High Data-Rate Drilling Telemetry System
Authors: Denison E.B. 
Published: December 2007

An electric telemetry system composed of modified drillpipe, an internal cable to span the bottomhole assembly, and a downhole instrument was used to drill a well to 5,100 ft (1550 m). System design, handling, performance, and downhole measurements are detailed. The system is compared with other systems.

Introduction - System Concept

The system discussed here establishes an electrical circuit from the surface to the bottom of the borehole. As shown in Fig. 1, the system is composed of two primary elements:special circuit-containing drillpipe from the surface to an intermediate position, andan armored cable "jumper" from that point to the instrument subsection immediately above the bit.

This system allows continuous transmission of down-hole data through the drillstring when drilling or not drilling, when the well is shut in, with no practical depth limitation, without a downhole power source, and at a data rate of more than 36,000 samples per minute.

System Performance

In late 1976, the complete system was used successfully to sidetrack an existing southern Louisiana well from 1,570 to 5,100 ft in 71 hours of rotary drilling and jetting. The system successfully provided steering and survey data, as well as continuous acceleration, pressure, and temperature data.

During this test, up to 71 joints (2,240 ft) of the special pipe were used at one time, while during a previous field pipe were used at one time, while during a previous field test, up to 56 joints had been used. A 1,200-ft collar jumper was used with the telemetry drillpipe to drill to 3,500 ft. At this point, 1,800 ft of the special drillpipe was replaced with standard pipe and a 3,000-ft jumper was installed and used to 5, 100 ft. Both jumpers were standard 7/32-in. single-conductor logging cables. The installation/removal hardware and the drillstring components all performed well.

The downhole instrument, special subsections, circuit-containing kelly cock and kelly, slip-ring assembly, high-pressure tool joint cleaners, and other equipment worked well. The special clean/dry mouse hole that had been used during rig testing on land was not needed on this inland barge rig.

Since 1972, three sets of prototype joints (8 to 10 joints each set), along with the present 105-joint drillstring, have been built and field tested. Several joints have accumulated a significant number of drilling hours (Table 1). The system was tested without the jumper in Oct. 1975.2 This is referred to as Test 1, whereas the complete system test with the jumper is called Test 2.

Downhole Data

The instrumentation system collected more than 150 hours of real-time, downhole data during the two field tests. The accuracy and utility of the survey and steering data were reported previously. The pressure and temperature data did not differ from expectations. However, the acceleration data have proven most interesting.

The output of each orthogonally mounted accelerometer was sampled 120 times per second to transmit real-time accelerations ranging from 0.2 to 20.0 Hz. These accelerometers also fed peak detector circuits that allowed the transmission of the peak accelerations (magnitude only, not sense) from 0.2 to about 1,000 Hz.

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