected with driving shallow wells, as is known, consists of the following main stages:

1) preliminary preparation of the workplace at the site (preparation of the area, digging of the circulation system and settling pits—when drilling with flushing);

2) installation of the drilling equipment at the site;

3) dismantling of the drilling equipment and transporting it to a new site;

4) drilling the well, accompanied by a whole series of auxiliary operations.

In most cases these works are performed consecutively, which is plainly irrational.

Proper arrangement of the work and rationalization of individual processes make it possible, as an analysis of the data available to us shows, to increase considerably the time spent on the actual drilling of wells, i.e., to raise the productivity of drilling work of the type under consideration.

Let us examine the principal issues touched upon.

Assembly, Dismantling, and Moving of Drilling Equipment from Site to Site

The expenditure of working time on assembly and dismantling operations when drilling shallow wells often accounts for a considerable percentage. This is especially strongly felt when using drilling equipment intended for stationary drilling and not adapted for rapid relocation, as is evident from the data presented (Table 1).

Thus, when drilling wells up to 50 m deep with a ZIV-75 drilling unit mounted on frames with a wooden derrick of the simplest type, the following amount of time was spent on average on assembling and dismantling the derrick and on assembly, dismantling, and transportation (by motor vehicle) of the equipment:

1) erection of the derrick and assembly of the equipment — 780 minutes,

2) dismantling of the equipment and disassembly of the derrick — 480 minutes,

3) transportation of the derrick and equipment over a distance of up to 500 m — 115 minutes.

Thus, these operations altogether took about 23 hours, that is, almost 3 shifts with the participation in the work of all shift crews (7 persons). Since the derrick was of the summer type and had no platforms and, moreover, pits were not dug for the circulation system (water was taken directly from a stream),

Table 1

this time is considerably less than that provided for by the unified standard norms. Since assembly work is carried out only during the day, the time spent on it accounts for an abnormally large share (up to 31% of the total time for sinking one borehole, Fig. 1), which sharply reduces the productivity of the unit.

Fig. 1. Diagram of the distribution of working time when drilling with the ZIV-75 rig (in percent).

1—time spent on drilling;
2—time for tripping operations;
3—time for cleaning the borehole;
4—time for assembly-and-dismantling operations and transportation.

In the diagram: 1—54.7; 2—12.5; 3—1.6; 4—31.2.

It should be noted that moving the BS-16 rig in the form in which it was supplied by the factory also took almost an entire shift, since the rig had to be loaded onto a vehicle, transported, unloaded, and set up; this could be done only during the day and with 7—8 people working simultaneously.

Even when working with the self-propelled PSK-300 drilling unit, moving it took a great deal of time, which is explained mainly by the need to suspend the rear axle. Therefore, assembly-and-dismantling work still required on average from 6 to 12% of the total time for sinking boreholes.

The figures given confirm the abnormal distribution of working time in the sinking of shallow boreholes, especially when rigs intended for stationary drilling are used.

In order to reduce the time spent on assembly and disassembly work when drilling shallow wells, drilling equipment is usually mounted on sledges or carts. In this case it is necessary to construct a rapidly installable mast, which is often beyond the capacity of drilling crews. Therefore, during moves, the derrick still has to be laid down and raised again at the new site.

Fig. 2. KA-2M-300 unit mounted on sledges.

When drilling wells in the area of survey work for the Stalingrad Hydroelectric Station, KA-2M-300 rigs mounted on sledges (Fig. 2), easily transported by tractor, were used.

Fig. 3. Diagram of moving a drilling derrick in working position.

Three-legged drilling derricks in this case were transported without disassembly by a rather original method. The legs of the derrick were tied with a cable (Fig. 3), the ends of which were fastened to the tractor. Thus the derrick was transported in its working position (Fig. 4a, b). This was, admittedly, facilitated by the level sandy surface of the island on which the drilling was being carried out.

The speed of the tractor with the derrick was about 4 km/hour.

The drillers of another crew followed the same path, carrying out the first experiment in transporting a drilling headframe in working position in the summer of 1953 (Figs. 5a, b).

