Borehole Electromagnetics –Diffusive and Propagation Transients - Wave Propagation in Drilling, Well Logging and Reservoir Applications - page 338

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Borehole Electromagnetics -
Diffusive and Propagation Transients
The subject of resistivity and electromagnetic logging is as old as
petroleum engineering itself - it is so broad, encompassing thousands of papers
authored by hundreds of investigators at equally numerous universities and
companies over five decades - thus, we will not attempt to provide any reviews
and discussions, preferring to focus only on our own contributions and
perspectives in this short chapter. Despite this intense research activity, there
are serious limitations in modern mathematical models used to guide hardware
design and to interpret logging data, problems which we will address. Another
fundamental problem is non-technical - it is the secret and proprietary nature by
which industry models and algorithms are developed. Most companies will not
publish analytical details nor discuss general formulations and limitations, but
instead, provide “field studies” and applications demonstrating how their
approaches helped discover new oilfields or bypassed oil zones. While such
successes are commendable, these presentations are hardly scientific: they do
not, in any way whatsoever, justify formulations from any engineering sense,
nor do they serve any useful educational purpose.
In fact, the present author, who minored in electrodynamics at the
Massachusetts Institute of Technology in his doctoral studies, in studying
dozens of well known papers, has not encountered a single one that presented
any formulation in useful detail (exceptions are Professor Liang Shen' s papers,
which provided important insights into many subtle questions raised by early
researchers). For instance, “propagation resistivity” is typically summarized
with simple remarks on phase delay and amplitude loss, the usual notes on
receiver and transmitter spacings, and of course, exploration successes. Papers
on laterolog tools are equally vague, typically augmented with hand-drawn
current streamlines showing advantages of new electrode placements, while
publications on micro-resistivity pad tools are almost non-existent. Advertising
for such devices, for example, do not state if the interpretation algorithm
assumed isotropic or anisotropic media, a question important to vertical versus
horizontal well applications. And again, no data analysis details; thus, more
questions are raised than are answered and progress is hindered further.
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