Ready or Not, Changes Will Keep Coming

This table compares conventional exploration plays to unconventional plays.
This table compares conventional exploration plays to unconventional plays.

“My concept of reservoirs has completely changed.”

I actually heard an engineer say these words – last summer, while attending a technical conference of geologists and engineers – and he was referring to the rapidly evolving concepts of reservoirs generated from shale gas reservoir research.

At the time it struck me that it was very unusual for an engineer to say this because, in my experience, engineers are sometimes more resistant to change than geologists.

Thinking of shales (or more correctly, mudstones) as reservoirs, however, is an example of a significant evolution of thinking – a progression also known as a paradigm shift.

For example, geologists of my generation learned that shales can act as source rocks when they contain abundant organic matter and as seals when they cover porous and permeable sandstones or carbonates.

Thinking of a shale as a reservoir, then, is a sometimes-difficult paradigm shift for geologists of my age.


Paradigm shifts occur from time to time – and, clearly, they can profoundly affect how petroleum geologists work. Exploring for gas shales, oily source rocks or tight oil reservoirs is profoundly different than exploring for more conventional reservoirs.

The accompanying table compares conventional exploration plays to unconventional plays – and as the table shows, exploring for shale gas, shale oil or tight oil reservoirs requires a different mindset.

Trap areas can cover many thousands of square miles or square kilometers; permeability is measured in nanodarcys – one billionth of a darcy – and the limit of permeability is determined by the size of the pore throats and the size of the molecules that can flow through them.

Not long ago, petroleum geologists were confronted by another non-geologic paradigm shift – using personal computers to manage and map geologic data. In the years since we first started using them, personal computers allowed petroleum geologists to be much more productive. One geologist now does what it used to require several geologists to do. Today, geologists work with more information and process it much more rapidly.

Some geologists, however, refused to make the transition to using computers to do geology. Those geologists are rare today and probably don’t work in larger companies! Using computers is not absolutely necessary but it is hard to imagine being competitive and surviving without them.

There are other examples: Sequence stratigraphy, for example, was a revolutionary method for interpreting patterns of strata caused by sea level fluctuation and basin tectonics. It created a prodigious lexicon of “seq-speak” – and inevitably left non-adopters in its wake.


To survive and prosper, geologists must evolve along with our science. We need to learn more about source rocks – for example, what is the relationship of pore creation to kerogen maturation.

The investigation of tight rocks is being achieved by technology we need to embrace: pulse decay perm, high resolution CT scanning and ion-milled samples with SEM imagery, for example.

We also need to learn more about completion technology, something that only engineers worried about in the not-too-distant past.

AAPG provides information to help you evolve and you should take advantage of that information. I suggest that during the coming year you consider:

  • Attending an AAPG conference or a Geoscience Technology Workshop.
  • Taking an AAPG school or online training course.
  • Really reading the AAPG BULLETIN or the EXPLORER.
  • Surfing Search and Discovery or AAPG Datapages.

Paradigm shifts require a response from us. We can refuse to learn about them and become extinct, or we can let our concepts and approaches evolve, allowing us to survive and thrive.

Editor's Note: Special thanks to AAPG member John McLeod, senior geologist for SM Energy Company in Tulsa, for his ideas and edits for this column.

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President's Column

President's Column - Ted Beaumont

Edward A. "Ted" Beaumont, AAPG President (2012-13), is an independent consultant with Cimarex Energy.

President's Column

AAPG Presidents offer thoughts and information about their experiences for the Association. 

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We describe the structure, microstructure, and petrophysical properties of fault rocks from two normal fault zones formed in low-porosity turbiditic arkosic sandstones, in deep diagenesis conditions similar to those of deeply buried reservoirs. These fault rocks are characterized by a foliated fabric and quartz-calcite sealed veins, which formation resulted from the combination of the (1) pressure solution of quartz, (2) intense fracturing sealed by quartz and calcite cements, and (3) neoformation of synkinematic white micas derived from the alteration of feldspars and chlorite. Fluid inclusion microthermometry in quartz and calcite cements demonstrates fault activity at temperatures of 195degC to 268degC. Permeability measurements on plugs oriented parallel with the principal axes of the finite strain ellipsoid show that the Y axis (parallel with the foliation and veins) is the direction of highest permeability in the foliated sandstone (10–2 md for Y against 10–3 md for X, Z, and the protolith, measured at a confining pressure of 20 bars). Microstructural observations document the localization of the preferential fluid path between the phyllosilicate particles forming the foliation. Hence, the direction of highest permeability in these fault rocks would be parallel with the fault and subhorizontal, that is, perpendicular to the slickenlines representing the local slip direction on the fault surface. We suggest that a similar relationship between kinematic markers and fault rock permeability anisotropy may be found in other fault zone types (reverse or strike-slip) affecting feldspar-rich lithologies in deep diagenesis conditions.
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The Gulf of Mexico (GOM) is the 9th largest body of water on earth, covering an area of approximately 1.6 million km2 with water depths reaching 4,400 m (14,300’). The basin formed as a result of crustal extension during the early Mesozoic breakup of Pangaea. Rifting occurred from the Late Triassic to early Middle Jurassic. Continued extension through the Middle Jurassic combined with counter-clockwise rotation of crustal blocks away from North America produced highly extended continental crust in the subsiding basin center. Subsidence eventually allowed oceanic water to enter from the west leading to thick, widespread, evaporite deposition. Seafloor spreading initiated in the Late Jurassic eventually splitting the evaporite deposits into northern (USA) and southern (Mexican) basins. Recent work suggests that this may have been accomplished by asymmetric extension, crustal delamination, and exposure of the lower crust or upper mantle rather than true sea floor spreading (or it could be some combination of the two).
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