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Features and Advantage:

• has increased depth;
• it is easy to remove when stuck;
• has battery power, is not sensitive to the properties and quality of the drilling fluid;
• works on aerated solutions and air purging;
• easily overcomes unfavorable for the electromagnetic channel cuts (salt, coal layers).

As a housing of bottom-hole assembling uses standard non-magnetic drill collar, as a housing of relay – standard heavyweight drill pipe (TBT).

Operating principle of ZTC-42KK telesystem

The telemetry system with the combined communication channel has been widely used relatively recently (since 2008) and the principle of its operation is known to far from everyone.

Therefore, below, in an accessible form and as briefly as possible, we tried to state its essence.

The combined communication channel of this telesystem is named because it combines the transmission of data in series in two ways – at first from the bottom hole by cable and then to the surface through the rock with the help of electromagnetic waves. Schematically, the layout of the drill string with the telesystem is shown in the figure.

The bottomhole unit includes sensors for the measurement of the fluids, vibration and GL. In addition, neutron logging and resistivimetry modules can be installed, as well as a near bit module. Data from the bottomhole unit is transmitted via cable to a retransmitter, which is usually installed at shallow depths. From the retransmitter, data is sent to the surface using an electromagnetic communication channel. The retransmitter can be located in the openhole, as well as in the casing. Thus, from the bottom hole to the well head, the data recorded by the sensors of the telesystem go sequentially along two different channels – first through the cable, then the electromagnetic one.

This type of communication channel has a number of advantages. Firstly, it is a depth in comparison with a purely electromagnetic channel. The length of the cable section is usually taken to the maximum with some limitations. Secondly – recoverability, and not just theoretical, but repeatedly tested on wells. This is especially important when working with sources of ionizing radiation. The third advantage is the independence of the circulation and the properties of the drilling fluid through the use of battery power. The fourth advantage is the independence from the electrical properties of rocks, to which the telesystems with the electromagnetic communication channel are very sensitive.

The drill-string running using this telesystem begins with the assembly of BHA, screwing of non-magnetic drill collars and an orientation sub-conductor into which the downhole block will descend later on the cable. Further, the drill tool is lowered to a certain depth, on which the retransmitter is installed. With the help of a geophysical elevator, which is part of the equipment of our telemetric team, the downhole unit on the cable is lowered. The duration of this operation depends on the depth of descent and is usually in the range of 0.5 … 2.5 h.

After landing the bottomhole unit in the orientation sub, the cable is cut off, and at its end a connector is mounted, which is connected to the retransmitter.

The retransmitter is screwed onto the drill string, and the tool is lowered to the bottom.

The presence of a cable does not limit the actions of the driller in any way, the layout with the telesystem can be rotated up to 40 rpm while observing the limitations imposed on the downhole motor by its manufacturer.

General view of ZTC-42KK telesystem