Hydrocarbon accumulation: the seven critical elements

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Exploring for Oil and Gas Traps
Series Treatise in Petroleum Geology
Part Predicting the occurrence of oil and gas traps
Chapter Value of geological fieldwork
Author Denise M. Stone
Link Web page
Store AAPG Store

Seven critical elements are necessary for subsurface hydrocarbon accumulations to occur:


Exploration risk is best understood by studying historically what has and has not been successful in a basin. In other words, what combination of the seven critical elements occurred to form existing fields and, conversely, what are the main reasons for the dry holes in that same basin? Is a common element responsible for the dry holes?

The goal of an exploration effort is to use all the data available to identify fully the technical risks and recommend the best course of action and investment. Action following a field project might range from no action, to acquiring more data in key areas, to drilling a well.

Critical element checklist

Figure 1 A summary of each of the seven critical elements of a hydrocarbon system with respect to the exploration maturity of the basin.

The following checklist summarizes key attributes of the seven critical elements. The working explorer should have a general understanding of these attributes in the basin studied.

Reservoir rock

General 3-D definition

  • Sedimentary rock type(s)
  • Gross thickness range
  • Lateral continuity (faulted?)
  • Mappability
  • Depth of burial
  • Structural relief of reservoir top
  • Outcrop occurrences

Character of upper and lower boundaries

  • Origin: erosional vs. depositional
  • Nature: abrupt vs. gradational
  • Seismic reflectivity
  • Conformability

Diagnostic features

  • Depositional environment
  • Facies distribution
  • Provenance
  • Internal stratigraphic subdivisions
  • Age diagnostic criteria: fossils, intrusives, marker horizons
  • Electric log responses
  • Pay distribution: vertical, lateral
  • Sedimentary structures

Petrographic characteristics

Source rock


Thermal history

  • Rates of deposition
  • Rates of burial
  • Paleogeothermal gradient
  • Tectonic history
  • Location of kitchen areas

Migration and trapping

Geologic history

  • Main tectonic events: compressional, tensional, wrench
  • Structural overprinting
  • Depositional history: continental, marine
  • Episodes of subsidence: regional, local
  • Controls on subsidence
  • Unconformities
  • Significant episodes of volcanism, subsidence, uplift, erosion
  • Rates of deposition
  • Paleotopography
  • Paleoclimate
  • Chronostratigraphy

Structural history and style

  • Compressional vs. tensional basin
  • Main structural elements
  • Tectonic development
  • Sequence of events
  • Structural overprinting
  • Fault trends: major and minor
  • Basin boundary faults
  • Major faults vs. minor faults
  • Zones of weakness
  • Dip domains
  • Outcrop patterns
  • Dip and strike trends
  • Average throw on faults

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Hydrocarbon accumulation: the seven critical elements
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