DEVICE FOR MEASURING THE MECHANICAL DRILLING SPEED

V. G. KHRAMENKOV

(Presented by the scientific seminar of the Department of Exploration Engineering)

Mechanical speed is one of the most important parameters of the drilling process. Knowledge of the instantaneous mechanical drilling speed makes it possible to solve many problems in a timely manner, achieving optimal operating conditions for the drilling rig and, most importantly, selecting the most rational operating modes for the bottom-hole bit and determining its service life. Visual observation of the rate of penetration is tedious and not always objective.

All instruments for measuring the mechanical drilling speed and penetration recorders that make it possible to determine the mechanical drilling speed by decoding the diagram of the dependence of deepening on time after completion of the run, according to the type of connection with the elements of the drilling rig, may be divided into three groups:

1. Instruments connected with elements of the drilling rig that have reciprocating motion:

a) with the drill rig feed screw—the instrument of V. M. Slavsky and B. E. Sveshnikov, the VSEGEI penetration recorder;

b) with the guide rod of the rotary head—the penetration recorder of G. L. Lebedinsky, the sensor and penetration-speed recorder of the DS type of the Special Design Bureau of the Ministry of Geology of the USSR, the KazIMS drilling stopwatch-speedometer, the KazIMS drilling recorder, and the KazIMS instrument for measuring drilling speed and penetration;

c) with the rotary-head crosspiece—the automatic recorder of E. I. Abramyan, A. A. Zhukovsky’s drilling-speed meter, and an instrument for mechanical logging (USA);

d) with the leading rod—the recorder of P. I. Fedotov;

e) with the swivel—the instrument of V. M. Slavsky and B. E. Sveshnikov, a drilling-duration recorder (USA);

f) with the traveling block—a remote recording instrument (USA);

g) with the cable of the moving strand of the hoisting system—a recorder of drilling-process parameters (USA).

1. Instruments connected with elements of the drilling rig that have rotational motion:

a) with the axle or sheave of the crown block—an instrument with an angular induction sensor, an instrument with selsyn coupling, a mechanical drillometer (USA);

b) with the shaft or drum of the winch—the acoustic signaler of N. I. Martyntsev.

1. Instruments associated with the hydraulic system of the drilling rig or with an attached hydraulic cylinder:

a) flowmeters—drilling-speed meters—indicator—S-TPI, differential pressure gauges;

b) P. F. Pal'yanov’s hydraulic cylinder.

In addition, all instruments may be subdivided into recording and indicating types. For various reasons, but mainly because of imperfection and low operating reliability, the instruments considered find little application in the practice of geological exploration workers. The integrated GP, PKM, and IRB apparatus makes it possible to obtain information on the mechanical drilling speed, but this apparatus is expensive and complex, and its individual units (mainly parameter sensors) often fail. All this causes great difficulties associated with its introduction.

The instrument for measuring the mechanical drilling speed developed at the Department of Exploration Engineering of the Tomsk Polytechnic Institute is intended for modern rigs with hydraulic feed. The instrument includes a sensor and the measuring part of the S-TPI coal-seam encounter indicator (also developed at the Department of Exploration Engineering of TPI), which underwent successful tests in 1965–1968 at coal deposits of Kuzbass and was recommended for series production.

The operating principle of the instrument is based on measuring the oil flow rate from the lower cavities of the feed hydraulic cylinders during the downward motion of the pistons, synchronized with the penetration. Therefore, an obligatory condition for its use is feed of the tool from the spindle.

The instrument consists of a float-type flowmeter—a sensor of mechanical drilling speed—and a panel. The sensor is installed in the break of the oil line from the lower cavities of the feed hydraulic cylinders to the hydraulic-control unit and is connected by a cable to the panel, installed in a visible place (on the rig, on the wall of the drilling shed).

The operation of the instrument is as follows. Oil, passing through the sensor, raises float 1 (Fig. 1) together with core 2, which enters the two-section inductive coil 3 to a height proportional to the oil flow rate, i.e., to the mechanical drilling speed. During the upward stroke of the spindle, the oil passes through check valve 4. The coil sections represent two adjacent arms of a differential-transformer circuit (Fig. 2). Entry of the core into the lower section increases its inductive resistance, thereby causing unbalance of the bridge and the appearance of a current in its diagonal. The current, rectified by means of a diode bridge \((D_1—D_4)\), is measured by an M24-type microammeter.

The instrument has two scales: the upper one—from 0 to 40 cm/min and the lower one—from 0 to 10 cm/min. At low drilling speeds it is more convenient to use the lower scale. Scale switching is carried out by switch \(P_2\), by means of which shunt \(R_{\mathrm{sh}}\) is switched on (the upper

Fig. 1. Diagram of the mechanical drilling-speed sensor. 1—float; 2—core; 3—two-section inductive coil; 4—check valve.

scale) and, in order to maintain a constant resistance in the microammeter circuit, an additional resistance \(R_d\). Limitation of the signal magnitude to the nominal current value of the instrument (in the case of rapid spindle descents, for example, when the tool string is being lowered) is carried out by means of the stabilitron \(D_5\).

When the instrument is installed on the rig, coarse adjustment of the instrument readings is performed by means of switch \(P_1\), which has a “Speed adjustment” scale. The instrument readings are finally brought

Fig. 2. Electrical circuit diagram of the device for measuring the mechanical drilling speed.

into conformity with the actual rate of descent of the spindle (the rate of deepening) by means of the regulating resistance \(R_{\text{reg}}\).

For automatic elimination or reduction of the error in the instrument readings due to changes in the temperature of the oil and in its lifting force, an \(R_t\) thermistor of type MMT-4 is introduced into the circuit. The thermistor is built directly into the sensor and is washed by the oil flow.

The instrument power-supply unit includes a ferroresonant voltage stabilizer, which makes it possible to obtain correct readings when the line voltage varies by \(\pm 30\%\).

As a result, during tests carried out in different periods in the Kuzbass, seven S-TsII signaling devices operated for more than two thousand rig-shifts; more than fifteen thousand linear meters of boreholes were drilled, with a maximum depth of 630 m. The tests were conducted on ZIF-650A rigs. The coal-bearing strata of the sections were represented by aleurolites, argillites, carbonaceous argillites, variegated sandstones, and coals; on average, the rock category by drillability was 5–5.5. No special drilling regimes were specified. The drilling regimes actually used, with a basic bit diameter of 92 mm, were as follows: axial load—700–1200 kg; rotation speed of the tool string—250–480 per minute; flushing intensity—100–150 l/min. Only hard-alloy bits of types SA, BT, and SM were used as working bits; the flushing fluid was water and clay mud of normal quality.

Under the drilling regimes actually used, the drilling speed of the rocks of the coal-bearing strata was within the following limits:

argillites — 2–9 cm/min,

aleurolites — 5–9 cm/min,

fine-grained sandstones — 10–15 cm/min,

coarse-grained sandstones — 15–25 cm/min and more;
coals — 25–40 cm/min and more.

Timekeeping observations of the mechanical rate of advance, conducted in parallel with the tests, showed good agreement between the observational data and the instrument readings (Table 1). The discrepancy in the readings did not exceed 10%.

Table 1

Comparative data from timekeeping observations and instrument readings

Devices for measuring the mechanical drilling speed were manufactured at the Department of Exploration Technology of the TPI and tested in the drilling laboratory. The devices are simple to handle, reliable in operation, and can be successfully used on many rigs with hydraulic feed.