Constraining the thermal history of carbonate reservoirs

Transcription

1 Constraining the thermal history of carbonate reservoirs Kristin Bergmann Victor P. Starr Assistant Professor Department of Earth, Atmospheric and Planetary Sciences MIT Earth Resources Laboratory 217 Annual Founding Members Meeting May 31, 217

2 Carbonate reservoirs reflect shallow crustal processes that occlude or enhance porosity DISSOLUTION CEMENTATION DOLOMITIZATION METEORIC REALM DISSOLUTION RAIN WATER DOLOMITIZATION MARINE REALM SEA WATER CEMENTATION ACD SUBSURFACE REALM DISSOLUTION CCD METAMORPHIC REALM BRINE DISSOLUTION CEMENTATION DOLOMITIZATION DOLOMITIZATION (Modified from Moore, 1989)

3 1 25 μm 25 μm Plane Polarized Light Plane Polarized Light 5 μm { SEM Backscatter Image Fe 25 μm Plane Polarized Light 6 μm Electron Microprobe Elemental Map 2

4 Tracking when and where key events occur is a function of T and W DISSOLUTION CEMENTATION DOLOMITIZATION METEORIC REALM DISSOLUTION RAIN WATER DOLOMITIZATION MARINE REALM SEA WATER CEMENTATION ACD SUBSURFACE REALM DISSOLUTION CCD METAMORPHIC REALM BRINE DISSOLUTION CEMENTATION DOLOMITIZATION DOLOMITIZATION (Modified from Moore, 1989)

5 Traditional δ 18 O measurements depend on both T and W CaC 16 O3 + H2 18 O K eq <-----> CaC 18 O 16 O2 + H2 16 O 2 δ 18 O calcite (VSMOW) = 3 Temperature ( C) δ 18 O water ( ; VSMOW)

6 Clumped isotope thermometry primer Ca 13 C 16 O3 + Ca 12 C 18 O 16 O K eq <-----> Ca 13 C 18 O 16 O2 + Ca 12 C 16 O3 1.5 T ( C) More Clumped Bonds 1.4 K eq Calcite Random Bonds /T 2 (K) DFT Model of clumping in calcite from Schauble et al., 26

7 CaC 16 O3 + H2 18 O K eq <-----> CaC 18 O 16 O2 + H2 16 O 2 Metamorphic δ 18 O calcite (VSMOW) = 3 Temperature ( C) 1 Meteoric hydrothermal Lakes and soils Sea water Early diagenesis Late diagenesis Evaporating marine δ 18 O water ( ; VSMOW)

8 Solid state reordering Stolper and Eiler, 215 Apatite and aragonite will begin to reorder >1 C over 1 6 years (Stolper and Eiler, 215 and Piasecki et al., 215) Calcite will begin to reorder at >15 C over years and fully-equilibrates above 2 C (Henkes et al., 214; Stolper and Eiler, 215) Dolomite does not reorder over ~ 25 C over 1 8 years (Lloyd and Eiler, 214)

9 The Bergmann Lab approach Sedimentological context and petrographic preservation Field observations and EBSD mapping Mn Trace metal and isotopic heterogenetity SIMS, Electron Microprobe, XRD, XANES, ICP-AES Precipitating temperature and fluid compositions Clumped Isotope Thermometry

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11 Diagenetic trends in marine carbonates Sultanate of Oman 66 Ma 252 Ma 541 Ma Period Quaternary Palaeogene Cretaceous Jurassic Triassic Permian Carbonif. Devonian Silurian Ordovician Cambrian Ediacaran Cryogenian I 541 Ma ~635 Ma Period Group EDIACARAN CAMBRIAN ARA NAFUN CRYOGENIAN ABU MAHARA Modified from Forbes et al., 21 II III Group 1: Eocene to Permian Thick limestones to mixed limestones and siliclastics Minor dolomite in the Permian Range of petrographic fabrics from micrite to grainstone with varying degrees of fossil preservation and cementation Group II: PC-C Ara Group Carbonate stringers floating in evaporites Dominantly dolomite although some calcite Range of petrographic fabrics with fine to coarse grained interlocking recrystallized fabrics Group III: Ediacaran Nafun Group Thick dolomites to mixed limestones and siliclastics Range of petrographic fabrics from micrite to grainstone to boundstone with similar preservation character to Group I

