Groundwater Control and Management for Oil Shale

Development

26th Oil Shale SymposiumColorado School of Mines

Need for Controls

Underground and open pit minesControl inflows and water pressuresReduce mining costs – pumping lift, equipment wear, ventilation, underground conditionsEnvironmental management - intercept water when it is ‘clean’

In-situ extractionControl the process – heating and subsequent extraction of oilEnvironmental management - intercept water when it is ‘clean’Provide control of the groundwater flow system (containment) during operations and closure

High Flow Environments

Sedimentary basins – permeable formations with recharge and storageFractured carbonate rocks and karstHigh rainfall areas with good vertical connection to ground surfaceRapid connection to surface watersConnection to high storage Tertiary/alluvial basinsInduced permeability – e.g., longwall, block caveRecirculation

High Flow Environments

Moderate Flow Environments

Permeable structure with limited storage and extentPermeable hydraulic block that is not connected to recharge sourceSystems with strong overlying “layer-cake” geology – natural barriers to flowInduced permeability in mine area only

Moderate Flow Environments

Importance of Characterization

Define geology – lithology, structures, compartmentalizationMeasure water pressures – flow directions and gradientsMeasure hydraulic characteristics – how is water transmitted and how much?Define water sources – where is the water coming from?Determine water quality

Piceance Basin

Regional flow east-west

Regional flow north-south

Hydrogeologic Variability

Active Dewatering Methods

Surface wellsStage-level wellsSub-horizontal wellsDrainage galleries

Vertical Wells

Design of Wells

Passive Dewatering Methods

Inflow groutingSource groutingGround freezingSlurry walls

Shell - Freeze Wall

From Shell EA, August 2006

Approach to Groundwater Control

Take advantage of the natural conditions –know the underground plumbing systemDewater ahead of miningMinimize the vertical pumping liftOnly pump the water onceOnly pump what is neededManage water quality

Criteria for Control Methods

Hydrogeological reasonsDepth of operationDegree of vertical hydraulic connectionLateral extent of operationDegree of hydraulic compartmentalizationAbility to identify and stop discrete inflow sourcesAbility to intercept water at shallow horizons

Operational reasonsRequirement to “tailor” inflows because of current installed pumping capacityAccess constraints within the operationsRequirement to control operating temperatures

Criteria for Control Methods

Environmental requirementsMinimize pumped water dischargeOptimize pumped water chemistryContain in-situ process solutions

Cost considerationsMinimize installation costsMinimize operating costsOptimize cash flow