stuart f simmons egi, u utah penrose conference, 19-23 oct, 2013, park city, utah
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
Stuart F SimmonsEGI, U Utah
Penrose Conference, 19-23 Oct, 2013, Park City, Utah
A Geochemical Perspective on Assessing/Sustaining Well Productivity
Fluid Compositions ReflectFluid flow paths (near & far field)Mineral dissolution-precipitationEquilibration temperatureChemical structure of reservoir(s)Extent of the resource Baseline vs production induced effectsOther potential resources (e.g., He, metals)
Questions (Where & What?)
ResourceFluid pathways inside & outside the reservoirNature of compositional variabilityHost rock & mineral influence (siliciclastic vs
carbonate units)State, extent & time-span of fluid-mineral equilibriaSources of aqueous/gaseous constituentsProxy Environments: Oil/Gas, Oil Shale, Conv. Geo.Paleo-geothermal reservoirs; Carlin/MVT deposits
extensional fault
volcano-intrusion
rese
rvoi
rs <
3 k
m d
epth
Geothermal Systems: Stored vs Flowing
sedimentary basin
reservoir
reservoir
reservoir
reservoir
?
Geothermal Wells>$ 5 million2 to 3 km deepfuel for power stationlifetimes >10 yrs1 or more feed zones
Production effectsPressure dropScaling-corrosionEnthalpy declineFlow decline
phot
o J.
Hed
enqu
ist
Application Tracers: Cl-, B, HCO3
-, SO4-2
N2, Ar, He, CO2, H2S, H2 18O/16O, D/H, 3He/4He
Indicators: Na+, K+, Ca+2, Mg+2, SiO2, CO2, H2
Engineering SiO2, Ca+2 , CO2, HCO3- , H2S, H2
(scaling-corrosion)
Environmental B, NH3, As, Hg, H2S
Species
Sedimentary Basins: Reservoirs
In pore spaces where fluid velocity is slow, fluid-mineral equilibria develops controlled by thermodynamically stable minerals.
In open fractures where fluid velocity is fast, cooling, mixing, & phase separation control fluid composition.
Natural State-Broad Physical Gradients
Sedimentary Basins: Reservoirs
springs
Exploration GeochemistryEquilibration Temperatures
Flow Paths
Sedimentary Basins: Reservoirs
exploration
Reservoir fluid(s)
Sedimentary Basins: Reservoirs
exploration
Leaky reservoirs (open vs closed)
exploration
Sedimentary Basins: Reservoirs
injectorproducer
Production induced effectsPressure drawdown
Scaling/Injection breakthroughInjectate Treatment/Conditioning
Time (>decades)
Geochemical Issues
Wide range of TDS (<100 to >100,000 ppm Cl)
Carbonate equilibria, CO2 & pH
Rocks & Minerals (lms, ss, evaporites, fldspars, qtz)
Thermogenic vs microbial gas productionsulfate reduction & H2S generationalkalinity change (calcite solubility)
Mixing & phase separation
Chemical geothermometers
Sedimentary Aquifer Thermal Waters (USA-NZ)
• 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
Water compositions (mg/kg) pH Na K HCO3 SO4 ClGrant Canyon 7GC (115°C) 8.3 2500 251 38 104 4350Bacon Flat 23-17 (122°C) 8.2 3040 312 33 128 5350Sen Emedio Nose (149°C) 7.7 4000 620 2870 38 3460Houston Halls Bayou (150°C) 6.8 20500 180 409 16 34500Thermo (177°C) 6.4 961 75 330 500 1014Ngawha (221°C) 7.2 850 82 14450 7 1279
Hulen et al, 1994; Kharaka & Hanor, 2003; Moore, unpub; Top Energy NZ
Sedimentary Aquifer Thermal Waters (USA-NZ)
SiO2 sat’d with quartz, chalcedony, or cristobalite.
All waters also sat’d in calcite & many are sat’din dolomite.
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)
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
Conductive Cooling
Qtz-supersat’d but unlikely to deposit
Extent of heating during injection could bring solution back to saturation in carbonates and sulfates.
Calcite & Carbonate Equilibria
Calcite precipitates due to loss of CO2, generally close to the site of first phase separation. Scaling is exacerbated by high CO2 concentrations.
2HCO3 + Ca2+ = CaCO3 + H2O + CO2
0 100 200 300Te m p era tu re d e g C
0
1
2
3
Anh
ydrit
e so
lubi
lity
(Ca2
+ m
g/kg
)ca
lcite
sol
ubili
ty (C
a2+ m
g/kg
)
temperature °C
In dilute hydrothermal solutions, calcite has reverse solubility, but this does not explain deposition as well scales.
Increase CO2 to dissolve calcite and drive rxn left; remove CO2 to precipitate calcite.
Fresh. Altered. Images left show enhanced porosity through calcite dissolution in Carlin Au deposits.Photos: courtesy of Jean Cline
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
Physical: Heat & mass transfer
Temperature-pressure gradients
Permeability-porosity
Hydrology & fluid flow
Chemical: Fluid compositions
Fluid-mineral equilibria
Mineral corrosion/deposition
Hydrothermal alteration
GEO
LOG
Y
Geoscience of Geothermal Energy