Hydrothermal Dolomitization of Fluid Reservoirs in the Michigan Basin, USA* By David A. Barnes 1, Thomas M. Parris 2, and G.

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1 Hydrothermal Dolomitization of Fluid Reservoirs in the Michigan Basin, USA* By David A. Barnes 1, Thomas M. Parris 2, and G. Michael Grammer 1 Search and Discovery Article #50087 (2008) Posted July 10, 2008 *Adapted from oral presentation at AAPG Annual Convention, San Antonio, Texas, April Geosciences - MGRRE, Western Michigan University, Kalamazoo, MI (barnes@wmich.edu) 2 Kentucky Geological Survey, University of Kentucky, Lexington, KY Abstract Mechanisms for dolomitization of primary carbonate facies imply flow properties, spatial distribution, and internal geometry of the resulting geo-body. Petrologic data from diagenetic carbonates in the St. Peter Sandstone, Trenton/Black River, Burnt Bluff, Niagaran, Bass Islands, and Dundee in the Michigan basin suggest that fracture-related, hydrothermal dolomitization was important in the origin of these reservoirs. The T/Br Gp is a famous example of a fracture-related hydrothermal dolostone reservoir. In all units, saddle dolomite is a replacive intergranular cement, fracture/vug fill, and/or primary carbonate matrix replacement. Other related diagenetic phases include pyrite; bitumen; quartz; fracture filling, calcite; anhydrite; and fluorite. Primary fluid inclusion Th/Tm from carbonate minerals indicates reservoir-forming episodes of diagenesis as a result of precursor carbonate mineral interaction with high salinity, hydrothermal fluids. In all of these Ordovician to Devonian units, hydrothermal carbonate minerals have oxygen isotopic composition from -5 to -12 δ 18 O and minimum formation temperatures of 80 o -170 o C. These data indicate diagenetic carbonate mineral formation from high salinity, δ 18 O enriched (+5 to +12 δ 18 O; PDB) fluids during at least one episode of fracture related, hydrothermal mineralization. Fluids resulting in hydrothermal alteration in the Michigan basin can be characterized by 1) high pressure gradients, 2) elevated temperature, 3) high salinity, and 4) δ 18 O enriched oxygen isotopic composition. A speculative model for hydrothermal dolomitization in the Michigan basin includes reactivated basement faults (coincident with Appalachian orogenic events), vertical migration of basinal brines (related to thick evaporite-rich units), and serpentinization of basement peridotite (associated with the deeply buried, Mid-Continent Rift System).

2 Hydrothermal Mineralization in the Michigan Basin, USA Occurrence and Possible Mechanisms DAVID A. BARNES, MGRRE - WMU Thomas M. Parris, KY GS G. Michael Grammer, MGRRE - WMU 1

3 Conclusions Hydrothermal Dolomite (HTD) reservoirs are widespread stratigraphically ti and spatially in the Michigan Basin USA, and HTD probably comprises a significant volume of sedimentary rock in the basin Fractures (due to recurring Paleozoic faulting) were primary hydrothermal fluid flow conduits, but much hydrothermal dolomite was also formed due to associated fluid migration through regional aquifers and other high fluid flow units Hydrothermal mineralization may be related to saline, basinal brine/rock-water interactions with mafic and ultramafic crust of the Mid-Continent Rift in the central Michigan Basin 2

4 Dolostone Reservoirs In carbonate systems, dolostone often forms the best reservoirs. The dolomitization of carbonate sediments and rocks increases crystal size and pore throat size, and decreases pore roughness. Without exception, the combination of these increases the permeability of the carbonate. In this way, dolomitization makes the reservoir with dolomite serving as the reservoir and the surrounding limestone forming the seal. Devonian Rogers City Fm, Mecosta Co., MI J.R. Allen and W.D. Wiggins,

5 Hydrogeological Models for Dolomitization faults X The hydrology and mass transfer by special dolomitizing fluids controls: Size Shape and Location of the dolostone body yproduced From: Alan and Wiggins, 1993; Modified from Land (1986) and Morse and Mackenzie (1990) 4