12 Diagenetic trends in marine carbonates: Cross section of central Oman SAUDI ARABIA A IRAN 5 km N A Ghaba Salt Basin Central Al Huqf Oman High South Oman Salt Basin Arabian Sea 1 km A A South Oman Salt Basin Map Legend Salt Basin Precambrian Outcrop Well locations Salt Dome location Outcrop locations Central Oman High Ghaba Salt Basin Permian - present carbonates Paleozoic siliciclastics Ara Salt Ara Carbonate Stringers Nafun Group Abu Mahara Basement Depth (km) Modified from Al Siyabi, 25

13 Eocene [357m, BT = 43 C]: T = 3 ± 2 C δ18owater =.2 ±.5 (n=3) Plane Polarized Light SEM Backscatter Image 5 μm 2 μm

14 Jurassic [138 m, BT = 54 C]: T = 34 ± 2 C δ 18 Owater =.3 ±.3 (n=2) Plane Polarized Light SEM Backscatter Image 5 μm 4 μm

15 Cretaceous [5.8 m, BT = 49 C]: T = 32 ± 4 C δ 18 Owater =.2 ±.8 (n=2) spar T = 48 ± 4 C; δ 18 Owater = 2.3 ±.7 (n=2) 2 cm

16 Group I: Eocene to Permian carbonates A subsurface well. Depth (km) Permian Jur. Cretaceous Tertiary Bulk carbonates show stabilization at low temperatures and very shallow depths (3-35 C) 25 5 Temperature (ºC) limestone dolomite sandstone siltstone evaporite geothermal gradient Eocene-Permian calcite Void and fracture calcite Permian dolomite

17 Group I: Eocene to Permian carbonates v. shallow stabilization - mod. W/R δ 18 O mineral ( ; PDB) δ 18 O water ( ; VSMOW) δ 18 O mineral ( ; PDB) Eocene-Permian calcite Void and fracture calcite Permian dolomite Low W/R High W/R 25 5 Temperature ( C)

18 Group I: Eocene to Permian carbonates v. shallow stabilization - mod. W/R δ 18 O mineral ( ; PDB) δ 18 O water ( ; VSMOW) δ 18 O mineral ( ; PDB) Eocene-Permian calcite Void and fracture calcite Permian dolomite Low W/R High W/R 25 5 Temperature ( C)

19 PC-C (Ara Group) [3148 m, BT = 77 C] T = 75 ± 5 C δ 18 Owater = 7 ± 1 (n=2) Plane Polarized Light SEM Backscatter Image 5 μm 1 μm

20 Group II: Precambrian-Cambrian Ara Group A subsurface well Depth (km) Cambrian Ordovician Carb. Permian Jur. Cretaceous Tertiary Temperature (ºC) limestone dolomite sandstone siltstone evaporite geothermal gradient Eocene-Permian calcite Void and fracture calcite Permian dolomite SOSB calcite Non-SOSB Birba dolomite

21 Group II: Precambrian-Cambrian Ara Group sample Ts approach the current geotherm Depth (km) SAUDI ARABIA IRAN 5 km A Ghaba Salt Basin Central Al Huqf Oman High South Oman Salt Basin Arabian Sea Map Legend Salt Basin Precambrian Outcrop Well locations Salt Dome location Outcrop locations Permian - present carbonates Paleozoic siliciclastics Ara Salt Ara Carbonate Stringers Nafun Group Abu Mahara Basement 5 Eocene - Permian Precambrian-Cambrain Ara Group Precambrian Birba carbonates Temperature ( C) A A A South Oman Salt Basin N 1 km Central Oman High Ghaba Salt Basin Depth (km)

22 Group II: Precambrian-Cambrian Ara Group δ 18 Owater compositions are enriched Depth (km) SAUDI ARABIA IRAN 5 km A Ghaba Salt Basin Central Al Huqf Oman High South Oman Salt Basin Arabian Sea Map Legend Salt Basin Precambrian Outcrop Well locations Salt Dome location Outcrop locations Permian - present carbonates Paleozoic siliciclastics Ara Salt Ara Carbonate Stringers Nafun Group Abu Mahara Basement 5 Eocene - Permian Precambrian-Cambrain Ara Group Precambrian Birba carbonates δ 18 O water (VSMOW, ) A A A South Oman Salt Basin N 1 km Central Oman High Ghaba Salt Basin Depth (km)

