Automatic Device for Determining the Optimal Drilling Time per Run
Abstract Generated abstract
This paper addresses the problem of selecting the economically optimal duration of a drilling run, since pulling the tool too late or too early reduces overall productivity. It proposes a simple automatic electrical device, combined with a clock mechanism, that analogizes run drilling rate to Ohm’s law by varying voltage in proportion to drilled footage and resistance in proportion to net drilling time. A specially graduated ammeter indicates run rate continuously, while a contact and signal lamp mark the point at which the rate reaches a maximum and begins to decline, indicating when the tool should be pulled. The proposed device is intended to automate a decision often based on operator judgment and is expected, according to cited calculations, to improve drilling productivity by about 5 to 20 percent.
Full Text
AUTOMATIC DETERMINATION OF THE OPTIMAL DRILLING TIME PER RUN
V. I. Zvarygin
(Presented by the scientific seminar of the Department of Exploration Engineering)
An important factor in increasing drilling productivity is the correct determination of the duration of a run.
It is known that, as the bit operates, its cutters wear over time; the total area of contact between the cutters and the rock increases, as a result of which the mechanical drilling rate decreases. In practice, the tool is pulled either when the mechanical rate is close to zero, if the borehole is deep, or while the mechanical drilling rate is still relatively high, if the borehole is of small depth.
In the first case, a significant amount of time is spent unproductively at a low mechanical rate toward the end of the run; in the second case, the duration of the run is unjustifiably limited. Therefore, in both the first and the second cases, the overall drilling productivity will be lower than the productivity that can be achieved with the optimal duration of the run.
To select the optimal duration of a run, it is necessary to develop an instrument that could give a timely signal that the maximum drilling productivity for the run has been reached.
Known devices for determining the optimal drilling time per run include Popov’s device, the DGI automatic determiner, and others.
The shortcomings of such determiners of the optimal drilling time are:
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Popov’s device requires constant attention from the shift foreman, measurements of penetration, and resetting of the instrument scale.
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The DGI automatic determiner is bulky and very difficult to manufacture.
The proposed design for automatic determination has the aim of:
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Providing the foreman with a simple and convenient instrument by which he could determine with sufficient accuracy the time for ending drilling with a given bit, calculated so that the total productivity per run under the given conditions (the given rock, the given bit, etc.) would be maximal.
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Automating the process of determining the most advantageous run time.
This is achieved, according to the present proposal, by manufacturing an electrical circuit in combination with a clock mechanism.
Theoretical calculations show that the most advantageous duration of a run corresponds to the maximum run drilling rate:
\[ v_{\mathrm{p}}=\frac{S}{t_{\mathrm{v}}+t_{\mathrm{b}}}, \tag{1} \]
\(S\)—footage drilled,
\(t_{\mathrm{v}}\)—time for auxiliary operations,
\(t_{\mathrm{b}}\)—time of net drilling.
Ohm’s law has an analogous formula
\[ I=\frac{U}{R}=\frac{U}{R_1+R_2}. \tag{2} \]
If an electrical circuit is made in which the resistance \(R_2\) can be varied in proportion to the time of net drilling, and the voltage \(U\) varied in proportion to the footage drilled, then a specially graduated ammeter connected into this circuit will indicate the run rate.
Such a circuit is precisely the electrical circuit shown in the drawing. The electrical circuit consists of a power source—1 (the power source may be either an alternating-current network or a direct-current battery), a variable resistance—2, serving to vary the voltage in the circuit in accordance with the footage drilled, a variable resistance—3 for varying the resistance of the circuit in proportion to the time of net drilling, and an ammeter 4.
The ammeter and variable resistance 2 are connected into the network in parallel. The sliders of resistances 2 and 3 are connected to one another by a separate wire. To balance the circuit, an additional resistance 5 may be connected between the ammeter terminal and the wire of the supply line.
To move the slider of variable resistance 3, a clock mechanism 14 is installed, which is switched off during stoppages, repairs, etc., not connected with the drilling process.
The drive for the slider of variable resistance 2 is a gear 7, connected with rack 8 of the drilling rig (when drilling with a cable, the gear is connected with the winch drum), and connected with the slider shaft through flexible shaft 9 and reducer 10.
The voltage taken from variable resistance 2 will vary continuously depending on the amount of footage drilled and at any given moment will be equal to (Fig. 1)
\[ U_1=I\cdot r, \]
\(I\)—current in circuit \(A\),
\(r\)—resistance between the terminals \(U_1\).
The current in circuit \(B\) (the ammeter reading) will be
\[ i=\frac{U_1}{R}=I\frac{r}{R}. \]
With equal resistivity and cross-section of variable resistances 2 and 3, we have
\[ i=I\frac{\rho_1 l_1 S_2}{\rho_2 l_2 S_1}=I\frac{l_1}{l_2};\qquad \frac{i}{I}=\frac{l_1}{l_2}=n, \]
\(I\)—a constant quantity,
\(n\)—the reading of the specially graduated ammeter.
Thus, during the drilling process, by changing the lengths of resistances 2 and 3 in proportion, respectively, to the footage and to the time of net drilling in the manner indicated above, it is possible at any moment to determine the run drilling rate.
Over time, during the drilling process, the run rate will increase; the ammeter pointer will move clockwise, pushing slider 11 ahead of it and thereby closing the contact in the line running from the power source through the wire laid in the pointer and the slider to lamp 13. As the run rate increases, the lamp remains lit; as soon as the run rate, having reached its maximum, begins to decrease, the pointer will move away from the slider, opening the contact, the lamp will go out, and this will serve as the signal to pull the tool.
Fig. 1. a) Electrical circuit of the automatic determiner of drilling time per run; b) kinematic diagram of the automatic determiner of the optimal drilling time per run.
To determine the magnitude of the footage and the time of net drilling, pointers are mounted on the shafts of sliders 2 and 3; on the graduated scales of panel 12 they indicate the corresponding value of footage and drilling time.
To switch off the clock mechanism during idle periods, an automatic switch connected to the spindle can be provided.
As a result of using the automatic determiner, it becomes possible to eliminate unproductive drilling at a low run rate and thereby to increase drilling productivity by 5–20% (according to calculations by E. F. Epshtein). This is especially important for geological-exploration drilling, where the end of a run is still determined by the intuition of the drilling foreman.