Diagenesis, mineral replacement and porosity generation. Andrew Putnis & Christine V. Putnis

Transcription

1 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

2 Blue sky background Thanks for the chance to be here!

3 What controls the porosity evolution in a sedimentary basin?

4 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

5 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

6 Pressure solution reduces porosity with depth Dissolution Dissolution Precipitation Precipitation Gratier et al., 1999

7 Compaction experiments on analogue salts can identify the key parameters controlling pressure solution

8 Compaction experiments on analogue salts can identify the key parameters controlling pressure solution

9 Compaction experiments on analogue salts can identify the key parameters controlling pressure solution

10 Single phase compaction pressure solution Stylolites in carbonate rock Image: PGP University of Oslo

11 Reaction-induced porosity generation during diagenesis in a sedimentary basin

12 Reactions at the mineral-fluid interface : Disequilibrium A solid phase out of equilibrium with an aqueous solution will tend to dissolve solid fluid

13 Reactions at the mineral-fluid interface : solid fluid

14 Reactions at the mineral-fluid interface : Ca 2+ SiO 4 4- Na 2+ - Na 2+ Cl - Cl - Ca-feldspar saline fluid

15 Reactions at the mineral-fluid interface : Ca-feldspar Local supersaturation with respect to - - Na 2+ Cl - saline fluid

16 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)

17 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

18 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)

19 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

20 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

21 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

22 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

23 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

24 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)

25 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

26 Porosity generation implies transfer of material from the solid to the solution i.e. more material is dissolved than reprecipitated

27 Example 1: Experimental The replacement of calcite (Carrara marble) by apatite

28 Cross section of cube of Carrara marble reacted with phosphate solution at C for 1 week Calcite is partially replaced by apatite E. Pedrosa

29 Calcite is being replaced by apatite, Ca 5 (PO 4 ) 3 (OH) E. Pedrosa

30 Only the fluid at the reaction interface needs to be supersaturated with respect to the precipitating phase.

31 Example 2: Experimental The replacement of calcite (Carrara marble) by magnesite and dolomite

32 T. Moraila Martinez

33 Example 3: Experiment Single crystal of KBr replaced by porous single crystal of KCl

34 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.

35 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

36 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

37 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

38 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.

39 Example 4: Nature Albitisation during diagenesis of mud-rocks

40 LEE, JAE IL & LEE, YONG IL Feldspar albitization in Cretaceous non-marine mudrocks, Gyeongsang Basin, Korea.Sedimentology 45 (4), (1998)

41 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

42 Applications: Understanding porosity evolution during compaction in flooding experiments using various fluid compositions

43 Acknowledgements: EU Network Project: Flow in transforming porous media