Porosity and Rocks Flashcards
What is permeability vs. porosity?
When a rock contains holes or spaces which can trap water or let it flow through the rock, it is considered porous .However, the ability of a rock to allow water to flow through interconnected pore spaces is permeability, this means a rock can be porous but not permeable if these spaces are separate from each other.
What factors affect porosity?
Compaction
Sorting of grains
Cementation
Orientation of Grains
What is the difference between Primary and Secondary porosity?
Primary porosity is porosity associated with the original depositional texture of the sediment. That is, primary porosity is the pore space in between the grains and within the depositional matrix.
Secondary porosity is porosity developed after the rock has been deposited as a result of fracturing, tectonic stresses, faults or solution weathering.
What is the difference between a confined and an unconfined aquifer?
Unconfined - Has a water table, and is only partially filled with water.
Rapidly recharged by precipitation
Confined - completely filled with water under pressure, separated from surface by aquitard
Very slowly recharged
What are Aquitards and Aquicludes?
An aquitard is a zone within the earth that restricts the flow of groundwater from one aquifer to another. An aquitard can sometimes, if completely impermeable, be called an aquiclude or aquifuge. Aquitards are composed of layers of either clay or non-porous rock with low hydraulic conductivity.
What is the piezometric surface?
The piezometric surface is the level to which water rises in a well. In a confined aquifer this surface is
above the top of the aquifer unit; whereas, in an unconfined aquifer, it is the same as the water table.
What is a recharge zone?
The area in which water enters an aquifer. In a recharge zone surface water or precipitation percolate through relatively porous,
unconsolidated, or fractured materials, such as sand, moraine deposits, or cracked basalt, that lie over a water bearing, or aquifer, formation.
