Downtown Houston


Seminar Date: May 21 2020

Registration Opens: May 13 2020 - May 20 2020

Time: 12:00 PM - 01:00 PM (US CDT)

Admission/Registration Link:

Meeting/Webinar Link: None

Contact: Hyungjoo Lee (, SPWLA Houston Chapter)


Fees: FREE


That the gamma ray emission from earth formations is more intense in clay-rich formations has long been recognized. I can trace the first suggestions of a linear relationship of the gamma ray index to shale volume to the early 1950s ; the first appearance of modern notations (in the western literature) is traceable to the early 1970s . At this same time, researchers in pulsed-neutron logging appear to have been discovering a non-linear relationship. Priority belongs to V. V. Larionov who published data suggesting this in 1969. Larionov’s work was published in Russian, and behind the “Iron Curtain”. It was introduced to Western formation evaluation in Dresser Atlas’ Neutron Lifetime Interpretation (published without a date, but c. 1970), with Larionov’s curves published on page 18 with the citation “after Larionov”. Contemporaneously, Stieber (1970) published a similar non-linear shale volume – gamma ray index function, and Clavier et. al (1971) published yet-another similar transform. These transforms were all developed to facilitate pulsed-neutron log interpretation; Stieber and Clavier did not support their transforms with data, and Larionov’s raw data was not published. The Larionov and Clavier functions were originally available only as graphical functions; Stieber’s function was developed by “trail and error”. All of these formulas are the inventions of anonymous “function fitters” rather than the authors they are attributed to. The functions are obviously similar. This should have spawned the question: Are these the same function? The answer is, more or less, yes! I will show that each of the functions can be generalized to a function of one parameter, and that by varying that one parameter each of the functions can be made to closely mimic any of the others. I will introduce a “new” function of two parameters based upon Bezier curves that can even more closely mimic any of these curves. By reversing the roles of the horizontal and vertical axes, you can see that these functions suggest that the earlier increments (say 0-10%) of shale volume are more radioactive than later increments (say 10-20%) over the entire range of shale volume. How can this be? Remember, when using these curves we are relying on the unknown data sets of Stieber and Clavier, and the regionally limited data set of Larionov (which remains unpublished in the west). If these curves are to be taken seriously, there should be a physical model that can account for this behavior. I will introduce such a model for your inspection and criticisms. Lastly, I will show that “Tertiary” is a mistranslation of “Mesozoic and Tertiary”, introducing an error in time equal to the duration of the Mesozoic, about 186 million years. Since about half of earth’s source rocks were deposited during this era, this seems to be a potentially significant error. 


David Kennedy began a career in the logging industry in 1973 following earning a B.S. in Physics at Georgia Tech. He entered the industry as a Schlumberger field engineer in California and Alaska, staying with Schlumberger for five years. Following that, Dave returned to school and earned Masters’ degrees in Physics and Earth Sciences at the University of Texas at Dallas, with further studies at U. C. Berkeley. In his career, he has worked in one or another capacity at Arco, Sohio Research and operations, Mobil Research and operations, ExxonMobil Research and operations, Baker-Hughes, PathFinder, and Southwestern Energy. David has been an SPWLA member for 40 years and served as V.P. Publications and Editor of Petrophysics from 1999-2002, V.P. Technology in 2009, and President (etc.) from 2014-2016. David is inventor or co-inventor on six U.S. Patents, and has published about 45 articles as author or coauthor in conference proceedings and refereed journals. His major research interest has been formation conductivity interpretation and electromagnetic logging instrumentation. David has been an educator all his life, having taught courses at the USMA at West Point, courses in computer science, physics, materials science, and electrical engineering at San Francisco Bay Area private and junior colleges.  He is now recently retired as a professor in the Petroleum Engineering Department at Texas A&M University instructing graduates and undergraduates in formation evaluation. Before all of that, David served as a Lieutenant of Infantry in Vietnam where he received both a Purple Heart and Bronze Star with V device.

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