The petroleum-mining sector has developed drilling technologies and methods that have greatly increased well depths over the years. The
average well depth increased only 64 percent from 3,635 to 5,964 feet
between 1949 and 2008, according to US Energy Information Administration data. However, by 1998, deep producing wells extended roughly five times as far, to about 29,000 feet for deep oil-producing wells
and 31,000 feet for deep gas wells, US Geological Survey records show.
By 2009, the now infamous Deepwater Horizon drilled a record
35,050-foot deep well under 4,132 feet of water. The location stability
of the dynamically positioned platform was maintained by eight thrusters capable of developing, in sum, 59,000
hp. On-board electricity was provided by
a 7 MW, 11 kV diesel-electric power plant
comprising six ABB AMG generators. For
those of us whose technological engagements are limited to objects, say, smaller
than a tractor-trailer, this two-acre rig is
difficult to fathom. I mention these few
large-scale attributes of modern petroleum
mining to note the contrast with some of the
sensing, measurement, and telemetry technologies on these same operations depend.
Physical phenomena such as temperature
and pressure are just two of the continuous quantities drilling rigs must monitor.
Sensors, signal conditioners, digitizers, and
telemetry interfaces for downhole measurements operate in perhaps the most hostile
environment of any electronic instrumentation. IC’s operating temperature upper limits for datasheet performance in commercial, industrial,
military, and automotive environments are typically 70°C, 85°C, 125°C,
and 140°C, respectively. In petroleum-mining applications, downhole
temperatures in active sensing areas can run in excess of 200°C, according to Moshe Gerstenhaber, Analog Devices Division Fellow.
For example, for sensor signal-conditioning circuits, Gerstenhab-
er’s team completed a new design from the ground up, specifically to
answer the challenges of high-temperature downhole applications. The
AD8229 is a hermetically sealed, low-noise instrumentation amplifier
specified for operation to 210°C. Its 1.1 nV/√Hz (max) input noise spec-
tral density and 1.5 pA/√Hz (typ) current noise spectral noise density
puts this in-amp in rare company. What caught my eye for downhole
applications, however, was the high temperature limit coupled with a 1
µV/°C (max) input offset voltage drift. This level of thermal stability is
an asset, particularly given the unusually large operating temperature
range and the difficulty of compensating drift terms in quasi-static
Technology developers have expended
much R&D effort developing sophisticated
fiber optic sensors, which offer the advantage of deploying with both sensor-ex-citation and sensor-signal-conditioning
electronics located at the top of the hole.
One example is APS Technology’s PetroMax downhole fluid monitoring sensor.
The way the popular press describes petroleum-mining well operations one might
think that if a rig drilled a well in a field
known to contain, say, South Louisiana
Sweet Crude, that what would come out of
the well would be South Louisiana Sweet.
Reality is messier, production well’s output
will include crude oil, water, and natural
gas. The specific composition varies as
pumping operations proceed.
According to APS Technology, the PetroMax sensor distinguishes
the chemical composition of fluids passing a downhole optical sensor
by directly measuring their unique near-infrared absorption spectra. A
source lamp located at the surface provides sensor excitation. Near-infrared light travels down an optical fiber to the sensor and passes
through a portion of the production fluid. Light that is not absorbed
returns to the surface where an analyzer can evaluate the signal and
display results in real time.
Figure 1: PitneyBowes’ Discover 3D visualization tool aides
in interpretation of sparse, but complex drillhole data for
field exploration and development. (PitneyBowes)