Properties of Aquifer Flashcards
Capacity to do work
Energy
The product of the net force exerted and the distance through which the force moves.
Work
The product of mass of the body and its acceleration.
Force
The mass multiplied to the gravitational force (~9.8 m/s 2 )exerted to it by the
weight
A fluid or solid is its mass per unit volume.
density
A substance is its weight per unit volume.
specific weight
The force applied to a unit area perpendicular to the direction of the force
Pressure
Value of standard atmospheric pressure is?
1.013x10^5 Pa
Pressure is measured relative to _________ which varies with changing weather patterns
atmospheric pressure
Resistance to relative motion is proportional to a fluid property known as the dynamic viscosity
newtonian fluid
The proportionality constant for compressibility
bulk modulus
True or False. If pressure is applied, the same mass of fluid will be contained within a smaller volume because water is a compressible fluid
TRUE
the density is _______ to the change in pressure.
proportional
Assemblages of individual grains that were deposited by water, wind, ice, and gravity.
sediments
Openings between the sediment grains
pore spaces
Express mathematically the porosity of earth materials is the percentage of the rock or soil that is void of material
porosity (n) = 100Vv/V
Vv - volume of void space in a unit of earth materials
V - unit volume of earth material
what is pore throats?
passageway typically smaller than pores
Equation of total porosity
porosity (n) = 100 [1-(Pb/Pd)]
TRUE or FALSE. Effective porosity of a sediment is not a function of the size of the molecules that are being transported relative to the size of the passageways that connect the pores
FALSE. Function of the size of the molecules.
Percentage of cube packing of spheres
47.65%
Percentage of rhombohedral packing of spheres
25.95%
True or False. Does the diameter of the spheres influence the porosity
False. Does not influence the sphere
True or False. Porosity is also affected by the shape of grains and the fabric/orientation of the particles
True
True or False. If a sediment contains a mixture of grain sizes, the porosity will be lowered
True
Sediments are classified by the basis of ________________
diameter size
Enumerate types of geologic porosity
primary porosity
secondary porosity
fracture porosity
vuggy porosity
A type of porosity generated by the dissolution of large features.
Vuggy porosity
A type of porosity associated with fracture system or faulting.
Fracture porosity
A type of porosity system in a rock or unconfined alluvial deposit.
Primary porosity
A type of porosity that enhances the overall porosity of rock. It can co-exist or replace the porosity.
Secondary porosity
True or False. Can gypsum and salt can also be cavernous.
True
What are the range value of limestone and dolomites?
1 - 30%
What is the percent porosity of sedimentary rock?
3 - 30%
It measures how well or poorly sorted the grains are.
uniformity coefficient
Refers to a size corresponding to the 10% line of the grain size curve.
effective grain size
Ratio of grain size
Cu = d60/d10
True or False. Does compaction reduces pore volume by rearranging the grains and reshaping them.
True
Refers to the dissolved pore fluid with increasing porosity
dissolution material
True or False. Does deposition of cementing materials such as calcite, dolomite, or silica will not reduce porosity.
False. Will reduce
True or False. A sample with a Cu less than 4 is well sorted
TRUE
True or False. A sample with a Cu less than 6 is poorly sorted.
False. More than 6.
__________ and ________ increases overall rock porosity.
weathering and fracturing
According to Stewart 1964 __________ and ________ can have a porosity in the range of _______ to _______.
weathered plutonic and metamorphic rocks
30% - 60%
True or False. Extrusive rocks cool and solidify quickly because they are formed in a surface environment this gives them radically different porosity characteristics
TRUE
Lava cooling rapidly at the surface will trap degassing products, resulting in ____________ in the rock.
Vesicular texture
According to Schoeller, 1962 porosity of basalt generally ranges from _______.
1 to 12%
According to Davis, 1969 pumice can have a porosity as high as _______.
87%
According to Keller, 1960, tuff has a porosity ranging from ______.
14% to 40%
Volcanic ash may have a porosity of _________.
50%
According to Davis, 1969, weathering of volcanic deposits can increase the porosity to values in excess of ______.
60%
It is the volume of water that drains from saturated rock owing to the attraction of gravity to the total volume of the rock
Specific Yield (Sy)
Water molecules cling to surfaces because of ___________.
surface tension
True or False. If gravity exerts a force on a film of water surrounding a mineral grain, some of the films will pull away and drip downward.
False. Exerts a stress
True or False. The remaining film will be thicker with a greater surface tension so that the stress of gravity will be exactly balanced by the surface tension.
False. Thinner
Moisture clinging to the soil particles because of surface tension.
Pendular water
The ratio of volume of water a rock can retain against gravity drainage to the total volume of rock.
Specific Retention (Sr)
The formula use for calculating the porosity of a rock/material.
n=Sy + Sr
It is the ability of a rock to transmit water that, together with its ability to hold water.
Hydraulic Conductivity
Examples of rocks that exhibit porosity but lack interconnected voids
Vesicular basalt
Example of rocks that have porosity but the pores are small that water flows through the rock with difficulty.
clay and shale
A French Engineer, made the first systematic study of the movement of water through a porous medium.
