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The driving forces for conventional accumulations (structural or stratigraphic traps) are Forces of Buoyancy which are due to differences in densities of hydrocarbons and water. In contrast, the driving forces for unconventional tight accumulations are Forces of Expulsion which are produced by high pressures. That is an enormous difference and creates unconventional petroleum systems that are characterized by very different and distinctive characteristics. The Force of Expulsion pressures are created by the significant increase in volume when any of the three main kerogen types are converted to hydrocarbons. At those conversion times in the burial history, the rocks are already sufficiently tight so the large volumes of generated hydrocarbons cannot efficiently escape through the existing tight pore system, thus creating a permeability bottleneck that produces an overpressured compartment over a large area corresponding to the proper thermal oil and gas maturities for that basin. The forces initially created in these source rocks can only go limited distances into adjacent tight reservoirs (clastics or carbonates) above or below the source. The exact distance will vary depending on the pressure increase, matrix permeability, and fractures of that specific tight reservoir system. In general, the distances are small, in the orders of 10s to 100s of feet for oil and larger for more mobile gas systems. Those exact distance numbers are subject to ongoing investigations.  

A plot of the pressure data versus elevation for a given formation is critical in determining whether an accumulation is conventional or unconventional. Conventional accumulations will have hydrocarbon columns of 10s to 100s of feet with the pressure in the hydrocarbons and that in the water equal at the bottom of the accumulation (at the HC-water contact). In contrast, the unconventional accumulations will show HC column heights of 1000s of feet with the pressure in the hydrocarbon phase and the water phase being the same at the top of the accumulation (at the updip transition zone). Those significant differences are critical for understanding and differentiating these two play types. Because the system is a pore throat bottleneck with very little or minimum lateral migration, the type of hydrocarbon s are closely tied to the thermal maturity required to generate those hydrocarbons. Thus the play concept begins with two important geochemical considerations: (1) where are the source rocks and what are the kerogen types and organic richness (TOC), and (2 ) where are they mature in the basin for oil, condensate, and gas in the basin. These parameters will very quickly define the fairway for the play. Then one has to add the critical information on the reservoirs themselves: composition (brittleness), thickness, and reservoir quality (matrix porosity and permeability). In summary, these tight unconventional petroleum systems (1) are dynamic , and (2) create a regionally inverted petroleum system with water over oil over condensate over gas for source rocks wit h Type I or II kerogen types.

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The past 30+ years have witnessed a wide variety of exploration strategies and a number of technological “revolutions” in the search for oil and gas. Although the exploration landscape and tools of the trade are so different than they were in the early 1980’s, in one aspect we appear to have come full circle, realizing that a deep understanding of our basins is the critical element in any success.
American Association of Petroleum Geologists (AAPG)
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The search for unconventional hydrocarbons is not new. It’s true that almost 100 years separated the early exploration successes in the synclinal valleys of Central Pennsylvania, to the exploitation of Coal-Bed Methane in a number of basins in the U.S. and Canada in the 1980’s. Since the 1980's, however, a quiet revolution began which by today has seen several waves of unconventional resources being pursued with economic success. Coal-bed methane was followed by the search for Center-Basin Gas, Shale Gas and most recently, Liquid-rich Shales (some of which aren't shales).

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The Arctic Ocean occupies a unique tectonic setting as a small, confined ocean between two much larger oceans - the subducting Pacific margin and the opening North Atlantic. Unlike many of the world's oceans, evidence on both timing and geometry is poor, and major elements of the plate tectonic evolution are still "up for grabs". The Arctic has experienced significant plate motion from Cretaceous to present, and because of the ambiguities in the oceanic signature, resolving the most likely kinematic history is critical in understanding paleogeography and hence reservoir and source distribution. I will show a 3-stage kinematic model which, while not a unique solution, seems to best satisfy the known constraints.

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