6 Ca ++ /Mg ++ ~ 0.3 in normal sea water From: Hardie, 1987 Fluid T-X Phase Diagram for Calcite & Dolomite Elevated temperature of formation favors dolomite alteration of limestone by most normal subsurface fluids The question really is: why aren t all buried limestones dolomitized? Mass transfer processes play a decisive role in large scale dolomitization In lithified carbonate rocks effective fluid conduits for dolomitizing fluids (like fractures and primary facies) RULE! 5

7 Reservoirs and Petroleum Production in Michigan } } Major Producing Intervals ~1.5 BBO; >6 TCF NG from multiple, mostly Paleozoic carbonate reservoirs after: Dolton, USGS 6

8 Upper and Middle Ordovician Trenton-Black River (T/BR): Classic HTD Reservoirs Petroleum occurs in stratigraphic/diagenetic traps: reservoir quality varies between a narrow fairway of vuggy, fractured, and cavernous dolostone and tight regional limestone Reservoirs in the Albion-Scipio field are fracture-controlled, hydrothermal dolostone (HTD) related to NW-SE fault and fold trends aligned to regional structural grain (Hurley and Budros, 1990) Faults (John Esch, MI OGS) and Mid-Continent Rift (Hinze, et al, 75) 7

9 T/BR Reservoirs Albion-Scipio Field Fracture related, hydrothermal dolomitization critical to reservoir quality in T/BR reservoirs.but diagenetically modified primary porosity and permeability also important to reservoir storage capacity and provided flow conduits for dolomitizing fluid to more distal (relative to fractures) portions of the reservoir fracture/void filling baroque (saddle) dolomite patchy, dolostone intercrystalline mesoporosity Tight Limestone Porous Dolostone 8

10 Dolomite Petrology: Albion-Scipio Field, Michigan Fluid Inclusions in Zoned Saddle Dolomite Fluid Inclusions in Late Calcite Saddle Dolomite T h : ~110 o C-160 o C δ 18 O: ~-5 to -9 Analysis: P. Swart, UM 9

11 Structural Models for HTD Reservoirs Hurley and Budros, 1990 Harding, 1974; Sylvester, 1976 Davies and Smith, 2006 Conceptual Model for Structural/Stratigraphic control on HTD distribution 10

12 St Peter Sst (aka PDC) Petrology Most reservoir porosity results from dissolution of saddle dolomite cement and k-feldspar detrital grains Late, secondary pore-filling illite (~350Ma) post-dates HTD and most reservoir porosity Barnes et al ndary Ø and pore filling clay Etched quart overgrowths Saddle dolomite cement 2ndary Ø after Saddle dolomite cement 11

13 St Peter Sst Petrology Analytical, isotope and fluid inclusion i T h data suggest elevated temperature (hydrothermal) origin for reservoir dolomite cement Barnes et al.1992 Saddle Dolomite T h ~120 o -160 o ; δ 18 O ~-10 to

14 Lee #1, 3466', Montcalm Co Dundee (Rogers City) Dolostone Reservoirs } Lee #1, 3467', Montcalm Co (Rogers City), top Buehler #1, ', Albion - Scipio Field Hillsdale Co. (Trenton - Black River Gp) bottom Tow #1, Montcalm Co., mm Fracture Filling Saddle Dolomite State Reading & Sparrow, 3886 Matrix Replacement dolomite State Reading & Sparrow 1-29, Clare Co

15 Dundee Field Scale Structure 50 14

16 Dundee Petrologic Data Reed City (eq) Dundee Analysis: P. Swart, UM 10 Rogers City Aqueous Th (C) Luczaj and Harrison, 2006 Saddle dolomite fracture fill and matrix T h ~120 o C to 140 o C; δ 18 O ~ -7 to