Fig. 4a. Transport of a drilling headframe by tractor

This method of transporting the equipment eliminates the time required for assembly and dismantling work, i.e., it does not require the assembly and disassembly of drilling rigs.

Fig. 4b. Transport of a drilling headframe by tractor

It is evident from this that the creation of drilling units that are easy to set up at the point and easy to transport will significantly increase the productivity of auger drilling in soft and loose rocks by increasing the useful-work coefficient of the drilling equipment by 20–25%.

Fig. 5a. Transporting a drilling headframe by tractor

Fig. 5b. Erecting the transported headframe in disassembled form at the site

Here it should be noted that drilling shallow wells often takes place in areas with broken relief and under off-road conditions. In such cases it is necessary to prepare the work site in advance, and the drilling rig must be self-propelled, with good cross-country capability: on crawler tracks or on all-terrain motor vehicles.

Drilling Shallow Wells in Soft and Loose Rocks and the Auxiliary Operations Associated with It

In the matter of increasing labor productivity, the rational use of working time in the process of drilling wells is even more essential. All operations performed in this process consist of the following principal elements:

a) preparation for work; b) assembly of the drilling tool; c) lowering of the drilling tool; d) advance to the bottomhole; e) net drilling; f) re-clamping of the chuck (regripping of the spindle); g) extension of the rods; h) raising of the drilling tool; i) extraction of the core; k) other operations accompanying the drilling of wells.

The chronometric data obtained show that the main amount of time in a shift and in a run is spent very irrationally on tripping operations, on assembling the drilling tool and extracting the core, on re-clamping the chuck and extending the rods (Figs. 6, 7, 8). Moreover, the higher the mechanical drilling speed and the smaller the advance per run, the greater the percentage of time accounted for by these operations. The time of net drilling constitutes only an insignificant part (Fig. 9).

With proper organization of work, such operations as assembling the drilling tool and extracting the core can be almost completely eliminated from the drilling cycle by using two drilling tools, which will free from 10 to 18% of working time in a run and in a shift.

The time spent on tripping operations can be reduced in several ways. For greater clarity, let us consider what elements make up the process of lowering and raising the rods.

The main elements during lowering are the following:

1) placing the elevator (the fork) on the stand (rod);
2) lifting the stand (rod) by means of the rig winch (suspending it above the well mouth);
3) attaching (screwing) the raised stand (rod) to the tool;
4) lowering the string by the length of the stand (rod);
5) suspending the tool on the fork;
6) disconnecting the elevator;
7) pulling the elevator up to the rod (if the stands are lying down) or raising the elevator (if the stands are standing).

When raising the tool, the process proceeds in a somewhat different order. Especially much time and labor in this case is spent on unscrewing the rods. The time required to carry out the majority of these elements depends, above all, on the qualifications of the drilling personnel. On the other hand, the rate of hoisting depends on the length of the stands and on the speed of winding the rope onto the winch drum. Both are connected with the design features of the rig.

It should be noted that in expeditions and parties rods of standard length are rarely found. Even if such rods do arrive from the factory, after some period of work they are recut and quickly lose their standard length. Therefore, especially taking into account frequent lifting of the drilling tool, it is rational to have a mast that permits stands up to 9 meters long to be raised. Such a mast height will, in addition, make it possible to increase the speed of winding the rope onto the winch drum.

Fig. 6. Diagram of the distribution of working time during a shift when operating the BS-16 rig (in percent).

1—time spent on actual drilling; 2—time for tripping operations; 3—time for assembling the tool; 4—time for extracting the core; 5—time for preparation for work; 6—idle time.

Fig. 7. Diagram of the distribution of working time during a shift when drilling with the ZIV-75 rig (in percent).

1—time spent on actual drilling; 2—time for tripping operations; 3—time for auxiliary operations; 4—time for preparation for work; 5—time for cleaning the borehole; 6—idle time.

Fig. 8. Diagram of the distribution of working time during a run when drilling with the ZIV-75 rig (in percent).

1—time spent on actual drilling; 2—time for tripping operations; 3—time for preparation for work; 4—time for assembling the drilling assembly; 5—time for advancing to the face; 6—time for rechucking the chuck; 7—time for adding rods; 8—time for extracting the core; 9—other operations.

