Search and Discovery Article
By Larry Meckel,Stephen A. Sonnenberg
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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American Association of Petroleum Geologists (AAPG)
Added on 17 February, 2017
Explorer Article
The AAPG Annual Convention and Exhibition will feature a variety of field trips that will bookend the meeting, spanning from March 26 to April 8.
American Association of Petroleum Geologists (AAPG)
Added on 01 February, 2017
Explorer Emphasis Article
By David Brown
The eastern Mediterranean Sea could become the hottest offshore play in the Middle East area, depending on the outcome of a key exploration attempt later this year.
American Association of Petroleum Geologists (AAPG)
Added on 01 February, 2017
Explorer Historical Highlights
By Paul Weimer
Today, there are 31 sedimentary basins worldwide that produce or have economic discoveries in deepwater, in terms of both modern water depths and reservoir type.
American Association of Petroleum Geologists (AAPG)
Added on 01 January, 2017
Explorer Geophysical Corner
By Eduardo Trinchero,Luis Vernengo,Satinder Chopra
Interpretation of seismic amplitude anomalies could be a direct solution to finding hydrocarbons, or defining lithology, but is usually a tricky problem.
American Association of Petroleum Geologists (AAPG)
Added on 01 January, 2017
Explorer Article
The AAPG European Regional Conference, “Hydrocarbons in the Mediterranean: revisiting mature plays and understanding new and emerging ideas,” will be held Jan. 18-19 in Larnaca, Cyprus.
American Association of Petroleum Geologists (AAPG)
Added on 01 December, 2016
Learn! Blog
By Susan Nash
The dynamics of fluid behavior and structural movement on the nano-scale can be complicated and not always what was expected. New research that analyzes the well information and cores using new techniques and technologies is yielding important and useful results. Welcome to an interview with Wen Zhou, Chengdu University of Technology, who discusses recent research findings.
American Association of Petroleum Geologists (AAPG)
Added on 24 October, 2016
Learn! Blog
By Susan Nash
Primary research in hydrocarbon generation is yielding new insights into the natural gas geochemical characteristics of conventional and unconventional reservoirs, along with discoveries relating to the geomechanical processes. Welcome to an interview with Chenglin Liu, China University of Petroleum-Beijing, who discusses enlightening new findings regarding the relationship between salinity and hydrocarbon geochemical characteristics.
American Association of Petroleum Geologists (AAPG)
Added on 20 October, 2016
Learn! Blog
By Susan Nash
Eastern Mexico has been one of the most prolific and most complex regions of the world, and many believe there is still great potential for undiscovered giant and super-giant fields. Welcome to an interview with Stephen Cossey, whose work in eastern Mexico, both onshore and offshore, are pointing to exciting new potential.
American Association of Petroleum Geologists (AAPG)
Added on 04 October, 2016
Learn! Blog
By Susan Nash
Geoscientists have more opportunities than ever to make working with drones and drone data part of their skill set and services rendered. But, there are often a number of misconceptions, especially when getting started. Welcome to an interview with Michael Nash, who provides a reality check about drones and drone capabilities.
Please note that the drones references are the small drones used by the general public, and are not the large UAVs used by the military and other entities.
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American Association of Petroleum Geologists (AAPG)
Added on 22 September, 2016