Trap classification levels

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

Basis for each level

A fairly flexible classification scheme has been devised in which each of the three trap systems is divided into three trap regimes, based primarily on the processes that control trap formation in the systems. The trap regimes can be divided into geometric classes and the classes into genetic families. Classifying traps using levels and the same basis at each level brings more consistency and value to classification. The table below shows the basis for each classification level and its definition.

Classification level	Basis	Function/Definition
System	Controlling geologic element	Dominant control of the trap—structural, stratigraphic, or fluidic.
Regime	Process	The dominant way of forming part or all of the trap closure. If the trap is structural, was the closure formed by folding, faulting, or fracturing? If the trap is stratigraphic, was the closure formed by depositional, erosional, or diagenetic processes? If the trap is fluidic, was closure formed by pressure, temperature, or chemical processes?
Class	Geometry and/or composition	Geometry—the external shape and size of the trap; may also include geometry of internal trap elements. Composition—the makeup of the reservoir, seal, or fluid that creates or defines the trap boundaries.
Family	Genesis	The way all or part of the trap closure came into being. For example, for an isolated marine carbonate trap, was the closure formed because of the reservoir/seal facies relationships of a reef, an oolite bar, or a tidal channel?

Sublevels

Using one term to classify traps geometrically, compositionally, or genetically is not always adequate. To solve this problem, intermediate groupings such as superfamilies or superclasses can be added where necessary. Trap classes can be subdivided into subclasses and styles if needed, and trap families can be subdivided into subfamilies and varieties. These extra levels allow a fuller description of traps.

Degree of interpretation at different levels

Classification requires different degrees of interpretation at different levels of the proposed scheme. The highest levels require presumably less interpretation than do the lower levels. The higher levels are broader generalizations and reveal broader relationships. Classification at lower levels is more interpretive and therefore more open to disagreement. For example, trap geometries, which establish trap classes, are typically well understood; whereas trap genesis, used to establish trap families, relies on interpretation, is often the subject of considerable disagreement and debate, and may be the last trap element fully understood.

Trap systems & corresponding regimes

The proposed classification scheme divides traps into the following systems and their corresponding regimes.

• Structural trap system
  • Fold Regime
  • Fault Regime
  • Fracture Regime

• Stratigraphic trap system
  • Depositional regime
  • Erosional regime
  • Diagenetic regime

• Fluidic trap system
  • Pressure Regime
  • Temperature Regime
  • Fluid-Composition Regime

Trap classes and families

As mentioned previously, the various trap regimes can be subdivided into trap classes and trap families, based on geometry, composition, and genesis. Ultimately, every oil accumulation can hopefully be classified correctly at the class and family levels.

See also

• Classification philosophy
• What is a trap?
• Classification basis
• Classifying traps
• Trap systems: structural, stratigraphic, and fluidic

External links

find literature about Trap classification levels

• Original content in Datapages
• Find the book in the AAPG Store