It is necessary to take into account that, in tripping operations, half of the machine time is spent on lowering or raising the elevator—the so-called idle stroke. Evidently, here too there is an opportunity to rationalize the process by eliminating from the work cycle a completely unproductive element—pulling the elevator up to the rod.

Fig. 9. Diagram of the distribution of working time when drilling with a BS-16 rig:

a—when drilling by the core method with flushing in rocks of categories II–VI; b—when drilling with an auger in holes 10 m deep in rocks of categories I–II; c—when drilling with an auger in holes up to 36 m deep in rocks of categories I–II.

1—time spent on actual drilling; 2—time for preparation for work; 3—time for assembling the tool; 4—time for lowering and raising the tool; 5—time for advancing the tool to the face; 6—time for adding rods; 7—time for switching on and off the forced feed; 8—time for extracting the core; 9—other operations.

When drilling shallow wells, this question can evidently be resolved by using a two-drum hoist, with operation by two cables and two elevators. In the arrangement we propose, this would look as follows (Fig. 10).

The drilling unit has a reversible winch 1. Two cables 2, passed over two sheaves 3, are wound onto the winch drum from different sides. The cables are provided with weights 4, ensuring free descent of the elevator 5.

During tripping operations three people are at work: the shift foreman, sitting at the winch on seat 6; the junior worker—at the mouth of the borehole; and the senior worker, performing the duties of a qualified motor operator and assisting in tripping operations.

When lowering or raising the tool according to this arrangement, two elevators operate. When one elevator goes upward while raising the tool, as shown in the figure, the second, with the unscrewed stand 7, descends; the stand is moved aside and placed on the trestles. The next stand raised from the borehole is unscrewed by the second worker. In this case, the process of unscrewing the rods must also be mechanized, which is readily feasible when a rotary table is used. Next, the second elevator is put onto the end of the rod suspended on fork 8, and the process is repeated, but the winch now rotates in the opposite direction.

To prevent accidents that may occur because of overhoisting of stands, especially when operating at high speeds, the hoisting device must be equipped with a safety device that switches off the winch in good time.

Thus, the solution of the question raised must proceed along the following lines: increasing the length of the stands and using quick-release connections, increasing the speed of rope winding, and, finally, rationalizing the very process of lowering and raising the rods.

Fig. 10. Diagram of lifting the tool with two elevators

All the measures listed will undoubtedly reduce the time spent on round-trip operations by at least half, which will increase drilling time per shift and per run by 10–15%.

On reclamping the chuck of the KA-2M-300 rig, an average of 1 minute is spent. The spindle of this rig permits drilling about 0.25 m. Thus, for each linear meter of advance it is necessary to reclamp the chuck four times, that is, to spend an average of 4 minutes. With large volumes of drilling this insignificant figure grows to substantial proportions. Suffice it to say that in drilling 100,000 meters of boreholes, 6,670 hours, or 830 rig-shifts, are spent solely on reclamping the chuck.

Such operations as reclamping the chuck and building up rods can and should generally be eliminated or reduced by using a leading square rod 2–3 meters long. This will give an additional increase in drilling time of approximately 15%.

Undoubtedly, there is a possibility of reducing the time spent on other similar operations in the drilling process, primarily through Stakhanovite labor.

An important point in this case is also the organization of uninterrupted work, for which it is necessary to have:

1) reliable supplying of drilling rigs with all necessary materials, this being handled by persons who do not take a direct part in the performance of drilling operations;

2) reliable work of the repair shop (preferably mobile), ensuring repair of drilling equipment at any time (in three-shift operation);

3) constant communication between the base and the drilling sites (when the latter are widely scattered).

Thus, the analysis we have made of the distribution of working time confirms that improving the organization of shallow-well drilling in soft and loose rocks can be achieved, first, through the rational use of working time and, second, through the creation of rational drilling equipment.

According to preliminary data, this will increase the time spent directly on drilling to more than 70% (instead of 20–30), which will raise the productivity of drilling operations by no less than a factor of two.