Erosional trap regime
| Exploring for Oil and Gas Traps | |
| |
| Series | Treatise in Petroleum Geology |
|---|---|
| Part | Traps, trap types, and the petroleum system |
| Chapter | Classification of exploration traps |
| Author | Richard R. Vincelette, Edward A. Beaumont, Norman H. Foster |
| Link | Web page |
| Store | AAPG Store |
Definition
Erosional traps are those in which trap boundaries occur along contacts between erosional surfaces and underlying or overlying reservoirs.
Classes and subclasses
Three trap classes have been identified, based on the geometry of the reservoir beds in contact with the unconformity surface. The hierarchical structure and definitions are shown below.
System: Stratigraphic traps
- Regime: Erosional traps
- Form as a result of erosional processes
<list-item>Class: Truncation traps</list-item><list-item>Up-dip reservoir boundary created by truncation of a reservoir beneath an unconformity, followed by deposition of sealing unit on top of an unconformity. The unconformity surface provides top seal, but closure usually requires the presence of depositional or tectonic side and bottom seals beneath the unconformity.
<list-item>Subclass: Regional subcrop</list-item><list-item>Uniformly or gently dipping reservoir bed beneath an unconformity. Top seal is provided by postunconformity beds; bottom seal is provided by sealing units beneath reservoir.</list-item><list-item>Subclass: Paleostructural subcrop</list-item><list-item>Folded and/or faulted reservoir beds beneath postdeformation unconformity.</list-item><list-item>Reservoir distribution and trap boundaries are controlled by preunconformity deformation and subsequent erosion.</list-item></list-item><list-item>Class: Erosional relief traps</list-item><list-item>Closure provided by topographic relief beneath an unconformity.
<list-item>Subclass: Buried hill</list-item><list-item>Top-seal closure created by positive erosional relief of reservoir beneath a sealing unconformity surface.</list-item><list-item>Subclass: Truncation edge</list-item><list-item>Side seal provided by truncation of a reservoir against later erosional valley, channel, or gorge wall and subsequent deposition of sealing beds in valley, channel, or gorge.</list-item></list-item>
Families
Families of the erosional trap regime have been established based upon the genesis of the unconformity surface that controls the trap boundaries. Two superfamilies are recognized: nonmarine erosion surfaces and marine erosion surfaces. Within these superfamilies, more detailed family classifications can be established. Where desired, trap varieties can be utilized to provide more details of reservoir and seal genesis. The outline below shows the superfamilies, families, and subfamilies of the subclass gorge-edge traps.
Regime: Erosional traps
- Class: Truncation traps
<list-item>Subclass: Regional subcrop
<list-item>Superfamily: Nonmarine erosional surface
<list-item>Family: Sequence-boundary unconformity</list-item><list-item>Reservoir variety: Marine sandstone subcrop</list-item><list-item>Seal variety:
<list-item>Top: Marine transgressive shale above unconformity and marine shale above sandstone.</list-item><list-item>Bottom: Marine shale beneath sandstone</list-item></list-item></list-item></list-item><list-item>Subclass: Paleostructural subcrop
<list-item>Style: Complex fold-fault subcrop
<list-item>Superfamily: Nonmarine erosional surface</list-item><list-item>Family: Sequence-boundary unconformity
<list-item>Subfamily: Postcompressional fold-fault unconformity
<list-item>Reservoir variety: Multiple truncated marine sandstones</list-item><list-item>Seal variety:
<list-item>Top: Postunconformity marine shale</list-item><list-item>Bottom: Underlying marine shale</list-item></list-item></list-item></list-item></list-item></list-item>
- Class: Erosional relief trap
<list-item>Subclass: Buried hill
<list-item>Superfamily: Nonmarine erosion surface
<list-item>Family: Sequence-boundary unconformity
<list-item>Subfamily: Local differential erosion
<list-item>Reservoir variety: Basement igneous complex</list-item><list-item>Seal variety: Marine shales above unconformity</list-item></list-item></list-item></list-item></list-item><list-item>Subclass: Truncation-edge traps
<list-item>Superfamily: Marine erosion surface
<list-item>Family: Submarine canyon or gorge trap</list-item></list-item><list-item>Superfamily: Nonmarine erosional surface
<list-item>Family: Channel-relief or valley-edge relief traps</list-item></list-item></list-item>
See also
External links
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