Geology Reference
In-Depth Information
Short wind tunnels, envisioned for torque and erosion objectives, are easily
and inexpensively designed and built within days. What is generally not known
is the justifiable use of intermediate length (100-200 feet) and very long wind
tunnels (say, 2,000 feet) in evaluating telemetry concepts, for instance, acoustic
'p signal strength, wave interference effects, surface signal processing schemes,
downhole wave-based signal optimization methods, and so on. There are two
reasons supporting such applications. For one, acoustic waves, even in wind
tunnels, are still “long” in the classical sense. The sound speed in air is
approximately 1,000 ft/sec. For a very high 100 Hz carrier wave, the
wavelength O = 1,000/100 ft = 10 ft still greatly exceeds the diameter of a
typical drillpipe, say, six inches. Second, it can be shown that if Z is circular
frequency, P is viscosity, U is mass density, c is sound speed and R pipe radius,
then the pressure P corresponding to an initial signal P
0
can be determined from
P = P
0
e
- D
x
where x is the distance traveled by the wave and D is the attenuation
rate given by D = (Rc)
-1
{(PZ)/(2U)} = (Rc)
-1
{(QZ)/2}. The kinematic
viscosity Q again appears, although fortuitously, but its presence indicates that
signal tests can be cleverly designed to mimic attenuation using air as the
working fluid
!
Thus, baseline MWD designs can be evaluated in air-
conditioned offices and labs using short and long wind tunnels, deferring
expensive hardware considerations related to mechanical reliability, vibrations,
dynamic seals, corrosion, and so on, to the tail end of the design process.
The subject matter of this monograph represents years of both mental
satisfaction and endless frustration, that is, continuing “love-hate” conflicts in
confronting imposing challenges. These chapters summarize key ideas and
highlight new theoretical results, physical insights, and testing and evaluation
strategies that were developed in thinking “outside the box.” But the endeavor
would not come full circle until the suggestions were put to real tests in real
engineering design and field testing programs.
Under the leadership of Dr. Yinao Su, Director of CNPC's Downhole
Control Institute, comprehensive wind tunnel facilities were developed, and
procedures, algorithms and theories were tested. The recent work described in
“High-Data-Rate Measurement-While-Drilling System for Very Deep Wells,”
Paper No. AADE-11-NTCE-74 presented at the American Association of
Drilling Engineers' 2011 National Technical Conference and Exhibition in
Houston, summarizes findings aimed at an MWD system architecture that
provides at least 10 bits/sec (without data compression) in very deep wells with
lengths up to 30,000 ft. An updated version concludes the present chapter,
providing an overview of current MWD project results and objectives. We
emphasize that all of the theoretical and experimental methods in this topic are
available to the industry. The authors hope that, by openly identifying and
discussing problems, solutions and strategies, petroleum exploration can be
made more efficient with greater emphasis on safety, while reducing economic
and exploration risk and educating the next generation of engineers.
Search WWH ::
Custom Search