17 Bass Islands Petrology } Core Energy State Charlton #4-30, Otsego Co. MI, 3469 Bass Islands Dolostone, Pink Saddle Dolomite Vug Fill Saddle dolomite fracture fill and matrix T h??; δ 18 O ~ -5 to -6 Vuggy, intercrystalline porosity with authigenic, saddle dolomite with double terminated quartz; Ø=27%, K=60md; Analysis: P. Swart, UM 16

18 Silurian Burnt Bluff Petrology } Saddle dolomite fracture fill and matrix T h ~140 o C to 170 o C; δ 18 O ~ -6.5 to -7 Analysis: P. Swart, UM Thompson 3-36, 8127 & 8145 Osceola Co., MI Porous Dolostone Tight Limestone Double term Qtz Late Calcite Patchy dolostone, intercrystalline mesoporosity Zoned Saddle Dolomite 17

19 HTD: δ 18 O, T h, and Source Fluids Michigan Basin Reservoirs *Niagaran Reef data for late dolomite and calcite : Cercone and Lohman, 1987 HTD Source Fluids isotopic composition: ~+5 to +10 δ 18 O 18

20 Pressure-Temperature Considerations, Basin Thermal History, & HTD Geothermal Gradient ~20 o C/km (21 o F/1000ft) + 15 o surface ~34 o C (100 o F) = Ambient Conditions Hydrostatic Gradient ~1500psia Dundee: ~125 o km Niagaran: ~ 80 o -120 o C@~2 km Burnt Bluff: ~160 o ~2.5 km Tr/Br: Much reservoir dolostone in all units is Hd Hydrothermal ~140 o ~1.5 km St Peter Sst : ~140 o km 19

21 Constraints On Conceptual Models for Hydrothermal Mineralization in The Michigan Basin Genetically related fluids (in part evaporative in origin), produced similar, hydrothermal diagenetic mineral paragenesis in multiple stratigraphic intervals/reservoirs A significant heat source and high pressure gradients were required for geologically ll rapid, cross formational hydrothermal fluid flow through fractures and high permeability aquifers Retain thermal energy Access short-lived fractures through mechanically plastic evaporite/shale successions A substantial mass transfer of magnesium was required for dolomitization of a large volume of limestone 20

22 Hydrothermal Mineralization: Regional NW-SE and conjugate NE-SW structural grain in the basin resulted from repeated regional reactivation of basement wrench faults Episodes of wrench faulting and concurrent propagation of Riedel shears into Paleozoic cover rock may be related to Appalachian orogenic events Mechanisms North American Stratigraphic Sequences (Sloss, 1964) and major orogenic episodes (Geology - An Introduction (2nd ed.), by Bates et al. 1973) 21

23 Hydrothermal Mineralization: Mechanisms Mid-Continent Rift Reidel shear-related fracture conduits: provided downward pathways for dense, saline basinal bines to Proterozoic mafic and ultramafic crust genetically related to the Mid- Continent rift in the central Michigan basin Rock-water interaction and serpentinization of Mid-continent rift ultramafic crust generated magnesium-rich, high pressure/high temperature hydrothermal fluids Albion - Scipio Field Dundee Fields Lithology Dolomite Limestone Gravity Anomalie map from Hinze et al., 1975; Basin Structures from: Esch (pers. comm) 22

24 Hydrothermal Mineralization: Mechanisms Wrench fault-related fractures provided vertical hydrothermal fluid-flow flow conduits to form HTD in various carbonate formations throughout the Paleozoic succession in the Michigan basin Hydrothermal fluids were also transported laterally through regional aquifer units including the St Peter Sst and/or other regional aquifers: Dundee, Bass Islands dolostone Formations with significant, primary porous and permeable fluid conduits experienced (enjoyed?) substantial lateral hydrothermal fluid migration and strataform hydrothermal mineralization Gravity Anomalie map from Hinze et al., 1975; Basin Structures from: Esch (pers. comm) and Prouty and Kimmel, 1983 Dundee Fields Lithology Dolomite Limestone 23

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