Diagram of a Drilling Hydraulic Unit

V. I. Zvarygin

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

On the basis of theoretical and experimental investigations, we have drawn the following conclusions:

1. To increase the mechanical drilling speed, one should strive to raise the technological drilling parameters, with a predominant increase in axial pressure. However, increasing the values of the technological drilling parameters is limited by the strength of the drill-rod string, the large expenditure of energy on rotating them, and vibration of the rig at high rotational speeds of the tool. Therefore, in order to eliminate the limiting factor in increasing drilling speed, it is recommended either to eliminate bending of the rods and their friction against the walls of the borehole by means of special protectors, or to abandon the rod method of drilling.

2. For automatic regulation of drilling modes and for loss-free transmission of energy to the drill bit, a hydraulic machine should be created.

3. To eliminate self-jamming of the core, reverse flushing should be used, or a suction pump should be installed above the core barrel.

As an example of such a machine satisfying the above requirements, a diagram of a drilling hydraulic unit is proposed.

The hydraulic unit consists of a hydraulic pump with an electric motor, a winch, and a submersible part. The submersible part of the unit consists of five main assemblies: a hydraulic motor, a hydraulic stabilizer, a feed cylinder, a reversing regulator for the feed cylinder, and a suction pump (Fig. 1).

As hydraulic motor 1, intended for rotating the tool, an improved hydraulic motor may be used. At present, hydraulic motors with a diameter of 130–150 mm and a power of up to 10 kW are available. With special development of hydraulic motors for drilling, motors of small diameters can be created.

The hydraulic stabilizer, intended for fastening the submersible part of the unit, is a bag 3 made of high-strength soft material, with serrated plates 4 riveted to its surface.

The feed cylinder 5 is intended to create axial pressure on the bottomhole and consists of a cylinder with gland seals and a through hollow rod 5—2 with piston 5—3.

Downhole Drilling Hydraulic Unit

(V. I. Zvorygin)

Section along A–A

Section along B–B

Fig. 1. Downhole drilling hydraulic unit: 1 — hydraulic motor, 2 — shaft, 3 — stabilizer, 4 — stabilizer plates, 5 — feed cylinder, 5-1 — outlet channel of the feed cylinder, 5-2 — hollow rod, 5-3 — rod stop, 6 — channel connecting the cavities of the stabilizers and the feed cylinder, 7 — feed-cylinder reversing regulator, 8, 9, 10, 11, 12, 13, 14, 15 — regulator channels, 16 — multistage centrifugal pump, reducer, 17 — sun gear, 18 — satellites, 19 — satellite shaft, 20 — bearing, 21, 22, 23 — channels for passage of drilling fluid in the pump, 24 — screen, 25 — sludge receiver, 26 — sludge-receiver cup.

The feed-cylinder reversing regulator serves to secure and lower the submerged part of the unit at the moment when the cylinder rod has extended to its full length. The regulator consists of body 7 with pressure (8, 10) and discharge (9, 11) channels and a hollow spool 15 with intermediate channels 12, 13, 14, 15.

As a flushing pump operating on the principle of suctioning fluid from the drill string, a centrifugal pump, a VAN-type pump, etc., may be used. Fig. 1 shows centrifugal multistage pump 16 with planetary reduction gear (17—20). The transmission of oil from the hydraulic pump to the submerged part of the unit and back may be carried out by means of a flexible pipeline made of high-strength material in a metal braid, designed for lifting the unit.

Principle of operation of the downhole part of the unit

After the submerged part of the unit is lowered to the bottom with the aid of a winch, the hydraulic pump is switched on; as a result, oil passes through the pressure branch of the pipeline and the channels of the hydraulic regulator into the chamber of the stabilizer, which expands and, by means of plates 4, secures the unit in the borehole. At the same time, oil enters the upper cavity of the feed cylinder and the hydraulic motor. Owing to the oil pressure in the hydraulic cylinder, the hollow rod of cylinder (5—2) extends and creates axial pressure on the drill string, while the hydraulic motor, operating under the action of the oil, rotates the tool. The amount of oil supplied to the hydraulic motor, the feed cylinder, and the stabilizer can be regulated by the different cross sections of the channels and the check valves. Oil from the lower cavity of the cylinder rises through pipeline 5—1 to the discharge pipeline, to which oil from the hydraulic motor is also discharged.

During rotation of the tool, the pump located above the drill string sucks the flushing fluid from it together with sludge and pieces of rock; coarse sludge and pieces of rock are retained by screen 24 and fall into cup 26 of sludge receiver 25.

Under the action of the pump, the flushing fluid rises through channels 21, 22, 23 and hollow shaft 2 to a height of 5—8 m, where it is again poured into the borehole.

After the tool has deepened by the amount of the extension of the feed-cylinder rod, the spool of regulator 7, under the action of the projection on shaft 2, will move downward and, by means of its channels 8, 9, 10, 11, 12, 13, 14, 15 and channel 5—1, will connect the lower cavity of the cylinder with the pressure line, and the upper cavity of the cylinder and the stabilizer cavity with the suction branch. As a result, the stabilizer will release the unit, and under the oil pressure in the feed cylinder it will move downward as far as stop 5—3 of hollow rod 5—2. During the lowering of the unit, the regulator spool will be stopped by the lower projection on shaft 2, move relative to the channels of the body, and connect the pressure branch of the pipeline with the stabilizer cavity, the upper cavity of the cylinder, and the hydraulic motor. Thus, the drilling process will continue.

As the bit wears during drilling, the depth of penetration of the cutters and the circumferential force acting on the bit will decrease. But since the upper cavity of the feed cylinder and the hydraulic motor are connected to the same pressure line, the reduction in the power required to rotate the tool will increase the power used to create axial pressure, and as a result the depth of penetration of the cutters, and consequently,

and the mechanical drilling speed will have a significantly lower rate of decrease.

If the power of the hydraulic motor and the pressure created by the feed cylinder prove insufficiently large, then several hydraulic motors and feed cylinders can be installed.

Taking into account that hydraulic motors with a diameter of 130 mm already exist at present, it may be assumed that the maximum diameter of the submerged part of the unit will be 130–150 mm. With appropriate refinement of the hydraulic motor, it is evidently possible to manufacture the submerged part of the unit with a diameter on the order of 90–100 mm.

The advantages of using this unit include:

1. Increasing the efficiency of the machine by eliminating the rod string and thereby improving technical-and-economic indicators.
2. A sharp reduction in the time required for tripping operations.
3. A sharp reduction in the time required for assembly and dismantling work.
4. Savings in funds and labor when using local flushing.
5. A reduction in the labor intensity of the main and auxiliary operations.
6. Smooth regulation of the axial pressure and the number of revolutions of the tool.
7. There are prerequisites for automating the selection of optimal drilling modes.
8. Elimination of core wedging.
9. An increase in core recovery by eliminating vibration of the tool and the flow of flushing fluid directed at the core.