Difference between revisions of "Diagenetic trap regime"

From AAPG Wiki
Jump to navigation Jump to search
(Initial import)
 
Line 20: Line 20:
  
 
'''System:''' [[Stratigraphic trap]]s
 
'''System:''' [[Stratigraphic trap]]s
 
+
:'''Regime:''' Diagenetic traps
* '''Regime:''' Diagenetic traps
+
::'''Class:''' Diagenetic reservoirs
 
+
::Form where [[porosity]] is created as a result of local diagenetic processes such as dissolution or dolomitization.
<list-item>'''Class:''' Diagenetic reservoirs</list-item><list-item>Form where [[porosity]] is created as a result of local diagenetic processes such as dissolution or dolomitization.
+
:::'''Subclass:''' Secondary dolomite reservoirs
 
+
:::Form as a result of localized secondary dolomitization.
<list-item>'''Subclass:''' Secondary dolomite reservoirs</list-item><list-item>Form as a result of localized secondary dolomitization.</list-item><list-item>'''Subclass:''' Leached (secondary) porosity</list-item><list-item>Form as a result of localized leaching of nonreservoir-quality rock to create enhanced porosity and [[permeability]]. Common beneath unconformity surfaces.</list-item></list-item><list-item>'''Class:''' Diagenetic seals</list-item><list-item>Trap boundaries created by plugging original reservoir porosity and permeability by diagenetic cements or minerals.
+
:::'''Subclass:''' Leached (secondary) porosity
 
+
:::Form as a result of localized leaching of nonreservoir-quality rock to create enhanced porosity and [[permeability]]. Common beneath unconformity surfaces.
<list-item>'''Subclass:''' Secondary anhydrite barriers</list-item><list-item>Form as a result of secondary anhydrite precipitating in original pore spaces.</list-item><list-item>'''Subclass:''' Secondary clay barriers</list-item><list-item>Form as a result of secondary clay, commonly kaolinite, precipitating in original pore space.
+
::'''Class:''' Diagenetic seals
 
+
::Trap boundaries created by plugging original reservoir porosity and permeability by diagenetic cements or minerals.
<list-item>'''Style:''' Secondary pore-throat trap</list-item><list-item>Caused by a reduction in the size of pore-throat radii of reservoir rocks by depositional or diagenetic processes. These trap types typically have relatively porous units in the sealing facies that are impermeable to oil [[migration]] due to capillary restraints but contain producible water.</list-item></list-item></list-item>
+
:::'''Subclass:''' Secondary anhydrite barriers
 +
:::Form as a result of secondary anhydrite precipitating in original pore spaces.
 +
:::'''Subclass:''' Secondary clay barriers
 +
:::Form as a result of secondary clay, commonly kaolinite, precipitating in original pore space.
 +
::::'''Style:''' Secondary pore-throat trap
 +
::::Caused by a reduction in the size of pore-throat radii of reservoir rocks by depositional or diagenetic processes. These trap types typically have relatively porous units in the sealing facies that are impermeable to oil [[migration]] due to capillary restraints but contain producible water.
  
 
==Discussion of diagenetic trap families==
 
==Discussion of diagenetic trap families==

Revision as of 17:03, 6 February 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

Diagenetic traps are those in which the trap boundaries are due to postdepositional diagenetic processes, which can create new reservoirs or new seals.

Classes

The hierarchical structure and definitions for diagenetic traps are shown below.

System: Stratigraphic traps

Regime: Diagenetic traps
Class: Diagenetic reservoirs
Form where porosity is created as a result of local diagenetic processes such as dissolution or dolomitization.
Subclass: Secondary dolomite reservoirs
Form as a result of localized secondary dolomitization.
Subclass: Leached (secondary) porosity
Form as a result of localized leaching of nonreservoir-quality rock to create enhanced porosity and permeability. Common beneath unconformity surfaces.
Class: Diagenetic seals
Trap boundaries created by plugging original reservoir porosity and permeability by diagenetic cements or minerals.
Subclass: Secondary anhydrite barriers
Form as a result of secondary anhydrite precipitating in original pore spaces.
Subclass: Secondary clay barriers
Form as a result of secondary clay, commonly kaolinite, precipitating in original pore space.
Style: Secondary pore-throat trap
Caused by a reduction in the size of pore-throat radii of reservoir rocks by depositional or diagenetic processes. These trap types typically have relatively porous units in the sealing facies that are impermeable to oil migration due to capillary restraints but contain producible water.

Discussion of diagenetic trap families

Families of diagenetic traps based on genesis of the diagenetic processes that created or modified either the reservoir or the seal are somewhat difficult to establish because not all diagenetic processes are well understood and disagreements often exist about the cause of specific diagenetic processes that trapped hydrocarbons. Furthermore, almost all reservoirs and seals have undergone some degree of diagenesis since deposition, making diagenesis at least a secondary trapping element in many fields.

The common occurrence of dolomitized reservoirs is a classic case in point. Dolomitized reefs and dolomitized tidal-flat carbonates are common oil and gas reservoirs. Although dolomitization was a critical element in creating commercial porosity and permeability in these reservoirs, exploration efforts usually focus on defining the original depositional fairway of these reservoirs, i.e., reefs or tidal flats. As a consequence, the primary trap classification of these reservoirs occurs under the depositional trap regime. For our purposes, diagenetic traps are those in which trap boundaries are created by diagenetic processes largely independent of the original depositional environment of reservoir or seal.

Families

Below is a suggested classification outline for some of the superfamilies, families, and subfamilies of the Diagenetic Reservoirs and Diagenetic Seals classes.

Regime: Diagenetic traps

  • Class: Diagenetic reservoirs

<list-item>Subclass: Secondary dolomite reservoirs

<list-item>Family: Hydrothermal diagenesis</list-item><list-item>Subfamily: Ascending hot brines</list-item></list-item><list-item>Subclass: Leached (secondary) porosity

<list-item>Family: Subunconformity diagenesis

<list-item>Subfamily: Dissolving</list-item><list-item>Variety: Karst and cavern formation</list-item></list-item></list-item>

  • Class: Diagenetic seals

<list-item>Subclass: Secondary anhydrite barrier

<list-item>Family: Subunconformity diagenesis</list-item><list-item>Subfamily: Cementation</list-item></list-item>

See also

External links

find literature about
Diagenetic trap regime
Datapages button.png GeoScienceWorld button.png OnePetro button.png Google button.png