23 Group II: Precambrian-Cambrian Ara Group low W/R ratio Low W/R High W/R δ 18 O water ( ; VSMOW) δ 18 O mineral ( ; PDB) Burial Fluids δ 18 O mineral ( ; PDB) δ 18 O mineral ( ; PDB) δ 18 O water ( ; VSMOW) Burial Fluids -1-5 δ 18 O mineral ( ; PDB) Qarn Alam Salt Dome SOSB dolomite SOSB calcite non-sosb Birba dolomite Temperature ( C) Temperature ( C)

24 Ediacaran (Nafun Group) [surface, est. 1-2km max] T = 55 ± 1 C, δ 18 Owater = -1.6 ±.4 (n=3) Plane Polarized Light SEM Backscatter Image 5 μm 8 μm

25 Group III: Ediacaran Nafun Group A subsurface well 3. Depth (km) Ediacaran Nafun Ara Temperature (ºC) limestone dolomite sandstone siltstone evaporite geothermal gradient Non-SOSB Birba dolomite Nafun Group calcite Nafun Group dolomite

26 T range is spatially and stratigraphically consistent for both dolomite and calcite in Nafun Group Well A T Mukhaibah Al Huqf Outcrop Khufai Dome Dome Well Well MQ B SAUDI ARABIA A IRAN A 5 km Ghaba Salt Basin Central Al Huqf Oman High South Oman Salt Basin Arabian Sea N 1 km A South Oman Salt Basin Map Legend Salt Basin Precambrian Outcrop Well locations Salt Dome location Outcrop locations Temperature ( C) boundstone including stromatolites and laminites grainstone including oolitic mudstone wackestone and packstone teepees sandstone siltstone limestone dolomite Non-SOSB Birba dolomite Nafun Group calcite Nafun Group dolomite (sedimentology from Bergmann, 213 and Osburn, 213)

27 Group III: Ediacaran Nafun Group change in fluid comp., low W/R in calcite Low W/R High W/R δ 18 O mineral ( ; PDB) δ 18 O water ( ; VSMOW) Temperature ( C) -1-5 δ 18 O mineral ( ; PDB) δ 18 O mineral ( ; PDB) δ 18 O water ( ; VSMOW) Temperature ( C) -1-5 δ 18 O mineral ( ; PDB) Nafun Group dolomite Nafun Group calcite

28 Group III: Ediacaran Nafun Group Ts in between Groups I & II Depth (km) Depth (km) A A South Oman Salt Basin Central Oman High Ghaba Salt Basin Eocene - Permian Precambrian-Cambrain Ara Group Precambrian Birba carbonates Precambrian Nafun Group Temperature ( C)

29 Group III: Ediacaran Nafun Group δ 18 Owater marine-like Depth (km) Observations: Nafun Group carbonates are petrographically well-preserved Co-occuring calcite and dolomite indicate similar T 5 δ 18 Owater compositions are seawater like for both calcite and dolomite Eocene - Permian Precambrian-Cambrain Ara Group Precambrian Birba carbonates Precambrian Nafun Group δ 18 O water (VSMOW, ) Options: partial solid state diffusion and long term change in δ 18 Owater change in temperature of shallow burial stabilization or initial temperature

30 Summary Using a combination of petrographic, microanalytical and clumped isotope analyses of specific textures we can reconstruct the timing of events critical to the evolution of carbonate reservoirs and the thermal history of basins Results from Oman indicate dolomites and limestones are more susceptible to burial diagenetic processes than solid state diffusion between -6 km over geologic timescales. Group I of Eocene-Permian limestones and dolomites suggest very early stabilization. Group II Ara Group limestones and dolomites show variable closed system behavior. Group III Nafun Group data are consistent with a higher temperature of stabilization at very shallow depths which could indicate the Ediacaran was 5-2 C warmer than the recent Phanerozoic.