7. Waste Options: Deep well injection Flashcards
Deep Well Injection history
-in use since the 1950s by oil and gas for disposal of oil field brines
2 Reasons for injecting fluids into the subsurface formations
-increase pressures i oil and gas reservoirs that have been on production for some time
(P increases, production rates of Oil and Gas Increase)
-Disposal of LIQUID hazardous wastes
5 Classes of injection/disposal wells in Alberta
-based on type of fluid injected Class IV Class III Class II Class Ib Class Ia
Class IV injection wells
- direct injection into a reservoir (not a disposal well) –> SAGD
eg. potable water, steam from potable water
Class III Injection well
- injection of hydrocarbons, inert gases or other gases
- purely used for storage of liquids in enhanced oil and gas recovery systems
- Fluid types include solvents for enhanced oil recovery, sweet gas storage, emergency fuel supply
Class II injection well
- injection or disposal of produced waters (mainly brines)
- brines originate from water produced during oil and gas production operations, water produced from solutions mining
Class Ib Injection well
- disposal or produced water, specific oilfield waste streams and waste streams meeting specific criteria
- regs provide liquids which can be disposed here
Class Ia Injection well
- disposal of oilfield or industrial waste fluids
- only waste to accept waste that’s not oil field waste
- liquids must be tested prior to disposal and must meet all criteria in ERCB directive 50
Fluid Waste Criteria for DWI
- pH between 4.5 and 12.5
- substance doesn’t meet surface water discharge criteria
- has a non-halogenated organic fraction of less than 10% by mass (except untreatable sand or crude oil/water emulsion, antifreeze or dehydration fluid)
- has one or more halogenated organic compounds in a total combined concentration less than 1000 mg/kg
- PCB concentration less than 50 mg/kg
Deep Well Injections regulated by:
ERCB directive 51, not Alberta Environment and Water
ERCB Regulations focus on 4 key areas
- Wellbore integrity
- Formation suitability for the disposal of fluids
- Waste stream suitability
- Reporting and manifesting
Wellbore Integrity
- both initial and ongoing containment of the injected fluids in the disposal/injection zone
- protection of ground water
- conservation of hydrocarbons
Formation suitability for the disposal of fluids
-make sure injection/disposal zone will continue to confine the injected fluids with that single zone
Wellbore Design
must result in complete isolation of the disposal zone from all other formations and especially from useable groundwater aquifers
Well head
includes well head and casing pressure gages
Surface Casing
Must extend below all useable ground water aquifers
Production Casing
Extends from surface to the base of the well
Annulus
Between casing and injection tubing
Packers
Isolates the annular fluids from the disposal/ injection fluids
Wellbore Integrity is ascertained by logging/testing the well:
- Prior to any fluids being injected into the disposal formation (if don’t meet this application will be denied)
- During the life of the disposal well (ongoing monitoring to ensure hydraulic isolation of the injection/disposal zone from other zones)
Initial logging/testing requirements include:
- cement on top location logging
- hydraulic isolation logging
- casing integrity logging
- initial pressure tests
Cement top location logging
- cement is used to hold the casing in place
- isolate various zones from one another
Hydraulic isolation logging
-ensures isolation of disposal zone
Casing integrity logging
-full length casing inspection to determine if corrosion is becoming an issue which can weaken the casing
Initial pressure tests
- test pressures up to about 7000 kPa for 15 min for all classes of wells
- ensures no leaks will occur once injection starts
Monitoring logging/testing requirements include (Class Ia wells):
- recording of annular and injection pressures daily
- hydraulic isolation logging every 5 years
- formation pressure surveys yearly
- packer isolation tests yearly
Requirements for the disposal zone of fluids (relating to formation suitability):
- porous (storage) and permeable zone (waste can flow)
- sandstones/conglomerates
- carbonates
- unconsolidated sands
- not fractured- may not be able to get hydraulic isolation
- below useable groundwater zones
- want formation waters to be saline
- confined
- deep
Waste Stream Suitability
Injection fluids must be chemically compatible with both the formation fluid and the rock matrix
Problems associated with deep well injection
- Contamination of ground water aquifers if hydraulic isolation of the disposal zone is not maintained
- Localized earthquakes because of increased subsurface pressure as fluids are injected
