Difference between revisions of "Fracture trap regime"

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Fracture traps are divided into three classes: extension, shear, and complex, based on the internal characteristics and geometry of the fractures that make up the reservoir. The outline below shows the classes, some subclasses, and possible styles into which these traps may be subdivided.
 
Fracture traps are divided into three classes: extension, shear, and complex, based on the internal characteristics and geometry of the fractures that make up the reservoir. The outline below shows the classes, some subclasses, and possible styles into which these traps may be subdivided.
 
==Outline==
 
==Outline==
'''Regime:''' Fracture trap
+
'''Regime:''' Fracture trap<br>
 
Lateral boundaries of the trap are provided by change from fractured reservoir to unfractured or less fractured rock or by change from open, permeable fractures to cement-filled or narrow-aperture, low-[[permeability]] fractures.
 
Lateral boundaries of the trap are provided by change from fractured reservoir to unfractured or less fractured rock or by change from open, permeable fractures to cement-filled or narrow-aperture, low-[[permeability]] fractures.
 
:'''Class:''' Extension fracture trap
 
:'''Class:''' Extension fracture trap

Revision as of 15:29, 16 April 2014

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

Fracture traps are divided into three classes: extension, shear, and complex, based on the internal characteristics and geometry of the fractures that make up the reservoir. The outline below shows the classes, some subclasses, and possible styles into which these traps may be subdivided.

Outline

Regime: Fracture trap
Lateral boundaries of the trap are provided by change from fractured reservoir to unfractured or less fractured rock or by change from open, permeable fractures to cement-filled or narrow-aperture, low-permeability fractures.

Class: Extension fracture trap
Dominant reservoir fractures are extension fractures.
Subclass: Parallel fractures
Open fractures in a fractured reservoir, predominantly unidirectional in both strike and dip.
Style: Mineralized fracture
Partially or totally mineralized by postfracture cements, typically calcite, gypsum, or silica.
Style: Nonmineralized fracture
Contains no postfracture cements or minerals.
Subclass: Intersecting fractures
Open fractures in fractured reservoir of several intersecting sets, either along fracture strike or fracture dip.
Style: Mineralized fracture
Style: Nonmineralized fracture
Class: Shear fracture trap
The dominant reservoir fractures are shear fractures.
Subclass: Parallel fractures
Style: Mineralized fracture
Style: Nonmineralized fracture
Subclass: Intersecting fractures
Style: Mineralized fracture
Style: Nonmineralized fracture</list-item></list-item>
Class: Complex fracture trap
Dominant reservoir fractures are complex fractures.
Subclass: Parallel fractures
Style: Mineralized fracture
Style: Nonmineralized fracture
Subclass: Intersecting fractures
Style: Mineralized fracture
Style: Nonmineralized fracture

Based on the interpretation of the genetic causes of fracture traps, two fracture trap families are recognized: tectonic and nontectonic.

Tectonic fracture trap families

The outline below shows the order of the families of the tectonic fracture trap superfamily and defines some of them.

Regime: Fracture

Superclass: Extension
Superclass: Shear
Superclass: Complex
Class: Parallel
Class: Intersecting
Superfamily: Tectonic fracture trap
Fractures were generated by crustal tectonic stresses, whether compressional, extensional, or transpressional.
Family: Fold-related fracture trap
Fractures are intimately associated with and controlled by tectonic folds.
Subfamily: Related to zone of maximum curvature.
Subfamily: Hydrofractures
Family: Fault-related fracture traps
Fractures are intimately associated with or controlled by tectonic faults.
Subfamily: Fractures related to normal faults
Subfamily: Fractures related to wrench faults
Family: Regional fracture trap
Fractures occur over a broad area unrelated to specific folds or faults and in which fractures are thought to have been created by regional tectonic stresses.

Fractures related to folding

Several mechanisms have been proposed to explain the common occurrence of highly fractured zones in various positions along tectonic folds, including bending-induced fractures along zones of maximum curvature, typically along the flanks of monoclines, anticlines, or synclines, as well as along the plunge axis of anticlines. Another cause of fracturing along compressive anticlines could be due to hydrofracturing during compression and squeezing of the folded rocks. Where appropriate, subfamilies can be established, such as maximum-curvature fracture traps and hydrofracture traps.

Fractures related to faulting

Numerous examples exist in which fracture intensity increases with proximity to faults. A number of fracture traps have been attributed to fault-induced or associated fracturing. Subfamilies can be established based on the type of fault with which the fractures are associated, e.g., normal-fault fracture trap or wrench-fault fracture trap.

Fractures related to regional stresses

Within regionally fractured areas, local fracture swarms with enhanced permeability and fracture frequency often occur. The transition from these high-permeability fracture swarms to areas of lower fracture frequency or fracture permeability often provides local lateral trap boundaries within the regional system. These fracture swarms may or may not be related to or associated with local secondary folds or faults.

Nontectonic fracture families

A wide variety of nontectonic elements have been interpreted to cause fractures and fracture traps. The more common ones include salt solution, piercement by mobile cores, meteorite impact, compaction drape, shrinkage due to cooling or diagenesis, pore-fluid overpressuring, erosional uplift and unloading, and hydrothermal fracturing. Each of these can be used as nontectonic fracture trap families. Where necessary, subfamilies and varieties can be created for any of these families. The outline below shows the order and some definitions for these traps.

Superclass: Extension fractures

Class: Parallel
Class: Intersecting
Superfamily: Nontectonic fracture trap
Fractures generated by nontectonic stresses, e.g., salt solution, piercement, shrinkage, and overpressuring.
Family: Solution collapse
Family: Piercement
Family: Impact
Family: Compaction drape
Family: Shrinkage
Subfamily: Chert diagenesis
Subfamily: Cooling joints
Family: Overpressuring
Subfamily: Source rock maturation
Subfamily: Geothermal pressuring
Subfamily: Clay dewatering
Family: Unloading
Family: Hydrothermal

See also

External links

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Fracture trap regime
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