Geology Reference
In-Depth Information
1.2
Paper No. AADE-11-NTCE-74 -
“High-Data-Rate MWD System for Very Deep Wells”
Significantly expanded with photographs and detailed annotations . . .
1.2.1 Abstract.
Measurement-While-Drilling systems presently employing mud pulse
telemetry transmit no faster than one or two bits/sec from deep wells containing
highly attenuative mud. The reasons - “positive pulsers” create strong signals
but large axial flow forces impede fast reciprocation, while “mud sirens”
provide high data rates but are lacking in signal strength. China National
Petroleum Corporation research in MWD telemetry focuses on improved
formation evaluation and drilling safety in deep exploration wells. A high-data-
rate system providing 10 bits/sec and operable up to 30,000 ft is described,
which creates strong source signals by using downhole constructive wave
interference in two novel ways. First, telemetry schemes, frequencies and pulser
locations in the MWD drill collar are selected for positive wave phasing, and
second, sirens-in-series are used to create additive signals without incurring
power and erosion penalties. Also, the positions normally occupied by pulsers
and turbines are reversed. A systems design approach is undertaken, e.g., strong
source signals are augmented with new multiple-transducer surface signal
processing methods to remove mudpump noise and signal reflections at both
pump and desurger, and mud, bottomhole assembly and drill pipe properties, to
the extent possible in practice, are controlled to reduce attenuation. Special
scaling methods developed to extrapolate wind tunnel results to real muds
flowing at any downhole speed are also given. We also describe the results of
detailed acoustic modeling in realistic drilling telemetry channels, and introduce
by way of photographs, CNPC's “short wind tunnel” for signal strength, torque,
erosion and jamming testing, “very long wind tunnel” (over 1,000 feet) for
telemetry evaluation, new siren concept prototype hardware and also typical
acoustic test results. Movies demonstrating new test capabilities will be shown.
1.2.2 Introduction.
The petroleum industry has long acknowledged the need for high-data-rate
Measurement-While-Drilling (MWD) mud pulse telemetry in oil and gas
exploration. This need is driven by several demand factors: high density
logging data collected by more and more sensors, drilling safety for modern
managed pressure drilling and real-time decision making, and management of
economic risk by enabling more accurate formation evaluation information.
Yet, despite three decades of industry experience, data rates are no better
than they were at the inception of mud pulse technology. To be sure, major
strides in reliability and other incremental improvements have been made. But
siren data rates are still low in deeper wells and positive pulser rates also
perform at low levels. Recent claims for data rates exceeding tens of bits/sec are
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