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Stuart F Simmons EGI, U Utah Penrose Conference, 19-23 Oct, 2013, Park City, Utah

A Geochemical Perspective on Assessing/Sustaining Well Productivity. Stuart F Simmons EGI, U Utah Penrose Conference, 19-23 Oct, 2013, Park City, Utah . Fluid Compositions Reflect Fluid flow paths (near & far field) Mineral dissolution-precipitation Equilibration temperature

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Stuart F Simmons EGI, U Utah Penrose Conference, 19-23 Oct, 2013, Park City, Utah

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  1. A Geochemical Perspective on Assessing/Sustaining Well Productivity Stuart F Simmons EGI, U Utah Penrose Conference, 19-23 Oct, 2013, Park City, Utah

  2. Fluid Compositions Reflect Fluid flow paths (near & far field) Mineral dissolution-precipitation Equilibration temperature Chemical structure of reservoir(s) Extent of the resource Baseline vs production induced effects Other potential resources (e.g., He, metals)

  3. Questions (Where & What?) Resource Fluid pathways inside & outside the reservoir Nature of compositional variability Host rock & mineral influence (siliciclasticvs carbonate units) State, extent & time-span of fluid-mineral equilibria Sources of aqueous/gaseous constituents Proxy Environments: Oil/Gas, Oil Shale, Conv. Geo. Paleo-geothermal reservoirs; Carlin/MVTdeposits

  4. Geothermal Systems: Stored vs Flowing volcano-intrusion extensional fault reservoir reservoir reservoir reservoirs < 3 km depth sedimentary basin reservoir ?

  5. photo J. Hedenquist Geothermal Wells>$ 5 million2 to 3 km deepfuel for power stationlifetimes >10 yrs1 or more feed zonesProduction effectsPressure dropScaling-corrosionEnthalpy declineFlow decline

  6. Application Species Tracers:Cl-, B, HCO3-, SO4-2 N2, Ar, He, CO2, H2S, H218O/16O, D/H,3He/4He Indicators: Na+, K+, Ca+2, Mg+2, SiO2, CO2, H2Engineering SiO2, Ca+2 , CO2, HCO3- , H2S, H2(scaling-corrosion) Environmental B, NH3, As, Hg, H2S

  7. Sedimentary Basins: Reservoirs • Natural State-Broad Physical Gradients In pore spaces where fluid velocity is slow, fluid-mineral equilibria develops controlled by thermodynamically stableminerals. • In open fractures where fluid velocity is fast, cooling, mixing, & phase separation control fluid composition.

  8. Sedimentary Basins: Reservoirs • springs Exploration Geochemistry Equilibration Temperatures Flow Paths

  9. Sedimentary Basins: Reservoirs exploration Reservoir fluid(s)

  10. Sedimentary Basins: Reservoirs exploration exploration Leaky reservoirs (open vs closed)

  11. Sedimentary Basins: Reservoirs producer injector Production induced effects Pressure drawdown Scaling/Injection breakthrough Injectate Treatment/Conditioning Time (>decades)

  12. Geochemical Issues Wide range of TDS (<100 to >100,000 ppm Cl) Carbonate equilibria, CO2& pH Rocks & Minerals (lms, ss, evaporites, fldspars, qtz) Thermogenicvs microbial gas production sulfate reduction & H2Sgeneration alkalinity change (calcite solubility) Mixing & phase separation Chemical geothermometers

  13. Reservoirs hosted in sedimentary rocks (Paleozoic-dolostone, Cenozoic-Ss/Sh, Mesozoic-Meta Ss) • Minerals controlling fluid-mineral equilibria are poorly known • Preliminary results with the aim of understanding potential chemical geothermometers Sedimentary Aquifer Thermal Waters (USA-NZ) Hulen et al, 1994; Kharaka & Hanor, 2003; Moore, unpub; Top Energy NZ

  14. SiO2sat’d with quartz, chalcedony, or cristobalite. All waters also sat’d in calcite & many are sat’d in dolomite. Sedimentary Aquifer Thermal Waters (USA-NZ)

  15. Sedimentary Aquifer Thermal Waters (USA-NZ) Fluids are out of equilibrium at the reported temperature with respect to feldspars & Na-K ratios Na-Li ratio unreliable indicator of temperature using empirical relationship(Fouilliac & Michard, 1981)

  16. Preliminary Assessments Silica appears to be most reliable Controls on cation ratios inadequately understood Reliability of temperature & analytical data unknown Need fluid analyses of CO2, HCO3-, & pH, other gases too Reaction path modeling suggests no scaling problems in production wells

  17. Conductive Cooling Qtz-supersat’d but unlikely to deposit Extent of heating during injection could bring solution back to saturation in carbonates and sulfates.

  18. Calcite & Carbonate Equilibria In dilute hydrothermal solutions, calcite has reverse solubility, but this does not explain deposition as well scales. Calcite precipitates due to loss of CO2, generally close to the site of first phase separation. Scaling is exacerbated by high CO2 concentrations. calcite solubility (Ca2+ mg/kg) temperature °C 2HCO3 + Ca2+ = CaCO3 + H2O + CO2 Increase CO2 to dissolve calcite and drive rxn left; remove CO2 to precipitate calcite. Images left show enhanced porosity through calcite dissolution in Carlin Au deposits. Altered. Fresh. Photos: courtesy of Jean Cline

  19. Exploration Carbonate rocks extend across eastern Great Basin Water compositions from Beowawe & Tuscaroa are HCO3-rich Na-K temperatures indicate ~250 deg C Is it possible that the point of equilibration is beneath the drilled depths of these systems, reflecting a hot laterally extensive resource? Allis et al 2012

  20. Geoscience of Geothermal Energy Physical: Heat & mass transfer Temperature-pressure gradients Permeability-porosity Hydrology & fluid flow GEOLOGY Chemical: Fluid compositions Fluid-mineral equilibria Mineral corrosion/deposition Hydrothermal alteration

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