Ch 8 - Field Investigations

API Units

American Petroleum Institute Units. A unit of measurement of gamma rays

Casing

A heavy metal pipe lowered into a borehole and cemented in place to prevent cave-in, loss of drilling fluid, and unwanted fluids from entering the borehole

Cone of Depression

A depression in the potentiometric surface of ground water that defines the area of influence of a well

Gamma Ray Log

commonly used to differentiate between shale (high gamma reading) and other sedimentary rocks

Gravity Survey

determines the density distribution by evaluating the gravitational pull

Ground-Penetrating Radar

low-frequency radar or radio wave antennas examine subsurface at great depths while the higher frequencies are used near the surface. (0-100 ft deep)

InSAR

studies ground deformation

Invaded Zone

between the flushed zone and uninvaded zone in a borehole, and refers to the degree to which the mud infiltrate penetrates the formation fluids

LiDAR

Light Detection and Ranging; records topographic changes

Lysimeter

determines soluble constituents removed by drainage, used to sample water chemistry in the vadose zone, measure deep percolation, and ET

Neutron Log

indicates the presence (not type) of fluid, used to distinguish porous and nonporous formations

Normal-Resistivity Log

measurements of the resistivity of formations

Packer Test

aquifer test that determines rock permeability

Percolation (Perc) Test

determines suitability of a soil for a sewage disposal system by measuring the rate of decline of the water table

Piezometer

measures in-situ pore water pressures

Pumping Test

observes the change in hydraulic head in the aquifer

Resistivity Log

quantitative measurements of the specific resistance of a material

Rippability

the ease with which soil or rock can be excavated mechanically

Rock Quality Designation (RQD)

measure of the intactness of rock core

Seismic Reflection

gives a detailed picture of subsurface structures

Seismic Refraction

maps layers of materials with differing densities

Shelby Tube

obtains undisturbed samples of cohesive soils

Slug Test

aquifer test

Standard Penetration Test (SPT)

blow count is correlated with soil conditions

Tensiometer

measures soil matric potential to determine irrigation needs and water consumption by plants

Test Pits

obtains bulk samples and identifies subsurface materials in-situ

Well Efficiency

well drawdown ratio (theoretical to actual)