Introduction to November’s Focus: AVO Inversion

‘Invert, always invert’
Carl Gustav Jacob Jacobi’s maxim (1804 – 1851) (And more recently, Charlie Munger and Warren Buffett)

“Most people, if you describe a train of events to them will tell you what the result will be. There are few people, however that if you told them a result, would be able to evolve from their own inner consciousness what the steps were that led to that result. This power is what I mean when I talk of reasoning backward.”
Sherlock Holmes – A Study in Scarlet, Sir Arthur Conan Doyle (1887) and found in An Introduction to Seismology, Earthquakes, and Earth Structure by Seth Stein and Michael Wysession

When facing an inextricable geophysical problem, I sometimes imagine I am a detective that must solve a mystery amid a continuing turmoil of complexity, overwhelming data and contradictions. Aren’t we the detectives of the “underground” world after all? Well, after long days you need to find motivation where you can...

This is why I have partnered with Sherlock Holmes today; he will dispense some of his perspicacity in this introduction – and a slight dose of British humour.

“Detection is, or ought to be, an exact science, and should be treated in the same cold and unemotional manner.”
Sherlock Holmes – The Sign of Four

In this special issue on inversion, I have the honour of introducing three very interesting articles which all use inversion techniques as well as deductive, inductive and Sherlock’s abductive reasoning to crack (sometimes literally) the mysteries of our reservoirs.

The first article by Carl Reine and Sean Lovric is a shale gas case study in the Horn River basin. Using geomechanics, a wide range of microseismic measurements and production data, they demonstrate the value of geophysical interpretation techniques (AVO inversion and fault intensity here) in providing hindsight into the geological interpretation and hydraulic fracturing operations.

“Breadth of view… is one of the essentials of our profession. The interplay of ideas and the oblique uses of knowledge are often of extraordinary interest.”
Sherlock Holmes – The Valley of Fear

The second article, by Rémi Moyen, introduces the world of uncertainties – often overlooked in seismic reservoir characterization. In the new paradigm of “quantitative interpretation” however, characterizing uncertainties should become a mandatory part of the process. This is illustrated through several brief case studies to highlight different types of uncertainty. One of the key messages of this paper is that, while it can be hard to determine an exact value of the uncertainty, the process of characterizing uncertainty itself deepens our understanding and is well worth the effort.

“Any truth is better than indefinite doubt.”
Sherlock Holmes – The Yellow Face

The third and last article, by Damien Thenin and Ron Larson, provides us with the geomodeler’s perspective on using geophysical data.

“Nothing clears up a case so much as stating it to another person.”
Sherlock Holmes – Silver Blaze

They demonstrate that the outputs of geophysical analyses (inversion, seismic stratigraphy and geomorphology in this case) can greatly improve earth models. The authors also recommend that interpreters stay involved in the building and QC’ing of the quantitative geomodel to ensure that the geophysical interpretation is properly captured in the data integration process.

“‘Data! Data! Data!’ he cried impatiently. ‘I can’t make bricks without clay.’”
Sherlock Holmes – The Adventure of the Copper Beeches

I sincerely hope you will enjoy reading these articles as much as I did. I would like to thank Jan Dewar for her help reviewing these documents and of course all the authors for sharing their work with our geoscience community.