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Desalination Concentrate Disposal Using Injection Wells: Technical Challenges
Robert G. Maliva, Ph.D., and Scott Manahan, P.E.Schlumberger
GWPC UIC ConferenceSarasota, Florida (January 22-24, 2013)
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Concentrate Disposal
Concentrate disposal is often the critical factor in the feasibility of desalination projects
Concentrate disposal option must:- Be permittable. All required regulatory approvals can be obtained (environmental and water quality
issues)- Be reliable over desalination system life (20+ years)- Be economically viable
Desalination projects have died because there was no economical option for concentrate disposal!
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Concentrate Disposal Options
Surface water (marine) outfalls- option in coastal areas, but difficult and expensive to permit (if possible)
Discharge to wastewater treatment plants- may be viable for small systems; impacts to treatment and reuse systems
Reuse- limited because of salinity
Zero-liquid discharge- high costs (energy), salt disposal
Evaporation ponds- arid areas, environmental concerns
Injection wells
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Shallow wells in coastal regions (Class I or V)Deep high-capacity wells (Class I or V)Deep high-pressure (Class I)
Key technical issuesFeasibility and system type depend upon local hydrogeologyOptimization of design and operation
Concentrate Injection Well Types
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Shallow Coastal Injection Wells
● Avoids coastal construction and point discharge impacts● Concentrate may eventually diffusely seep out● Systems are used on some Caribbean islands
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Shallow Class V Injection Wells
● Shallow unconfined aquifer containing saline water underlain bya well confined USDW aquifer (e.g., Little Gasparilla Island, FL)
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Deep High-Capacity Injection Well Systems
Depths => 500 m (1,500 ft)Capacities => 3,800 m3/d (1 Mgd)One well may dispose of entire concentrate flow
Key technical issuesRequires very high-transmissivity injection zone that can accept concentrate flows → uncommonUpward migration of injected concentrate is retarded by density stratification
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Deep High-Capacity Injection Well SystemsCommonly used in South Florida for disposal of concentrate from brackish RO Injection zone is the “Boulder Zone” of Floridan Aquifer SystemKay Bailey Hutchison Desalination Plant , El Paso
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Deep High-Capacity Injection Well Systems
Umm Er Radhuma Formation in Arabian Gulf Region
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Deep High-Pressure Injection Wells
Depths => 1,500 m (5,000 ft)Injection pressures => 7,000 Kpa(1,000 psi)Oil-field technologyLow to moderate capacities(< 1,900 m3/d, 0.5 Mgd) Existing oil-gas injection wells may be used- oil and gas injection wells typically operate at relatively low flow rates
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Deep High-Pressure Injection Wells
Applications Inland RO facilities in which there are no other viable concentrate disposal options.Brackish RO systems with high recoveries and low concentrate flows (secondary RO or other treatment to reduce volume).- It may be much less expensive to reduce the volume of
the concentrate flow than to install additional injection well capacity.
- Injection may be less expensive than final volume reduction for ZLD.
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Deep High-Pressure Injection Wells Technical Issues
Deep high-pressure injection wells are far more complicated that other injection and production wells!Low transmissivity aquifer – vulnerability to cloggingGeochemical compatibility (scaling) – high TDS and ion concentrationsTemperature and salinity viscosity effectsManagement of pressure – high pressures can induce fracturing and in some locations low-level seismicityOptimization of completion (perforated vs. liner or screened; hydraulic fracturing [fracking])Improper design or geochemical incompatibility can cause permanent well damage
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Deep High-Pressure Injection Wells Tools
Quantitative log analysis – reinterpretation of existing dataPressure transient test – evaluate reservoir size and evaluate skin damageAdvanced borehole geophysical logging (e.g., NMR, FMI) –locate and characterized permeable intervalsPerforation technology – tailor to project specificsScreens and liners Formation sampling and testing technology – e.g., Modular Formation Dynamic Tester (MDT)Advanced data workflow (Petrel) and modeling software (Eclipse)
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Fundamental Injection Well IssuesLocation of an injection zone and designing injection well system that can provide the target disposal rate and volume over the life of the plant (20+ years)
Avoiding adverse impacts to the environment or groundwater resources from the migration of injected water out of the injection zone
Maintaining well performance (management of clogging)- Specific injectivity (injection rate/injection pressure)- O&M (workover/rehabilitation program needs to be effective and affordable)
Regulatory issues- Obtaining project approval- Monitoring requirements
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Technical IssuesInjection wells are more challenging to design and operate than production wells because the flow of water is into the formation.
The entire injected water flow and all entrained materials must pass through a relatively small surface (screen and borehole wall).
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Technical Issues - CloggingManagement of clogging is the critical injection well system design and operational issue
Additional causes of clogging:1) Clay mineral dispersion and swelling2) Air entrapment3) Particle rearrangement
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Fate of Injected Water
Requires detailed aquifer characterization and (density-dependent)solute-transport modeling.
South Florida upwardMigration study
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Injection Well Issues and Opportunities
● Well designOptimization of design –high efficiency completions are critical
For example,- Maximization of screen open area- Use of open hole completion- Accurate identification of most
permeable strata for perforation- Proper development – material left in
well or near borehole wall will be forced into the formation during injection
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Injection Well Issues and Opportunities
● Clogging Management- characterization of injected fluids
and analysis of its compatibility with injection zone water and rock (geochemical modeling)
- pretreatment (e.g., filtration andchemical adjustments)
- Assessment of causes of clogging- Pressure transient testing for
formation damage- Borehole geophysics
- Well rehabilitation (workover) – part of normal operations and maintenance
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Injection Well Issues and Opportunities
● Where does injected water go?- Aquifer characterization and
groundwater modeling are fundamental tools
- Traditional groundwater tools such as pump testing and basic geophysical logging
- Advanced borehole geophysical logging
- Pressure transient testing –reservoir size
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Concentrate Injection Well Design Issues● Injection well systems are more complex than production
wells and cannot be designed in the same manner!
● Water quality, geochemistry, and aquifer characterization are critical
● Improper design or geochemical incompatibilitycan cause permanent well damage
● Injection wells typically require more frequent rehabilitation than production wells
● Fate and transport of injected waters needsto be evaluated (groundwater modeling)
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Conclusions
● Injection wells are a valuable tool for the sustainability of desalination by providing an environmentally safe means for concentrate disposal
● Injection well systems require favorable hydrogeologic conditions, which may not be locally present
● Technical challenge is the optimization of both the design and operation of the wells in order to ensure reliable long-term performance
● Key lesson is approaching projects with an understanding of their complexity