Henry Darcy, 1856
True or False. The discharge, Q is proportional to the difference in the height of the water, h (hydraulic head) between the ends and inversely proportional to the flow length, L.
TRUE
True or False. The quantity of flow is inversely proportional to a coefficient, K, which is dependent upon the nature of the porous medium.
False. Proportional
Formula for Darcy’s Law
Q = - KA [( hA - hB )/L] or Q = -KA (dh/dl)
Note: The negative sign indicates that flow is in the direction of decreasing hydraulic head
Where dh/dl is known as the ______. The quantity _____ represents the change in head between two points that are very close together, and _____ is the distance between these points.
hydraulic gradient; dh; dl
A measure of the quantity of any fluid flow over unit time. And it is directly proportional to the specific weight y.
discharge
The force exerted by gravity on a unit volume of fluid
specific weight
A function of the size of the openings through which the fluid moves.
Intrinsic Permeability
True or False. Discharge is also proportional to the dynamic viscosity of the fluid, μ.
False. Inversely proportional
True or False. For well-sorted sediments the intrinsic permeability is proportional to the grain size of the sediment.
True
True or False. Unconsolidated coarse-grained sediments do not represent some of the most prolific producers of groundwater.
False. It represents
Several factors relating to intrinsic permeability to grain size.
- As the median grain size increases, so does permeability.
- Permeability will decrease for a given median diameter as the standard deviation of particle size increases. The increase in S D indicates a more poorly sorted sample.
- Coarser samples show a greater decrease in permeability with an increase in standard deviation than fine samples.
- Unimodal (one dominant size) samples have a greater permeability than bimodal (two dominant size) samples
The hydraulic conductivity of earth materials can be measured in the laboratory thru the use of _________.
permeameters
Let us recap the permeability of rocks!
Clastic sedimentary rocks have primary permeability characteristics similar to those of unconsolidated sediments. However, diagenesis can reduce the size of the throats that connect adjacent pores through cementation and compaction
Crystalline rocks typically have a low primary permeability
Volcanic rocks can have a high porosity and if the openings are large and well connected, then they may also become highly permeable
Undulating surface at which pore water pressure is equal to atmospheric pressure.
Water table
A _______ water table indicates the groundwater is flowing
sloping
______________ are in topographical low spots
Groundwater discharge zones
True or False. Groundwater generally flows away from topographical high spots toward topographical lows
true
It is a geologic unit that can store and transmit water at rates fast enough to supply a reasonable amount to wells.
Aquifer
Example of rock units of aquifer.
sand and gravels
sandstone
limestone
dolomites
basalt flows
fractured plutonic and metamorphic rocks
__________ of aquifers would range about 10^-2 darcy upward.
Intrinsic permeability
_______________ geologic unit having little or no intrinsic
permeability less than 10^-2 darcy.
Confining Layer
Confining layers can be classified as:
Aquifuge, Aquitard, Aquiclude
Absolutely impermeable unit that will not transmit any water.
Aquifuge
A layer of low permeability that can store groundwater and also transmit it slowly from one aquifer to another (also called as leaky confining layer).
Aquitard
A rock unit or geologic formation through which inappreciable quantity of water moves or is transmitted.
Aquiclude
An aquifers that can be close to the land surface, with continuous layers of materials of high intrinsic permeability extending from the land surface to the base of the aquifer.
water table aquifer or unconfined aquifer
________ (also called artesian aquifers) are overlain by confining layers.
Confined aquifers
________ a confined aquifer is the surface representative of the level to which water will rise in a well cased to the aquifer.
Potentiometric surface
A layer of saturated soil that forms above the main water table.
Perched aquifer
The measure of the amount of water that can be transmitted horizontally through a unit width by the saturated thickness of the aquifer under a hydraulic gradient of 1.
It is also the product of the hydraulic conductivity and the saturated thickness of the aquifer.
Transmissivity
The volume of water that a permeable unit will absorb or expel from storage per unit surface area per unit change in head
Storage Coefficient (Storativity)
In the saturated zone, the head creates pressure, affecting the arrangement of mineral grains and the density of the water in the voids If the pressure increases, the mineral skeleton will expand if it drops, the mineral skeleton will contract.
Elasticity
The amount of water per unit volume of a saturated formation that is stored or expelled from storage owing to the compressibility of the mineral skeleton and the pore water per unit change in head.
Specific Storage (Elastic Storage Coeffcient)
At a given plane in a saturated aquifer, downward stress is placed on the aquifer skeleton by the weight of the overlying rock and water.
Total stress
There is upward stress on the plane caused by the fluid pressure. The upward stress will, in part, counteract the total stress, so the resulting stress that is actually borne by the aquifer, called the ________________.
effective stress
Unit is one that has the same properties at all locations
Homogenous
__________ formations, hydraulic properties change spatially One example would be a change in thickness
Heterogeneous
Units that have the same intrinsic permeability in all directions
Isotropic
If the geometry of the voids is not uniform then there may be a direction in which intrinsic permeability is greater.
Anisotropic
It exemplify massive porosity located in New Mexico
Carlsbad cavern
Hydraulic conductivity of earth materials can be measured in the laboratory thru the use of ___________.
Permeameters
