Diagenesis, mineral replacement and porosity generation Andrew Putnis & Christine V. Putnis The Institute for Geoscience Research (TIGeR), Curtin University, Perth, Australia & Institut für Mineralogie, University of Münster, Münster, Germany IOR Conference, Stavanger University, April 2015
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What controls the porosity evolution in a sedimentary basin?
Single phase compaction pressure solution The evolution of the reservoir quality, i.e. porosity and permeability, is for a large part controlled by compaction due to pressure solution. Precipitate
Single phase compaction pressure solution The evolution of the reservoir quality, i.e. porosity and permeability, is for a large part controlled by compaction due to pressure solution. Renard et al., 1999
Pressure solution reduces porosity with depth Dissolution Dissolution Precipitation Precipitation Gratier et al., 1999
Compaction experiments on analogue salts can identify the key parameters controlling pressure solution
Compaction experiments on analogue salts can identify the key parameters controlling pressure solution
Compaction experiments on analogue salts can identify the key parameters controlling pressure solution
Single phase compaction pressure solution Stylolites in carbonate rock Image: PGP University of Oslo
Reaction-induced porosity generation during diagenesis in a sedimentary basin
Reactions at the mineral-fluid interface : Disequilibrium A solid phase out of equilibrium with an aqueous solution will tend to dissolve solid fluid
Reactions at the mineral-fluid interface : solid fluid
Reactions at the mineral-fluid interface : Ca 2+ SiO 4 4- Na 2+ - Na 2+ Cl - Cl - Ca-feldspar saline fluid
Reactions at the mineral-fluid interface : Ca-feldspar Local supersaturation with respect to - - Na 2+ Cl - saline fluid
Reactions at the mineral-fluid interface : Ca-feldspar - - Precipitation of Na-feldspar on the surface Na 2+ Cl - saline fluid Precipitation inside the diffusion profile enhances the dissolution rate and couples it to the precipitation (Autocatalysis)
Reactions at the mineral-fluid interface : Ca-feldspar Migration of Na-feldspar into the parent - - Na 2+ Cl - saline fluid Migration of the product phase into the parent until it is all replaced Pseudomorphic mineral replacement
Reactions at the mineral-fluid interface how this looks in nature : Albitization Ca-feldspar Note the porosity developed in the product phase Na-feldspar The crystal structure is preserved across the sharp interface Engvik et al.(2008)
A brief outline of fluid mineral re-equilibration 1. When a fluid interacts with a mineral phase with which it is out of equilibrium it will tend to dissolve the mineral 2. The resultant fluid may be supersaturated with respect to another, more stable phase. 3. This product phase may nucleate within this interfacial fluid 4. The dissolution and precipitation may be coupled in space and time : 5. Mineral replacement by interface coupled dissolutionprecipitation
A brief outline of fluid mineral re-equilibration 1. When a fluid interacts with a mineral phase with which it is out of equilibrium it will tend to dissolve the mineral 2. The resultant fluid may be supersaturated with respect to another, more stable phase. 3. This product phase may nucleate within this interfacial fluid 4. The dissolution and precipitation may be coupled in space and time : 5. Mineral replacement by interface coupled dissolutionprecipitation
A brief outline of fluid mineral re-equilibration 1. When a fluid interacts with a mineral phase with which it is out of equilibrium it will tend to dissolve the mineral 2. The resultant fluid may be supersaturated with respect to another, more stable phase. 3. This product phase may nucleate within this interfacial fluid 4. The dissolution and precipitation may be coupled in space and time : 5. Mineral replacement by interface coupled dissolutionprecipitation
A brief outline of fluid mineral re-equilibration 1. When a fluid interacts with a mineral phase with which it is out of equilibrium it will tend to dissolve the mineral 2. The resultant fluid may be supersaturated with respect to another, more stable phase. 3. This product phase may nucleate within this interfacial fluid 4. The dissolution and precipitation may be coupled in space and time : 5. Mineral replacement by interface coupled dissolutionprecipitation
A brief outline of fluid mineral re-equilibration 1. When a fluid interacts with a mineral phase with which it is out of equilibrium it will tend to dissolve the mineral 2. The resultant fluid may be supersaturated with respect to another, more stable phase. 3. This product phase may nucleate within this interfacial fluid 4. The dissolution and precipitation may be coupled in space and time : 5. Mineral replacement by interface coupled dissolutionprecipitation
Interface-coupled dissolution-precipitation crystal a b c d e (a) Dissolution of even a few monolayers of the parent crystal may result in an interfacial fluid layer which is supersaturated with respect to another phase (b) This product phase may nucleate on the surface of the parent Putnis & Putnis, J.Solid State Chem. 180, 1783 (2007)
Interface-coupled dissolution-precipitation crystal a b c d e (c) The porosity generated depends on both the solid molar volume change and the relative solubilities of parent and product in the fluid (d-e) A reaction/replacement interface moves through the parent crystal
Porosity generation implies transfer of material from the solid to the solution i.e. more material is dissolved than reprecipitated
Example 1: Experimental The replacement of calcite (Carrara marble) by apatite
Cross section of cube of Carrara marble reacted with phosphate solution at 150 0 C for 1 week Calcite is partially replaced by apatite E. Pedrosa
Calcite is being replaced by apatite, Ca 5 (PO 4 ) 3 (OH) E. Pedrosa
Only the fluid at the reaction interface needs to be supersaturated with respect to the precipitating phase.
Example 2: Experimental The replacement of calcite (Carrara marble) by magnesite and dolomite
T. Moraila Martinez
Example 3: Experiment Single crystal of KBr replaced by porous single crystal of KCl
Experimental set up KBr Saturated KCl solution A pure crystal of KBr 2 x 2 x 5 mm was placed in a small glass beaker and saturated KCl solution added up to but not covering the surface. Observations were made using time lapse photography with a camera fitted to a stereoscope microscope.
When a single crystal (~2 x 3 mms) of KBr is immersed in a saturated KCl solution, it is pseudomorphically replaced by a highly porous single crystal of KCl. KBr single crystal KCl saturated solution
10min 1min 3min 1mm 20min 40min KBr is progressively replaced by a new K(Br,Cl) phase formed at a sharp interface which moves through the crystal. 5min 120min After 2 hours KBr is completely replaced by KCl
The replacement of KBr by KCl - porosity development 100 µm 10 µm A single crystal of KBr can be replaced by a single crystal of KCl at room temperature
Porosity coarsening and elimination as a function of time 12 days 7 weeks Porosity, like all microstructures, is a transient phenomenon associated with the mechanism and kinetics.
Example 4: Nature Albitisation during diagenesis of mud-rocks
LEE, JAE IL & LEE, YONG IL Feldspar albitization in Cretaceous non-marine mudrocks, Gyeongsang Basin, Korea.Sedimentology 45 (4), 745-754 (1998)
Summary: Understanding porosity and permeability evolution in a sedimentary basin involves: The mechanism of pressure solution and porosity reduction coupled with Dynamic porosity generation and destruction during mineral-fluid reactions
Applications: Understanding porosity evolution during compaction in flooding experiments using various fluid compositions
Acknowledgements: EU Network Project: Flow in transforming porous media