IMPROVEMENT OF A HINGED DEFLECTOR FOR SIDETRACKING WELLS

Yu. L. Boyarko, V. V. Vinogradov

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

A deflector for sidetracking wells consists of two main assemblies: a universal hinge and a coring tool with a mechanism that holds the bit in the lower part of the bottomhole of an inclined well.

The coring tool consists of a short core barrel, inside which a device is mounted for holding the bit in the lower part of the bottomhole. The device consists of a spike with a sharp pobedit tip and a spring, one end of which rests on a flange welded to the spike and the other end on a thrust washer secured inside the core barrel.

The procedure for using the deflector consists of the following operations. The assembled deflector is lowered to the bottomhole, which is first leveled with a full-bottom bit. If there is sludge, the deflector is brought to the bottomhole with flushing and rotation. After reaching the bottomhole, the deflector is raised by 10–15 cm and lowered onto the bottom without rotation. Under the action of gravity, the coring tool comes to rest on the low side of the borehole and, upon meeting the bottomhole, is held in this position by the spike.

When pressure is transmitted to the bottomhole, the spring is compressed, the spike is recessed into the pipe, and the drill bit comes to rest on the bottomhole. During drilling, as the bit deepens into the bottomhole, the spike gradually compresses the spring. Drilling is carried out until the spring is fully compressed, after which the assembly is raised. Then a short core barrel with a shot, diamond, or carbide bit (depending on the hardness of the rock and the type of drilling) is lowered to the bottomhole on the hinge, and the drilled cup is deepened with core recovery.

After several trips, with a gradual increase in the length of the core barrel up to 1.5 m, the well is reamed in the new direction to the previous diameter with the aid of conical or stepped bits.

When the described deflector was used under field conditions, a design deficiency was discovered: when working with the coring tool, the depth of the drilled direction (5–8 cm) does not ensure core breakage, and as a result it is difficult for the assembly to enter the drilled cup during subsequent lowering. In addition, the length of the first run is too small.

At present the deflector has been redesigned in light of the comments received and represents a tool design that makes it possible—

Fig. 1. Deflector for sidetracking wells, SVS-3:

I — hinged adapter; II — whipstock assembly;
1 — adapter;
2 — core barrel;
3 — ball retainer;
4 — expanding sleeve;
5 — support sleeve;
6 — spring;
7 — bit;
8 — channel for passage of drilling fluid;
9 — support bearing;
10 — bit crown.

This, with the features listed above, makes it possible to drill out, in the first run, a cup 25–30 cm deep; moreover, when drilling hard rocks, core recovery is possible.

In redesigning the deflector, the thrust washer in it, previously welded into the casing pipe, was replaced by a ball locking mechanism consisting of two bushings and two balls (Fig. 1).

The support bushing is held against axial displacement by balls that partly enter the holes in the casing pipe. The balls are held in this position by an expansion bushing.

As the spring is gradually compressed, the wedge, with its end face, pushes the expansion bushing upward. The balls cease to hold the support bushing when the bit has deepened by 2–3 cm at the bottom. Subsequently, drilling of the deflected cup is carried out in the usual way, while the retaining mechanism is lifted upward along the pipe by the core. At the end of the run, the core is wedged and lifted.

Because of the increase in the length of the first run, it was necessary to verify experimentally the possibility of cutting the cup at the bottom with the aid of a shot bit, since in very strong rocks only 5–10 cm can be drilled with a carbide bit. The experiments showed that the use of a shot bit for cutting is possible. The procedure for producing the deflection remains the same as for a carbide bit.

The use of the deflector of the modernized design makes it possible, in addition to reducing unproductive time losses, to increase the reliability of fixing the deflector at the bottom. This is achieved by lengthening the outer end of the wedge. The length of the outer end of the wedge is determined by the amount by which the spring can be compressed, minus 2–3 cm for cutting the bit into the bottom. Thus, if in the old deflector design the spring was compressed by 10 cm and the wedge protruded from the bit by only 2–3 cm, then in the modernized deflector the projection of the wedge from under the bit can be brought to 6–7 cm, which doubles the reliability of fixing the sidetracking tool at the bottom.